Polycystic Disease

Clinical
Autosomal-dominant polycystic disease, also called adult polycystic kidney disease and Potter type III, is the most common hereditary renal disorder. It is not a simple entity; no family history of renal disease is obtained in about half the patients, and variable penetrance and expressivity are apparent. Many of these patients develop hypertension. Renal failure is a late finding. These patients are also prone to developing aortic and cerebral aneurysms with their related complications.
A rare disorder called oral-facial-digital syndrome type 1 includes polycystic kidney disease as one component. The syndrome is X-linked, with affected males dying before birth. Although renal findings resemble autosomal polycystic disease and a dominant inheritance pattern is evident, histopathology reveals mostly glomerular cysts. There are two subtypes of autosomaldominant polycystic disease. Polycystic kidney disease type 2 (PKD2) has a milder clinical phenotype than PKD1; the median age at death or onset of end-stage renal disease is 53 years for individuals with PKD1 and 69 years for those with PKD2. About half of these patients also develop liver cysts; far fewer develop pancreatic or splenic cysts or even adrenal cysts. A rare patient also has Caroli’s disease, but this association is less common than with autosomalrecessive polycystic disease. Polycystic kidney disease can develop in a horseshoe kidney. Histologically, cystic changes occur both in nephrons and collecting ducts. Eventually multiple cysts of varying size are found in both the renal cortex and the medulla. Subcapsular cysts also develop.
Abdominal pain is a common presentation. Many patients develop hypertension. An occasional cyst rupture into the collecting system leads to hematuria. Enlarged kidneys are palpable in some individuals. Renal stones with their related complications are more prevalent than in the general population. Eventually renal failure ensues. The rare emphysematous pyelonephritis is probably due to superimposed infection rather than polycystic disease. Likewise, renal cell carcinoma developing in a setting of polycystic disease is probably fortuitous.
Typically few cysts are detected early in life, but gradually multiple bilateral cysts enlarge and interstitial fibrosis develops with loss of normal renal tissue. Not uncommonly progressive worsening of renal function manifests in early adulthood. The cysts compress and distort adjacent calyces and eventually little renal
parenchyma is detected.Why the loss of normal renal tissue is part of this condition is puzzling. Still, the kidneys are larger than normal. Several criteria are used to identify patients at risk for developing adult polycystic kidney disease. One scheme is that the presence of at least two renal cysts (either unilateral or bilateral) n individuals at risk and younger than 30 years is regarded as sufficient to establish the diagnosis; in those 30 to 59 years of age at least two cysts in each kidney and in those above 60 years of age at least four cysts in each kidney are required. Ultrasonography can be used to screen for these cysts.
Imaging
Initially cysts are small, but eventually imaging identifies bilateral enlarged kidneys, at times markedly asymmetrical, and containing multiple cysts. The cysts vary in size and distort surrounding parenchyma. Computed tomography shows most cysts to resemble simple cysts, although hemorrhage into cysts is common and these are hyperdense to water. Some have a fluid–fluid level or even appear as a solid tumor. Renal calcifications are generally secondary to calculi, prior hemorrhage into a cyst, or cyst wall calcifications.
Computed tomography or MR is useful to evaluate for any associated liver disease. The sensitivity of renal US in individuals under 30 years of age at risk for autosomaldominant polycystic kidney disease was 95% for those with PKD1 but only 67% for those with PKD2, but US sensitivity for either PKD type in individuals aged 30 years or older was 100%; DNA genetic linkage analysis was the gold standard.
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Radiology images of polycystic disease. Transverse CT image through the kidneys reveals numerous cysts varying in size. Little renal parenchyma is left.


These cysts vary from hypo- to hyperintense both with T1- and T2-weighted images, presumably due to prior hemorrhage. A fluid-fluid level is identified in some.

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radiology images of polycystic disease. A: Cysts, hyperintense on T2–weighted magnetic resonance imaging (MRI), have replaced most of renal parenchyma. Even more hyperintense cysts are present in the liver. B: Very little renal parenchyma is left to enhance after IV contrast. (Source: Burgener FA,Meyers SP,Tan RK, Zaunbauer W. Differential Diagnosis in Magnetic Resonance Imaging. Stuttgart: Thieme, 2002, with permission.) C: T2– weighted MRI in another patient with polycystic kidneys identifies cyst intensity variations reflecting their content differences.


Therapy Follow-up of these patients is generally by US. Computed tomography is useful to evaluate for a suspected complication. Intravenous urography has no role in follow-up. Open transperitoneal bilateral renal cyst reduction surgery is an option in symptomatic patients; one advantage of this approach is that any liver cysts are also amenable to therapy. Laparoscopic cyst unroofing (decortication or marsupialization) for relief of pain is also an option; intraoperative US aids cyst detection during the laparoscopic procedure. Some of these patients require repeat cyst unroofing efore pain relief is achieved. A number of these patients eventually undergo renal transplantation. Some surgeons recommend nephrectomy prior to renal transplantation, although others disagree and reserve nephrectomy for those with intracystic hemorrhage, significant hematuria, pyonephrosis, or other complications.

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