Medullary sponge kidney

In this condition there is dilatation of the distal collecting tubules in the medullary papillae. The aetiology is uncertain but it is probably a developmental anomaly and links with various other disorders such as hemi-hypertrophy, Ehlers-Danlos syndrome, Marfan's syndrome and Caroli's disease have been reported.52 The true prevalence in the population is unknown as most patients remain asymptomatic unless calculi, haematuria or pain develop. Estimates of 0.5% of all intravenous urograms have been suggested53 and approximately 17% of patients with renal calculi have been shown to have medullary sponge kidney.54

The diagnosis is usually made on urography, or CT, but ultrasound may show early nephrocalcinosis before this is seen radiographically, or even with CT.55 Usually several pyramids are involved but occasionally the abnormalities may be limited to just two or three pyramids. If calculi form these may be detected in the region of the pyramids or calyces (Fig. 23.10) and if ureteric obstruction results then this too can be detected on ultrasound.

Figure 23.9 Papillary necrosis. Small cystic areas containing necrotic papilla fragments in the periphery of the sinus echoes in a patient with papillary necrosis.

Figure 23.10 Medullary sponge kidney. A and B: Two examples of medullary sponge kidneys with calcifications in the medullary pyramids in two different patients.

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