8 Miscellaneous urological diseases of the kidney

Simple renal cysts: do not communicate with any part of the nephron or the renal pelvis. They are mainly confined to the renal cortex, are filled with clear fluid, and contain a membrane composed of a single layer of flattened or cuboidal epithelium. They can be single or multiple, ranging from a few millimetres to several centimetres in diameter. They can be unilateral or bilateral and often affect the lower pole of the kidney.

Parapelvic cysts: describe simple parenchymal cysts located adjacent to the renal pelvis or hilum.

Increases with age, the precise prevalence depending on the method of diagnosis. On CT, 20% of adults have renal cysts by age 40y and 33% by the age of 60.¹ At post-mortem, 50% of subjects aged >50y have simple cysts. Cysts do not usually increase in size with age, but may increase in number. Males and females are affected equally.²

Both congenital and acquired causes have been suggested. Chronic dialysis is associated with the formation of new simple cysts.

Simple cysts are most commonly diagnosed as an incidental finding following a renal ultrasound scan (USS) or CT performed for other purposes. The majority are asymptomatic; however, very large cysts may present as an abdominal mass or cause dull flank or back pain. Acute severe loin pain may follow bleeding into a cyst (causing sudden distension of the wall). Rupture (spontaneous or following renal trauma) is rare. Rupture into the pelvicalyceal system can produce haematuria. Infected cysts (rare) present with flank pain and fever. Very occasionally, large cysts can cause obstruction and hydronephrosis.

Simple cysts are round or spherical, have a smooth and distinct outline, and are ‘anechoic’ (no echoes within the cyst, i.e. sound waves are transmitted through the cyst). USS using microbubble contrast agents can improve diagnostic accuracy. Evidence of calcification, septation, irregular margins or clusters of cysts requires further investigation (renal triphasic CT). In the absence of these features, no further investigation is required.

Simple cysts are seen as round, smooth-walled lesions with homogenous fluid in the cavity (with a typical density of –10 to +20 Hounsfield units) and with no enhancement after contrast (enhancement implies that it contains vascular tissue or communicates with the collecting system, i.e. that it is not a simple cyst). Hyperdense cysts have a density of +20–90 Hounsfield units, do not enhance with contrast media, and are <3cm in diameter.

Image-guided cyst aspiration or biopsy can be used to help diagnose indeterminate cysts and prevent unnecessary surgery.

A simple cyst (type I: round or spherical, smooth wall, distinct outline, and no internal echoes) requires no further investigation, no treatment, and no follow-up. In the rare situation where the cyst is thought to be the cause of symptoms (e.g. back or flank pain), treatment options include percutaneous aspiration ± injection of sclerosing agent or open or laparoscopic surgical excision of the cyst wall. In the rare event of cyst infection, percutaneous drainage and antibiotics are indicated.

Cysts with features on USS suggesting possible malignancy (calcification, septation, irregular margins) should be investigated by CT with contrast.

A calyceal diverticulum is a spherical outpouching of the renal collecting system (specifically from a calyx) which protrudes into the corticomedullary region of the kidney. It communicates with the renal calyx via a narrow neck or channel. It is lined by a transitional cell epithelium and is covered by a thin layer of renal cortex. They range in size from only a few millimetres to many centimetres in size.

The exact aetiology of calyceal diverticula is unknown. Some may be congenital. Acquired calyceal diverticula can develop after obstruction of a calyceal infundibulum or following blunt renal trauma.

They are usually asymptomatic and are discovered incidentally on an IVU, most commonly seen in upper pole calyces. Symptoms may result from the development of a stone or infection within the diverticulum, presumably caused by urinary stasis.

On IVU, a calyceal diverticulum appears as a rounded collection of contrast medium next to a papilla, although often, the connecting channel is too narrow to be clearly seen. They can be identified on CT, MRI, and USS; however, the distinction between a renal cyst and an obstructed calyx may be difficult on unenhanced images.

Stones that form within the calyceal diverticulum may be treated by flexible ureteroscopy and laser lithotripsy or, if large, by percutaneous nephrolithotomy (PCNL) if percutaneous access is possible. Endoscopic dilatation or incision of the neck of the diverticulum may be attempted at the time of stone surgery to prevent recurrence and this technique can also be employed if the diverticulum is thought to be the cause of recurrent urinary infection. Open surgery has also been used to remove stones and to de-roof calyceal diverticula. Extracorporeal shock wave lithotripty (ESWL) therapy is not helpful. ESWL may result in stone fragmentation, but it may be difficult for the stone fragments to get out of the diverticulum and they may simply reform into a larger stone.

A congenital cystic disorder of the kidneys characterized by dilatation of the distal collecting ducts associated with the formation of multiple cysts and diverticula within the medulla of the kidney.

Difficult to know as it may be asymptomatic (diagnosed on an IVU performed for other reason or at post-mortem). Estimated to affect between 1 in 5000 to 1 in 20 000 people in the general population; 1 in 200 in those undergoing IVU (a select population). In 75% of cases, both kidneys are affected.

The renal medulla resembles a sponge in cross section due to dilated collecting ducts in the renal papillae and the development of numerous small cysts. This is associated with urinary stasis and the formation of small calculi within the cysts. Some report a familial inheritance. It can be associated with other congenital or inherited disorders, including hemihypertrophy and Beckwith–Wiedemann syndrome^*.

The majority of patients are asymptomatic. When symptoms do occur, they include ureteric colic, renal stone disease (calcium oxalate ± calcium phosphate), UTI, and haematuria (microscopic or macroscopic). Up to 50% have hypercalciuria due to renal calcium leak or increased gastrointestinal calcium absorption. Renal function is normal unless obstruction occurs (secondary to renal pelvis or ureteric stones).

Other causes of nephrocalcinosis (deposition of calcium in the renal medulla, e.g. TB, hyperparathyroidism, healed papillary necrosis, multiple myeloma).

Asymptomatic MSK disease requires no treatment. General measures to reduce urine calcium levels help reduce the chance of calcium stone formation (high fluid intake, vegetarian diet, low salt intake, consumption of fruit and citrus fruit juices). Thiazide diuretics may be required for hypercalciuria resistant to dietary measures and are designed to lower urine calcium concentration. Intrarenal calculi are often small and as such, may not require treatment, but if indicated, this can take the form of ESWL or flexible ureteroscopy and laser treatment. Ureteric stones are again usually small and will, therefore, pass spontaneously in many cases with a period of observation. Recurrent UTI may need prophylactic antibiotics. Renal function tends to remain stable in the long term. Rarely, recurrent infection and nephrocalcinosis may lead to the complication of renal impairment.

A cystic degenerative disease of the kidney with ≥5 cysts visualized on CT scan. By definition, this is an acquired condition, as opposed to ADPKD which is inherited (in an autosomal dominant fashion). It is predominantly associated with chronic and end-stage renal failure and as such, is commonly found in patients undergoing haemodialysis or peritoneal dialysis. Over one third of patients develop ARCD after 3y of dialysis. Clinically important because it may cause pain and haematuria and is associated with the development of benign and malignant renal tumours. The male to female ratio is 3:1.

Usually multiple, bilateral cysts found mainly within the cortex of small, contracted kidneys. Cysts vary in size (average 0.5–1cm) and are filled with a clear fluid which may contain oxalate crystals. They usually have cuboidal or columnar epithelial linings and are in continuity with renal tubules (and, therefore, cannot be defined as simple cysts). Atypical cysts have a hyperplastic lining of epithelial cells, which may represent a precursor for tumour formation. Renal transplantation can cause regression of cysts in the native kidneys.

The exact pathogenesis is unknown, but several theories have been proposed. Obstruction or ischaemia of renal tubules may induce cyst formation. Renal failure may predispose to the accumulation of toxic endogenous substances or metabolites, alter the release of growth factors, and result in changes in sex steroid production or cause cell proliferation (secondary to immunosuppressive effects) which result in cyst formation.

There is an increased risk of benign and malignant renal tumours. The chance of developing RCC is 720%, 3–6 times greater than the general population (males > females). When on dialysis, RCC usually develops within the first 10y of treatment.

Flank pain; UTI; visible haematuria; renal colic (stone disease); hypertension.

This depends on the presenting symptoms.

Persistent macroscopic haematuria can become problematic, exacerbated by heparinization (required for haemodialysis). Options include transferring to peritoneal dialysis, renal embolization or nephrectomy (acceptable as these patients already on dialysis by definition have non-functioning kidneys). Infected cysts, which develop into abscesses, require percutaneous or surgical drainage. Radical nephrectomy is indicated for renal masses with features suspicious of malignancy. Smaller asymptomatic masses require surveillance. Patients with ARCD on long-term dialysis should also be considered for renal surveillance with ultrasonography or CT.

An autosomal dominant inherited disorder involving multiple expanding renal parenchymal cysts (Fig. 8.2).

Incidence is 0.1–0.5%; 95% are bilateral. ADPKD can affect children and adults, although symptoms usually occur between ages 30–50y. ADPKD accounts for 10% of all renal failure (which usually manifests at >40y old).

The kidneys reach an enormous size due to multiple fluid-filled cysts and can easily be palpated on abdominal examination. Expansion of the cysts results in ischaemic atrophy of the surrounding renal parenchyma and obstruction of normal renal tubules. End-stage renal failure occurs at around age 50y.

Ten to thirty percent incidence of Circle of Willis berry aneurysms (associated with subarachnoid haemorrhage), cysts of the liver (33%), pancreas (10%), spleen (<5%) and seminal vesicles, mitral valve prolapse; aortic root dilatation, aortic aneurysms, and diverticular disease. Of note, the incidence of renal adenoma is 720%; however, the risk of RCC is the same as the general population.

Two genes have been identified in ADPKD. The PKD1 gene is localized on the short arm of chromosome 16 (16p13.3) and accounts for 85% of cases. The PKD2 gene is on the long arm of chromosome 4 (4q21) and causes 15% of cases. A third gene, PKD3, is also implicated. Pathogenesis theories include intrinsic basement membrane abnormalities, tubular epithelial hyperplasia (causing tubular obstruction and basement membrane weakness), and alterations in the supportive extracellular matrix due to defective proteins, all of which may cause cyst formation.

Other forms of renal cystic disease (multiple simple cysts, autosomal recessive polycystic kidney disease (ARPKD), familial juvenile nephronophthisis, medullary cystic disease; see  p. 676).

Multiple renal cysts are also found in other autosomal dominant conditions:

This depends on the presenting symptoms:

The aim is to preserve renal function for as long as possible (monitor and control hypertension and UTI). Infected cysts should be drained. Persistent, heavy haematuria can be controlled by embolization or nephrectomy. Progressive renal failure requires dialysis and ultimately, renal transplantation.

Due to the high risk of inheritance of ADPKD, offsprings should be fully counselled and offered genetic testing or USS screening at an appropriate time.

Vesicoureteric reflux (VUR) is the retrograde flow of urine from the bladder into the upper urinary tract with or without dilatation of the ureter, renal pelvis, and calyces (see  p. 662).

Reflux is normally prevented by low bladder pressures, efficient ureteric peristalsis, and the ability of the vesicoureteric junction (VUJ) to occlude the distal ureter during bladder contraction. This is assisted by the ureters passing obliquely through the bladder wall (the ‘intramural’ ureter) which is 1–2cm long. Normal intramural ureteric length to ureteric diameter ratio is 5:1. VUR of childhood tends to resolve spontaneously with increasing age because as the bladder grows, the intramural ureter lengthens.

Primary: a primary anatomical (and therefore, functional) defect, where the intramural length of the ureter is too short (ratio <5:1).

Secondary: to some other anatomical or functional problem.

VUR is commonly seen in duplex ureters (the Weigert–Meyer law)² and associated with PUJ obstruction. Cystitis can cause VUR through bladder inflammation, reduced bladder compliance, increased pressures, and distortion of the VUJ. Coexistence of UTI with VUR can cause pyelonephritis. Reflux of infected urine under high pressure may lead to reflux nephropathy, resulting in renal scarring, hypertension, and renal impairment—although this is much less common in adults compared to children. More commonly, this would manifest as loin pain in adults.

The definitive test for the diagnosis of VUR is cystography, which may be apparent during bladder filling or during voiding (micturating cystourethrography). Where clinically indicated, urodynamics establishes the presence of voiding dysfunction. If there is radiographic evidence of reflux nephropathy, check BP and the urine for proteinuria, measure serum creatinine, and arrange a ^99mTc-DMSA renogram study to assess renal cortical scarring and determine split renal function.

VUR is harmful to the kidney in the presence of infected urine and/or where bladder pressures are markedly elevated (due to severe BOO, poor compliance, or high-pressure overactive bladder contractions). In the absence of these factors, VUR is not harmful, at least in the short term (months). Subsequent management depends on:

PUJO is an obstruction of the proximal ureter at the junction with the renal pelvis, resulting in a restriction of urine flow (see  p. 672); known as ‘uretero-pelvic junction obstruction’ (UPJO) in North America.

PUJ stricture secondary to ureteric manipulation (e.g. ureteroscopy); trauma from passage of calculi; fibroepithelial polyps; TCC of urothelium at PUJ; external compression of ureter by retroperitoneal fibrosis or malignancy.

Flank pain precipitated by diuresis (high fluid intake, especially after consumption of alcohol); flank mass; UTI; haematuria (after minor trauma). It may also be associated with VUR.

Surgery is indicated for recurrent episodes of bothersome pain, renal impairment, where a stone has developed in the obstructed kidney and where infection has supervened (an acutely infected obstructed kidney in a septic patient will require nephrostomy insertion). In the absence of symptoms, consider watchful waiting with serial MAG3 renograms. If renal function remains stable and the patient remains free of symptoms, there is no need to operate. A non-functioning ‘burnt-out’ kidney with PUJO may require nephrectomy to avoid the complication of pyonephrosis.

Pyeloplasty (see  p. 782)

A double J ureteric stent is left for 6 weeks post-operatively, which can be removed with flexible cystoscopy as an outpatient procedure.

A minimally invasive technique to treat PUJO, but tends not to be offered as first-line therapy other than in older or frail patients. It can be utilized after pyeloplasty has failed. A full thickness incision is made through the obstructing proximal ureter from within the lumen of the ureter down into the peripelvic and periureteral fat, using a sharp knife or Holmium:YAG laser. The incision is stented for 4 weeks to allow re-epithelialization of the PUJ. Generally not used for PUJO >2cm in length. The incision may be made percutaneously or by a retrograde approach via a rigid or flexible ureteroscope or by using a specially designed endopyelotomy balloon, the Acucise^® technique. Here, an angioplasty-type balloon (over which runs a cautery wire) is inflated across the PUJ. An electrical current heats the wire and this cuts through the obstructing ring of tissue at the PUJ.

The presence of a combination of PUJO and a renal stone that is suitable for PCNL is an indication for combined PCNL and percutaneous endopyelotomy.

Success rates in terms of relieving obstruction: percutaneous endopyelotomy, 60–100% (mean 70%); cautery wire balloon endopyelotomy, 70%; ureteroscopic endopyelotomy, 80%.

Repeat MAG3 renogram is usually performed 3 months post-operatively. If there has been no improvement, this can be repeated 6–12 months post-operatively. Failure may need re-do surgery or endopyelotomy.

Abnormalities of renal fusion and ascent occur in weeks 6–9 of gestation, when the embryonic kidney is ‘ascending’ to its definitive lumbar position in the renal fossa (‘ascending’ as a result of rapid caudal growth of the embryo).

Most common example of renal fusion. Prevalence 1 in 400. Male to female ratio 2:1. The kidneys lie vertically (instead of obliquely) and are joined at their lower poles (in 95%) by midline parenchymal tissue (the isthmus). The inferior mesenteric artery obstructs ascent of the isthmus. Consequently, the horseshoe kidney lies lower in the abdomen (L3 or L4 vertebral level). Normal rotation of the kidney is also prevented and therefore, the renal pelvis lies anteriorly, with the ureters also passing anteriorly over the kidneys and isthmus (but entering the bladder normally). Blood supply is variable, usually from one or more renal arteries or their branches or from branches off the aorta or inferior mesenteric artery (Fig. 8.7).

A proportion of individuals with horseshoe kidneys have associated congenital abnormalities (Turner’s syndrome, trisomy 18, genitourinary anomalies, ureteric duplication), VUR, PUJ obstruction, and renal tumours (including Wilms’ tumours).

Most patients with horseshoe kidneys remain asymptomatic; however, infection and calculi may develop and cause symptoms. The diagnosis is usually suggested on renal USS and confirmed by IVU (calyces of the lower renal pole are seen to point medially and lie medially in relation to the ureters) or CT. Renal function is usually normal.

The kidney fails to achieve its normal position and may be located in the thorax, abdomen, lumbar (in iliac fossa), or pelvis (on the contralateral side or crossed). The prevalence of renal ectopia is 1 in 900, with both sexes affected equally. The left kidney is affected more often than the right and bilateral cases are seen in <10%. The affected kidney is smaller, with the renal pelvis positioned anteriorly (instead of medially) and the ureter is short, but enters the bladder normally. Pelvic kidneys occur in 1 in 2000–3000 and lie opposite the sacrum and below the aortic bifurcation and are supplied by adjacent (aberrant) vessels (Fig. 8.8). Renal ectopia has an increased risk of congenital anomalies, including contralateral renal agenesis and genital malformations.

Most are asymptomatic. Diagnosis is made on renal USS, IVU, or renography. Complications include hydronephrosis (secondary to VUR, VUJ obstruction, and PUJO), stones, and infection.

Unilateral renal agenesis is the absence of one kidney due to embryological abnormality or absence of the ureteric bud. This results in failure of the ureteric bud to contact the metanephric blastema with failed induction of nephrogenesis. The incidence is 1 in 1000, left side > right, males > females. Absence of a kidney may also be caused by involution of a multicystic dysplastic kidney in utero or post-natally. Many patients are asymptomatic; however, it is associated with Turner’s syndrome and cardiac, respiratory, gastrointestinal, and musculoskeletal abnormalities. Associated genitourinary anomalies include absence of the ipsilateral ureter, abnormal trigone, VUR, PUJO, VUJO, uterine abnormalities (unicornuate—one side has failed to develop; bicornuate—partially divided uterus; didelphys—double uterus), vaginal agenesis, anomalies of seminal vesicles, and absence of vas deferens. Often discovered as an incidental finding on USS performed for other reasons or during investigation of associated abnormalities. Long-term follow-up of renal function, urinalysis, and BP should be considered.

Bilateral renal agenesis is rare and incompatible with life. It is associated with complete ureteric atresia, bladder hypoplasia or absence, intrauterine growth retardation, pulmonary hypoplasia, and oligohydramnios (reduced amniotic fluid), causing characteristic ‘Potter’ facial features (blunted nose, low set ears, depression on the chin) and limb abnormalities.

The kidney is located in a normal position, but the renal pelvis fails to rotate to the normal medial orientation. Often seen with horseshoe kidneys and renal ectopia and associated with Turner’s syndrome. The incidence is 71 in 1000, with a male to female ratio of 2:1. The renal shape may be altered (flattened, oval, triangular, or elongated) and the kidney retains its foetal lobulated outline (Fig. 8.9). It is associated with increased deposition of fibrous tissue around the renal hilum, which can produce symptoms due to ureteric or PUJ obstruction (causing hydronephrosis, infection, or stone formation). Most patients, however, remain asymptomatic. The diagnosis is made on USS, IVU, or retrograde pyelography.

A duplex kidney has an upper renal moiety and a lower renal moiety, each with its own separate pelvicalyceal system and ureter. The two ureters may join to form a single ureter at the PUJ (bifid system; Fig. 8.10) or more distally (bifid ureter) before entering the bladder through one ureteric orifice. Alternatively, the two ureters may pass down individually to the bladder (complete duplication; Fig. 8.11). In this case, the Weigert–Meyer rule states that the upper moiety ureter always opens onto the bladder medially and inferiorly to the ureter of the lower moiety, thereby predisposing to ectopic placement of the ureteric orifice and obstruction (due to the longer intramural course of the ureter through the bladder wall). The lower moiety ureter opens onto the bladder laterally and superiorly, reducing the intramural ureteric length which predisposes to VUR (in up to 85%; Fig. 8.2).

Ureteric duplication occurs in 1 in 125 individuals. Female to male ratio is 2:1. Unilateral cases are more common than bilateral, with right and left sides affected equally. Risk of other congenital malformations is increased.

In duplication, two ureteric buds arise from the mesonephric duct (week 4 of gestation). The ureteric bud situated more distally (lower moiety ureter) enters the bladder first and so migrates a longer distance, resulting in the superior and lateral position of the ureteric orifice. The proximal bud (upper moiety ureter) has less time to migrate and consequently, the ureteric orifice is inferior and medial (ectopic) (see  p. 668). Interaction of each ureteric bud with the same metanephric tissue creates separate collecting systems within the same renal unit. With bifid ureters, a single ureteric bud splits after it has emerged from the mesonephric duct.

Ectopic ureters are associated with upper renal moiety hydronephrosis (secondary to obstruction), renal hypoplasia or dysplasia (maldevelopment of the kidney correlating with the degree of ectopic displacement of ureteric orifice)¹, and ureteroceles (Fig. 8.10). Lower moiety ureters are prone to reflux, resulting in hydroureter and hydronephrosis. Bifid ureters can get urine continuously, passing from one collecting system to the other (yo-yo reflux), causing urinary stasis (and predisposing to infection).

Symptoms of UTI, flank pain, or an incidental finding.

Uncomplicated complete or incomplete ureteric duplication does not require any intervention. In symptomatic patients, the aim is to reduce obstruction and reflux and improve function. Where renal function is reasonable, common sheath ureteric reimplantation (where a cuff of bladder tissue is taken that encompasses both duplicated ureters) can treat both conditions. A poorly functioning renal moiety (i.e. upper moiety associated with ectopic ureter and/or reflux or lower moiety associated with a ureterocele) may require heminephrectomy and ureterectomy. Where both renal moieties have poor function or dysplasia, nephroureterectomy is indicated.