Anatomy and pathology of the masticator space

OBJECTIVE: This article reviews and illustrates the anatomy and pathology of the masticator space (MS). BACKGROUND: Pathology of the masticator space includes inflammatory conditions, vascular lesions, and tumours. Intrinsic tumours of this space can be benign and malignant, and they may arise from the mandibular ramus, the third division of the trigeminal nerve, or the mastication muscles. Malignant tumours may appear well defined and confined by the masticator fascia, without imaging signs of aggressive extension into neighbouring soft tissues. Secondary invasion of the masticator space can also occur with tumours of the nasopharynx, oropharynx, oral cavity, and parotid glands. Perineural tumour spread (PNS), especially along the trigeminal nerve, can also occur with masticator space malignancies. CONCLUSION: Masses of the MS are difficult to evaluate clinically, and computed tomographic (CT) and magnetic resonance (MR) images are essential for the diagnosis and characterisation of these lesions. Malignant tumours may appear well defined and confined by the fascia. Thus, when a mass is identified, a biopsy should be done promptly. PNS may occur in tumours involving the MS and its recognition on imaging studies is essential to plan the appropriate treatment. TEACHING POINTS: • Differentiating between intrinsic and extrinsic lesions is essential to the differential diagnosis • Infections of the MS may cross the fascia and mimic neoplasms on imaging studies • Malignant tumours may show no aggressive signs, such as bone erosion or violation of the fascia • Perineural spread (PNS) is often clinically silent and frequently missed at imaging and leads to tumour recurrence