Abscessed Lumbar Hypodermatitis Revealing Pyonephrosis: A Diagnosis to Keep in Mind

Pyonephrosis resulting from an obstructing calculus commonly presents with symptoms such as loin pain, fever, and signs indicative of a urinary tract infection. In some cases, significant thinning of the renal parenchyma in pyonephrosis may lead to direct rupture into the retroperitoneum, and exceptionally rarely, into the lumbar abdominal wall, potentially mimicking an isolated abdominal wall abscess, which can be mistaken for a complication of hypodermatitis. Our case is a good illustration of a condition that is not well known among practitioners, particularly family physicians and dermatologists. This lack of awareness can explain the diagnostic delay, which may sometimes result in the patient's death.