Introduction Leiomyoma with bizarre nuclei (LBN) is defined histologically by significant cytologic atypia, but high mitotic rate and tumor cell necrosis are absent. Despite its benign clinical behavior, differential diagnosis from leiomyosarcoma can sometimes be difficult.

There have been a few sizable studies that have described the clinical and pathologic features of LBN with follow-up data.

Objective we investigated the clinical and pathologic features of LBN and compared them with related studies.

Methods A total of 10 patients diagnosed with LBN in our department were included.

In all cases, clinical data, macroscopic with microscopic features, and follow-up data were evaluated.

Results The median age of the patients was 46 years. Six patients had undergone hysterectomy and 4 myomectomies. The mean tumor diameter was 6 cm.

The tumor was intramural in all cases. Margins were regular in 7 cases, but expansive in 3 cases.

Microscopically, the bizarre cell distribution was multifocal. Their density was low in 8 cases and high in 2 cases. Mitosis was observed in 3 cases, not exceeding 8/10 high power fields. The prognosis was favorable in all cases, with no signs of recurrence or metastasis after a median follow up of 10 years.

Conclusion LBN is a histologic variant of benign uterine smooth muscle tumors. Expansive margins, a multifocal distribution with a high density of the bizarre cells, are possibly noted. Other morphologic criteria for malignancy, such as high mitotic rate and coagulative tumor cell necrosis, should be excluded. Additional sampling may be needed for an accurate diagnosis.