Septated urinomas in the neonate

Perirenal urinomas may develop when obstruction to urinary flow creates sufficient back pressure to produce extravasation of urine. Such fluid collections have been described as mainly sonolucent. However, in the last 2 years, we have imaged five neonates with multiple, marked septations of the urinoma, four with posterior urethral valves and one with a ureteropelvic junction obstruction. Diagnostic confusion may arise when the kidney is not identified, when the septated nature of the urinoma is not recognized, and when urinary tract obstruction is not seen.