Pictorial Review: Benign and Malignant Pterygo-masseteric Muscle Complex

Swelling of the side of the face is a common clinical problem which infrequently requires radiological investigation. Computed tomography (CT) is well suited for the demonstration of the masticator space [1]. The masseter and pterygoid muscles comprise the major muscles of mastication. The masseter is a rectangular muscle lying anterior to the parotid gland. It arises from the zygomatic arch and inserts on the lateral surface of the angle, ramus and coronoid process of the mandible. The medial and lateral pterygoids are paired muscles arising from the pterygoid plates and roof of the infratemporal fossa and inserts onto the medial aspect of the mandibular ramus and temporomandibular joint. Benign masseteric hypertrophy (BMH) is the commonest cause of isolated enlargement of these muscles. Less commonly, enlargement may be due to neoplasia or inflammation. Malignant infiltration of the masseter is exceedingly rare. The reported CT appearances of such involvement with the exception of lymphoma [2] include heterogeneously-enhancing soft tissue masses within the muscle with disruption of overlying soft tissue planes [3,4].