Approach to cystic kidney disease: Clinical sciences

Kidney cysts are fluid-filled sacs lined by a thin wall of cells that can be located either in the cortex, the medulla, or both. Kidney cysts can be associated with acquired or inherited renal conditions and might cause no symptoms or lead to progressive loss of renal function and end-stage renal disease. There are several different renal conditions associated with kidney cysts, including simple renal cysts, medullary sponge kidney disease, and acquired renal cystic disease, as well as autosomal dominant polycystic kidney disease and autosomal dominant tubulointerstitial kidney disease.

If your patient presents with a chief concern suggesting cystic kidney disease, start by obtaining a focused history and physical exam.

Your patient might report symptoms specific to kidney conditions, like flank pain and hematuria. Additionally, there might be a history of kidney stones or a family history of kidney disease.

Next, the physical exam may reveal elevated blood pressure and palpable kidneys with costovertebral angle tenderness.

With these findings, consider a kidney disorder. Your next step is to order labs, including BMP, serum uric acid, and urinalysis.

Also, don’t forget a renal ultrasound. If the renal ultrasound reveals a single or multiple kidney cysts, diagnose cystic kidney disease and assess for a family history of kidney disease.

Now, if there’s no family history of kidney disease, consider simple renal cysts, medullary sponge kidney disease, or acquired renal cystic disease.

When it comes to simple renal cysts, they are typically incidentally found, as they are asymptomatic with no abnormalities on the physical exam and labs. The renal ultrasound reveals normal-sized kidneys with sharply demarcated cysts with smooth walls without septa, calcifications, or solid components. With these findings, diagnose simple renal cysts, which typically do not require treatment or follow-ups.

Here’s a clinical pearl to keep in mind! Unlike simple cysts, complex cysts have thicker walls and may contain solid material. They are a sign of an underlying cystic kidney condition, so be sure to monitor these patients over time, as some cysts could progress to renal cell carcinoma.

Medullary Sponge Kidney Disease Next up is medullary sponge kidney disease, which is caused by a developmental malformation of the renal collecting ducts in the medulla resulting in ductal dilatation and cyst formation. This collecting duct dilatation, or ectasia, is associated with the formation of both small, meaning microscopic, and large medullary so-called "cysts" that are often diffuse but do not involve the cortex.

Due to poor reabsorption of calcium, oxalate, and uric acid, as well as stagnation of the urine, these patients often report a history of kidney stones, hematuria, and recurrent urinary tract infections.

On the flip side, their physical exam is typically normal, with normal serum creatinine levels and urinalysis revealing hematuria.

In these individuals, the ultrasound shows normal-sized kidneys with small and large cysts in the renal medulla where in the majority of cases there is associated nephrocalcinosis and kidney stones.

If you see this, consider medullary sponge kidney disease and order additional imaging methods, such as intravenous pyelogram or CT urogram. If the imaging confirms the presence of kidney stones and nephrocalcinosis; and reveals pooling of contrast at the junction of the papilla and calyces producing a feathered- or brushlike appearance, diagnose medullary sponge kidney disease.

Moving on to acquired renal cystic disease. These patients are usually asymptomatic with a history of chronic kidney disease, particularly end-stage renal disease requiring dialysis. The physical exam is typically normal, but their labs are significant for elevated creatinine before the renal cyst development.