Myositis Ossificans Circumscripta in the Masseter Muscle Mimicking Phleboliths

Abstract

To the Editor: Myositis ossificans circumscripta (MOC) is defined as extraosseous nonneoplastic new bone formation within skeletal muscle or soft tissue. Etiological factors include (single or repetitive) traumatic penetration and crushing injury to the muscle. 1,2 Here, the authors report a case of MOC involving the unilateral masseter muscle, the imaging features of which resembles phleboliths. CLINICAL REPORTA 64-year-old woman was referred to our clinic because of pain, which was exacerbated by opening the mouth and chewing. Clinically, moveable and painful solitary masses were evident in the superior external oblique ridge, and just anterior to the anterior border of the ramus, upon bimanual palpation of the left masseter muscle. She had no limitation in mandibular range of motion, and the skin over the left cheek region and the intraoral soft tissue, were normal. The left Stenson's duct exhibited normal salivary flow. Her medical history and systemic review were unremarkable. She reported that a blunt trauma had been applied to her left cheek a few years before.Panoramic radiography revealed 2 ovoid calcified masses and 1 rather small calcified mass in the region of the left anterior mandibular ramus (Fig. 1A). Computed tomography (CT) imaging revealed 2 calcified masses featuring small rounded radiolucent areas with central calcifications, surrounded by peripheral highdensity rings, suggestive of mature bone, and 1 small completely calcified mass clearly separated from the lateral mandibular ramus (Fig. 1B). Upon coronal CT, all calcified masses were localized within the left masseter muscle (Fig. 1C). A combination of patient's history, and the clinical and radiographic findings, allowed us to diagnose an MOC involving the masseter muscle.

Myositis Ossificans Traumatica of the Temporal Muscle: a Case Report and Literature Review Emphasizing Radiographic Features on Computed Tomography and Magnetic Resonance Imaging

“…Besides malignant neoplasms, the differential diagnosis of MO may include pathological processes such as nodular fasciitis, haemangiomas with multiple phleboliths [31] and benign neoplasms, such as osteomas [24]. While considering these hypotheses, some imaging features should be noted.…”

“…While considering these hypotheses, some imaging features should be noted. For instance, osteomas are well-defined radiopaque lesions, in contrast to MO, which often exhibits ill-defined or diffuse borders [11,26,36,38,43,47,48,57], although some reports of MO did show round and well defined areas [24,31,41,51]. Nodular fasciitis, although of a similar aetiology to MO, does not appear as radiopaque masses [15].…”

“…Haemangiomas with multiple phleboliths can be excluded due to the main imaging feature of phleboliths, which usually include a radiopaque core with the appearance of concentric rings, also called 'laminations' [59,60]. However there is a case of MO in the masseter muscle which had imaging features similar to phleboliths [31]. When considering malignant neoplasms, despite the fact that calcifications can be noted, the destruction or invasion of adjacent structures or tissues is often observed, which is not seen in MO cases.…”