A primary psoas abscess with renal fistulization: A rare case in a 2-year-old child

Iliopsoas abscess is a rare condition in children, yet it carries a significant risk of morbidity and mortality if not promptly diagnosed and treated. We report an unusual case of a primary psoas abscess in a previously healthy 2-year-old male, complicated by fistulization into the kidney. The patient presented with a painless left lumbar mass and low-grade fever. Contrast-enhanced computed tomography (CT) revealed a multiloculated retroperitoneal abscess involving the left psoas and quadratus lumborum muscles, with extension into the ipsilateral kidney. Laboratory tests showed leukocytosis and elevated inflammatory markers. Surgical drainage of the abscess identified Staphylococcus aureus as the causative pathogen. Postoperative antibiotic therapy led to a favorable outcome. This case highlights the importance of considering psoas abscess in the differential diagnosis of pediatric lumbar masses and underscores the need for early imaging and intervention to prevent severe complications such as renal fistulization.