Disorder characterised by malformation of the terminal collecting ducts, resulting in cystic dilation (ectasia) and diverticula confined to the pyramids.
About 1 in 5000, with majority remaining asymptomatic or diagnosed incidentally.
Thought to likely be congenital, arising from disruption at interface between ureteric bud and metanephric blastema.
Often found in younger stone formers, and recurrent calcium stone formers.
Clinical features
Usually benign, remaining asymptomatic.
Often presents in 20s and 30s with:
- Stones (usually calcium oxalate, at times calcium phosphate)
- Haematuria
- Recurrent UTIs
- Incidental finding on imaging
Usually associated with metabolic abnormalities:
- Hypercalciuria (30 – 50 %)
- Distal type 1 RTA (30 %)
- Hypocitraturia (often associated with RTA)
Associated with rare congenital abnormalities:
- Beckwith-Wiedemann syndrome
- Ehlers-Danos
- Hemihypertrophy
Nephrocalcinosis is often seen.
Some patients seem to have chronic flank pains in the absence of obstructing renal or ureteric stones.
Stones form due to stasis in collecting ducts, plus potential renal leak hypercalciuria and RTA from tubular dysfunction.
Pathological appearance
Dilated intra-papillary collecting ducts and small medullary cysts, giving cross-section appearance of a sponge.
Endoscopically – may be ectasia with ‘web-like’ appearance.
70 % bilateral. May be affecting one or all calyces.
Diagnosis and imaging
Classic imaging findings:
- Enlarged kidneys, often with medullary calcification and medullary calcinosis
- Elongated papillary tubules or cavities which fill with contrast
- ‘Contrast filled streaks’ arising from papillae extending into pyramids
- Papillary contrast ‘blush’ with persistent medullary opacification
- IVP classically “bouquet of flowers” or “paint-brush”
DDx – ADPCKD – look at the liver and family history.
Management
- In conjunction with renal physician
- Look for concurrent diagnoses especially if medullary nephrocalcinosis present also (RTA, PTH, sarcoid)
- Treat stones on merits
- Metabolic workup and treatment of hypercalciuria, hypocitraturia as appropriate
- Potassium citrate usually
Prognosis usually fine from a renal function point of view (assuming obstruction is treated on its merits).