Rare benign mesenchymal tumours with skeletal muscle differentiation
Extracardiac rhabdomyomas are very rare neoplasm, comprising less than 2% of the neoplasm of the skeletal muscle origin. Because of their extreme rarity, the incidence of genital rhabdomyomas is unknown.
In males, the average age is lower than in women, affecting mainly adolescents and infants.
Only rare cases have been reported in males.
The most commonly affected sites are the epididymis, spermatic cord, tunica vaginalis, or paratesticular regions. One prostatic rhabdomyoma is also reported.
Surgical intervention with complete excision is normally curative. Radiation therapy and chemotherapy are not usually required.
The prognosis is excellent with surgical intervention and completes removal of the lesion, even though the tumors may be deep seated. Recurrences are reported only after incomplete excision.
Typically it consists of a dense, submucosal, slow growing encapsulated polypoid mass rarely >40 mm in size. Cut surface of the tumor is solid, tan-white, with a fascicular pattern.
Dense collagenous tissue with a moderately cellular infiltrate composed of mature, elongated, well-differentiated rhabdomyoblasts with pale abundant eosinophilic cytoplasm with distinct cross-striations, scattered in a haphazard fashion. Vascularity may be abundant. No pleomorphism, necrosis, or atypical mitotic figures are seen.
- 1.Adult type (Fig. 1): Usually located in the head and neck of older patients. This neoplasm may be multinodular and crystalline cytoplasmic inclusions of hypertrophic Z-band material are observed.
Genital type: A mass commonly described in the genital tract of middle-aged women. The tumor shows greater maturity of the myocytes.
Fetal type: Rare form that affects the head and neck region. There is a wide spectrum of histology reflecting the degree of differentiation.
An exceedingly rare, distinct sclerosing variant, composed by dense collagenous stroma around individual skeletal muscle cells, has been described in only nine cases.
Desmin and muscle-specific actin are generally strongly positive, while positivity for myogenin and S100 may be focal. Smooth muscle actin, calponin, caldesmon, and MDM-2 are negative. Proliferation index (Ki67) is usually very low (<3%).
The most important differential diagnosis is with embryonal or spindle cell rhabdomyosarcoma. Rhabdomyosarcoma, besides being far more cellular, shows necrosis, increased mitotic activity, abnormal mitoses, nuclear atypia, pleomorphism, anaplasia, and a higher proliferation index (Ki67 >5%).
Heterologous rhabdomyoblastic differentiation can be observed in dedifferentiated liposarcoma (which is MDM-2 positive) and malignant peripheral nerve sheath tumor.
The presence of cross-striations rules out leiomyomas and fibromatosis. Moreover, in contrast to fibromatosis, rhabdomyoma is a circumscribed subcutaneous mass that lack the well-developed fascicles seen in fibromatosis.
- Wehner, M. S., Humphreys, J. L., & Sharkey, F. E. (2000). Epididymal rhabdomyoma: Report of a case, including histologic and immunohistochemical findings. Archives of Pathology & Laboratory Medicine, 124, 1518–1519.Google Scholar