73-YEAR-OLD woman was evaluated for 4 months of pain in the left temporomandibular joint region. The pain was dull and aching and was referred to her ear and temporal scalp area. She denied any history of trauma to this region. The pain was not exacerbated by chewing. She also denied any history of dry mouth or dry eyes. Her medical history was otherwise unremarkable. On physical examination, the oral cavity and both ears were normal, and the oropharynx was symmetrical. Normal salivary flow was observed from the Stenson ducts. There were no masses palpated in the parotid glands or the neck. Facial nerve function was symmetrical. No scalp lesions were present. Magnetic resonance imaging scans of the neck and face revealed a well-circumscribed mass in the deep lobe of the left parotid gland. The mass was cone shaped, with its narrowest point laterally. It was isointense on T1-weighted images with respect to brain, hyperintense on T2-weighted images, and enhanced with gadolinium (Figure 1). The patient underwent a left total parotidectomy, with the intent of preserving the facial nerve. At the time of surgery, a well-circumscribed, tan, fleshy mass was identified immediately deep to, and adherent to, the upper division of the facial nerve. A small biopsy specimen was sent for frozen section, which showed multiple spindle cells, few mitoses, and no evidence of malignancy. With the use of the operating microscope, the mass was then dissected free from the facial nerve, with preservation of all branches except a small buccal branch (Figure 2 [the left parotid tumor (T) can be seen in the deep lobe under the upper division (UD) of the facial nerve, which has been retracted with white vessel loops. MB indicates marginal mandibular branch; CB, cervical branch; and BB, buccal branch]). Postoperatively, the patient had a grade IV-V (HouseBrackmann scale) weakness in the upper distribution of the left facial nerve, which had improved to normal symmetrical motion on follow-up examination. No other deficits were visible. Histologic examination of the specimen, which is shown in Figure3, demonstrated a tumor (T) arising from an adjacent nerve branch (N) and surrounded by a capsule (C). The tumor contained both hypercellular and hypocellular regions showing spindled nuclei with tapered ends, some wavy and undulating, with long, bipolar cytoplasmic extensions with indistinct borders (Figure4). No mitotic figures were identified. Immunohistochemical stains were strongly positive for anti–S100 protein (Figure 4, inset). What is your diagnosis?