Leiomyoma

A leiomyoma is a very common benign tumour of smooth muscle. Leiomyomas fit into the soft tissue group of lesions. They are extremely common in the uterus. They may also be seen in the skin.

General

• Benign.

Cutaneous leiomyomas

• May be part of Hereditary Leiomyomatosis and Renal Cell Cancer (HLRCC).

Uterine leiomyoma

Main article: Uterine leiomyoma

• Often called "fibroids".
• Extremely common... 40% of women by age 40.
• Can be a cause of AUB (abnormal uterine bleeding).
• Large & multiple leiomyomas are associated with infertility.

Gross

• Sharply circumscribed.
• Gray-white.
• Whorled appearance.

Factors that raise concern for leiomyosarcoma:

• Haemorrhage.
• Cystic degeneration.
• Necrosis.

Microscopic

Features:

• Spindle cells arranged in fascicles.
  • Fascicular appearance: adjacent groups of cells have their long axis perpendicular to one another; looks somewhat like a braided hair that was cut.
• Whorled arrangement of cells.

Uncommonly present - see note:

• Necrosis (low power) - suggestive of leiomyosarcoma.
• Hypercellularity.
• Nuclear atypia seen at low power.
• Few mitoses.

Note:

• Leiomyosarcoma is diagnosed if all of the following are present: (1) high mitotic rate (dependent on site), (2) marked nuclear atypia (seen at low power), (3) necrosis.

DDx:

• Leiomyosarcoma.
• Dermatomyofibroma.
• Myopericytoma / myofibroma.

Variants

• Lipoleiomyoma - with adipose tissue.
  • Image: Lipoleiomyoma - low mag. (WC).
• Hypercellular leiomyoma - hypercellularity assoc. with more mutations.
• Atypical leiomyoma (AKA symplastic leiomyoma) - leiomyoma with nuclear atypia.
  • Image: Atypical leiomyoma (WC).
• Benign metastasizing leiomyoma.
  • This is just what it sounds like. Some believe these are low grade leiomyosarcomas.

IHC

Work-up of suspicious leiomyomas:

• CD10 +ve.
• Ki-67 -ve.
• SMA +ve.
• Desmin +ve.

Other stains:

• H-caldesmon +ve.

See also

• Leiomyosarcoma.
• Soft tissue lesions.