Encyclopedia of Pathology

Living Edition
| Editors: J.H.J.M. van Krieken


  • Raffaele Gaeta
  • Alessandro FranchiEmail author
Living reference work entry
DOI: https://doi.org/10.1007/978-3-319-28845-1_4930-1



Rare benign mesenchymal tumours with skeletal muscle differentiation

Clinical Features

  • Incidence

    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.

  • Age

    In males, the average age is lower than in women, affecting mainly adolescents and infants.

  • Sex

    Only rare cases have been reported in males.

  • Site

    The most commonly affected sites are the epididymis, spermatic cord, tunica vaginalis, or paratesticular regions. One prostatic rhabdomyoma is also reported.

  • Treatment

    Surgical intervention with complete excision is normally curative. Radiation therapy and chemotherapy are not usually required.

  • Outcome

    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.

Three subtypes have been reported: (1) adult, (2) genital, and (3) fetal.
  1. 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.
    Fig. 1

    This adult type rhabdomyoma consists mainly of rhabdomioblasts with clear cytoplasm

  2. 2.

    Genital type: A mass commonly described in the genital tract of middle-aged women. The tumor shows greater maturity of the myocytes.

  3. 3.

    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%).

Differential Diagnosis

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.


  1. Han, Y., Qiu, X. S., Li, Q. C., et al. (2012). Epididymis rhabdomyoma: A case report and literature review. Diagnostic Pathology, 7, 47.CrossRefGoogle Scholar
  2. Jo, V. Y., Reith, J. D., Coindre, J. M., & Fletcher, C. D. (2013). Paratesticular rhabdomyoma: A morphologically distinct sclerosing variant. The American Journal of Surgical Pathology, 37(11), 1737–1742.CrossRefGoogle Scholar
  3. Tanda, F., Rocca, P. C., Bosincu, L., Massarelli, G., Cossu, A., & Manca, A. (1997). Rhabdomyoma of the tunica vaginalis of the testis: A histologic, immunohistochemical, and ultrastructural study. Modern Pathology, 10, 608–611.PubMedGoogle Scholar
  4. 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

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Department of Translational Research and of New Technologies in Medicine and SurgeryUniversity of Pisa, ItalyPisaItaly