Table 1 Leiomyoma subtypes and associated microscopic findings

Benign leiomyoma

Findings include fascicles of spindle cells mixed with varying levels of collagen. Large blood vessels are present, and there is mild to absent cellular atypia and mitosis [58].

Mitotically active leiomyoma

Fibroid findings include necrosis, hemorrhage, vascular intrusion. Contains 5–9 mitotic figures (MF) per 10 high power fields (HPF) with no atypia [59].

Leiomyomas with bizarre nuclei (LBNs)

Microscopically, LBNs have the presence of aytipical pleomorphic nuclei. They may have high cellularity, and contain 2–7 MF/10HPFs [60].

Hydropic leiomyoma

These fibroids have focal collections of edema-like fluid and show hyaline degeneration [61].

Myxoid leiomyoma

Findings include large collections of acellular myxoid matrix, rich in acid mucins. They demonstrate a low mitotic rate (<2 MF/10 HPFs) [58].

Epitheloid leiomyoma

These benign leiomyomas have at least 50 % of cells as epitheloid, but demonstrate a low mitotic rate (<3MFs/10HPFs) [58].