Polycystic Kidney Disease

Overview

PKD = major renal parenchyma → cysts. 2 forms: Adult (AD) vs Infantile (AR) — genetically/clinically distinct.

ADPKD

Common (1:400-1000), ~4% of dialysis ESRF. AD inheritance: PKD-1 (chr16, >85%) or PKD-2 (chr4). Kidneys abnormal from birth but function preserved till adult symptoms (30-50yr).

Morphology: Gross — bilateral, SYMMETRIC enlargement, heavy (up to 4kg), LOBULATED surface. Cysts throughout (tiny-4-5cm), variable contents. Cysts DO NOT communicate with pelvis (key distinguisher from hydronephrosis). Micro — cysts from ALL nephron segments (some with glomerular tufts, some tubule/duct-lined), some normal intervening parenchyma. Acquired lesions (pyelonephritis, nephrosclerosis, fibrosis) accumulate with age.

Clinical: onset 3rd-5th decade. Earliest/commonest: dull lumbar ache. Also haematuria, renal colic, HTN, UTI, progressive CRF+polyuria+proteinuria.

SYSTEMIC disease: ~1/3 liver cysts; less often pancreas/spleen/lung cysts; ~15% INTRACRANIAL BERRY ANEURYSMS (circle of Willis) — critical SAH risk. Acquired renal disease more common in polycystic kidneys.

ARPKD

Distinct, less common (1:20,000 births), AR — family history usually ABSENT (contrast ADPKD). Chr 6p21, PKHD1 gene. Always bilateral. Perinatal-juvenile presentation, often serious AT BIRTH, death from renal failure in early childhood.

Morphology: Gross — bilateral enlargement, SMOOTH surface, reniform shape retained. Small fusiform/cylindrical cysts radiating medulla→cortex = “SPONGE-LIKE.” No recognisable normal parenchyma. Pelvis/calyces/ureters normal. Micro — NORMAL nephron number, cysts from DILATED COLLECTING TUBULES (cylindrical/saccular); many glomeruli also cystic.

Clinical: severity by age. Severe: may obstruct delivery. Early infancy: early renal failure. Nearly all: hepatic epithelium-lined cysts/portal bile ductule proliferation. Older children: congenital hepatic fibrosis → portal HTN+splenomegaly.

Comparison

Clinical relevance

Non-communication of ADPKD cysts with pelvis = single most useful gross/imaging discriminator from hydronephrosis — separates structural obstruction from primary cystic disease. Berry aneurysm association (~15%) = high-yield, potentially life-saving — screening consideration follows from recognising ADPKD as systemic disease, not purely renal. Cyst-origin distinction (all nephron segments vs collecting tubules only) explains different gross appearance (diffusely cystic/lobulated vs radial sponge-like) — anatomic pattern is direct visual consequence of affected segment. ARPKD’s near-universal hepatic involvement (→ congenital hepatic fibrosis) = never purely kidney disease — portal HTN complications become major long-term outcome determinant in survivors, not just renal failure.

Overview

Polycystic kidney disease (PKD) converts a major portion of renal parenchyma into cysts of varying size, occurring in two genetically and clinically distinct forms: adult (autosomal dominant) and infantile (autosomal recessive).

Adult Polycystic Kidney Disease (ADPKD)

Relatively common (1:400–1:1000), causing ~4% of haemodialysis-requiring end-stage renal failure. Autosomal dominant: PKD-1 gene (chromosome 16) mutated in >85% of cases (ADPKD-1), PKD-2 (chromosome 4) in the remainder (ADPKD-2). Kidneys are abnormal from birth, but renal function is preserved until symptoms emerge in adult life (30–50 years).

Morphology: grossly, always bilaterally, symmetrically enlarged, heavy (up to 4 kg), externally lobulated from underlying cysts. Cut surface: cysts throughout the parenchyma, tiny to 4–5 cm; contents range from clear straw-yellow fluid to reddish-brown. Pelvis/calyces present but distorted; critically, cysts do NOT communicate with the pelvis — the key gross feature distinguishing ADPKD from hydronephrosis. Microscopically, cysts arise from all parts of the nephron — some containing recognisable glomerular tufts (Bowman’s capsule origin), others lined like proximal/distal tubule or collecting duct; intervening tissue shows some preserved normal parenchyma. Acquired lesions (pyelonephritis, nephrosclerosis, fibrosis) accumulate with age.

Clinical features: onset typically 3rd–5th decade; earliest/commonest feature is dull lumbar ache. Also haematuria/blood clots, renal colic, hypertension, UTI, progressive CRF with polyuria and proteinuria.

ADPKD is a genuine systemic disease, not purely renal:

• ~1/3 of patients have liver cysts.
• Less frequent: pancreatic, splenic, pulmonary cysts.
• ~15% have intracranial berry aneurysms of the circle of Willis — a clinically critical association given subarachnoid haemorrhage risk.
• Acquired renal disease occurs more readily in already-polycystic kidneys.

Infantile Polycystic Kidney Disease (ARPKD)

Distinct disease, less common (1:20,000 births), autosomal recessive — family history usually absent (contrast ADPKD). Mutation on chromosome 6p21, PKHD1 gene. Always bilateral. Presentation spans perinatal to juvenile, but serious manifestations are often present at birth, causing death from renal failure in early childhood.

Morphology: grossly, bilaterally enlarged kidneys with smooth external surface, retained reniform shape. Cut surface: small fusiform/cylindrical cysts radiating from medulla to outer cortex — a “sponge-like” appearance; no grossly recognisable normal parenchyma. Pelvis, calyces, ureters normal. Microscopically, total nephron number is normal — cysts form from dilated collecting tubules (cylindrical/saccular, cuboidal-to-low-columnar lining); many glomeruli are also cystically dilated.

Clinical features: severity depends on age at presentation — severe cases may obstruct delivery; early infancy often brings early renal failure. Nearly all cases have associated hepatic epithelium-lined cysts or portal bile ductule proliferation; older children develop congenital hepatic fibrosis, which can progress to portal hypertension and splenomegaly.

ADPKD vs ARPKD — Contrasted

Clinical Relevance

• The non-communication of ADPKD cysts with the renal pelvis is the single most useful gross/imaging discriminator from hydronephrosis, since both conditions can produce a grossly cystic, distorted kidney — this one anatomic fact (communicating vs non-communicating) is what separates a structural obstruction problem from a primary cystic disease.
• ADPKD’s berry aneurysm association (~15%) is a high-yield, potentially life-saving fact — screening consideration in ADPKD patients, particularly those with a family history of subarachnoid haemorrhage, follows directly from recognising ADPKD as a systemic connective-tissue-adjacent disease rather than a purely renal one.
• The cyst-origin distinction (all nephron segments in ADPKD versus specifically collecting tubules in ARPKD) explains the different gross appearances (diffusely cystic and lobulated versus radially “sponge-like”) — the anatomic pattern of cyst distribution is a direct visual consequence of which nephron segment is affected in each disease.
• ARPKD’s near-universal hepatic involvement (evolving into congenital hepatic fibrosis) means this is never purely a kidney disease either — recognising the combined hepatorenal fibrocystic phenotype is essential, since portal hypertension and its complications become a major determinant of long-term outcome in survivors, not just renal failure.

• ADPKD vs ARPKD compared: inheritance, gene, cyst origin, and gross appearance
• ADPKD as a systemic disease: renal cysts alongside liver/pancreas/spleen cysts and berry aneurysms

Multiple Choice Questions (2)