A 21-month-old boy presented 6 weeks after falling off a bar stool and striking the left side of his face and jaw. After the fall, a firm swelling developed along the left jawline. The swelling, which had initially resolved, subsequently recurred and progressively enlarged. The patient had no oral bleeding and was consuming a normal diet at presentation. His mother treated his occasional discomfort effectively with acetaminophen. His medical history was unremarkable.
Physical examination revealed a smooth, nontender mass at the angle of the mandible. Intraoral examination demonstrated a submucosal swelling of the posterior left lower alveolus and retromolar trigone. No trismus, cranial nerve neuropathy, or lymphadenopathy was noted. Magnetic resonance imaging demonstrated a uniform gadolinium-enhancing mass with expansile growth from the posterior body and ramus of the mandible (Figure 1). The lesion was accessed transorally with a mucosal incision over the retromolar trigone and by cutting a small window in the thinned outer cortex of the mandibular ramus. A curet was used to scoop the soft tumor out of the marrow space. Histopathologic examination revealed a circumscribed but unencapsulated nodular proliferation at low power (Figure 2). Spindle cells with characteristics between those of fibroblasts and smooth muscle cells arranged in fascicles compressing slitlike vessels were seen at higher power (Figure 3). There was no significant mitotic activity. Immunohistochemical stains were positive for smooth muscle actin and negative for S100 protein and myogenin.
Turner J, Skinner M, Caplan MJ, Gillespie MB. Pathology Quiz Case 1. Arch Otolaryngol Head Neck Surg. 2007;133(6):620. doi:10.1001/archotol.133.6.620