The sections show a highly cellular, infiltrative mesenchymal proliferation underlying a stratified squamous epithelial surface. The lesion is composed of bundles and fascicles of spindle-shaped cells and epithelioid cells with eosinophilic cytoplasm. Some cells exhibit elongated, "strap-like" appearances with eccentric nuclei, and there are areas suggesting primitive rhabdomyoblastic differentiation (cells with abundant pink cytoplasm). The stroma appears variably myxoid to collagenous with a prominent vascular pattern. While the surface epithelium appears intact in some areas, the dense cellularity and infiltrative growth pattern in a pediatric patient are highly concerning for a malignant small blue round cell tumor or a spindle cell sarcoma.
Differential diagnosis includes Embryonal Rhabdomyosarcoma (specifically the spindle cell variant), Infantile Fibrosarcoma, or a Spindle Cell Tumour with NTPK fusion. Immunohistochemical studies are recommended (Desmin, Myogenin, CD34, S100, ALK, and Ki-67).
Painless 2 cm x 2 cm oval-shaped swelling with lipid content located on the middle dorsal tongue, extending laterally and deep to the ventral surface, with no palpable lymph nodes.
Soft tissue fragments collectively measured 1.3x1x0.5 cm, totally embedded.
Middle dorsal tongue mass, incision biopsy: