Denervation hypertrophy may mimic local tumor spread on magnetic resonance imaging.

We report a patient with an extensive paranasal sinus carcinoma. One year after tumor resection, magnetic resonance imaging (MRI) showed swelling of the ipsilateral masticatory muscles with signal increase on T2-weighted images and gadolinium-DTPA uptake, suggestive of local tumor infiltration. However, electromyography, biopsy, and follow-up MRI confirmed denervation pseudohypertrophy of the muscles innervated by the mandibular nerve and excluded tumor recurrence. Muscle denervation and pseudohypertrophy should be considered in the differential diagnosis of appropriate patients with suspected tumor recurrence.