A review of the natural progression of medullary sponge kidney and a novel grading system based on intravenous urography findings.

PURPOSE: Medullary sponge kidney (MSK) is a developmental abnormality of the medullary pyramids of the kidney, characterised by cystic dilatations of the collecting ducts. We investigated a cohort of patients with MSK to gain further information about its presentation, clinical course and treatment required. We devised a grading system based upon findings at diagnostic intravenous urography (IVU) and established a relationship between severity of IVU findings and severity of disease.

MATERIALS AND METHODS: The clinical notes and imaging of 29 patients with MSK were analysed. The severity of IVU findings was classified as follows: grade 1 (one calyx, unilateral), grade 2 (one calyx, bilateral), grade 3 (more than one calyx, unilateral) and grade 4 (more than one calyx, bilateral).

RESULTS: The age range at diagnosis was 12-69 (mean 39), mean follow-up period was 12.7 years. Increasing grade of IVU findings correlated with more frequent symptomatic stone episodes (grade 1: 0.09 episodes per patient per year; grade 4: 0.34). Higher grade was also related to the number of hospital admissions (grade 1: 0.182 per patient per year; grade 4: 0.282) and the number of procedures required (either surgery or extracorporeal shock wave lithotripsy; grade 1: 0.0 interventions per patient per year; grade 4: 0.24).

CONCLUSIONS: MSK presents over a wide age range and can cause long periods of intermittent episodes. Patients can be graded using a novel system based on IVU findings, which correlates with severity of disease. Management strategies such as intensity of follow-up can be modified using this grading.