48. Tumours of smooth and striated muscle (leiomyoma, leiomyosarcoma, rhabdomyoma and rhabdomyosarcoma, types)

Tumors of smooth muscle

Leiomyoma and leiomyosarcomas are the benign and malignant smooth muscle tumors, respectively.

Leiomyomas occur in five different subtypes:

  • Classic leiomyoma – most common type
  • Cutaneous leiomyoma – originates from arrector pili
  • Deep soft tissue leiomyoma – in the retroperitoneum or abdominal cavity
  • Genital leiomyoma – originates from genital smooth muscle in the nipples or external genital organs
  • Vascular leiomyoma – originates from vascular smooth muscle

Most cases of (classic) leiomyoma occur in the uterus or the subcutaneous tissue. Leiomyomas virtually never undergo malignant transformation.

Uterine leiomyoma is further described in topic 57.

Leiomyosarcoma is the malignant counterpart of leiomyoma. They most frequently occur in the subcutaneous tissue and retroperitoneum (GI tract, IVC) and less frequently in the uterus. They’re aggressive tumors that locally infiltrate and metastasize, giving them a poor prognosis.

The tumor cells are spindle shaped with cigar-like nuclei. The neoplastic cells are PAS+ as they contain glycogen.

Leiomyosarcoma is differentiated from leiomyoma histologically by the number of mitotic figures.

Tumors of skeletal muscle

Rhabdomyoma and rhabdomyosarcoma are the benign and malignant skeletal muscle tumors, respectively. Both types are rare, but rhabdomyosarcomas are actually more common than rhabdomyomas.

Rhabdomyoma occur in five different subtypes:

  • Adult rhabdomyoma – head and neck region in adults
  • Foetal rhabdomyoma – head and neck region in children
  • Genital rhabdomyoma – affecting the vagina or vulva
  • Cardiac rhabdomyoma – affecting the heart

Rhabdomyomas are very rare tumors. Most of them occur in the head and neck regions.

Rhabdomyosarcoma is the malignant counterpart of rhabdomyoma. They’re more common in children and adolescents than in adults, and they’re the most common soft tissue sarcoma in childhood. We distinguish three subtypes:

  • Embryonal rhabdomyosarcoma – most common
  • Alveolar rhabdomyosarcoma – resemble alveolar structure
  • Pleomorphic rhabdomyosarcoma – very very rare, most common in adults

These tumors interestingly most frequently occur in the head and neck or genitourinary tract, sites where there is very little skeletal muscle. Rhabdomyosarcomas are aggressive and highly malignant tumors.

Alveolar rhabdomyosarcoma is associated with a t(2;13) translocation.


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47. Tumours of adipose tissue and peripheral nerves, synovial sarcoma

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49. Congenital malformations, inflammations and tumors of the penis

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