Preoperative Diagnosis of Proliferative Myositis by Enhanced Computed Tomography and the Apparent Diffuse Coefficient Map from Magnetic Resonance Imaging

Proliferative myositis is a rare intramuscular inflammatory lesion that occurs in the head and neck and which could be resolved without treatment. Herein, we present the imaging characteristics for its preoperative diagnosis, potentially mitigating the need for surgery. We describe the enhanced computed tomography (CT) and magnetic resonance imaging (MRI) findings of two patients. We observed a checkerboard-like pattern in the sternocleidomastoid muscle on enhanced CT in one patient. We also identified the involvement of two heads of the sternocleidomastoid muscle. Coronal enhanced CT imaging was also useful in the preoperative diagnosis because it revealed a lattice structure, equivalent to muscle fibers. On MRI, diffusion-weighted sequences showed hyperintensity, and the apparent diffusion coefficient map showed hypointensity in proliferative myositis. Enhanced CT and MRI-based diffusion-weighted sequences and the apparent diffusion coefficient map are useful in the preoperative diagnosis of proliferative myositis and could be useful for avoiding the need for complete surgical excision.