Blood clots seen in: \200 \200 \200 \200 bleeding renal tumors; arteriovenous malformations; following renal trauma; patients with p olycystic kidney disease. Uroepithelial malignancy: may occur in the renal pelvis, ureter and bladder. Ureteral stric tures: secondary to radiotherapy or retro- peritoneal surgery. Worldwide infection with Sch istosoma haematobium is an important cause. Ova may lodge in the distal ureter and bladder causing ureteral strictures, and contraction of the bladder in up to 50% of chronically inf ected patients. Urethral strictures: usually only in males secondary to urethral instrument ation or infection. Neurological conditions: can result in either a contracted (spastic) or a flaccid (atonic) bladder (depending on whether the lesion affects upper or lower motor n eurons) and cause impaired bladder emptying, e.g. multiple sclero- sis, spinal cord trauma. Extrinsic causes of obstruction Females: \200 Etiology It is useful to consider whether the obstruction is: \200 \200 carcinoma of the cervix: direct extension of the tumor to involve the urinary tract occurs in up to 30% of patients; congenital or acquired; due to disease intrinsic or extrinsic to the renal tract; CHAPTER 16.3 Urinary tract obstruction 653 Extrinsic causes of obstruction Intrinsic causes of obstruction Stricture Tumors Calculi Renal pelvis Retroperitoneal pathology Fibrosis Aortic aneurysm Malignancy (1 or 2 ) Inflammation Granuloma Calculi Clot Tumor Strictures Ureters Gravid uterus Female Benign ovarian mass Malignant ovarian mass Endometriosis Carcinoma of cervix Tumors Neurological conditions Bladder Male Benign prostatic hypertrophy Carcinoma of the prostate Posterior urethral valves Urethral strictures Urethra Fig. 16.3.1 Diagrammatic representation of urinary tract showing the common sites and cause s of obstruction. \200 benign and malignant uterine and ovarian masses; pelvic pathology: abscesses, endometriosis , and pelvic in \202 ammatory disease; inadvertent ligation of the ureter during surgical proce- dures; pressure from a gravid uterus on the pelvic rim: right ureter more commonly a ffected than the left. It is usually asymptomatic and the changes resolve rapidly following delivery (non-obstructed ureteral dilatation is also seen in pregnancy as a result of horm onal effects, especially progesterone on smooth muscle). Glomerular \201 ltration The glomerular effects of obstruction are complex. Obstruction c an alter all the determinants of glomerular \201 ltration: \200 mean hydraulic pressure gradient between the glomerular capillary lumen and Bowman \200\231 s space; renal plasma \202 ow; ultra \201 ltration coef \201 cient of the glomerular ca pillary wall; mean oncotic pressure difference across the glomerular wall. \200 Males: \200 \200 Early obstruction is typically characterized by: \200 progressive intrarenal vasoconstric tion; \200 shunting of blood to non \201 ltering areas; \200 proportionately greater f all in GFR; \200 fall in \201 ltration fraction. benign prostatic hyperplasia: commonest cause; carcinoma of the prostate: either from direc t extension of the tumor to the bladder outlet or ureters or from metastases to the ureter or lymph nodes. Either sex: \200 These changes are modulated by generation of vasocon- strictors such as thomboxane and angi otensin II, a decrease in the generation of vasodilatory prostaglandins and nitric oxide an d an in \201 ltrate of macrophages \200\223 the latter has also been implicated in the pa thogenesis of the structural changes that occur following prolonged obstruction. Whole kidn ey GFR will usually return to normal after short- term obstruction (days). However, even re latively short periods of obstruction may lead to a permanent loss of nephrons with whole k idney GFR recovering at the expense of hyper \201 ltration in the remaining functional nep hrons. Once extensive chronic structural changes have occurred within the kidney the patien t will be left with a decreased GFR and CKD even after the effective relief of the obstruct ion. retroperitoneal malignancy: either primary (lymphoma and sarcoma) or metastases; retroperit oneal \201 brosis: either idiopathic (rare) or second- ary to in \202 ammatory aortic an eurysms, drugs (methy- sergide, B-blockers bromocriptine), radiation, trauma or granulomato us disease (TB, Crohn \200\231s, sarcoid, Wegener \200\231s); vascular abnormalities: aneur ysmal dilatation of the aorta or iliac vessels, aberrant vessels, or anatomic varia- tions in the location of the ureter (retrocaval ureter). Acquired urinary tract obstruction (most ly prostatic dis- ease in men) accounts for 3 \200\2235% of the cases of ESRD in patients a ged >65 years. Pathophysiological changes within the kidney Obstruction of the renal tract rapidly results in alteration in both glomerular and tubular function. These changes depend on the duratio n of the obstruction, the patient \200\231s hydration state and whether there is a con- tra lateral functioning kidney. Ultimately irreversible structural damage leads to CKD. Tubular function Abnormalities in tubular function are common in urinary tract obstruction and may include: \200 \200 \200 \200 altered renal handling of electrolytes; changes in the regulation of water excretion; impai rment of urinary concentrating ability; urinary acidi \201 cation defects. K. HARRIS 654 Investigations General investigations Urinalysis This is commonly negative but depending on the cause of obstruction can show: \200 \200 \200 \200 \200 Recovery of tubular function following release of obstruc- tion is slow and it may remain a bnormal even after whole kidney GFR has returned to normal. Clinical features Symptoms Symptoms depend on the patient \200\231s age and the site, dura- tion, degree and cause of the obstruction. Congenital obstruction may cause: \200 \200 \200 \200 hematuria; bacteriuria; pyuria; crystalluria; low grade proteinuria. oligohydramnios; distended bladder; failure to thrive; vomiting. Full blood count Anemia may be found if obstruction has resulted in CKD, but polycythemia h as been described in short-term obstruction from erythropoetin release. Acquired obstruction may cause: \200 \200 \200 \200 \200 \200 changes in urine output; \202 ank pain; hematuria; lower urinary tract symptoms; urinary tract infections; no symptoms. Renal function tests These may range form near normal (especially if the obstruction is uni lateral or partial without damage to the upper renal tract) to advanced CKD. Electrolytes These may demonstrate a hyperchloremic hyperkalemic (type IV) metabolic acidos is and hypernatremia. Changes in urine output: anuria occurs following complete bilateral obstruction or unilater al obstruction in patients with a single functioning kidney. In partial obstruction, urine output may be normal or increased (polyuria). Flank pain and tenderness are typical of uppe r tract obstruction and may be severe and crescendo in nature radiating to the labia, the t esticles, or the groin (renal colic) if the obstruction is acute. Hematuria: trauma to the uroepithelium from calculi or a uroepithelial malignancy can result in either visible (macr o) or invisible (microscopic) hematuria. Lower urinary tract symptoms are typical of bladde r out \202 ow obstruction: \200 \200 \200 \200 Imaging investigations Imaging is key to diagnosing the site and cause of obstruc- tion and may require complementary use of a number of different modalities. No single investigation should be relied upon to rule out obstruction if the clinical suspicion is high. The imagi ng techniques below have largely replaced the use of IVU in the evaluation of suspected ren al tract obstruction. Ultrasound (Fig. 16.3.2A) Useful \201 rst-line investigation but operator dependent. Avoi ds ionizing radiation. Readily detects hydronephrosis but not its cause. Can be used to ass ess bladder emptying in patients with lower urinary tract symptoms. Should be combined with a KUB X-ray to look for areas of calci \201 cation in the line of the ureter (stones). Fa lse positives (nonobstructed dilatation, as may be seen in re \202 ux nephropathy) and fal se negatives (nondilated urinary tract obstruction) can occur. poor urine stream; dribbling; hesitancy; nocturia. Urgency, frequency, and urinary incontinence can also result from incomplete bladder emptyi ng. \200\230Prostatism \200\231 is used to describe these symptoms in men as they are comm only (but not always) due to prostatic hypertrophy. Urinary tract infections (UTIs): lower urinary tract obstruc- tion predisposes to the development of UTIs because of urinary stasi s. Further investigation to exclude obstruction should be undertaken following a single UTI in men or young children of either sex, recurrent infections in women or infections with a n atypical organism. Obstruction should be considered in any patient with CKD. CT scan (Fig. 16.3.2B) Noncontrast helical CT is excellent at detecting stones and is there fore the imaging modality of choice for patients with acute \202 ank pain. It can provide good anatomical de \201 nition and de \201 ne the nature and the site of the obstructing lesion, especially when this is extrinsic to the urinary tract. IV contrast can improve th e diagnostic potential but may be contraindicated in patients with renal impairment. Exposu re of the patient to ionizing radiation limits the ability to use it repetitively. Signs Physical examination may demonstrate: \200 \200 \200 \200 \202 ank tenderness; a \202 ank mass (enlarged hydronephrotic kidney); a distended blad der (bladder out \202 ow obstruction); evidence of malignancy \200\223 rectal and pelvic examinations are important (enlarged prostate and gynecological malignancy); hypertension ( sodium and water retention and abnor- mal release of renin); hypotension (polyuria and volu me depletion); MR urography (Fig. 16.3.2C) Can provide both functional and anatomic information without ex posure to ionizing radiation (and may allow a diagnosis without using multiple investigatio ns such as nuclear scans, voiding cystourethrography and USS). CHAPTER 16.3 Urinary tract obstruction 655 Has similar accuracy to spiral CT (when used in conjunc- tion with KUB). The potential for gadolinium to cause nephrogenic sclerosing dermopathy limits the use of MR in patients with moderate \200\223severe CKD. Are invasive and have generally been replaced by USS, CT and MR. Treatment Close collaboration between nephrologists, radiologists and urologists is essenti al. The treatment required is determined by the duration and location of the obstruction, t he underlying cause, and the degree (if any) of renal impairment. Goals of treatment must i nclude: \200 Renography (Fig. 16.3.2D) [99mTc]MAG-3 renography with IV furosemide at 20 min (diuresis re nogram) can help determine whether a dilated collecting system is due to functional obstruc tion: persist- ence of the isotope suggests obstruction. The test is unhelpful when renal f unction is poor. It may overdiagnose obstruction in those aged <2 years (the renal pelvis n ormally expands during diuresis in this age group). prompt relief of the obstruction to allow recovery of renal impairment and reduce the possi bility of CKD in the long term; management of any metabolic and \202 uid and electrolyte disturbance; a long-term management plan to de \201 nitively deal with the pathology which caused the obstruction. Retrograde/antegrade pyelography Can be used to accurately localize and characterize obstru cting lesions. May be combined with therapeutic interventions (neph- rostomy, ureteric sten ting). May be combined with functional tests of obstruction (Whitaker test, urodynamics). Dialysis should only be required in a minority, for example where life-threatening hyperkal emia or fluid overload has to be corrected to get the patient \201 t for the planned inte rvention. Bladder out \202 ow obstruction can usually be treated by a urethral catheter. B A C D Fig. 16.3.2 (A) Longitudinal USS of an obstructed kidney showing well-preserved parenchyma (a) and a dilated pelvis (b). (B) Abdominal CT of a patient with bilateral renal stones. Th ere is a calculus on the left (a) and a dilated renal pelvis on the right (b). (C) MR urogr am showing a hydronephrotic kidney (a), a dilated lower ureter (b), a \201 lling defect i n the ureter (c) and bladder (d). (D) Diuresis renogram. The trace of the right kidney is n ormal (a), but the trace of the left obstructed kidney continues to rise after furosemide ( b). On delayed images the left kidney has not emptied (c). K. HARRIS 656 Suspected obstruction History/examination Urinalysis and MSU Assessment of renal function Flank pain USS of kidneys and bladder KUB X-ray CT Scan Nondilatated PC system Large residual Volume in bladder Dilatation of PC system Obstruction still suspected Nephrostomy Ureteric stenting Catheterize Further imaging to define lesion Diuretic renogram Retrograde pyelogram Plan definitive therapy Fig. 16.3.3 Algorithm for the investigation and management of obstruction. If a catheter cannot be passed per urethra a suprapubic catheter should be inserted. Upper urinary tract obstruction can be rapidly relieved by placement of a nephrostomy under local anesthetic, and this is the treatment of choice in an emergency setting or where infection above the site of the obstruction is suspected. When both kidneys are obstructed, the neph rostomy should be placed in the kidney with the best-preserved parenchyma. A nephrostomy al lows time for renal function to recover and to plan de \201 nitive therapy, although it ma y be used long term in patients who either have an incurable malignancy or who are un \201 t for surgery. Antegrade stenting of the ureter may be possible following a nephrostomy to establish internal drainage of the kidney into the bladder. Cystoscopy and retrograde sten ting of the ureter(s) offers an alternative approach to relief of upper urinary tract obstr uction. Once the obstruction has been relieved and wherever possible, de \201 nitive treat ment of the obstructing lesion should be undertaken. The therapy required depends on the si te and nature of the obstructing lesion and a full discussion is beyond the scope of this c hapter. The general approach to the investigation and manage- ment of obstruction is shown in Fig. 16.3.3. Postobstructive diuresis This is typically seen following the release of bilateral obstruct ion or obstruction in a single functioning kidney. It may result from both an appropriate e xcretion of retained salt and water and an inappropriate loss of salt and water due to tubu lar dysfunction following obstruction. Without appropriate management volume depletion and electrolyte disturbances can occur with failure of the renal function to recover. Managemen t includes: \200 regular assessment of the patient \200\231s \202 uid balance includ- ing hourly urine out put and weighing daily; regular measurement of serum electrolytes: at least daily and more frequently if the diuresis is massive; appropriate \202 uid replacement: once the patient is euvo- lemic, replacement of urine losses plus an allowance for insensible losses is req uired. Intravenous therapy may be required and bicarbonate, potassium, calcium, phos- phate , and magnesium replacement may be necessary. Follow-up Many patients will recover normal renal function following effective relief of th e obstruction. The follow-up of such patients relates to that required for the underlying c ondition which caused the obstruction or to the postoperative follow up required for any su rgery that was undertaken to treat the obstruction. CHAPTER 16.3 Urinary tract obstruction 657 However, if the kidney had sustained structural damage following prolonged obstruction, the patient may be left with a varying degree of CKD. Treatment is then the same as for any pa tient with CKD with attention paid to: \200 \200 \200 Vaglio A, Palmisano A, Corradi D, Salvarani C, Buzio C. Retroperitoneal fibrosis: evolving concepts. Rheum Dis Clin North Am 2007; 33: 803 \200\223817. Internet resources Retroperitoneal \201 brosis patient and carer information: control of blood pressure; use of ACEIs if there is ongoing signi \201 cant proteinuria; a ggressive management of cardiovascular risk factors. Progression of CKD (even if severe) is likely to be slow if the obstruction has been effectively relieved and hypertension is con trolled. http://www.retroperitonealfibrosis.com/ Schistosomiasis information: http://www.cdfound.to.it/html/gen1.htm#sh5 See also Imaging in renal disease, p. 20 Renal stone disease, p. 269 Congenital abnormaliti es of the urinary tract, p. 658 Malignancy of the kidney and urinary tract, p. 667 Further reading Leyendecker JR, Barnes CE, Zagoria RJ. MR urography: techniques and clinical applications. Radiographics 2008; 28: 23 \200\22346. Proesmans W. The neurogenic bladder: introducing four contribu- tions. Pediatr Nephrol 2008; 23: 537 \200\223540. S.D. MARKS 658 Congenital abnormalities of the urinary tract Introduction Antenatal USS screening has increased the prenatal detec- tion and early postn atal management of a group of diseases of abnormal early renal development called congenita l abnormalities of the kidney and urinary tract (CAKUT). CAKUT comprise 1 in 500 fetal USS, up to 30% of all ante- natally diagnosed fetal anomalies and are the most common cause of CKD and ESRD in infants and children. Genetic studies have implicated mutations in various genes (including HNF-1b, PAX2, EYA1, SIX1, and SALL1) and are providing further evidence th at there is a polygenic trait of inheritance with incomplete and variable penetrance. Some of the diverse anatomical renal and ureteric anoma- lies are discussed in this and other ch apters (Tables 16.4.1 and 16.4.2). Commonly encountered CAKUT include: \200 \200 \200 \200 \200 \200 \200 Investigations Postnatal USS together with micturating cystourethrog- raphy and nuclear med icine imaging may noninvasively diagnose the speci \201 c CAKUT, although cystoscopy may b e required (for example, when obstructive uropathy due to posterior urethral valves is susp ected in a male infant). Genetic testing may be appropriate if there are speci \201 c feat ures of CAKUT-associated syndromes. Multicystic dysplastic kidney This is due to failure of union of the ureteric bud with rena l mesenchyme resulting in a multiloculated mass with thin- walled cysts, atretic proximal u reter and no functional renal parenchyma (as seen on nuclear medicine scan). The renal pare nchyma is replaced by multiple noncommuni- cating different-sized cysts. renal hypodysplasia; polycystic kidney disease; hydroureteronephrosis; vesicoureteric re \202 ux (VUR); mega-ureter; ureteroceles; urinary tract obstruction (posterior urethral val ves, pelviureteric and vesicoureteric junction obstruction). Clinical features 90% of cases who survive are unilateral. It is commoner in boys. It is as sociated with contralateral renal anomalies including: \200 contralateral renal agenesis (resulting in Potter \200\231s syndrome); pelviureteric junction obstruction; VUR. \200 Clinical evaluation of CAKUT As in other birth defects, it is important to undertake a full evaluation with history, examination and appropriate investigations. Investigations Renal ultrasound This normally demonstrates hyperechoic scanty renal tissue among cysts in a nonreniform mass (Fig. 16.4.1). History A detailed maternal history (including prescribed and recreational drug use) is imp ortant. The history of the antenatal period is also important, including oligohydramnios or anhydramnios, results of ante- natal USS (with degree of dilatation at various gestational ages). A complete family history should be taken (diabetes mellitus, hearing and/or visual loss, congenital and urinary tract anomalies). If there is a normal contralateral kidney this will show compensatory hypertrophy although a normal bladder without ureteric dilatation should be identi \201 ed. DMSA scan To assess the solitary functioning kidney. Formal measurement of glomerular \201 ltration rate This should be considered in all infa nts at 12 months of age where there is no evidence of compensatory hypertrophy or concerns with renal dysfunction (such as elevated plasma creatinine). Examination Any dysmorphic features should be identi \201 ed including: \200 \200 \200 \200 \200 \200 \200 Differential diagnosis Renal dysplasia (or renal cystic dysplasia) where there is functioni ng tissue in the affected kidney(s), although some studies show different spectrums of dise ase with both renal dysplasia and multicystic dysplasia occurring within some families. pre-auricular tags or pits; branchial arch abnormalities; retinitis pigmentosa; coloboma; a niridia; abnormal number or shape of digits and/or toes; external genitalia. Prognosis Multicystic dysplastic kidneys spontaneously involute (usu- ally by 2 years of ag e when size is <5 cm), so that many solitary kidneys which were labeled as contralateral re nal agenesis may now be detected on antenatal USS screening as multicystic dysplastic kidne ys. Recent evidence suggests that the risks of developing hypertension and/or malignancy ar e negligible and routine nephrectomy is not advised. Hypertension and/or malignancy are mor e likely to occur when size is >7 cm (spontaneous involution is unlikely). Major and minor anomalies associated with syndromes including: \200 VACTERL (Vertebral, Ano-rectal Cardiac, Tracheo- esophageal fistula, Esophageal atresia, Ra dial/renal, Limb) association; CHARGE (Coloboma (iris, choroids or retina), Heart defects, Atresia choanae, Retarded growth and devel- opment, Genital anomalies and Ear anomalies or deafness). CHAPTER 16.4 Congenital abnormalities of the urinary tract 659 Table 16.4.1 Different patterns of renal anomalies Unilateral or bilateral (without any functioning renal tissue resulting in Potter \200\231s syndrome). Agenesis Fusion of upper to lower pole. Crossed renal ectopia Patients mostly asymptomatic. Duplication Secondary to error in ascent. Pelvic location most common. Ectopia Complete fusion of the kidneys is rare with lower pole fusion commoner (horseshoe kidney). Fusion Mostly congenital with no functioning renal parenchymal tissue and associated with vesicour eteric re \202 ux (although hypothetical risks of hypertension and malignancy). Multicystic dysplastic kidneys Fig. 16.4.1 A left multicystic dysplastic kidney with the largest cyst shown on USS image m easuring 7 mm. There was no normal renal parenchyma tissue but only a few small cysts seen in the left \202 ank (overall the collection of cysts measured 1.7 \227 1 cm). Autosomal recessive or dominant polycystic kidney disease with bilaterally enlarged echogen ic kidneys and cysts. Polycystic kidneys Bilateral duplication is relatively rare accounting for 15% of all duplication cases. Dupli cation has been detected frequently in postmortem studies of asymptomatic individuals. Table 16.4.2 Other CAKUT conditions Primary mega-ureter without infravesical obstruction and secondary mega-ureter with high in travesical pressure (obstruction, neuropathy). Mega-ureter Clinical features Kidneys are larger than normal. Common occurrence (1% of population). Usu ally familial. Often asymptomatic (usually females). Obstructive uropathy Most commonly posterior urethral valves which affects male children on ly, although anterior urethral valves have been described in females. Accompanied by bilate ral (can be unilateral) hydroureteronephrosis with or without VUR, renal dysplasia and CKD Complete duplication There are two moieties. Either both ureters enter the bladder with the upper pole ureter opening inferomedially or one ureter is ectopic, draining into the vagin a or posterior urethra. This carries an increased risk of complications including: \200 Functional obstruction of the junction between renal pelvis and ureter. Pelviureteric junction obstruction Cystic dilatation of the terminal ureter which can be: \200 intravesical (less obstructiv e, often Ureterocele obstruction of the upper moiety (ureterocele or VUJ obstruction); VUR of the lower moiety u reter due to its short intra- mural tunnel as it traverses the bladder wall. asymptomatic) or extravesical (located at bladder neck, often associated with renal duplication). Duplication is often associated with: \200 \200 \200 \200 \200 \200 Functional obstruction of the junction between bladder and ureter. Vesicoureteric junction obstruction ectopic ureters; ureteroceles; VUR; pelviureteric junction obstruction; dysplastic moiety; family history or as part of a syndrome. Nephrectomy may be indicated if there are severe and recurrent infections as surgical inter vention carries a low complication rate and obviates the need for long-term follow-up if th e contralateral kidney and bladder are normal. Partial duplication A functionally single, uncomplicated system with a divided pelvis or the ureters joining al ong their length (commonly over sacroiliac joint). Follow-up Long-term follow-up is required if there is evidence of CKD (usually due to solit ary contralateral dysplastic kidney). Investigations Renal ultrasound Ultrasound imaging can delineate the collecting systems and con \201 rm the presence of dilatation and/or ureteroceles (Fig. 16.4.2). No further imag ing is required if the duplication is uncom- plicated (for example no dilatation) and/or if the patient is asymptomatic where clinical detection was via abdominal USS for another cau se. Duplication Renal duplications of the upper urinary tract result in a duplex kidney and col lecting system caused by the devel- opment of an accessory ureteric bud and are associated with chromosomal defects: \200 \200 Turner syndrome (45XO); trisomy 13 and 18. S.D. MARKS 660 A MAG3 scan should be carried out where there is clinical suspicion of pelviureteric and/or vesicoureteric junction obstruction and micturating cystourethrogram if there is or has be en ureteric dilatation. Formal measurement of glomerular \201 ltration rate should be con sidered in all infants at 12 months of age where there is no evidence of compensatory hyper trophy or concerns with renal dysfunction (such as elevated plasma creatinine). Follow-up Long-term follow-up is required if evidence of CKD (usually due to solitary contr alateral dysplastic kidney). There is no evidence base for any dietary or physical activity restrictions, although general advice regarding healthy life- style in patients with solit ary kidneys should be given. Fig. 16.4.2 An obstructed duplex in the upper pole of the left kidney on USS. Renal ectopia This is a developmental anomaly of abnormally shaped and (usually) functionin g kidneys where there is a failure of ascent during embryogenesis usually resulting in pelv ic placement (although rare cases can be found in the thorax and abdomen). Ectopic kidneys are usually: \200 \200 \200 \200 Intravenous pyelography This is rarely performed in pediatric practice but can delin- eate a bladder ureterocele (which can also be seen on micturating cystourethrogram) and a dilate d upper pole moiety compressing a dilated lower pole moiety due to VUR. unilateral (90%); pelvic (60%); hypoplastic; left-sided. Nuclear medicine imaging This is helpful in providing information on the differential funct ion between the kidneys as well as of the respective moieties of the duplex kidney and deli neating if there is an obstructive element. Renal ectopia can be associated with: \200 ureteric abnormalities (including retrocaval and ectopic ureter); VUR; pelviureteric juncti on obstruction; genital abnormalities (including vaginal agenesis, and bicornuate uterus). Renal agenesis This is caused by failure of the ureteric bud to communicate with the metane phric blastema during the \201 rst trimester of pregnancy. It is associated with other ma lformations including: \200 \200 \200 \200 \200 \200 \200 pelviureteric and vesicoureteric junction obstruction; VUR; genital abnormalities; genetic conditions; syndromes and nonsyndromic conditions. Antenatal USS screening may detect some cases, although some children present with pelvic m asses incidentally where constipation and tumors remain the most likely differential diagno ses. Crossed renal ectopia This is an abnormally rotated kidney crossing the midline inferomedia lly to the normally sited kidney with its upper pole usually fused to the normal kidney \200\231s lower pole and the ureter from the ectopic kidney usually inserted to its normal position. Crossed renal ectopia can occur with (85%) or without renal fusion and can be sol itary or bilateral, often associ- ated with ureteric, lower tract, cloacal and anorectal an omalies. Crossed renal ectopia usually occurs in males with crossing occurring from left to right and can be associated with VACTERL and agenesis of the corpus callosum. Bilateral renal agenesis This is rare and results in Potter \200\231s syndrome: \200 \200 \200 \200 \200 facial appearance of \202 at face and nasal bridge; micrognathia, low-set malrotated ears ; anhydramnios; fetal anuria; pulmonary hypoplasia. Fetal or neonatal death results. Unilateral renal agenesis This may be as a result of spontaneous involution of a multicysti c dysplastic kidney (which may have been detected on antenatal USS screening as above) or f ailure of the metanephros to develop. Familial cases are common. Parents can be reassured w hen the contralateral kidney and bladder are normal and when follow-up reveals normal renal function and contralateral compensatory hypertrophy. Fusion Renal fusion is commonly associated with syndromes and other urological, neurologica l, skeletal, cardiovascular and gastrointestinal anomalies and is rarely complete resulting in a single renal mass. Fusion commonly occurs at the poles with horseshoe kidney being th e most common (95%) entity where embryological fusion of the lower poles of metanephric tis sue interferes with the normal process of renal ascent, vascularization and rotation. Investigations Abdominal and pelvic USS as well as nuclear medicine scanning with DMSA scan should be undertaken to exclude ectopic renal tissue (Fig. 16.4.3). CHAPTER 16.4 Congenital abnormalities of the urinary tract 661 Fig. 16.4.3 DMSA scan in a case of right renal agenesis delineating a normal left kidney wi thout evidence of a right or ectopic kidney. Horseshoe kidney This describes the con \201 guration with fusion of the lower poles of th e kidneys by a narrow isthmus, which usually comprises functioning tissue, but may be compo sed of dysplastic or \201 brous tissue (Fig 16.4.4). The isthmus can lie: \200 beneath the origin of the inferior mesenteric artery at the level of L4 (40%); at the level of the lower poles of normally placed kidneys (40%); in the pelvis (20%). Horseshoe kidneys are usually asymptomatic and undete- cted as they do not cause clinical p roblems. They lie more caudally than normal with the lower poles adjacent to the spine. Hor seshoe kidneys are commoner in males, although they are frequently associated with Turner s yndrome (45XO) in females and with trisomy 13, 18 and 21. Clinical presentation may be with : \200 \200 \200 \200 Fig. 16.4.4 DMSA scan of a horseshoe kidney with functional renal parenchyma in the isthmus . hematuria; abdominal pain; abdominal mass; urinary tract infection. S.D. MARKS 662 Complications include: \200 \200 \200 \200 \200 \200 abnormalities, including inguinal herniae, epispadias, hemi- clitoris and anterior anus. Ne onatal bladder closure is required with pelvic bone osteotomies and latter reconstructive s urgery to normalize the urogenital tract and ensure continence. Infants with cloacal extrop hy have the defects of bladder exstrophy with exomphalos, imperforate anus and lum- bosacra l spinal defects. hypertension; VUR; pelviureteric junction obstruction; nephrolithiasis; malignancy; trauma to the isthmus due to its close relationship with the spine. Cloacal anomaly There is a urethra, vagina and colon single channel and opening in girls du e to failure of the urorectal septum to develop. This may result in stenosis and obstructio n of urinary tract, uterine cavity and gastrointestinal tract. Surgical relief of obstructi on and later reconstructive surgery may be required. Obstruction occurs due to compression of the pelviuret- eric junction and proximal ureter b y the aberrant vessels commonly found at the renal hilum or due to distortion of the proxim al ureter as it loops over the renal isthmus. The continuity of both lower poles may be mis sed on USS. Intravenous pyelography is rarely performed in pediatric practice and con \201 rmation of diagnosis by CT or MRI scan- ning is very infrequently required. Urogenital sinus There is a urethra and vaginal single channel and opening in girls due to failure of the urethrovaginal septum to develop. This may result in stenosis and obstructio n of the urinary tract and/or uterine cavity (resulting in hydrocolpos). Urological surgery is required to separate the urethra and vagina. Lower and other urinary tract defects Prune belly syndrome Absent abdominal wall musculatur e, Eagle \200\223Barrett or triad syndrome. It is caused by failure of mesenchymal developm ent predom- inantly in males (otherwise pseudo prune belly syndrome). Clinical features inc lude: \200 Further reading Hiraoka M. Medical management of congenital anomalies of the de \201 ciency or absence of anterior abdominal wall muscu- lature with wrinkled, lax appe arance; bilateral cryptorchidism with empty hypoplastic scrotum; ureter, bladder and urethr al abnormalities (usually mega- cystis, mega-ureter due to dysplasia). kidney and urinary tract. Pediatr Int 2003; 45: 624 \200\223633. Limwongse C, Cassidy SB. Syndromes and malformations of the urinary tract. In: Avner ED, Ha rmon WE, Niaudet P (eds), Pediatric nephrology, 5th edn. Philadelphia: Lippincott Williams & Wilkins; 2004. Miyazaki Y, Ichikawa I. Ontogeny of congenital anomalies of the kidney and urinary tract, CAKUT. Pediatr Int 2003; 45: 598 \200\223604. Nakai H, Asanuma H, Shishido S, Kitahara S, Yasuda K. Changing concepts in urological management of the congenital anoma lies of kidney and urinary tract, CAKUT. Pediatr Int 2003; 45: 634 \200\223641. Nakanishi K , Yoshikawa N. Genetic disorders of human congenital anomalies of the kidney and urinary tr act (CAKUT). Pediatr Int 2003; 45: 610 \200\223616. \200 It is associated with: \200 renal dysplasia; \200 VUR; \200 urinary stasis; \200 na rrowed urethra; \200 obstruction of ureteric, pelviureteric and vesicoureteric junctions; poorly contractile, thick-walled (nontrabeculated) bladder with large diverticulae; uracha l cyst or patent urachus; postmicturition residual volumes; malrotation; gastroschisis; imp erforate anus; constipation; congenital heart disease; talipes equinovarus; developmental d ysplasia of the hips. Schedl A. Renal abnormalities and their developmental origin. Nat Rev Genet 2007; 8: 791 \200\223802. Internet resources Evaluation of congenital anomalies of the kidney and urinary tract (UpTo Date): \200 \200 \200 \200 \200 \200 \200 \200 http://patients.uptodate.com/topic.asp?file= pedineph/17792 Human Renal Tract Malformations : Unraveling The Genes \200\223 summary of lecture by Prof. A. Woolf at the XLIII ERA- EDT A Congress: http://www.ndt-educational.org/ woolfslide2006txt.asp National Congenital Anomaly System: Long-term follow-up is required if there is evidence of CKD. A formal measurement of GFR sh ould be performed at 12 months of age when it is associated with renal dysplasia and/or the re are concerns about renal dysfunction (such as elevated plasma creatinine). http://www.statistics.gov.uk/downloads/theme_ health/National_Congenital_Anomaly_System/ CA _text_v2.pdf NHS Perinatal Institute: Bladder extrophy There is exposure of the posterior wall of the bladder. It occurs due to a breakdown of the cloacal membrane caused by the infra-umbilical mesenchyme failing to sepa - rate the cloaca component that develops into the bladder from the overlying ectoderm. It is commoner in boys with lower abdominal wall defects, symphisis pubis diastasis, pelvic, b ladder, urethral and genital http://www.perinatal.nhs.uk/car/anomaly/renal/ renal.htm See also Renal dysplasia, p. 646 Vesicoureteric re \202 ux and re \202 ux nephropathy, p. 648 Rare syndromes with renal involvement, p. 640 This page intentionally left blank S.D. MARKS 664 Medullary sponge kidney Introduction Medullary sponge kidney (MSK) is also called renal tubular ectasia or Cacchi \200\223Ricci disease. It is a congenital renal developmental abnormality and part of a gro up of renal cystic disorders but rarely encountered even in pediatric nephrological practic e. Its name is derived from the sponge appearance of the renal medulla which can occur foca lly in one or both kidneys (usually both kidneys) due to collect- ing duct ectasia and cyst formation in one or more renal pyramids. MSK is believed to arise from hyperplasia or obst ruction of fetal collecting tubules and hypercalciuria with increased urinary pH causing th e associated nephrolithiaisis and structural changes. Renal duplication or malrotation. Caroli \200\231s disease. Congenital heart disease. Pylor ic stenosis. Parathyroid adenoma. Hemihypertrophy. Beckwith \200\223Wiedemann syndrome (wit h associated increased malignancy rates). Marfan and Ehlers \200\223Danlos syndrome. Differential diagnosis Polycystic kidney disease, especially ADPKD. Renal papillary necrosi s or tuberculosis. Calyceal diverticulum. Nephrolithiasis. Epidemiology MSK is commoner in males than females (although more females are affected with hypercalciuria). It affects children (from 2 years of age) and adults, although commoner i n adolescents and young adults with progres- sive degeneration of the collecting tubules oc curring later in life. The prevalence is 1 in 5000 \200\22320 000 individuals but this is a n underestimate as many patients are asymptomatic. MSK is detected in 0.5 \200\2231% of pat ients undergoing intrave- nous pyelography. Investigations Abdominal X-ray Linear/rounded clusters of medullary nephrocalcinosis. Nephr olithiasis within renal pelvis, ureter or bladder. Renal ultrasound Normal-sized kidneys or renal hypertrophy (especially if associated with A DPKD) with echogenic medullary pyramids with calci \201 cation. Genetics Most cases are sporadic. Familial clustering (including autosomal dominant inherit - ance) has been described. Intravenous pyelography Findings include: Discrete linear papillary striations due to dilat ed collecting tubules of renal medulla (Fig. 16.5.1). Nephrolithiasis arranged in groups ar ound a calyx (bunch of grapes pattern). Hypertrophy of renal pyramids. Distorted calyces, w hich are broad and shallow (Fig. 16.5.2). Clinical features Presentation Incidental \201 nding in asymptomatic patient. Failure to thrive (with growth failure due to distal renal tubular acidosis). Loin pain Microscopic (> 90% of patients) and macroscopic (<20% of patients) hematuria. Urinary tract infection (30% of symptomatic patients) with possible recurrent acute and chronic pyelonephritis due to u rinary stasis and nephrolithiasis.