Renal Mass (Case 18)

Pφ

There are two major types of autosomal-dominant PCKD. Autosomal-dominant PCKD type 1 is the most common and most severe, with approximately 50% of affected individuals requiring dialysis by the age of 60 years. It is linked to an abnormal gene on chromosome 16, named PKD1. Autosomal-dominant PCKD type 2 is less common and less severe, and is linked to an abnormal gene on chromosome 4, named PKD2. PKD1 and PKD2 encode the proteins polycystin-1 and polycystin-2, respectively. These proteins are involved in cell-cell and cell-matrix interactions. Mutations in these genes lead to cyst formation through an as-yet-undefined mechanism.

TP

Often affected patients present with flank pain, resulting from an infected cyst, hemorrhagic cyst, or nephrolithiasis. Other patients present with renal insufficiency and hypertension. Still others present with extrarenal cystic manifestations. Hepatic cysts can be detected in over one half of cases and are more commonly seen in women and in patients over the age of 40 years. An additional manifestation includes intracranial aneurysms, which tend to cluster in families.

Dx

For patients who are older than 15 years and at risk for the disease, the diagnosis is made by demonstrating multiple cysts on sonography. The number of cysts necessary to make a diagnosis depends on the patient’s age. Genetic testing can be considered for patients with equivocal results on sonography or in patients who are younger than 30 years and need a definite diagnosis.

Pφ

Acquired cystic kidney disease is a specific disorder in which renal cysts develop in the kidneys of patients with advanced kidney disease. These cysts have an increased risk of malignant transformation. In acquired cystic kidney disease the cysts are limited to the kidney and not dependent upon the underlying cause of kidney failure, which suggests a local rather than systemic cause of cyst development. The cysts likely develop as a result of progressive nephron loss and compensatory hypertrophy and hyperplasia in the remaining nephrons. When the tubular segment of these hyperplastic nephrons becomes obstructed, cyst development occurs. Activation of proto-oncogenes may lead to malignant transformation.

TP

Typically acquired cystic kidney disease is asymptomatic and found incidentally on unrelated imaging. Occasionally patients present with flank pain and fever suggestive of cyst infection, hematuria due to cyst hemorrhage, or systemic signs of malignancy after the development of renal cell carcinoma.

Dx

Diagnosis is established through imaging studies. Ultrasound, CT scan, and MRI are all sensitive tests. At the time of diagnosis, patients often have multiple bilateral renal cysts. The cysts are usually <0.5 cm in diameter.

Pφ

MSK is caused by a developmental abnormality in the terminal collecting ducts of the kidney. This developmental error is associated with the formation of renal cysts involving the renal medulla, but not the renal cortex. The mechanism of cyst development is not well understood. Although some families seem to have an autosomal-dominant inheritance, there is no evidence of hereditary transmission.

TP

Patients with MSK are usually asymptomatic, and their condition is only discovered incidentally during unrelated radiographic testing. When symptoms do occur they can be related to kidney stones, which are more common in this population.

Dx

The diagnosis has historically been made by IVP, but CT scan with contrast has recently proven to be a sensitive alternative. The appearance of a “brush” radiating from the renal calyx is the typical finding. Calcium stones, resulting from urinary stasis, can appear in the renal calyces. Ultrasonography is less specific than IVP but typically reveals a uniformly echogenic corticomedullary junction due to calcium deposits in the affected regions.

Pφ

Renal cell carcinoma is a common malignancy arising from the renal tubular epithelium. There are several distinct histologic types. Clear cell is the most common type, accounting for the majority of tumors. It originates from the proximal tubule and is specifically associated with VHL disease. Chromophilic or papillary cell carcinoma is the second most common type, and also originates from the proximal tubule. Chromophobic tumors are less common than clear cell or chromophilic carcinoma, and are thought to arise from the cortical collecting duct. Oncocytomas constitute approximately 5% of renal neoplasms; they are believed to originate from the distal collecting tubule and rarely metastasize.

TP

The classic triad of flank pain, abdominal mass, and hematuria is rarely present at the time of diagnosis. Other patients present with fever, weakness, and weight loss, or paraneoplastic syndromes (hypercalcemia or polycythemia). Systemic symptoms at the time of diagnosis are often a sign of advanced disease.

Dx

CT scan is the preferred method to evaluate potentially malignant renal masses. It can determine the size of the mass, as well as any possible spread, which will allow staging. Tissue diagnosis is required.

Pφ

Renal angiomyolipomas are benign neoplasms. They can occur sporadically or as part of the tuberous sclerosis complex. They are composed of adipose tissue, smooth muscle cells, and blood vessels. When they are found as part of tuberous sclerosis they are usually bilateral and larger, while when they occur sporadically they are usually unilateral and small.

TP

Small angiomyolipomas are usually asymptomatic. Larger lesions can rupture and cause flank pain and life-threatening retroperitoneal hemorrhage. Some lesions can become large and impinge upon normal renal tissue, resulting in hypertension and renal failure.

Dx

The diagnosis is most often made by CT scan, which shows that the lesion has the density of fat. Patients with angiomyolipomas should be evaluated for undiagnosed tuberous sclerosis.