Oral Adult Rhabdomyoma

Abstract

This report describes a case of an adult rhabdomyoma (ARM) occurring in the oral cavity. A 47-year-old man was referred for the diagnosis of a painless, well-circumscribed, submucous nodule located on the floor of the mouth, measuring approximately 6.0 cm in length. Computed tomography revealed a well-defined, solid, and hypodense mass. A benign salivary gland or mesenchymal tumor were the main diagnostic hypotheses. Under local anesthesia, the patient underwent surgical excision. Microscopically, the tumor comprised large polygonal well-defined cells with abundant, eosinophilic granular cytoplasm with cross striations. No atypia or mitosis was observed. The cells were positive for muscle-specific actin, desmin, and sarcomeric alpha-actin. Based on these features, a diagnosis of ARM was established. No recurrence was observed after 48 months. Although rare, ARM should be considered in the differential diagnosis of oral submucosal nodules, especially those located on the floor of the mouth.

Keywords: Benign neoplasms; Diagnosis; Differential; Immunohistochemistry; Mouth; Rhabdomyoma; Therapeutics.

Fig. 1

Large, painless, well-circumscribed submucous nodule located at the right side of the floor of the mouth. The lesion was covered by smooth, intact, and normal-color mucosa

Fig. 2

A Microscopically, at low magnification, the lesion appeared as a well-circumscribed and partially encapsulated nodule, with irregular margins (hematoxylin-eosin, 50x). B Large polygonal cells exhibited abundant, eosinophilic, and granular cytoplasm, which often presented complete or partial vacuolization; so-called “spider cells” (yellow arrows) (hematoxylin-eosin, 100x). C Large tumor cells with well-defined borders, and central or eccentric nuclei. Cytoplasmic vacuolization is also observed (“spider cells”—yellow arrows) (hematoxylin-eosin, 200x). D Most cells exhibiting granular cytoplasm, with complete or partial vacuolization (“spider cells”—yellow arrows). Prominent nucleoli (black arrows) and cross-striations (orange arrows) were also observed (hematoxylin-eosin, 200x)

Fig. 3

A Tumor cells presenting strong positivity for desmin (streptavidin-biotin-peroxidase method, 100x). B Tumor cells exhibiting strong positivity for sarcomeric alpha actin. Cross-striations are evident (streptavidin-biotin-peroxidase method, 400x)