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.

Leiomyoma
Diagnosis in short
Lipoleiomyoma. H&E stain.
LM	spindle cells arranged in fascicles, +/-nuclear atypia, rare mitoses (allowable mitotic rate dependent on specific site)
Subtypes	lipoleiomyoma, hypercellular leiomyoma, atypical leiomyoma (symplastic leiomyoma), benign metastasizing leiomyoma
LM DDx	leiomyosarcoma, STUMP, dermatomyofibroma
Gross	well-circumscribed, whorled appearance, firm
Site	skin, uterus, others
Syndromes	hereditary leiomyomatosis and renal cell cancer (cutaneous leiomyomas)
Symptoms	skin: pain, uterus: bulky
Prevalence	very common - esp. uterine
Prognosis	benign

General

• Benign.

Cutaneous leiomyomas

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

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.
• +/-Medium-sized artery seen at the periphery of the lesion.
  • Often arise from a muscular artery.

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.
  • Lipoleiomyosarcoma - very rare.
• Dermatomyofibroma.
• Myopericytoma / myofibroma.
• Smooth muscle tumour of uncertain malignant potential (STUMP) - do not fulfill criteria for leiomyosarcoma.

Variants

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

• 

  Atypical leiomyoma - low mag. (WC/Nephron)

• 

  Atypical leiomyoma - intermed. mag. (WC/Nephron)

• 

  Atypical leiomyoma - high mag. (WC/Nephron)

• 

  Lipoleiomyoma - low mag. (WC/Nephron)

• 

  Lipoleiomyoma - high mag. (WC/Nephron)

IHC

Work-up of suspicious leiomyomas:

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

Other stains:

• H-caldesmon +ve.

Sign out

SKIN LESION, RIGHT LEG, EXCISION:
- LEIOMYOMA.
- NEGATIVE FOR MALIGNANCY.

COMMENT:
The lesion stains for desmin and SMA. It is negative for S-100 and has minimal staining with Ki-67.

Micro

The section shows unremarkable hair-bearing skin with a well-circumscribed subcutaneous lesion with a fascicular architecture. The lesion has no nuclear atypia and no mitotic activity is identified. At the periphery of the lesion is a medium-sized muscular artery from which the lesion appears to arise.

See also

• Leiomyosarcoma.
• Soft tissue lesions.