Rare Uterine Lipoma Diagnosed Post-Surgery: Case Report

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Uterine representation

Uterine lipomatous tumors are an exceedingly rare occurrence, with pure uterine lipomas being exceptionally uncommon. Only a handful of cases have been reported in medical literature. The exact origin or histogenesis of these lipomatous neoplasms remains unclear, and multiple theories have been proposed to explain their development. In this report, we present the case of a 70-year-old woman who was diagnosed with uterine lipoma postoperatively through histopathological examination.  

The patient’s medical history included hypertension, hypercholesterolemia, and a history of two uncomplicated vaginal births with subsequent prolapse. There was no history of hormone replacement therapy. She presented to her general practitioner with recurrent urinary tract infections and was incidentally found to have a large, painless abdominal mass during a physical examination. She did not report any systemic symptoms related to the mass. This rare case report was covered by Case Reports in Women’s Health. 

Computed tomography (CT) imaging revealed the presence of a sizable fatty mass measuring 160 × 123 × 144 mm. Given its location and characteristics, the favored initial differential diagnosis was uterine lipoleiomyoma. However, due to the complexity of distinguishing this mass from the right ovary, a pelvic ultrasound was also performed. The ultrasound imaging indicated a 124 × 123 × 111 mm mass, favoring the possibility of a dermoid cyst arising from the right ovary. 

Due to the conflicting radiological findings and the need for a definitive diagnosis, the decision was made to proceed with elective surgery. The patient underwent a hysterectomy and bilateral salpingo-oophorectomy, and the excised specimen was sent for a detailed histopathological examination. 

Upon examination of the uterus, it was noted to weigh 1666 g. The cut surface of the uterine specimen revealed a round yellow mass, consistent with adipose tissue, located in the posterior wall. This fatty mass measured 150 × 140 × 125 mm and displayed no macroscopic evidence of hemorrhage or necrosis. Aside from a small paratubal cyst, the fallopian tubes and ovaries appeared unremarkable. 

Microscopic examination of the excised mass revealed that it was composed of benign, mature adipocytes. Septa containing thick-walled blood vessels with occasional perivascular smooth muscle were observed. Notably, there was no evidence of malignancy or atypia within the adipocytes. In addition to the uterine findings, the examination revealed atrophic changes in the endometrium, benign Nabothian cysts in the cervix, and the presence of ovarian cortical inclusion cysts and paratubal cysts. 

Immunohistochemical staining was performed to further characterize the tissue. The results showed focal desmin and smooth muscle actin (SMA) positivity around the blood vessels, indicating the presence of smooth muscle in the fibrous septa. However, other markers, including MDM2, HMB-45, and Melan-A, were negative. Furthermore, the Ki-67 proliferation index was very low, providing additional evidence of the lesion’s benign nature. 

Based on the comprehensive histopathological evaluation, the final diagnosis was established as a benign intramural uterine lipoma with focal smooth muscle around blood vessels. The patient’s postoperative recovery was uneventful, with no complications reported. Subsequent follow-up examinations indicated that she remained in good health and exhibited no adverse effects from the surgery. 

Lipomatous tumors of the uterus encompass various entities, including pure lipomas, lipoleiomyomas, angiomyolipomas, fibromyolipomas, lipofibromas, and liposarcomas. Differential diagnosis of pelvic tumors containing fat also includes ovarian teratomas, myelolipomas, and pelvic lipomatosis. 

Uterine lipomatous tumors, particularly pure lipomas, are exceedingly rare, with reported incidences ranging from 0.03% to 0.25%. These benign tumors are more commonly encountered in post-menopausal women and are typically located in the fundus of the uterus. 



The histogenesis or origin of these tumors remains a subject of debate, mainly because adipose tissue is not a normal constituent of the uterus. Several hypotheses have been proposed, including lipoblastic differentiation of misplaced embryonic mesoderm, metaplasia of smooth muscle or connective tissue into adipose cells, fatty infiltration or degeneration of connective tissue, perivascular fat cell proliferation, and migration of adipose cells through uterine vessels. 

Distinguishing lipomas from other mixed lipomatous tumors can be challenging. However, lipomas are typically diagnosed when lesions are predominantly composed of encapsulated mature adipose tissue, sometimes containing fibrovascular septa. The presence of smooth muscle, when it occurs, is usually limited to the periphery of the tumor or, as seen in our case, can exhibit very focal smooth muscle around blood vessels within the fibrous septa. 

Immunohistochemistry can aid in differentiating lipomas from other entities containing adipose tissue. SMA and desmin staining can highlight the presence of smooth muscle and its extent, aiding in distinguishing lipomas from lipoleiomyomas. Other markers, such as HMB-45 and Melan-A, are positive in angiomyolipomas, while MDM2 is positive in liposarcomas. Additionally, a low Ki-67 proliferation index, as observed in our case, further supports the benign nature of the lesion. 

Uterine lipomas are exceptionally rare benign tumors, often encountered in post-menopausal women. While radiological imaging may suggest a preliminary diagnosis, most cases are ultimately confirmed through histopathological examination. To ensure an accurate diagnosis and differentiation from other lipomatous uterine tumors, thorough sampling, and immunohistochemical staining are crucial. This case underscores the importance of considering uterine lipomas in the differential diagnosis of pelvic masses and highlights the need for further research to better understand the histogenesis of these rare tumors. 

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