Multifocal rhabdomyoma of the neck. Report of a case studied by fine-needle aspiration, light and electron microscopy, histochemistry, and immunohistochemistry.

A 32-year-old Caucasian man presented with a tumor in the right side of the neck. Preoperative fine-needle aspiration showed large multinucleated cells with abundant granular cytoplasm that were consonant with the features of a granular cell tumor. At surgery, two separate tumors were found. Histologically, the tumor proved to be an adult rhabdomyoma, the 11th such multifocal case reported. The striated muscle origin of this benign tumor was confirmed by immunohistochemical and ultrastructural studies. The tumor cells were desmin-, myoglobin-, and actin-positive. They showed variable numbers of thick and thin filaments, as well as hypertrophic Z-band material. Histochemical studies showed the presence of basophilic muscle cells, vesicular nuclei, ragged red fibers, and diffuse acid phosphatase positivity. These features, together with the absence of actual muscle cell proliferation and the assumption that the mass of the tumor could be explained by the enormous swelling of the muscle cells, lead us to conclude that an adult rhabodomyoma is merely the result of a process of disorderly degeneration and regeneration rather than a real neoplasm or a hamartomatous lesion.