PMC7298327_01
Right postauricular bulging mass which is asymptomatic, soft, and slightly movable (a). The temporal bone computed tomography shows a well-defined, low-attenuated, and nonenhancing mass (arrow) lateral to the mastoid process (b). Intraoperative view of a well-circumscribed intramuscular benign lipoma (c). A benign lipoma surrounded by muscle fibers. The tumor was composed of mature adipocytes without lipoblasts or cytologic atypia (d) (H&E x 100).
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fig1
The physical examination of the patient revealed a slightly movable and oval-shaped mass with soft and smooth margin (Figure 1(a)). The computed tomography (CT) revealed a well-circumscribed 4.4 x 1.3 cm sized mass, with an adipose tissue signal density beneath the mastoid insertion site of the right SCM muscle (Figure 1(b)). The surgical removal was performed under local anesthesia, and the well-circumscribed lipomatous mass was noted between the SCM muscle fibers (Figure 1(c)). Some of lipocytes were infiltrated into the striated muscle tissue (Figure 1(d)).
PMC7298327_02
Right postauricular bulging mass which is asymptomatic, hard, and non-movable (a). Temporal bone computed tomography shows a huge, well-demarcated, and bony mass on the right mastoid cortex (b). The intraoperative view of a large bony tumor after elevation of the periosteum (c). The microscopic finding showing areas composed primarily of compact, mature, lamellar bone with organized Harvesian canals (d) (arrows, H&E  x 100).
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fig2
On a physical examination, a 3 x 3 cm, hard, smooth, painless, and unmovable mass in the mastoid area was observed (Figure 2(a)). The temporal bone CT showed that a 2.3 x 1.4 x 3.0 cm sized outgrowing osteoma with irregular surface was observed in the right mastoid cortex (Figure 2(b)). The resection of tumor was performed via a retroauricular approach under general anesthesia (Figure 2(c)). The histologic findings showed a dense compact lamellar bone, consistent with a compact osteoma (Figure 2(d)).