Hereditary Multiple Exostoses Presenting with Urinary Tract Obstruction Secondary to Imaging-Suspected Malignant Transformation: A Case Report.

Background: Hereditary multiple exostoses is a rare autosomal dominant skeletal disorder characterized by the development of multiple osteochondromas, with imaging findings suggestive of malignant transformation to chondrosarcoma occurring in a small proportion of patients. Such transformation typically presents with localized pain or deformity. Few reports describe urinary tract manifestations of pelvic osteochondromas; however, presentation with urinary obstruction secondary to imaging-suspected malignant transformation appears to be exceptionally rare. Case Presentation: A 28-year-old Iranian man presented with a three-week history of dull right lower back pain and progressive urinary difficulty. No gross hematuria was reported although microscopic hematuria was detected on urinalysis. Ultrasonography demonstrated moderate right-sided hydronephrosis. Contrast-enhanced computed tomography of the abdomen and pelvis revealed multiple osteochondromatous lesions arising from the bilateral iliac and femoral bones, along with an infiltrative heterogeneous soft-tissue mass originating from the largest pelvic exostosis, were suspicious for malignant transformation to chondrosarcoma. The mass caused extrinsic compression of the right distal ureter, explaining the patient's urinary symptoms. Based on imaging findings, a provisional diagnosis of hereditary multiple exostoses complicated by secondary chondrosarcoma was made. Histopathological confirmation was not obtained because the patient was lost to follow-up, therefore the diagnosis remained presumptive. Conclusion: This case highlights a rare and atypical presentation of hereditary multiple exostoses with suspected malignant transformation manifesting primarily as urinary tract obstruction. Clinicians should consider underlying skeletal pathology in patients with unexplained urinary obstruction, particularly when imaging reveals pelvic masses. Early recognition of imaging features suspicious for malignant transformation through cross-sectional imaging is crucial for timely diagnosis and management in patients with hereditary multiple exostoses.