S-100 Immunohistochemical Positivity in Rhabdomyoma: An Underestimated Potential Diagnostic Pitfall in Routine Practice

Abstract

A 66-year-old man presented with a 2.8 cm lesion of the left vocal cord. On contrast-enhanced computed tomography scans, the tumor extended to the supraglottis, subglottis, paraglottic space and anterior commissure, causing partial obstruction of the laryngeal lumen. At another hospital, a fragmented incisional biopsy was diagnosed as a granular cell tumor, as to the S-100 immunohistochemical positivity. After excision, the tumor revealed to be an adult-type laryngeal rhabdomyoma. The typical cytoplasmic rod-like inclusions and cross striations were more evident in the second specimen. We confirmed the unusual S-100 immunohistochemical positivity (variable intensity, >90% of tumor cells). Muscle markers were not performed on the previous biopsy, resulting positive in our specimen (Desmin: strong, diffuse expression; Smooth Muscle Actin: strong staining in 10% of tumor cells). Melan-A, CD68, GFAP, pan-cytokeratins, CEA, calretinin and neurofilaments resulted negative. To our brief, systematic literature review, S-100 positivity (usually variable, often weak or patchy/focal) was globally found in 19/34 (56%) adult-type rhabdomyomas of the head and neck region. Especially on fragmented biopsy material, the differential diagnoses of laryngeal rhabdomyomas may include granular cell tumors, oncocytic tumors of the salivary glands or of different origin, and paragangliomas.

Características clínicas y patológicas del tumor de células granulares en cuerda vocal. Revisión de la literatura

“…Tras la extirpación completa, el tumor resultó ser un rabdomioma laríngeo de tipo adulto, por lo que realizaron una revisión sistemática de la literatura y concluyeron que la positividad para S-100 se encontró en hasta un 56% de los rabdomiomas de tipo adulto de la región de la cabeza y el cuello. Por lo que, dichos autores, aconsejan, que especialmente en material de biopsia fragmentado, se realicen diagnósticos diferenciales de los TCG con los rabdomiomas laríngeos, los tumores oncocíticos y los paragangliomas [11]. En la serie de casos durante 12 años de Saraydaroglu O. et al 657 pacientes fueron diagnosticados de tumores laríngeos, y dentro de los tumores no epiteliales benignos los más comunes fueron el schwannoma y el hemangioma, seguidos por el neurofibroma plexiforme y el TCG [12].…”