Abstract / Summary
Background: Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis characterized by multisystem infiltration by CD68+/CD1a− foamy histiocytes. Retroperitoneal and perirenal involvement, known as "hairy kidney," is a hallmark of the disease, present in 50–68% of patients. Diagnosis is often delayed due to its nonspecific clinical and radiological presentation. Case presentation: We report the case of a 72-year-old male who underwent an abdominal computed tomography (CT) scan for evaluation following a motor vehicle accident (MVA). Imaging incidentally revealed a well-defined, bilobed, soft-tissue density lesion abutting the left kidney, isodense to the renal parenchyma without contrast enhancement. The renal parenchyma appeared non-infiltrated with normal portal-phase enhancement. Lymphoma was initially suspected. Ultrasound-guided percutaneous biopsy was performed, revealing infiltration by a non-Langerhans histiocytic neoplasm with morphological and immunophenotypic features consistent with Erdheim-Chester disease. Conclusion: This case illustrates the incidental discovery of an ECD with an atypical presentation on an abdominal CT scan and highlights the importance of considering this rare diagnosis in cases of perirenal soft tissue lesions. A biopsy remains essential for establishing a definitive diagnosis, and a comprehensive multisystem evaluation is required once the diagnosis is confirmed.