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Renal Cysts & Polycystic Diseases

Notes

Renal Cysts & Polycystic Diseases

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Renal cysts are fluid-filled sacs that form in the kidney epithelia; they are often asymptomatic, but in some cases can cause end-stage renal failure.

Simple Cysts

Bosniak Grade 1

Very common and are often found incidentally – it is estimated that up to 40% of people have these renal cysts.

We show a simple cyst in the periphery of the renal tissue with watery, straw-colored fluid.

Simple cysts are usually acquired, and the number of cysts increases with age.

They are generally asymptomatic with no malignancy potential, and do not require intervention.

However, indicate that simple renal cysts can be become infected or rupture and cause hemorrhaging, and larger cysts can cause obstructive problems.

Complex Cysts

Bosniak Grade II

Grade II cysts have very thin "hairline" septa.

Grade II F (F is for follow-up) cysts have thicker walls and multiple thick septa with increasing calcification; these cysts are larger, with diameters of 3 cm or more.

Grades II and IIF have low malignancy potential, but, as its name implies, Grade IIF requires follow-up due to slightly higher malignancy potential.

Bosniak Grade III

Grade III cysts have thick walls with multiple nodules and CT enhancement.

Bosniak Grade IV

Grade IV cysts comprise solid masses with cystic and necrotic components; on CT we see enhancement of the soft tissue and cystic components.

Grades III and IV have increasingly higher malignancy risk, and partial or total nephrectomy is recommended.

Polycystic kidney diseases

Can be autosomal dominant, recessive, or sporadic (sporadic is very rare).

Characterized by multiple, bilateral fluid-filed cysts caused by defects in the primary cilia of the renal tubule cells.

The exact role of the primary cilia in renal cyst formation is uncertain, but it's thought to play a key role in the signaling pathways that establish and maintain functional tubule epithelium differentiation.

Cysts arise from the tubule epithelial cells: the dysregulated tubules dilate and fill with filtrate, and eventually separate to form cysts.

As they grow and multiply, the cysts enlarge the kidneys and impair renal functioning by displacing normal parenchyma and compressing the vasculature, which can lead to renal failure.

Autosomal dominant polycystic kidney disease (ADPKD)

Caused by mutations in the genes PKD1 or PKD2, which code for the polycystin proteins.

This disorder has complete penetrance; clinical manifestations are present in many patients by age 30, and are present in all patients by age 80.

Because patients don't typically experience signs or symptoms of autosomal dominant polycystic kidney disease until adulthood, we used to call this form of polycystic disease "adult polycystic disease."

The most common direct signs and symptoms include:

  • Flank and abdominal pain with proteinuria and hematuria
  • Hepatic cysts
  • Renal stones and urinary tract infections
  • Hypertension (due to activation of the renin-angiotensin-aldosterone system), cardiovascular problems, and intracranial aneurysms.

Treatments: There is no cure for autosomal dominant polycystic kidney disease, but we can give Tolvaptan to slow the growth of kidney cysts and antihypertensive drugs (ACE inhibitors and ARBs) to help manage the disorder.

Autosomal recessive polycystic kidney disease

Caused by mutations in PKHD1 (which codes for fibrocystin, aka, polyductin) and DZIP1L (which has a role in cilia formation).

Rarer and more severe than the autosomal dominant form, and, because it often leads to renal failure in early childhood, was formerly called "pediatric" or "infantile" polycystic kidney disease.

The cysts tend to be in the collecting tubules and create a dilating radial pattern.

In addition to polycystic kidneys, children with autosomal recessive polycystic kidney disease also tend to have hepatic fibrosis and hypertension; fetuses with severe renal impairment may have pulmonary hypoplasia, which is often fatal.

Due to early and severe renal impairment, patients require hemodialysis and kidney transplants.

Autosomal dominant tubulointerstitial kidney disease

A group of disorders associated with specific genes.

Includes medullary cystic kidney disease.

These disorders are associated with progressive renal function loss, and, while renal cysts are likely, they are not necessary for diagnosis.

Congenital cystic dysplasia

A group of renal disorders characterized by urinary tract defects that block urine flow.

Includes multicystic dysplastic kidney, which comprises multiple cysts in a setting of dysplastic tissue; in most cases, only one kidney is affected, and it regresses over time.

Medullary sponge kidney

Characterized by numerous diffuse, small medullary cysts that arise from abnormally dilated collecting ducts; both kidneys are often affected.

This is congenital disorder, but most patients are not diagnosed until after age 30 due to minimal clinical manifestations.

Patients have increased risk of calcium kidney stones and urinary tract infections.

Board Review

Polycystic Kidney Disease

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