Benign Masseteric Muscle Hypertrophy : Imaging , clinical findings , pathology , treatment , epidemiology

Benign Masseteric Muscle Hypertrophy

Epidemiology

This is an uncommon entity that begins in adolescence or early adulthood and demonstrates slowly progressive enlargement of the affected muscles. Masseteric muscle hypertrophy is usually bilateral but may be seen as a unilateral lesion. The etiology is uncertain but is thought to be related to bruxism or excessive chewing. This has also been described in patients with acquired immune deficiency syndrome.

Clinical Findings

This condition may be discovered incidentally, or the affected individuals may complain of facial fullness. The masslike hypertrophy is not painful or tender to palpation. It hardens and enlarges when the teeth are clenched

Pathology

Histologic examination shows normal skeletal muscle tissues.

Treatment

No treatment is required. However, surgical intervention may be elected for treatment of cosmetic deformities

Imaging Findings

CT

 CT shows enlargement of the masseteric muscle. The most commonly involved muscles include the masseter and temporalis muscles. The attenuation value of the affected muscles is normal. An exostosis at the angle of the jaw may also be demonstrated

MR

The signal intensiry of the enlarged muscles is similar to normal skeletal muscle of different pulse sequences. No abnormal enhancement is present in affected muscles.

Imaging Pearls

• Unilateral masseteric muscle enlargement may simulate a neoplasm. The lesion, however, maintains a smooth outline and shows normal attenuation or signal intensiry on imaging. This diagnosis is confirmed upon the detection of associated enlargement of the other muscles of mastication.

•         Unilateral masseteric muscle atrophy may give the impression of atrophy of the normal contralateral muscle. However, the atrophic muscle may show fatry infiltration or abnormal signals on MR imaging

• Bilateral mild to moderate masseteric muscle hypertrophy may not be easily recognizable on imaging and radiological findings should be correlated with clinical history.