Myolipoma of the uterus with bizarre-nucleated cells: a case report and literature review.

BACKGROUND

Myolipoma is a rare benign mesenchymal tumor composed of mature adipose tissue, smooth muscle bundles and blood vessels, which predominantly occurs in the retroperitoneum, inguinal region and abdominal wall. Primary uterine involvement is extremely uncommon, and the presence of bizarre-nucleated cells within such tumors is even rarer. The morphological features of these cells may mimic malignant neoplasms, posing great challenges for clinical and pathological diagnosis.

METHODS

We report a 61-year-old female patient with imaging and ultrasonographic findings suggestive of a uterine space-occupying lesion. Histopathological examination and immunohistochemical staining were performed on the surgically resected specimen, with the detected markers including smooth muscle actin (SMA), Desmin, HMB45, Melan A, S-100 and Ki-67.

RESULTS

Pelvic magnetic resonance imaging (MRI) revealed a well-demarcated heterogeneous signal mass in the anterior wall of the uterine corpus, consistent with the manifestations of a benign tumor containing adipose components. Gross examination showed a well-circumscribed intramural mass of the uterus with a grayish-yellow and heterogeneous cut surface. Microscopically, mature adipocytes and benign smooth muscle cells were scattered with bizarre-nucleated cells characterized by markedly enlarged and irregular nuclei; no mitotic figures or necrotic foci were identified. Immunohistochemically, the smooth muscle component showed diffuse and strong positivity for SMA and Desmin, while HMB45, Melan A and S-100 were all negative. The Ki-67 proliferation index was extremely low (<1%), confirming the diagnosis of uterine myolipoma with bizarre-nucleated cells.

CONCLUSION

Uterine myolipoma with bizarre-nucleated cells is an exceedingly rare benign tumor, and no recurrence or metastasis was observed during postoperative follow-up, indicating its indolent biological behavior. Accurate diagnosis requires the combination of imaging features, adequate sampling, meticulous histological evaluation and targeted immunohistochemical detection to distinguish it from leiomyosarcoma, liposarcoma and perivascular epithelioid cell tumor (PEComa).