Unexpected diagnosis of an intramuscular myxoma arising from the masseter muscle

Intramuscular myxomas are myxoid neoplasms that mainly affect the muscles of the thigh, upper arm, and gluteus. In the head and neck region they are rare, and we know of only two reported cases in the masseter muscle. We think that this is the third. A 60-year-old woman presented with a painless nodule on the right side of her face. Magnetic resonance imaging showed a well-defined mass restricted to the muscle, with no infiltration into adjacent structures. Microscopic analysis confirmed the gross examination, and showed a tumour with copious myxoid stroma, scattered spindle to stellate cells, and an absence of atypia, which did not stain for CD34, S100, or smooth-muscle actin. A final diagnosis of intramuscular myxoma was made. Despite its rarity, it is important to consider this neoplasm in the differential diagnosis of tumours with a gelatinous-like appearance that involve masticatory muscles of the head and neck.