Cystic Renal Diseases

hematuria or symptoms and signs of infection. Hypertension is rare. If there are multiple cysts and renal function is impaired, consider acquired cystic disease (see below).

■ Diagnosis:

■ Incidental finding on ultrasound (US), computed tomography (CT) of the abdomen, or magnetic resonance imaging (MRI) of the abdomen (see below)

■ Absence of liver cysts

■ Absence of family history

■ Imaging studies

■ US criteria for benign lesions:

• Round and sharply demarcated with smooth walls

• No echoes (anechoic) within the mass

• Strong posterior wall echo indicating good transmission through the cyst and enhanced transmission beyond the cyst

■ CT criteria (Bosniak classification): Cysts can be classified based on morphologic and contrast enhancement characteristics (Israel & Bosniak, 2005)

• Category I: Benign simple cyst with a thin wall without septa, calcifications, or solid components; water density; no contrast enhancement; no follow-up needed

• Category II: Benign cystic lesions in which there may be a few thin septa; the wall or septa may contain fine calcification or a short segment of slightly thickened calcification; less than 3 cm in diameter, well-marginated, and nonenhancing; no follow-up needed

• Category IIF: Multiple thin septa or minimal smooth thickening of the septa or wall, which may contain calcification that may also be thick and nodular; no measurable contrast enhancement; may be more than 3 cm in diameter; require follow-up to ascertain that they are nonmalignant

• Category III: Indeterminate cystic masses with thickened
irregular or smooth walls or septa; measurable enhancement is present. Risk of malignancy is ~50% (cystic renal cell carcinoma [RCC] and multiloculated cystic RCC); require further imaging and consideration of surgery

• Category IV: These lesions have all the characteristics of category III cysts, plus they contain enhancing soft-tissue components that are adjacent to and independent of the wall or septum; these lesions are very likely malignant and require surgery

■ Treatment:

■ If patient is symptomatic or develops significant obstruction, percutaneous aspiration and obliteration with a sclerosing agent may be needed.

■ If the cyst becomes larger than 500 mL, consider drainage even in absence of symptoms

■ Infected cysts may require surgery

■ Cysts that are likely malignant generally require surgery (see above)

ACQUIRED CYSTIC KIDNEY DISEASE (ACKD)

■ Definition: Noninherited small cysts distributed throughout the renal cortex and medulla of patients with renal failure, especially end-stage kidney disease (ESKD).

■ Pathophysiology: Uremia causes epithelial hyperplasia which promotes the development of cysts and tumors. However, a relationship between cyst formation and efficacy of dialysis has not been established. Transplantation stops the progression of cyst formation and may cause regression. Cysts can recur in rejected kidneys; cyclosporine may cause cyst formation.

■ Symptoms: Gross hematuria, flank pain, renal colic, fever, palpable renal mass, and rising hematocrit may be present.

■ Diagnosis

■ Incidental finding on US, CT of the abdomen, or MRI of the abdomen

■ RCC is three times more common in ACKD; RCC is six times more common in large cysts. However, RCC associated with ACKD has lower risk of metastasis and carries a better prognosis.

■ Follow-up and treatment:

■ US or CT of the abdomen should be performed after 3 years of dialysis followed by screening at 1- to 2-year intervals.

■ Bleeding should be treated with bed rest and analgesia. Persistent bleeding is associated with a high risk of RCC and warrants nephrectomy.

■ Renal masses greater than 3 cm should be treated with nephrectomy. A renal mass that is <3 cm can also be treated with nephrectomy or it may be observed with annual CT.

■ Nephrectomy should be bilateral in end-stage kidney disease (ESKD) patients because RCC in the setting of ACKD is usually multicentric and bilateral.

MEDULLARY SPONGE KIDNEY

■ Definition: Dilated collecting ducts and cysts confined to medullary pyramids.

■ Pathophysiology: Medullary sponge kidney is probably usually acquired but a familial form has been described. Associated with formation of calcium stones (13%), probably due to urinary stasis and anatomic abnormality. Also associated with primary hyperparathyroidism, Ehlers-Danlos syndrome.

■ Symptoms: Patients may present with gross or microscopic hematuria, urinary tract infection, renal colic due to calcium oxalate or calcium phosphate stones.

■ Diagnosis:

■ Plain X-rays—Dilated collecting ducts without ureteral obstruction. May see renal calculi or nephrocalcinosis

■ CT of the abdomen—Cortical layer is free of cysts

■ Absence of family history (usually)

■ Renal tubular acidosis (RTA) often present

■ Treatment:

■ Treat stones and/or urinary tract infections

■ Alkali for RTA may promote calcium phosphate stones

AUTOSOMAL DOMINANT POLYCYSTIC KIDNEY
DISEASE (ADPKD)

■ Definition: Multiple cysts found on imaging of the kidneys usually in a patient with autosomal dominant family history of polycystic kidneys. Five percent of patients do not have a family history

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