A N 89-YEAR-OLD WOMAN PRESENTED WITH a rapidly progressive mass in the right parotid gland that extended into the middle cranial fossa. She denied constitutional symptoms, weight loss, and problems with speech, swallowing, or respiration. Her medical history was remarkable for liposarcoma of the right arm that had been treated with surgical resection 2 years earlier. Physical examination revealed a 3-cm fullness in the right preauricular area. There was no trismus, cranial nerve deficits, or neck lymphadenopathy. Computed tomography (CT) demonstrated a 4.0 3.0 2.7-cm mass with smooth, erosive changes of the temporomandibular joint (TMJ) and skull base with flocculent calcifications (Figure 1). The mass demonstrated inhomogeneous contrast enhancement on postcontrast T1-weighted magnetic resonance images (MRIs) (Figure2). Fine-needle aspiration (FNA) revealed abundant chondroid-appearing material with associated degeneration, changes consistent with a low-grade chondroid neoplasm. The patient underwent resection of the infratemporal fossa mass by way of a right parotidectomy with facial nerve dissection, mandibular condylectomy, and wide resection of the middle fossa cranial base and associated dura. Intraoperative frozen section showed atypical chondrocytes that were suggestive of a low-grade chondroid malignant neoplasm. Gross pathologic inspection revealed a white, friable, gritty mass. On microscopic examination, several areas showed atypical chondrocytes with occasional binucleated chondrocytes, which were interpreted as chondroid metaplasia (Figure 3, arrows). The mass was also surrounded by multinucleated giant cells (Figure 3, arrowheads). The mass demonstrated needleand rhomboid-shaped basophilic crystals that displayed positive birefringence on polarized microscopy (Figure 4). What is your diagnosis?