Incidence is 1 in 1,000 with a slight increased frequency on the left side and an autosomal dominant inheritance noted in recent studies. Absence of the ipsilateral hemitrigone is usually diagnostic; however, a normal trigone does not rule out renal agenesis. The diagnosis is made by renal scan and ultrasound (US). A high association with other congenital anomalies, such as absence of vas deferens in males and absence or hypoplasia of the tubes, ovaries, uterus, or vagina (Mayer-Rokitansky syndrome) in females on the affected side, is noted. Gastrointestinal anomalies such as imperforate anus are also found.

This rare condition is incompatible with life. Absence of intrauterine urine production results in oligohydramnios; death is usually secondary to pulmonary hypoplasia. Characteristic Potter’s facies is noted.

Oligomeganephronia is a congenital renal disease occurring primarily in male infants (3:1), with progressive renal failure by age 12 to 15 years. The kidneys have fewer than normal nephrons (oligonephronia) but are hypertrophied (mega). Patients present within the first 2 years of life with vomiting, polydipsia, polyuria, and dehydration. They are treated medically with high fluid intake and correction of salt loss until eventually dialysis and transplantation are required.

Autosomal recessive polycystic kidney disease (ARPKD) is a rare anomaly with no sex predilection usually presenting early in life. The disease is transmitted on a single gene (PKHD1) located on chromosome 6 that produces protein fibrocystin and is inherited in an autosomal recessive pattern. Neither parent shows evidence of the disease, and siblings of either sex have a one in four chance of being affected. US will show massively enlarged kidneys bilaterally and intravenous urogram (IVU) will show characteristic radial or medullary streaking of the nephrogram from cystic dilatation of the collecting tubules. Renal insufficiency occurs early. Infants with evidence of the disease at birth often die within the
first 2 months. Patients will have some form of liver disease ranging from periportal biliary ectasia to congenital hepatic fibrosis. A liver biopsy can establish the diagnosis. For those patients who survive infancy (50%), the course and progression of the disease are variable; however, cardiac, renal, and hepatic failure can be expected. ARPKD has no known cure.

Autosomal dominant (adult) polycystic kidney disease (ADPKD) is the most common form of cystic kidney disease in humans and is responsible for ˜10% to 15% of all cases of end-stage renal disease (ESRD). Approximately 500,000 Americans have been diagnosed. The trait has 100% penetrance and 50% of an affected individual’s offspring will be affected. ADPKD is transmitted by the PKD1 gene on chromosome 16 (90%) or the PKD2 gene on chromosome 4 (10%) which is associated with a later onset of clinical symptoms.

This condition is characterized by diffuse bilateral progressive cystic degeneration of the kidneys, hypertension, and progressive renal failure. The eventual cause of renal failure is not clear in ADPKD. Only 1% of nephrons develop cysts. Pressure necrosis of nondilated nephrons has been speculated. The cysts also cause renal ischemia from stretching of intrarenal vessels and renninmediated hypertension, which may play a secondary role. Most cases are identified between the ages of 30 and 50 years. Typical signs or symptoms include gross or microscopic hematuria, flank pain, gastrointestinal symptoms (colonic diverticula), renal colic (from clots or stones), and hypertension. Associated anomalies include hepatic cysts or fibrosis, berry aneurysms (10%—40%), mitral valve prolapse, and colonic diverticulosis.

Congenital multicystic kidney disease is a common benign nongenetic dysplastic malformation of the fetal kidney associated with ureteral atresia or agenesis. It is one of the most common causes of an abdominal mass in infants and presents predominantly in male infants, on the left side, as a large, unilateral, multicystic, nonfunctioning renal abdominal mass (a “bunch of grapes”). There is a 10% to 15% incidence of significant anomalies of the contralateral upper urinary tract. Elective surgical excision is indicated if the mass interferes with respiration or alimentation of the child or is associated with severe hypertension. Otherwise, attention is primarily directed toward identifying any abnormalities of the contralateral urinary tract and monitoring for hypertension or malignant degeneration (Wilms’ tumor).

The most common cystic lesions of the kidney, simple cysts, may be solitary or multiple, unilateral or bilateral. They present clinically as an abdominal mass or more commonly as an incidental finding on US, computed tomography (CT), or IVU and are increasingly common with age. Differentiation among cystic neoplasms, lymphatic cysts, perirenal effusions, and renal abscesses must be made in addition to polycystic disease when they are multiple. A cystic renal cell carcinoma must be considered.

A simple cyst is characteristically unilocular, avascular, smooth walled, and filled with a clear fluid with low fat and protein content and a low lactic dehydrogenase with no malignant cells on cytology. Most complex cysts (Bosniak III or IV) on US or CT should undergo surgical exploration (see Chapter 15).

Medullary sponge kidney is a congenital deformity of the renal medulla consisting of multiple, puddle-like dilatations of the collecting ducts in the papillae on IVU. These ectatic tubules are not true cysts but give a characteristic fan-shaped pyramidal blush on IVU that is diagnostic. The disease is bilateral in 75% of patients. Although its course and progression are generally benign, its clinical importance is its predisposition to calcium phosphate nephrolithiasis in the adult, presenting with renal colic
and hematuria secondary to stone passage. Treatment consists of preventing infection and stone formation.

Tuberous sclerosis is a familial autosomal dominant condition characterized by congenital tumors. Two genes, TSC1 on chromosome 9 and TSC2 on chromosome 16, have been identified as being responsible for its transmission. Clinical features include the following:

von Hippel-Lindau disease is an autosomal dominantly inherited syndrome manifested by retinal and cerebellar hemangioblastomas; cysts of the kidney, pancreas, and epididymis; pheochromocytomas; and renal cell carcinoma in 30% to 40% of patients. Renal cysts are often multiple and bilateral and appear to be precursors of malignant tumors. Yearly abdominal CT or renal US is recommended in these patients because of the high incidence of renal cell carcinomas. Shelling out these tumors rather than radical surgery is appropriate in view of their multiplicity.

Acquired renal cystic disease (ARCD) is the appearance of bilateral multiple cysts in previously noncystic native kidneys of patients with ESRD. The risk of developing these cysts appears to be related to uremic toxins. Their significance lies in their apparent premalignant nature. The incidence of renal cell carcinoma is three to six times greater in patients on dialysis. Complaints of flank pain and/or hematuria in an ESRD patient should be investigated for ARCD or renal cell carcinoma.

Pelvic kidney is the most recognizable ectopic kidney, with an incidence of 1 in 2,000, and usually occurs in males on the left side. Fifty percent of these will be pathologic with poor function, and 10% are solitary. Other coincident genitourinary anomalies, such as cryptorchidism or absence of the vagina, are common. These kidneys are difficult to identify on IVU because of their poor function and position against the bony pelvis. Reflux is common. Voiding cystourethrogram (VCUG) can help make the diagnosis; however, CT scan is the most useful diagnostic modality.

Thoracic kidneys are extremely rare; mostly occur in males on the left side.

These kidneys are more commonly fused than not fused and are usually on the right with the crossed kidney lying inferiorly. A 2:1 male preponderance is noted. The ureteral orifices are located normally. The shape of the fused kidney can be quite unusual.

Horseshoe kidney is the most common type of fusion occurring in 1 in 400, with 90% fused at the lower poles. They are often associated with other urogenital anomalies and an increased incidence of renal pelvic tumors. One-third of patients remain asymptomatic, whereas others may present with symptoms of hydronephrosis (ureteropelvic junction [UPJ] obstruction), infection, or stones. The renal axis is shifted on kidney, ureter, and bladder film so that the lower poles are closer to the vertebral bodies. The ureters lie anterior to the renal pelvis and isthmus on IVU or CT. Reflux and UPJ obstruction occur often. Ureteroneocystostomy to treat reflux maybe necessary. Dividing the renal isthmus is usually not necessary.

Extrarenal pelvis predisposes to stasis, infection, and stone formation.

Bifid pelvis is a normal variant that occurs in 10% of the population.

Congenital calyceal diverticulum is a cystic cavity lying in the peripheral renal parenchyma connected to a calyx or the renal pelvis. Distention with urine can cause pain; however, infection and stone formation secondary to stasis are the most common complications. Diagnosis is made by IVU, retrograde pyelogram, or CT scan.

Hydrocalycosis is a rare cystic dilatation of a major calyx secondary to obstruction at the level of the infundibulum.

Congenital megacalyces is a stable malformation of markedly enlarged calyceal cavities without evidence of obstruction. It occurs in males, in a 6:1 ratio, is highly associated with megaureter, and predisposes to infection and stones. The diagnosis is made by IVU CT or, with a negative Lasix renal scan or Whitaker test. Preventing infection and stone formation with a high fluid intake is the goal of management.