Giant Paratesticular Leiomyosarcoma Mimicking a Benign Paratesticular Neoplasm: Multimodality Imaging and Radiologic-Pathologic Correlation

Paratesticular leiomyosarcoma is an uncommon malignant mesenchymal tumor with nonspecific imaging features that may overlap with benign paratesticular neoplasms.We report the case of a 46-year-old man presenting with progressive enlargement of the right hemiscrotum over six months.Ultrasonography demonstrated a large, well-defined heterogeneous solid-cystic paratesticular mass with a separately visualized testis and no significant internal Doppler vascularity.CT confirmed a large heterogeneous right scrotal/paratesticular mass with inferior displacement of the testis.MRI demonstrated a 14.6 × 11.1 × 10.5 cm well-defined solid-cystic lesion with T1-hypointense and T2/short tau inversion recovery-hyperintense signal, scattered hypointense solid components, delayed enhancement, prominent tortuous intralesional vessels on susceptibility-weighted imaging, and no convincing diffusion restriction.The imaging appearance favored a benign paratesticular neoplasm, with cellular angiofibroma and epididymal leiomyoma considered the principal differential diagnoses.Radical orchiectomy yielded an 850-g mass measuring 18.5 × 11.3 × 9.3 cm.Histopathological examination demonstrated a circumscribed spindle-cell neoplasm arranged predominantly in fascicles, confirming leiomyosarcoma.Immunohistochemistry showed positivity for smooth muscle actin and desmin, with a Ki-67 proliferation index of approximately 10%.The tumor demonstrated 8 mitoses per 10 high-power fields, with no tumor necrosis, and was classified as French Federation of Cancer Centers Sarcoma Group Grade 1 (total score: 3).This case highlights that a very large paratesticular leiomyosarcoma can retain well-defined margins and lack convincing diffusion restriction, thereby mimicking a benign lesion.Accurate localization, multimodality assessment, and radiologic-pathologic correlation are important when evaluating a large or progressively enlarging paratesticular mass.