MRI scan illustrating numerous widespread cysts with extensive hepatic involvement.
Findings: Autosomal Dominant Polycystic Kidney Disease.
Imaging of Autosomal Dominant Polycystic Kidney Disease can be difficult because of the size and sheer number of cysts and the associated spread to neighbouring organs and structures (as clearly demonstrated in Image 1). It is necessary for the radiographer to examine all the cysts for atypical features. A ‘simple kidney cyst’ is usually spherical in shape, the membranes (or wall) of the cysts are usually very thin and regular and it is filled with yellow or clear fluid. A ‘complex kidney cyst’ will have some type of irregularity inside it such as septations (or walls) and possibly tissue that enhances, which means has a blood supply.(1) Complex kidney cysts may indicate further complications such as hemorrhage, infection or a malignancy such as renal cell carcinoma.(2) Renal cell carcinoma for patients with ADPKD does not occur more frequently than in the general population although it does manifest itself differently.(3)
Autosomal Dominant Polycystic Kidney Disease (APKD)
ADPKD is an inherited systemic disease that causes cysts, (small fluid-filled membranous sacs of abnormal character) to develop in the kidneys. Other organs can also be affected including the pancreas, brain, liver and arterial blood vessels. Around half of people diagnosed with APKD will eventually develop end stage kidney disease, resulting in the need for dialysis or kidney transplantation. APKD is an inherited condition and children are born with it but usually they remain asymptomatic until around 30 – 60 years of age; end stage kidney disease usually happens from around the ages of 40 to 60 years old.(4) ADPKD is caused by a genetic defect in two genes. In 85% of patients it is caused by mutations in the gene PKD1 and in 15 % of patients by PKD2.(5) Both forms of the genes exhibit the same symptoms but type PKD1 tends to be more severe.
CT (contrast enhanced) in a patient with Autosomal Dominant Polycystic Kidney Disease shows slightly enlarged kidneys (bilaterally) which are almost completely replaced by small renal cysts, many of which contain calcifications in the walls (purple arrows).
If too many cysts grow, or the cysts become too large, as in the extreme examples shown here in Images 1 and 2, the normal kidney tissue is gradually replaced and kidney function becomes compromised resulting in end stage kidney failure. ADPKD is relatively uncommon and affects about 1 in 400 to 1 in 1,000 people worldwide.(6) Approximately 600,000 people in the United States have ADPKD and it is the fourth leading cause of kidney failure.
1. Landman Dr. : Kidney Cancer Institute: kidney Cysts Simple and Complex http://www.kidneycancerinstitute.com/kidney-cyst.html
2. Guermazi A. Imaging of kidney cancer. Springer Verlag. (2006) ISBN:3540211292
3. Peter C Harris, PhD and Vicente E Torres, MD. ‘Polycystic Kidney Disease, Autosomal Dominant’ GeneReviews
January 10, 2002; Last Update: December 8, 2011.
4,5. Grantham, Jared (Oct 2, 2008). “Autosomal Dominant Polycystic Kidney Disease”.New England Journal of Medicine 359 (14) 14771485. doi:10.1056/NEJMcp0804458.PMID 18832246.
6. Torres, Vicente; Harris, Peter C (20 May 2009). “Autosomal dominant polycystic kidney disease: the last 3 years”. Kidney International 76 (2): 149–168. doi:10.1038/ki.2009.128. PMC 2812475. PMID 19455193.