Rhabdomyoblastic Differentiation in Head and Neck Malignancies Other Than Rhabdomyosarcoma

Abstract

Rhabdomyosarcoma is a relatively common soft tissue sarcoma that frequently affects children and adolescents and may involve the head and neck. Rhabdomyosarcoma is defined by skeletal muscle differentiation which can be suggested by routine histology and confirmed by immunohistochemistry for the skeletal muscle-specific markers myogenin or myoD1. At the same time, it must be remembered that when it comes to head and neck malignancies, skeletal muscle differentiation is not limited to rhabdomyosarcoma. A lack of awareness of this phenomenon could lead to misdiagnosis and, subsequently, inappropriate therapeutic interventions. This review focuses on malignant neoplasms of the head and neck other than rhabdomyosarcoma that may exhibit rhabdomyoblastic differentiation, with an emphasis on strategies to resolve the diagnostic dilemmas these tumors may present. Axiomatically, no primary central nervous system tumors will be discussed.

Keywords: Head and neck malignancies; MyoD1; Myogenin; Rhabdomyoblastic differentiation; Rhabdomyosarcoma; Skeletal muscle differentiation; Soft tissue sarcomas.

Fig. 1

Rhabdomyosarcoma (RMS). Alveolar RMS grows between fibrous septa as nests of dyscohesive small round cells with high nuclear-cytoplasmic ratios (a). In the alveolar form of RMS, myogenin immunoexpression is diffuse (b). Embryonal RMS grows as round to spindle cells, often condensing beneath epithelial surfaces in a “cambium layer” (c). Myogenin is also positive in embryonal RMS, but the distribution is less diffuse than what is seen in the alveolar subtype (d)

Fig. 2

Malignant Triton tumor. Malignant peripheral nerve sheath tumor often arises in the background of a benign nerve sheath tumor, usually neurofibroma (a). Malignant peripheral nerve sheath tumor often grows in a herringbone pattern of alternating fascicles. Often lighter staining areas alternate with darker areas creating a “marbleized” appearance (b). Eosinophilic rhabdomyoblasts stand out in the background of the pale staining malignant peripheral nerve sheath tumor (c). The rhabdomyoblasts are highlighted by a myogenin immunostain (d)

Fig. 3

Sarcomatoid carcinoma. This laryngeal tumor demonstrates both epithelial differentiation in the form of invasive squamous cell carcinoma (center) as well as mesenchymal differentiation (a). Only the squamous nest is positive for cytokeratin immunohistochemistry (b), while the remaining spindle cell tumor component is positive for desmin (c) and myogenin (d), features diagnostic of rhabdomyoblastic differentiation

Fig. 4

Olfactory neuroblastoma. This example of olfactory neuroblastoma grows in the typical fashion, as nests in the sinonasal submucosa (a). At high power, rhabdoid cells with abundant eccentric cytoplasm are evident (inset of a). As expected, this tumor was diffusely positive for synaptophysin (b) and had a peripheral (i.e., sustentacular) pattern of S100 immunostaining (c). The rhabdoid cells seen in areas of the tumor are confirmed to be rhabdomyoblasts by myogenin immunohistochemistry (d)

Fig. 5

Teratocarcinosarcoma. Sinonasal teratocarcinosarcoma exhibits admixed zones of primitive small round cells, spindled cells, squamous epithelium with clear cytoplasm, and glands (a). Primitive and/or spindled components of teratocarcinosarcoma demonstrate rhabdomyoblastic differentiation (b) which is strongly suggested by cytoplasmic cross-striations (inset) and is confirmed by immunohistochemistry for myogenin or MyoD1