Surface

Surface?Anatomy?and?Relationships
The kidneys are paired ovoid, retroperitoneal organs that lie on the psoas muscles in the posterior part of the abdomen on each side of the Vertebral column (Elkoushy et al., 2016).
The longitudinal axes of the kidneys are oblique with their upper poles lying more medial and posterior than inferior poles and its medial aspect rotates about 30 degree anteriorly (Anderson et al., 2012).
The position of the kidney varies with respiration as it moves down about 3 cm or one vertebral body during inspiration and also its position varies with changing position from erect to supine .The right kidney is 2 cm lower than the left one due to downward displacement by the Liver so the right kidney lies between lower border of L1and upper border of L3 while the left kidney lies between lower border T12 an upper border of L3 (Kabalin et al., 2011).
The kidney is about 10 to 12 cm in length, 5 to 7.5 cm in width and 2.5 to 3cm in thickness . The weight of the kidney is about 125 to 170 gram in males and from 10 to 15 gram less in females. In children the kidneys are relatively larger with prominent fetal lobulations that disappear by the first year of life (Tanagho et al., 2013) .

(Fig. 1) Normal rotational axes of the kidney. A, Transverse view showing approximate 30-degree anterior rotation of the left kidney from the coronal plane, relative positions of the anterior and posterior rows of calyces, and location of the relatively avascular plane separating the anterior and posterior renal circulation. B, Coronal section demonstrating slight inward tilt of the upper poles of the kidneys. C, Sagittal view showing anterior displacement of the lower pole of the right kidney. (Quoted from Netter FH. Atlas of human anatomy. 5th ed. Philadelphia: Saunders2010)

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Relationships of the kidney
(1)Posterior relationships:
The kidneys are related posterosuperioly to the inferior surface of the diaphragm and the ribs, 12th rib on the right and 11th and 12th rib on the left . therefore , traumatic fracture lower ribs can lead to renal injury and excision of large renal masses can lead to diaphragmatic tear as well as pleural tear and pneumothorax. There is increased risk of pleural and even lung injury with supracostal approach through 10th intercostal space (Kabalin et al., 2011).
Posteroinferiorly , the kidneys are related to the psoas major muscle medially and both the quadratus lumborum and the transversus abdominis aponeurosis muscles laterally with the subcostal nerve and vessels and the iliohypogastric and ilioinguinal nerves descending obliquely across the posterior surfaces of the kidneys (Anderson et al., 2012).

Figure (2) Subcostal and supracostal percutaneous access to an upper pole calyx. The supracostal approach provides more direct access and provides a better angle for endoscopy of the rest of the kidney. However, there is increased risk for pleural injury. (Quoted from Hinman F, Stempen PH. Atlas of urosurgical anatomy. Philadelphia:WB Saunders; 1993).

Figure (3) posterior relations of the kidney
(Quoted from Netter FH. Atlas of human anatomy. 5th ed. Philadelphia: Saunders2010.)

(2)Anterior relationships
The kidneys are related anteriorly to other organs .The right kidneys related anterosuperiorly to both intraperitoneal and retroperitoneal bare portions of the liver and superomedially to the adrenal gland and to small intestine and hepatic flexure of the colon inferiorly while medially it is related to second part of the duodenum and head of the pancreas (Anderson et al., 2012).
The hepatorenal ligament is formed by parietal peritoneum bridging between upper pole of kidney and liver , therefore excessive downward traction on the right kidney can lead to tear of the liver capsule and massive intraperitoneal bleeding (Kabalin et al., 2011).
The left kidney is related anteriorly to the adrenal gland superomedially , stomach and spleen superiorly, jejunum and splenic flexure of the colon inferiorly , and tail of the pancreas with splenic vessels medially (Tanagho et al., 2013).
The splenorenal ligament is formed by parietal peritoneum bridging between upper pole of left kidney and spleen , therefore excessive downward traction on the left kidney can lead to splenic capsular tear and splenic hemorrhage (Kabalin et al., 2011).

Figure (4) Anterior relations of the kidney
Quoted From Drake, Vogl, Mitchell, Tibbitts and Richardson 2008.

Perirenal coverings :
The kidneys are surrounded by fibrous capsule which is surrounded by perinephric fat that extends through renal hilum into renal sinus and surround kidney with its vessels and adrenal glands (Anderson et al., 2012)
The Gerota fascia is a condensed membranous layer that surrounds the kidney , adrenal gland with their surrounding perinephric fat . It extends medially to fuse with the contralateral side and continues inferiorly around the ureter as periureteral fascia (Tanagho et al., 2013).
The Gerota fascia is closed superiorly where it is continuous with the fascia on the undersurface of the diaphragm and laterally and therefore it acts as an anatomical barrier to the spread of malignancy and as a mean of containing perinephric fluid collections , but it is open inferiorly so, perinephric fluid collections can track inferiorly into the pelvis. (Elkoushy et al., 2016).
The Para nephric fat surrounds the gerota fascia which is attached to it by collagen bundles keeping the kidney fixed in position (Anderson et al., 2012).

Figure (5 ) Superior view of a transverse section of the kidneys at the level of the 2nd lumbar vertebra shows that the kidneys are angled 30 to 50°behind the frontal (coronal) plane. FA = frontal plane of the body; RA = renal frontal (coronal) axis. (Quoted from Smith et al., 2006)

Figure (6) Lateral view of a longitudinal section through the retroperitoneum, reveals the posterior (P) and the anterior (A) layers of the renal fascia. Pe = peritoneum; K = kidney. (Quoted from Smith et al., 2006).
Gross?and?Microscopic?Anatomy of the kidney:
The renal sinus narrows medially to form the renal hilum through Which the renal vessels and renal pelvis exit. The kidney parenchyma is composed , both grossly and microscopically from a dark central part called the renal medulla and a peripheral pale part called the renal cortex(Anderson et al., 2012 ).
The renal medulla is composed of about 8 to 18 conical shaped striated areas called the renal pyramids. Each renal pyramid has an apex called renal papilla which is cupped by a minor calyx and a base toward corticomedullary junction . (Elkoushy et al., 2016)
The renal cortex is about 1cm thick and it covers the base of the pyramid and extends in between the renal pyramids and this part is known as columns of Bertin which contain the interlobar arteries therefore percutaneous renal access is preferred to be through the renal papilla to calyx to avoid these columns of Bertin containing larger blood vessels (Anderson et al., 2012).
The kidney can be divided into lobes with each lobe composing of a renal pyramid and its associated cortex , these lobes are visible on the external surfaces of the kidneys in fetuses (Elkoushy et al., 2016).

Figure (7) Internal structure of the kidney
(Quated From Drake RL, W, Vogl Mitchell AWM Gray’s anatomy for students. Philadelphia: Churchill Livingstone;2005.)
The nephron is the functional unit of the kidney with each kidney containing from 0.4 to 1.2 million nephrons with each nephron composing of glomerulus which consist of tuft of capillaries and Bowman capsule .The glomeruli are responsible for urine filtration at a rate of 125ml/minute known as the glomerular filtration rate (GFR). The other parts of the nephron are the proximal convoluted tubule ,distal convoluted tubules that lie in the cortex and loop of Henle and collecting ducts that lie in renal pyramids (Tanagho et al., 2013 ).
The collecting ducts join to form about 20 papillary ducts which open at the papil¬lary surface known as (area cribrosa papillae renalis) that drains the urine into the fornix of a minor calyx (Elkoushy et al., 2016).
There are about 5 to 14 minor calyces . the minor calyx could be single draining one papilla or compound draining multiple papillae , the polar calyces especially the upper pole ones are mainly compound (Tanagho et al., 2013).
The minor calyces may drain directly into an infundibulum or join to form major calyces that subsequently drain into infundibula which are considered the primary divisions of the pelvicalyceal system (Elkoushy et al., 2016).

Figure (8) schematic diagram of the microanatomy of the kidney
(Quoted from Anon, (2018) Available at: http://www.med-health.net/function-of-nephron.html.)

Figure (9) Anterior view of a pelvicalyceal endocast from a left kidney, obtained according to the injection-corrosion technique. B, Schematic drawing of the endocast shown in A, indicates the essential elements of kidney collecting system. cc = compound calyx; sc = single calyx; mc = minor calyx; Mc = major calyx; f = caliceal fornix, i = infundibulum; P = renal pelvis Quoted from (Smith et al., 2006).
Arrangement of renal calyces :
The upper and lower polar calyces are usually compound and project in polar direction while the other calyces are arranged in anterior raws making angle 70 degrees with the frontal plane of the kidney and facing laterally and posterior raws making angle 20 degrees with the frontal plane of the kidney and facing medially . On occasion, the converse applies (anterior calyces 20 and posterior calyces 70) as described by Hodson (Drake et al, 2007).

Renal Blood Supply:
The renal pedicle consists of a single artery and a single Vein entering the kidney at the renal hilum with the vein lying anterior to the artery and the renal pelvis and ureter located posterior to these vascular structures (Kabalin et al., 2011).
Renal Artery
The right renal artery arises from the aorta and courses under the IVC toward the right kidney while the left renal artery courses directly laterally to the left kidney. Both renal arteries give branches to the respective adrenal gland, renal pelvis, and ureter (Elkoushy et al., 2016).
The renal artery, upon reaching the kidney divides into 4 or more, mainly 5 segmental branches with each segmental branch supplying portion of the kidney . these segmental branches are end arteries with no collateral circulation in between them , so injury or occlusion of these arteries by a thrombus or embolus leads to segmental infarction of the kidney (Kabalin et al., 2011).
The segmental arteries include the posterior segmental artery which separates from the renal artery before it enters the renal hilum and run posterior to the renal pelvis and four anterior segmental arteries from superior to inferior apical, upper, middle, and lower which pass anterior to the pelvis (Kabalin et al., 2011).

Figure (10) Typical segmental circulation of the right kidney, shown diagrammatically. Note that the posterior segmental artery is usually the first branch of the main renal artery and it extends behind the renal pelvis (Quoted from from Hinman F, Stempen PH. Atlas of urosurgical anatomy. Philadelphia:WB Saunders; 1993.)

Figure (11) Intrarenal arterial anatomy (Quoted from from Hinman F, Stempen PH. Atlas of urosurgical anatomy. Philadelphia:WB Saunders; 1993.)
The segmental arteries then divide into lobar arteries which divide in renal parenchyma into interlobar arteries within the columns of Bertin that lie inbetween renal pyramids and in close association to the infundibulum of renal minor calyces. (Anderson et al., 2012).
These interlobar arteries give rise to the arcuate arteries that course horizontally at the base of the pyramids at the corticomedullary junction that then gives rise to the interlobular arteries that eventually divide to form the afferent arteries to the glomeruli (Elkoushy et al., 2016).
Blood flows from the afferent arteriole into glomerular capillaries then leaves it via the efferent arteriole which continues to one of two locations: secondary capillary networks around the urinary tubules in the cortex or descends into the renal medulla as the vasa recta(Kabalin et al., 2011).
Brodel’s line is avascular plane that lie 1-2 cm posterior to the lateral margin of the kidney at The junction between the anterior and posterior divisions of the renal artery with no anatomic landmark on the surface to demonstrate it that is why the safest place to puncture the kidney is just posterior to the line of maximal convex curvature (Brodel’s line) (Elkoushy et al., 2016)
Papillary percutaneous renal access is better than infundibular approach especially through the lowermost calyx to avoid large vessels and major branches that cross the infundibular surfaces, for example, The superior pole infundibulum is encircled by the upper segmental artery anteriorly and the posterior segmental artery posteriorly(Elkoushy et al., 2016)
Renal veins
The venous drainage of the kidney correlates closely to its arterial supply. The interlobular veins drain the post glomerular capillaries then drain to arcuate veins , interlobar veins ,lobar veins , segmental veins, five venous trunks that combine to form the renal vein (Anderson et al., 2012).
Unlike the arterial supply, the venous drainage of the kidney has extensive collateral circulation that communicates freely through venous collars around the infundibula (Tanagho et al., 2013).
The renal vein lies directly anterior to the renal artery, but , This position can vary up to 1-2 cm cranially or caudally relative to the artery. The right renal vein is about 2 to 4 cm in length and enters the right kidney lateral to posterolateral edge of the IVC. while ,the left renal vein is typically 6 to 10 cm in length and enters the left lateral aspect of the IVC after passing between the superior mesenteric artery posteriorly and the aorta anteriorly (Kabalin et al., 2011) .

Figure (12) Renal vasculature. (Quoted From Drake RL, W, Vogl Mitchell AWM Gray’s anatomy for students.Philadelphia: Churchill Livingstone;2005.)
The left renal vein tributaries include the left adrenal vein superiorly, the lumbar vein posteriorly, and left gonadal vein inferiorly while the right renal vein typically does not receive any tributaries (Anderson et al., 2012).
Common Variants in Renal Anatomy :
The most common variation in the renal vasculature is supernumerary renal arteries, with up to five arteries reported which occurs more often on the left and these additional arteries can enter through the hilum or directly into the parenchyma (Elkoushy et al., 2016).
Lower pole arteries on the right tend to cross anterior to the IVC But if lower pole arteries on either side crossed anterior to the collecting system, they can cause a ureteropelvic junction obstruction (Anderson et al., 2012).
In ectopic kidney, supernumerary arteries are even more common and their origin is even more variable which can arise from the celiac trunk, superior mesenteric artery, or iliac arteries all possible sources of ectopic renal arteries. Supernumerary veins occur as well, but this is a less common entity (Tanagho et al., 2013).
The most common renal vein anomaly is duplicate renal veins draining the right kidney via the right renal hilum. Polar veins are quite rare. Finally, the left renal vein may course behind the aorta or divide and send one limb anterior and one limb posterior to the aorta, resulting in a collar-type circumaortic formation (Elkoushy et al., 2016).

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Anatomical And Physiological variations between adult and pediatric kidneys :
The corticomedullary index (cortex: medulla ratio) increases from 1.64:1 in the newborn infant (due to cortical immaturity) to 2.59:1 in adults (Vlajkovi? et al., 2005).
Regarding the kidney dimensions, there is a prominent correlation between the kidney length and volume and the age of children, their height, weight and body surface. It has been established that the kidney length correlates best with the height of the child, and that the left kidney is somewhat longer and larger (?ukuranovi? et al., 2002).
The level of glomerular filtration in a newborn is about 30% of its value in an adult. The fetal kidney receives only 2% – 3% of the minute heart volume in comparison to 15% – 18% of the adult cardiac output. The adult values of the renal blood flow are reached by the kidney by the end of the first year of life (Piscione et al., 2015).
Postnatally there is a sharp increase in GFR, which doubles by 2 weeks of age; however, it is not until 2 years of age that the corrected GFR reaches the corresponding adult-corrected value) Trompetor R, 2008).
The human kidney reaches the concentration capacity of the adult level at the age of 18 months (Vlajkovi? et al., 2005).
During the infant age as well as the age of adolescents and young adults there is ongoing full functional renal maturation as regard excretory function, water, electrolyte and acid base balance and endocrinal function ) ?ukuranovi?R? et al., 2006).

Percutaneous renal access depends on (1) Preoperative imaging to assess : stone burden(size and number ) and to delineate the anatomy of the kidney and its relations ,(2) Intraoperative imaging to guide percutaneous puncture, endoscopic inspection, and pleural screening, and (3)Post-operative imaging to detect presence of residual stones and to assure antegrade drainage (Park et al, 2006).
(1)Preoperative imaging :
(a) Pelviabdominal Ultrasonography:
Renal Ultrasonography is an excellent imaging modality to assess renal parenchymal abnormalities, it can also differentiate solid from cystic structures, and evaluate degree of hydronephrosis .Stones on ultrasonography are hyperechoic with an acoustic shadow. Different tissues of the kidney have different echogenicity, the renal capsule echogenicity differs from the surrounding fat delineating kidney outline. The renal sinus fat is highly echogenic, and this area also contains the renal pelvis and branches of the arterial, venous, and lymphatic systems (Bhayani S.B. et al., 2007).
Kidney echogenicity varies with age. The echogenicity of the renal Cortex of an infant is relatively higher compared to that of an adult . In infant kidney there is a smaller and less apparent central band of echoes. But in adult , the echogenicity of the renal cortex is usually hypoechoic in regard to the liver(SIEGEL et al., 2011).

.

figure (13) ultrasonography of the normal kidney. Longitudinal (A) and transverse (B) ultrasound views outline the contour of the right kidney (R), the parenchyma of which is hypoechoic relative to the liver (L). The renal sinus fat (S) appears echogenic. (Quoted from O’Neill WC. Atlas of renal ultrasonography. Philadelphia: Saunders; 2001).
The renal capsule is clearly visible while the renal cortex is of low homogenous echogenicity and the renal medulla is of sonolucent structure . Hydronephrosis is identified by being hypoechoic cavity surrounded by a central echo complex (Robinson et al,.2011)
(b)Plain Abdominal Radiography:
The use of plain radiographs has been limited due to the increasing use of ultrasonography and computed tomography(CT) . The kidney ureter-bladder (KUB) radiograph may demonstrate urinary stones. But, approximately 10% of urinary stones are not visualized by plain radiography because they radiolucent , and also radiopaque stones may be obscured by bowel gas. In the pelvis, phleboliths (calcified venous thrombosis) may be mistaken for ureteric stones but , they can be differentiated from urinary stones by their radiolucent centre,. (Paul Tait, 2011).
Radioopaque stones include most calcium-containing stones especially when large, not obscured by overlying stool or bowel gas, and not overlying the spine or bony pelvis. the most radio-opaque of calcium-containing stones are Brushite and calcium oxalate monohydrate stones , followed by calcium apatite and calcium oxalate dihydrate stones. Faint opaque stones include Cystine and struvite stones while radiolucent stones include uric acid stones , although they can be faint radiopaque if mixed with calcium, or if of a large size (Jackman et al., 2000).
Advantages of KUB include being rapid, available, and cheap but it is of limited use due to low sensitivity for the detection of renal calculi as Sensitivity and speci?city rates for KUB in the detection of renal and ureteral calculi range from 58% to 62% and 67% to 69%, respectively (Jackman et al., 2000).
(c)Intravenous Urography(IVU):
It was considered historically the study of choice for assessing patients with suspected urinary stones and for planning therapy. It delineates collecting system anatomy, by obtaining appropriate oblique and anteroposterior views. It can show the relationship of the kidney to the ribs and the need for supracostal approach . (Bishoff et al, 2016).
Percutaneous puncture can be done guided by IVU for selecting the appropriate calyx depending on the location of the stone, the infundibulopelvic angle, and the spatial anatomy of the collecting system. It can detect if the stone is within a calyceal diverticulum . The stone bearing calyx is the site of optimal access in many cases but in other cases, as a complete stag horn stone , or a partial stag horn stone occupying the renal pelvis and multiple lower pole calyces, an upper pole posterior calyx may is the site of optimal access (Thiruchelvam et al., 2005).
Nowadays , non-enhanced spiral computed tomography with three dimensional reconstruction is considered superior to IVU in detecting urinary stones , delineating anatomy of the pelvicalyceal system and assessing relations of kidney to the ribs and nearby organs (Thiruchelvam et al., 2005).

Figure (14)(A) Noncontrast CT demonstrates a left renal calculus (arrow). (B) Scout ?lm from intravenous urogram demonstrates that the left renal stone seen on CT is composed of multiple small stones (arrow). (C) Ten-minute ?lm from intravenous urogram shows that the stones are located within a calyceal diverticulum (arrow). Noncontrast CT alone was not sufficient to reveal the caliceal diverticulum. (D) Oblique ?lm shows that the stone-bearing diverticulum (arrow) projects posteriorly from the upper pole calyx (Quoted from Park et al, 2006).
(d) Computed tomography :
Computed tomography is now considered the standard diagnostic tool to evaluate renal colic. Benefits of CT over IVU include avoiding contrast and being able to exclude other causes of abdominal pain (Rastinehad et al.,2016).
Non enhanced spiral three dimensional CT can diagnose radiolucent stones which can be missed on IVU, as well as small stones even in the distal ureter (Salim et al.,2011).
Non contrast enhanced helical CT can detect all renal and ureteric stones except for some indinavir stones (Tu¨rk et al., 2016).
For urinary stones Sensitivity of Non enhanced CT ranges between 96% and 100% and specificity ranges between 92% and 100% (Memarsadeghi et al., 2005).
Cross sectional imaging is essential in Patients with a retro renal colon or spinal deformity to guide safe percutaneous renal access ( Bhayani S.B. et al.,2007).
Enhanced three dimensional CT urogram has the advantage of delineating the renal parenchyma , the pelvicalyceal system , the relations of the kidney to surrounding structures and to guide safe access to the pelvicalyceal system but it has the disadvantage of inability to distinguish stones from the contrast material within the pelvicalyceal system (Leder and Nelson 2001).

Figure(15) CT urogram reconstructed with delayed contrast-enhanced images. The three-dimensional relationship of the collecting system to the ribs, pleura, and colon can be delineated (Quoted fromPark et al, 2006).

(e)Magnetic Resonance Imaging(MRI):
MRI is considered the imaging modality of choice in pregnant women And in patients with renal impairment or contrast allergy with no risk of secondary malignancies from radiation exposure as compared to other imaging modalities (Berrington de González and Darby, 2004).
Drawbacks of use of MRI as preoperative imaging modality for PCNL include being expensive, less accurate than ultrasound in detecting urinary stones and obstruction and being less available (McAleer and Loughlin, 2004).
(2)Intraoperative Imaging :
(a)Fluoroscopy:
For antegrade percutaneous renal access fluoroscopic guidance is most commonly used imaging modality. Although retrograde instillation of air and or contrast material is not absolutely essential but it enhances fluoroscopic guided percutaneous access (Tabibi et al., 2007).
It delineates the anatomy of the intrarenal collecting system and if Contrast enhanced it can show pathology as well . Also it can monitor all the steps of the procedure (Osman et al., 2005) .
Combining both ultrasound guided percutaneous access to make sure of placing the needle in the desired calyx and fluoroscopic guidance to monitor the following steps is considered an excellent approach (Osman et al.,2005) .
Puncture of the posterior calyx is preferred to avoid major vascular structures that surround renal pelvis but , sometimes anterior calyceal puncture is required especially in case of a stone in calyceal diverticulum or if posterior calyceal puncture is not possible (Multescu et al.,2016 ).
Puncture of renal pelvis and medial puncture should be avoided due the risk of injury of larger branches of renal artery leading to severe bleeding (Geavlete et al., 2016 ).
Upper pole puncture allow access to isolated upper calyceal stones , large and complex renal stones , uretropelvic junction stones and lower pole partial staghorn stones (Munver et al.,2001).
While , lower pole puncture gives access to lower pole stones and renal pelvis stones , Mid pole puncture gives direct access to isolated mid pole stones with difficult access to either upper or lower poles through this approach (Geavlete et al., 2016 ).
Correct placement of nephrostomy after finishing stone disintegration and extraction is confirmed by intraoperative nephrostogram (Sakurai et al.,2004).
Finally , intraoperative chest fluoroscopy can reveal the presence of hydrothorax and the need for chest tube placement which can be done intraoperative while the patient is anesthetized (Munver et al.,2001).
(b)Ultrasonography:
Ultrasonography is considered the imaging modality of choice if there is difficulty with attaining retrograde accesss as in kidneys above urinary diversions or above a completely obstructed ureter, transplanted kidneys, , or if radiation exposure is a concern. Also it is useful in the case of skeletal abnormalities or anomalous kidneys (Chen et al., 2013; Penbegul et al., 2013).
Advantages of ultrasonography include being portable , less need for maneuver like fluoroscopy , no radiation exposure , no need for retrograde access, can visualize tissue layers during tract establishment and less incidence of bowel injury (Falahatkar et al., 2010)
Drawbacks of Ultrasonography include difficult visualization of the tip of the needle within the pelvicalyceal system, limited field of vision and difficult monitoring of the following steps of percutaneous access (Chen et al.,2013).
Using 3.5- or 5-MHz ultrasound transducer allows selecting the proper calyx for puncture then advancing the needle in the plane of visualization of the probe ,removing the obturator and urine aspiration confirms that the needle is within the pelvicalyceal system (Yagci et al.,2013).
Saline infusion or administration of a diuretic like furosemide improves visualization especially in non-dilated pelvicalyceal system (Yagci et al.,2013).
Doppler ultrasonography has the advantage of visualization of blood vessels and therefore associated with less blood loss and less need for blood transfusion (Tzeng et al,2011).

Figure (16) Ultrasonography guided placement of puncture needle . (Yagci et al, 2013).

(c) Computed tomography and Magnetic Resonance Imaging:
Percutaneous access via CT and MRI guidance is considered in complex Cases as in anatomic abnormalities ,non dilated pelvicalyceal system, ileal conduit patients and associated angiomyolipoma due to risk of bleeding (kim,2015) .
This approach has the benefits of greater accuracy , less incidence of bowel and visceral injury , less blood loss and less need for blood transfusion as compared to standard fluoroscopy (Li et al,2012).
Drawbacks of this approach include being expensive , time consuming ,not available in all operating theatres(Mantugupt et al.,2007).
Radiation Exposure And Safety of Endourologists:
Radiation exposure carries the risk of inducing certain malignancies especially in young children with repeated exposure to fluoroscopy guided procedures as leukemia and thyroid cancer (WOLF S J et al., 2016).
Endourologists also are exposed to this risk mainly due to radiation emitting from patient body so exposure depends on the distance from the patient (Bishoff et al., 2016 ).
Methods of protecting endourologists against hazards of radiation exposure include distance from fluoroscopy source , wearing protective shield and limiting fluoroscopic time of exposure by using fluoroscopic equipment with time alarms and under table fluoroscopic sources, using grid controlled technique rather than continuous fluoroscopy(Rastinehad et al., 2016) .
(d)Blind Access:
Blind percutaneous renal access is considered when ultrasonography is not available and there is complete ureteric obstruction that prevents opacification of the collecting system by IV contrast or retrograde instillation through ureteric catheter(Chien and Bellman, 2002)

The lumbar notch is the landmark for obtaining blind access . this notch is bounded by 12th rib and the latissimus dorsi muscle superiorly , transversus abdominis and external oblique muscles laterally , quadratus lumborum and sacrospinalis medially and internal oblique muscle inferiorly (Basiri et al.,2007) .
So , blind access can be obtained by inserting the needle at 30 degree angle 3 to 4cm deep into lumbar notch to enter the pelvicalyceal system (Basiri et al.,2007).
Another way to get blindly into pelvicalyceal system is through inserting a needle 1 to 1.5 cm perpendicularly lateral to L1 vertebra , then injecting contrast or air through it to opacify the pelvicalyceal system and to guide another needle insertion if needed (Basiri et al.,2007).

Figure (17)The lumbar notch and its boundaries as an anatomic landmark for blind access. (Basiri et al, 2007)
(3)Postoperative Imaging :
(a)Plain Abdominal Radiography :
The value of postoperative KUB is to detect any residual fragments and the need for second look nephroscopy with the benefits of being cheap , rapid but it has low sensitivity (Gerst et al.,2013).

(b)Computed Tomography :
CT in detecting residual stones has sensitivity of 100% and specifity of 62% while KUB has sensitivity of 46% and specifity of 82% so , CT can eliminate the need for unneccesary second look nephroscopy) Tu¨rk et al., 2016)
(c)Antegrade Nephrostogram:
Antegrade nephrostogram assure good antegrade drainage for safe removal of nephrostomy tube and the presence or absence of residual fragment and its location and therefore the need for second look nephroscopy. (Park et al., 2006).
Principles of stone formation in children
Renal stones in children is considered endemic in Egypt, Turkey, Pakistan , and in some south Asian ,African and south American states
( Tekgül S et al., 2015).
In two large observational studies it was found that high fluid intake has a beneficial effect on stone prevention therefore , it is inversely related to the risk of incidence of kidney stone formation.
(Pearle et al., 2016 ).
A prospective, randomized trial assessed the effect of fluid intake on stone recurrence among first-time idiopathic calcium stone formers, urine volume was significantly higher in the group assigned with high fluid intake compared with the control group receiving no recommendations, and, concluded that stone recurrence rates were significantly lower (12% vs. 27%, respectively) (Gnessin et al., 2010).
The concentration product of solution containing ions or molecules of a sparingly soluble salt is a mathematic expression of the product of the concentrations of the pure chemical components (ions or molecules) of the salt (Antonelli et al., 2016).
The solubility product (Ksp) is the concentration product at which a pure aqueous solution of a salt is considered saturated when it reaches the point at which no further added salt crystals will dissolve (Antonelli et al., 2016).

when concentration of solutes in urine exceeds solubility product, precipitation occur but crystallization does not necessarily occur due to presence of inhibitors and other molecules that allow higher concentrations of solutes to be held in solution before precipitation or crystallization occurs (Stoller et al., 2013) .
The formation product is when the concentration of solutes exceeds solubility product so solution becomes unstable and crystals form (Gnessin et al., 2010) .
The metastable range is the range of concentration between the solubility product and the formation product and in this area any change in urine characters as PH , obstruction or stasis in the upper urinary tract , increase in solute concentration leads to crystallization (Miller et al.,2007 ).
Nucleation?and?Crystal?Growth:?
In normal human urine, the concentration of calcium oxalate is four times higher than its solubility in water. factors that favor stone formation include low volume concentrated urine hypocitrituria , increased concentration of calcium, oxalate, phosphate, and uric acid (Stoller et al.,2013).
Crystallization of calcium oxalate can potentially occur Once the concentration product of calcium oxalate exceeds the solubility product, however, calcium oxalate precipitation occurs only when supersaturation exceeds solubility by 7 to 11 times due to presence of urinary inhibitors and other substances (Pearle et al., 2016).

There are two types of enucleation : homogenous and heterogeneous. Homogeneous nucleation is the process by which nuclei form in pure solution , urinary inhibitors can destabilize nuclei , while heterogeneous nucleation is when crystals adsorb on the surface of epithelial cells , cell debris or other crystals (Gnessin et al., 2010).
Urinary inhibitors are the substances that inhibit crystal growth or aggregation and they include Magnesium , citrate , Nephrocalcin, Tamm-Horsfall mucoprotein , uropontin and Bikunin, the light chain of inter-?-trypsin (lotan et al., 2016).
Metabolic disorders in children :
(1)Hyperoxaluria:
Hyperoxaluric stone formers absorb more oxalate in response to an oral oxalate load than non-stone formers with normal oxalate excretion (Krishnamurthy et al., 2003) .
Another study found no difference in oxalate intestinal absorption or renal excretion between stone formers and normal people. (Knight and colleagues., 2007).
Primary hyperoxalurias types ( 1,2 ;3 ) are rare autosomal recessive inherited disorders due to deficiency of alanine-glyoxylate aminotransferase (AGT) which is synthesized in the liver peroxisome leading to defective conversion of glyoxylate to glycine leading to increased oxidative conversion of glyoxylate to oxalate so ,markedly high levels of oxalate in urine ( ; 100 mg /day ) leads to urine supersaturation , crystallization and stone formation (Hoppe et al., 2009) .
Usually, calcium oxalate crystals attach to tubular cells then aggregation of crystals occur leading to stone formation but sometimes , crystals become internalized into renal tubular cells and then extruded to interstitium leading to marked nephrocalcinosis. The most aggressive form of hyperoxaluria is type 1 , that can lead to End stage renal disease by the second or third decade of life (Hoppe et al.,2009) .
(2)Hypercalcuria
Hypercalciuria is increased calcium excretion in urine greater than 200mg calcium/day after adherence to a 400-mg calcium, 100-mg sodium diet for 1 week (Pearle et al.,2016).
Hypercalciuria is also defined as increased calcium excretion in urine greater than 4 mg/kg/day or greater than 7 mmol/day in men and 6 mmol/day in women (Antonelli et al.,2016)
Hypercalciuria is divided into three subtypes: 1-Absorptive hypercalciuria due to increased intestinal absorption of calcium and vitamin D–independent and dependent processes, as well as to upregulation of the vitamin D receptor, 2- renal hypercalciuria due to primary renal leak of calcium, and 3- resorptive hypercalciuria due to increased bone demineralization (lotan et al., 2016).
Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is due to mutations in claudin-16 (paracellin-1) and claudin-19 which are a family of tight junction proteins involved in energy dependent para cellular transport of calcium and magnesium in thick ascending limb and distal convoluted tubule (Konrad et al.,2006 ).

Bartter syndrome is an autosomal recessive disorder due to dysfunction in the thick ascending limb of the loop of Henle Resorptive hypercalciuria is associated with primary hyperparathyroidism which is the cause of nephrolithiasis in about 5% cases (Pearle et al., 2016).
(3)Hyperuricosuria:
Hyperuricosuria is increased urinary uric acid excretion more than 600 mg/day. As 10% of calcium stone formers have high urinary uric acid levels as an isolated abnormality, but it is found in combination with other metabolic abnormalities in up to 40% of calcium stone formers (Pearle et al., 2016).
Hyperuricosuria has been hypothesized to lead to increase urinary levels of monosodium urate that promotes calcium oxalate crystallization through heterogeneous nucleation, or epitaxial crystal growth (Pearle et al., 2016) .
Hyperuricosuria is usually due to increased dietary purine intake. however, acquired and hereditary diseases may also be accompanied by hyperuricosuria, as gout, myeloproliferative and lymphoproliferative disorders, multiple myeloma, secondary polycythemia, pernicious anemia, hemolytic disorders, hemoglobinopathies as thalassemia, complete or partial Hypoxanthine Guanine phosphoribosyl pyrophosphate deficiency, overactivity of phosphoribosyl pyrophosphate synthetase, and hereditary renal hypouricemia (lotan et al.,2016).

(4)Hypocitraturia
Hypocitrituria is a urinary citrate level less than 1 mg/day It is usually due to metabolic acidosis that causes increased renal Reabsorption of citrate and decreased citrate synthesis in peritubular cells (Antonelli et al, 2016).
A study comparing normal subjects and stone formers noted comparable mean serum citrate levels and filtered citrate loads in the two groups; but , 24-hour urinary citrate and the fasting citrate-to creatinine ratio were significantly reduced and mean tubular reabsorption of citrate was significantly increased in the stone formers compared with control subjects (Gnessin et al., 2010).
(5)Renal Tubular Acidosis:
It is a clinical syndrome which is characterized by metabolic acidosis due to defects in renal tubular hydrogen ion secretion or bicarbonate reabsorption(Stoller et al., 2013) .
There are three types of Renal Tubular Acidosis (1, 2, and 3).Type 1 (distal) RTA is of particular significance as it is the most common form of RTA it is the form of RTA most frequently associated with stone formation, which occurs in up to 70% of affected individuals. Nephrolithiasis led to the initial diagnosis of RTA in up to of 50% of cases (Antonelli et al., 2016) .

(6)Cystinuria:
It is an inherited autosomal recessive disorder (or rarely autosomal dominant with incomplete penetrance) which is due to a defect in intestinal and renal tubular transport of dibasic amino acids, resulting in excessive urinary excretion of cystine (Ng and Streem., 2001) .
In children, cystinuria is the cause of up to 10% of all stones (Knoll et al., 2005).
Infection Stones:
Infection stones are composed primarily of magnesium ammonium phosphate hexahydrate but may in addition contain calcium phosphate in the form of carbonate apatite (Pearle et al., 2016) .
It is hypothesized that urea splitting organisms like proteus vulgaris use their urease enzyme to covert urea to ammonia leading to alkaline urine which favors precipitation of triple phosphate ( Ammonium magnesium phosphate ) leading to formation of infected stones (struvite stones ) (Pearle et al., 2016) .
Anatomic predisposition to pediatric nephrolithiasis :
In patients with ureteropelvic junction obstruction (UPJO) the incidence of renal calculi is about 20% ( lotan et al., 2016) .
In two series of children with UPJO with concurrent renal calculi findings support a metabolic contribution to stone formation in the presence of renal obstruction. (Tekin and colleagues., 2001) .
There is a 70-fold increased risk of stone formation in the pediatric population with UPJO compared with normal children (Pearle et al 2016).
Horseshoe kidneys have an associated rate of renal calculi of 20% (Antonelli et al., 2016).
In horseshoe kidney there is high insertion of the ureter into the renal pelvis, leading to impaired urine drainage that leads to increased risk of stone formation rather than metabolic derangements (Antonelli et al., 2016).
Medullary sponge kidney causes recurrent infection and urinary stasis within the ectatic tubules increasing the risk for stone formation (Antonelli et al., 2016) .
The Dindo-modified Clavien system is used to categorize complications following percutaneous nephrolithotomy (Seitz et al., 2012).
(1)Intraoperative complications :
1-Bleeding :
Acute hemorrhage is the most common significant complication of percutaneous access into the upper urinary tract collecting system (WOLF S J et al., 2016) .
Factors that are associated with bleeding during percutaneous renal access include patient characteristics, multiple access sites, supracostal access, increasing tract size, tract dilation with methods other than balloon dilation, prolonged operative time, and renal pelvic perforation (Keoghane et al., 2012).
Bleeding can also occurs due to technical errors , infundibular access which can leads to injury of interlobar arteries , anterior calyceal access or access into a calyx that does not provide direct access to the stone leading to excessive manipulation by the sheath and rigid endoscope and bleeding ,also , misuse of tools like lithotrites , resectoscopes, wires, sheaths, graspers and baskets (Yamaguchi et al., 2011) .
In children undergoing MiniPCNL the incidence of bleeding requiring blood transfusion is about 0.4-24% and it is correlated to stone burden, nephrostomy tract size, number of tracts, and operative time (Bilen et al., 2007).
In children undergoing MiniPCNL to minimize intraoperative bleeding ,the optimum tract size should be between 14 Fr and 20 Fr and multiple tracts should be avoided (Guven et al,.2010).
The access sheath provides intraoperative tamponade of parenchymal bleeding and postoperative hemostasis is accomplished by coaptation of the renal parenchyma over itself (De Sio et al, 2011).
The best management of intraoperative bleeding is to insert and occlude a nephrostomy tube, applying pressure to the incision, and allowing the collecting system to clot off , other measures include cauterization or placement of hemostatic material and in severe cases use of a Kaye Nephrostomy Tamponade Balloon which is a nephrostomy tube surrounded by a balloon should be considered . (WOLF S J et al., 2016).
2-Collecting system injury :
Renal pelvic perforation occurs during initial access or during dilation. It also occurs due to pushing too hard on a renal pelvic stone during lithotripsy, or misusing a lithotripter or resectoscope (Etemadian et al., 2012).
Intraoperative signs of renal pelvis perforation include collapse of previously distended renal pelvis and extravasation of contrast material under fluoroscopy (Ghai et al., 2003).
Renal pelvis perforation can present postoperative as abdominal distention, ileus, and or fever ( Etemadian et al., 2012).

If renal pelvis perforation is detected intraoperative , the procedure should be terminated with adequate drainage of the collecting system via nephrostomy tube and internal ureteral stent or nephroureteral stent then doing nephrostogram 2 to 7 days later before tube removal , but , if detected postoperative beside good drainage of collecting system , percutaneous drain may be needed in cases of large urinoma ( Etemadian et al.,2012).
3-Visceral injury :
The rate of Colon injury during percutaneous renal surgery in the prone position is less than 1% with the left colon being injuried twice as often as the right colon due to greater apposition to the kidney especially with lower pole puncture (Kachrilas et al., 2012).
Risk factors for colon injury include advanced patient age, dilated colon, previous colon surgery or disease, thin body habitus, and the presence of a horseshoe kidney ( Korkes et al., 2009).
If not detected intraoperative colon injury is suspected postoperative by developing unexplained fever ,prolonged ileus, unexplained leukocytosis, rectal bleeding, evidence of peritoneal inflammation, or fecaluria or pneumaturia also, it can present as clinically apparent nephrocolonic fistula or accidently discovered on postoperative nephrostogram (Goger et al., 2012) .
Colon injury is usually extraperitoneal and managed conservatively by giving nothing per mouth, broad spectrum antibiotics, drawing nephrostomy back then replacing it by larger tube to act as colostomy tube and collecting system drainage either through a new percutaneous access or internal ureteral stent ,but , If the injury is intraperitoneal, or if the patient develops peritonitis or sepsis, then open surgical repair may be required ( Winer et al.,2009).
Small bowel injuries are less common than colonic injury and described only in a few case reports ( Traxer.,2009).
Small bowel injuries Present clinically as peritonitis or discovered during nephrostography as nephroenteric fistula , conservative management by using percutaneous intraduodenal catheterization or simple nasogastric or nasoduodenal drainage, combined with drainage of the upper urinary tract, fasting, and parenteral feeding but , open surgery may be required (Ricciardi et al., 2007).
The incidence of hepatic and splenic injury increases with presence of hepatomegaly and splenomegaly respectively and with supracostal percutaneous approach which can be managed conservatively especially with liver injury but , splenic injury if associated with severe hemorrhage may need laparotomy and splenectomy (Desai et al., 2010).
The risk of pleural injury, pneumothorax , hydrothorax and nephropleural fistula ,which is a direct communication between collecting system and pleural cavity increases with supracostal percutaneous renal access (Maheshwari et al., 2009).
Pleural complications of supracostal percutaneous access and the need for intercostal tube placement can be determined by intraoperative fluoroscopy which is less sensitive than postoperative chest radiography ,but , some authors report that thoracotomy was never required on the basis of postoperative chest radiography when intraoperative chest fluoroscopy was negative (Bjurlin et al., 2012).
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4-Metabolic complications :
Saline is the irrigant of choice in percutaneous renal surgery except if monopolar electrocautery is being used in this case we can use glycine or other isotonic nonelectrolyte fluids , while water as an irrigant if excessively absorbed as a result of large venous injury or collecting system perforation can lead to dilutional hyponatremia and hemolysis of red blood cells with hepatic or renal dysfunction and mental status changes (WOLF S J et al., 2016) .
On the other hand , excessive saline absorption as a result of large venous injury or collecting system perforation leads to volume overload presenting as respiratory distress or cardiac failure (Ganpule et al.,2016).
Venous gas embolism is a rare , but , potentially fatal complication of percutaneous renal surgery which can occurs during percutaneous surgery with or without retrograde air pyelography as a result gas passes into venous system and through the right heart into the pulmonary circulation blocking right heart outflow leading to hypoxemia, hypercapnia, and depressed cardiac output. (Ganpule et al., 2016).
(2)Postoperative Complications :
1- Delayed hemorrhage :
Postoperative hemorrhage occurs in about 1% of percutaneous renal surgeries with the nephrostomy tube in place , at tube removal or after tube removal (Keoghane et al.,2012).
Postoperative bleeding occurs due to arteriovenous fistula which commonly causes continuous frank hematuria due to rupture into the collecting system , but , rarely causes drop of hematocrit with clear urine if ruptured outside the kidney and arterial pseudo aneurysm which is less common than arteriovenous fistula and usually causes intermittent bleeding (WOLF S J et al., 2016).
Angiography is diagnostic in more than 90% of bright frank hematuria after percutaneous renal surgery and selective angioembolization is highly effective in treatment of arteriovenous fistula and arterial pseudo aneurysm (Ji et al, 2012).
If angioembolization failed , nephrectomy may be required or alternatively endovascular placement of covered stent to occlude the site of injury and maintain the patency of the feeding artery or ultrasonography guided puncture of the pseudo aneurysm with injection of thrombin or adhesive fibrin tissue into the pseudo aneurysm (Sakr et al., 2009).
2-Postoperative Fever and Sepsis :
Risk factors for postoperative fever and sepsis include diabetes mellitus , paraplegia, indwelling ureteral stent or nephrostomy tube, previous percutaneous nephrolithotomy, multiple access tracts, infection stone, positive preoperative urine culture, larger stones, and hydronephrosis (Kumar et al., 2012).
15% to 30% of patients after percutaneous nephrolithotomy develop a fever (Gutierrez et al., 2013).

Careful observation, appropriate diagnostic evaluation, and initiation of antimicrobial therapy and other supportive care are indicated a postoperative fever does not resolve promptly (Aron and associates, 2005 ).
Sepsis occurs in 0.5% to 2.5% of patients after percutaneous nephrolithotomy (Li et al., 2013).
Preventing postoperative sepsis implies proper treatment of preoperative urinary tract infection and in cases of infected stones or indwelling nephrostomy suppressing bacterial counts as much as possible is the goal to prevent postoperative infectious complications (Korets et al., 2011).
Upon initial percutaneous renal access if pus is aspirated the best approach is to abort the procedure and leave a nephrostomy tube for drainage (Aron and associates, 2005 ).
3-Tube dislodgement :
Tube dislodgement can be prevented by securing it at the skin. Cope retention mechanism is more secure than malecot catheter but not as secure as balloon catheter (Canales et al., 2005).

Figure(18) Cope catheter, with the retention string (Maher et al,. 2002)
The time from insertion to dislodgement is important as if this time is short then complete dislodgement often leads to complete loss of percutaneous access as the tract is not yet mature enough (WOLF S J et al.,2016).
4-Collecting system obstruction :
Distal ureteric obstruction can occur due to blood clot , edema , residual stone impaction that is why antegrade nephrostogram or transient clamping of nephrostomy tube should be done before tube removal (Seitz et al.,2012).
Stricture can develop postoperative at the ureteropelvic junction or at an infundibulum .If this stricture developed early it leads to nephrocutaneuos fistula but if developed later on it leads to hydronephrosis or hydrocalycosis (Seitz et al, 2012).
Risk factors for postoperative stricture include large stone burden , long or multiple procedures , prolonged nephrostomy tube drainage , previous open stone surgery, diabetes mellitus, and obesity ( Lopes-Neto et al., 2008).
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Table (1): Modified Clavien-Dindo grading system for the classification of surgical complications (( Dindo et al,, 2004).
Any deviation from the normal postoperative course without the need for pharmacological treatment or surgical, endoscopic and radiological interventions. Acceptable therapeutic regimens are: drugs such as antiemetics, antipyretics, analgesics, diuretics and electrolytes, and physiotherapy. This grade also includes wound infections opened at the bedside Grade I
Requiring pharmacological treatment with drugs other than those allowed for grade I complications. Blood transfusions and total parenteral nutrition are also included. Grade II
Requiring surgical, endoscopic or radiological intervention Grade III
Intervention not under general anesthesia Grade III-a
Intervention under general anesthesia Grade III-b
Life-threatening complication (including CNS complications: brain hemorrhage, ischemic stroke, subarachnoid bleeding, but excluding transient ischemic attacks) requiring IC/ICU management Grade IV
Single organ dysfunction (including dialysis) Grade IV-a
Multiorgan dysfunction Grade IV-b
Death of a patient Grade V
If the patient suffers from a complication at the time of discharge the suffix “d” (for disability) is added to the respective grade of complication. This label indicates the need for a follow-up to evaluate the complication fully Suffix “d”

1- MiniPCNL :
Helal et al. were the first to describe a technique for pediatric percutaneous nephrolithotomy performed on a 2-year-old premature female child with the use of instruments with smaller access diameters . They described the use of a 15 Fr Hickman peel-away sheath as the working sheath in the removal of three stones of 5-7 mm. A 10 Fr pediatric cystoscopy and grasping forceps was used to remove the stone with success (Helal et al.,1997).

Figure(19) 15 Fr Hickman peel-away sheath (Helal et al 1997).
Mini-perc was introduced in 1997 by Jackman et al. They used a 7 Fr pediatric cystoscope and a 9.8 Fr flexible ureteroscope through an 11 Fr tract in 11 children (Jackman et al., 1998).
Mini-perc can be defined as PCNL with tract size equal or less than 20 Fr (Ganpule et al., 2015).

Figure(20)MiniPCNL kit: Wolf metal kit consists of the12F and 15F metal dilators and a 16F metal PCNL sheath(Wah et al 2013).
The uptake of this technique was slow, because there were reservations regarding the short and long-term effects of using large instruments in small, pediatric kidneys. A 24F sheath in an infant is said to correspond approximately to a72F sheath in an adult (Wah. et al., 2013).
The advantages of the mini-perc technique include reduced incidence of bleeding and other complications, and shorter hospital stay (Irving et al., 2005).
When mini-PCNL performed in children and adults were compared, there was no significant difference in perioperative total complication rate However, major complications (Clavien-Dindo Grade IV and V) were not observed in children.( Zeng et al., 2013).
Mini-perc shares comparable clearance rate as the standard PCNL, but is associated with less hemoglobin drop, hospital stay, analgesic requirements and complication rates (Mishra et al., 2011).
The limitations to this technique: miniature-sized instruments are required, and the operative time is prolonged due to the need to remove greater numbers of smaller stone fragments through a narrower track(Irving et al., 2005).
With the recent advances in technology and development of miniature endourological instruments, Mini PCNL in children has become a widely accepted practice(Kapoor et al., 2008).
General indications for mini-PCNL that may also exist for the conventional method include previous failure of ESWL or ureteroscopic lithotripsy, cystine calculi and anatomic abnormalities precluding retrograde access or the distal passage of stones . Mini-PCNL may also be useful in patients with a narrow (30 mm) infundibulum or as a secondary access for inaccessible or residual fragments resulting from standard PCNL (Chan et al., 2000).
Current literature reports a range of 68–89 % of stone free clearance rates on initial intervention in children using adult-sized instrumentation (Razvi H et al., 2018).
For children undergoing PCNL using the mini-perc technique, the success rate for stone clearance is reported to be 80–89 %( Wah. et al., 2013).
Miniaturized PCNL techniques can deliver high SFRs for stones up to 2 cm with a small risk of Clavien I/II complications(Jones et al.,2017).

Compared with ESWL, mini-PCNL has been reported to have signif- icantly higher stone-free rates, especially f or renal stones greater than 1 cm (Zeng et al., 2012).
Compared to Retrograde Intrarenal Surgery (RIRS), mini-PCNL has shown better stone-free rates for the management of larger renal stones(2-3) cm and large impacted upper ureteral stones but similar effectiveness was reported when treating smaller renal stones between both procedures (Kirac et al., 2013 , Knoll et al., 2011).
2- Micro-Perc :
Micro-perc consists of a 4.5 Fr needle, which has three parts: an outer sheath for passage of optics and energy source, a central part which comprises of a hollow needle and an innermost which comprises of a radiopaque stylet (Ganpule et al.,2015 ).
The all-seeing needle was presented in 2010 by Bader et al at the American Urological Association Annual Meeting in San Francisco (Desai et al.,2011).

Figure(21)Microperc Kit, AandB, fiber-optic telescope. C, multijointed mounting arm. D, 4.85Fr sheath assembled for microperc. Laser fiber passes through the central channel. Irrigation connection and telescope are each attached to 1 side port(Desai et al 2011).
Micro-perc is used for renal calculi less than 10mm, renal calculi in the lower calyx less than 10mm, not susceptible to flexible ureteroscopy because of difficult anatomy. In addition, Micro-perc could be used in pediatric urolithiasis and anomalous kidney such as ectopic kidneys. (Ganpule et al.,2015 ).
Micro-perc is a new technological advancement in the field of percutaneous management for renal stones that has a promising future for treating nonbulky urolithiasis. This technique appears feasible, safe and efficacious, and has the potential of decreasing the morbidity associated with standard PNL(Desai et al.,2011).
Successful stone free-rate is reported in the range of 85-93% (Martinez et al., 2015)
In a recent study in children (aged 18 months to 11 years) who underwent Micro-perc lithotripsy overall stone-free rate was 100% at one month without ancillary procedures (Caione et al., 2015 ).
3- Ultraminiperc :
The basic component is a 6-Fr Mininephroscope which can be passed through an 11-to 13-Fr metal sheath. Stones are fragmented with 200-to 300-?m laser at 10-20W (Ganpule et al., 2015).

Figure (22) Ultra-mini-percutaneous nephrolithotomy equipment(Agrawal et al 2016).
Ultramini-perc is indicated for stone less than 1.5cm (Ganpule et al., 2015)
4-Retrograde Intrarenal Surgery :
With the introduction of small flexible URS in clinical use, the Ureteroscopic management of renal calculi has become possible even in Pediatric patients . The complication rate of pediatric URS ranges from 1.3 to 5.2 % in the literature, whereas the success rates range from 77 to 100% ( Kim et al.,2008 ).

Figure(23) Olympus URF-P3 flexible ureteroscope (Sharma et al 2011).
Resorlu et al evaluated, retrospectively, the records of 201 pediatric patients who underwent mini-perc or RIRS. They observed minor complications classified as Clavien I or II in 17% and 8.4% in mini-perc and RIRS respectively. No major complications (Clavien III-V occurred in either group) . Overall, they observed that complication rates in mini-perc were higher, but the differences were not statistically significant . However, the mean hospital stay, fluoroscopy, and operation times were significantly longer in the mini-perc group (Resorlu et al., 2012).
Retrograde intrarenal surgery (RIRS) is nowadays considered a well-established, effective, minimally invasive procedure for treating pediatric kidney stones. However, neither the AUA nor the EAU guidelines recommend it as the first-line treatment option for pediatric intrarenal stones (Tekgu¨l S et al.,2016).
To evaluate the safety, efficacy, and morbidity as well as the usefulness of modified tubeless minimally invasive percutaneous nephrolithotomy (mini-Perc) for management of renal stones in children.
Management of renal stones in children includes ESWL, flexible ureteroscopy, PCNL and open surgery(Wah et al., 2013).
Hence, open surgeries are now considered rarely, PCNL has been identified globally as a safe procedure associated with appreciable greater success rate along with lesser major associated surgical complications replacing open surgeries in many cases (Ramchandraiah et al., 2016).
Recently, several reports have suggested that the risk of bleeding is associated with sheath size. Thus, to decrease morbidity related to larger tracts, such as bleeding, postoperative pain, and potential renal damage, modifications to technique and the size of the instruments have been made, therefore the mini-PCNL or miniperc, was originally developed for the management of renal stones in pediatric patients(Yamaguchi et al., 2011).
Mini-perc shares comparable clearance rate as the standard PCNL, but is associated with less hemoglobin drop, hospital stay, analgesic requirements and complication rates (Mishra et al., 2011).
When mini-PCNL performed in children and adults were compared, there was no significant difference in perioperative total complication rate However, major complications (Clavien-Dindo Grade IV and V) were not observed in children.( Zeng et al., 2013).
Compared with ESWL, mini-PCNL has been reported to have signif- icantly higher stone-free rates, especially for renal stones greater than 1 cm (Zeng et al., 2012).

Compared to Retrograde Intrarenal Surgery(RIRS), mini-PCNL has shown better stone-free rates for the management of larger renal stones (2-3)cm and large impacted upper ureteral stones but similar effectiveness was reported when treating smaller renal stones between both procedures (Kirac et al., 2013).
In the standard technique of PCNL, nephrostomy tube is placed at the end of the procedure to act as a tamponade to stop bleeding, provides adequate renal drainage, higher analgesic requirement and makes an additional endoscopic procedure easier but, it is associated with prolonged hospitalization, urine extravasation, and postoperative pain and discomfort (Chung et al., 2016).
Since totally tubeless PCNL was first introduced by Wickham et al. in 1984 without external and internal ureteral stents it then gained popularity and was found to be associated with shorter length of hospitalization, and lower analgesic requirement and nephrostomy tube site complications but, it doesn’t provide access back for second look in case of residual stones (Chung et al., 2016).
The modified tubeless technique is associated with less postoperative pain and discomfort, shorter hospital stay, less analgesic requirement and provides access back for second look (Agrawal et al., 2014).
For this in our study we try to evaluate the safety, efficacy, and morbidity as well as the usefulness of modified tubeless minimally invasive percutaneous nephrolithotomy (mini-Perc) for management of renal stones in children.
In this study the total number of studied cases was 50 child, 32 boys (64%) and 18 girls (36%) , mean age was 8.64±3.19 (4.0-16.0). BMI in Kg/sq.m mean ± SD(Range) was 20.98±2.82 (17.0-29.0) , BMI was between 17