Renal cyst disorders

Renal cyst disorders are a group of kidney diseases characterized by the formation of fluid-filled sacs (cysts) within the kidneys. These conditions vary in genetic inheritance patterns, clinical presentation, and prognosis. Here’s a breakdown of key renal cyst disorders relevant to USMLE Step 1 preparation.

1. Autosomal Dominant Polycystic Kidney Disease (ADPKD)

Key Features

Pathophysiology: Numerous cysts develop in the cortex and medulla, causing bilateral kidney enlargement and eventual destruction of kidney parenchyma.
Clinical Presentation: Often includes:
- Flank pain
- Hematuria (blood in urine)
- Hypertension
- Urinary tract infections
- Progressive renal failure (~50% of cases)

Gene	Mutation Percentage	Chromosome
PKD1	85%	Chromosome 16
PKD2	15%	Chromosome 4

Genetic Mutation

Complications

Chronic kidney disease (CKD)
Hypertension (due to increased renin production)
Associated Conditions:
- Berry aneurysms
- Mitral valve prolapse
- Benign hepatic cysts
- Diverticulosis

Treatment

Hypertension/Proteinuria Management: ACE inhibitors or ARBs.

2. Autosomal Recessive Polycystic Kidney Disease (ARPKD)

Key Features

Pathophysiology: Cystic dilation of the collecting ducts, often evident in infancy.
Clinical Presentation:
- Severe oliguric renal failure in utero, potentially causing Potter sequence.
- Systemic hypertension
- Progressive renal insufficiency
- Portal hypertension (due to congenital hepatic fibrosis)

Complications

Congenital hepatic fibrosis
Concerns Beyond Neonatal Period:
- Systemic hypertension
- Progressive renal insufficiency
- Portal hypertension due to congenital hepatic fibrosis

3. Autosomal Dominant Tubulointerstitial Kidney Disease (ADTKD)

Key Features

Alternate Name: Medullary cystic kidney disease.
Pathophysiology: Causes tubulointerstitial fibrosis and progressive renal insufficiency with an inability to concentrate urine.
Clinical Presentation:
- Medullary cysts were usually not visible on ultrasound.
- Smaller kidneys on imaging.
- Prognosis: Generally poor due to progressive renal failure.

4. Simple vs Complex Renal Cysts

Feature	Simple Cysts	Complex Cysts
Contents	Filled with ultrafiltrate (anechoic on ultrasound)	May contain septations, enhancements, or solid components
Prevalence	Very common; majority of renal masses	Less common; requires further investigation
Clinical Management	Typically asymptomatic and found incidentally	May need follow-up or removal due to renal cell carcinoma risk

Key Differences

Simple Cysts: Generally benign and asymptomatic.
Complex Cysts: Require follow-up or removal if they present certain features on imaging, due to a higher risk of malignancy.

Points to Remember

ADPKD is the most common type of renal cyst disorder, often manifesting in adulthood and having both renal and extrarenal complications.
ARPKD is usually diagnosed in infancy and is associated with severe outcomes, including Potter sequence and portal hypertension.
ADTKD leads to progressive renal insufficiency, with an inability to concentrate urine and smaller kidneys on imaging.
Complex Cysts carry a risk for renal cell carcinoma, while simple cysts are generally benign.

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USMLE Step 1 Review Series

Curriculum

Renal cyst disorders

1. Autosomal Dominant Polycystic Kidney Disease (ADPKD)

Key Features

Complications

Treatment

2. Autosomal Recessive Polycystic Kidney Disease (ARPKD)

Key Features

Complications

3. Autosomal Dominant Tubulointerstitial Kidney Disease (ADTKD)

Key Features

4. Simple vs Complex Renal Cysts

Key Differences

Points to Remember

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