Epidemiology & Risk Factors
Simple Cysts : Common, incidence increases with age (>50% of individuals >50 yo have simple cysts).Autosomal Dominant Polycystic Kidney Disease (ADPKD) : Most common inherited kidney disease; PKD1 (chromosome 16, 85%, more severe) or PKD2 (chromosome 4, 15%) mutations.Acquired Cystic Kidney Disease (ACKD) : Occurs in pts with ESRD on dialysis (risk increases with duration of dialysis; up to 90% after 10 years).Medullary Sponge Kidney : Congenital ectasia of collecting ducts; associated with nephrolithiasis and recurrent UTIs.
Clinical Features
Simple Cysts : Asymptomatic, incidental finding on imaging. Rare flank pain or hematuria if cyst ruptures/infects.ADPKD :
Bilateral flank pain, hematuria, progressive renal insufficiency.
Extrarenal manifestations : Intracranial berry aneurysms (highest yield association), hepatic cysts, pancreatic cysts, mitral valve prolapse (MVP), colonic diverticula, abdominal/inguinal hernias.Physical Exam: Bilateral palpable flank masses , HTN (due to localized ischemia driving renin-angiotensin activation).
ACKD : Often asymptomatic; presents with hematuria, flank pain, or sudden retroperitoneal hemorrhage.
Diagnosis
Initial : Renal Ultrasound (US) .
Simple Cyst Criteria : Anechoic, thin/smooth wall, posterior acoustic enhancement, no septations/calcifications (Bosniak I ). No further follow-up required.Complex Cyst Criteria : Thick walls, septations, calcifications, solid components, contrast enhancement (Bosniak II-IV ).
Confirmatory / Characterization : Contrast-enhanced CT or MRI of abdomen/pelvis (essential for grading complex cysts using the Bosniak Classification to rule out Renal Cell Carcinoma [RCC] ).Genetic Testing : Done in atypical ADPKD cases or for family screening if US is equivocal.
Differential Diagnostics
Renal Cell Carcinoma (RCC) : Diff by solid enhancing components on CT, fever, weight loss, cachexia, and a Bosniak IV classification.Renal Abscess : Diff by systemic infectious symptoms (fever, chills), leukocytosis, and a complex cystic structure with a thick, irregular wall on US.Hydronephrosis : Diff by US showing dilation of the renal pelvis and calyces in a branching pattern, rather than discrete parenchymal cysts.
Management
Simple Cyst :
Asymptomatic : No treatment or follow-up needed. c Symptomatic (Pain/Obstruction) : Percutaneous aspiration with sclerotherapy.
Complex Cyst (Bosniak Class IIF - IV) :
Bosniak II/IIF : Serial imaging follow-up (US or CT).Bosniak III/IV : Surgical resection (partial or total nephrectomy) due to high risk of malignancy.
ADPKD :
Strict BP Control : Target <130/80 mmHg; ACEi or ARBs are first-line (counters renin-angiotensin-aldosterone system [RAAS] activation).Slowing Cyst Progression : Tolvaptan (Vasopressin V2 receptor antagonist) for rapidly progressing disease.Symptomatic control : Pain management, prompt Abx for cyst infections (lipid-soluble Abx like Ciprofloxacin or Bactrim to penetrate cysts).ESRD : Hemodialysis/peritoneal dialysis or renal transplantation.Screening : Do NOT routinely screen for berry aneurysms unless pt has family history of aneurysms/SAH, high-risk occupation, or symptoms.