Benign & malignant neoplasms of smooth and striated muscle. Microscopic & gross pathomorphology
Skeletal muscle neoplasms
- Almost all malignant, Rhabdomyoma (benign type) is rare, often found in the heart
- Rhabdomyosarcoma is the most common soft tissue sarcoma of children, appearing before the age of 20, found in head and neck.
- Histologically classified into embryonal, alveolar and pleomorphic
- Identified by rhabdomyoblast cells found in the neoplasm, they are tadpole in shape.
Smooth muscle neoplasia
- Leiomyomas are benign smooth muscle tumours and are quite common. They can be found in any smooth muscle but most commonly in the uterus.
- Asymptomatic, large swellings appear on uterine section.
- Microscopic appearance shows bundles of normal looking smooth muscle cells
- Leiomyosarcomas are malignant, occurring more commonly in females than males in the skin, deep soft tissues of the extremities and the retroperitoneum.
- These manifest as large painless masses. Histological examination shows spindle cells with cigar shaped nuclei.
Gross, uterine leiomyoma (fibroid): a large, sharply circumscribed mass in the fundal wall, distorting the uterine cavity; the cut surface is firm, with a whorled pattern.
Image: “Leiomyoma of the Uterus” by Ed Uthman, MD., Public domain, via Wikimedia Commons.
Remember: uterine leiomyomas are often multiple, firm, grey-white and whorled on cut section. Leiomyosarcoma is usually solitary and soft, with haemorrhage and necrosis; it is diagnosed by nuclear atypia, a high mitotic count and tumour cell necrosis, and it arises de novo rather than from a fibroid.