Nodular Pseudogout of the Skull Base Arising From the Temporomandibular Joint

The authors report a case of a rare, large, nodular pseudogout which developed from the temporomandibular joint (TMJ).An 83-year-old female was referred to the hospital with swelling on her left cheek. Imaging studies revealed a large calcified mass surrounding the left mandibular condyle, partially destroying the adjoining bone and extending to the skull base. Magnetic resonance imaging (MRI) revealed soft tissue masses with low signal intensity on T1- and T2-weighted images and were enhanced after intravenous gadolinium injection.The mass was clinically and radiologically suspected to be a neoplastic lesion, such as chondrosarcoma or fibrous dysplasia. However, histological analysis showed that the mass contained granulomatous lesions with numerous multiple nodular rod-shaped and diamond-shaped crystal deposits, which validated the diagnosis of pseudogout. X-ray diffraction (XRD) was performed to identify the tumor's deposited materials and revealed that these were calcium pyrophosphate dihydrate (CPPD) crystals. This result confirmed the histopathological diagnosis of "tophaceous pseudogout."