A very rare benign tumour in the parotid region: calcium pyrophosphate dihydrate crystal deposition disease.

Calcium pyrophosphate dihydrate crystal deposition disease, exhibits several clinical manifestations, from absence of symptoms to severely destructive arthropathy or conditions simulating neoplasm, which is frequently related to the temporomandibular joint. Fifteen of the 31 reported cases of tophaceous pseudogout were found in the head and neck region. A patient presented with a parotid swelling, which initially was suspected to be malignant because of the following findings: radiodensity, progression into the joint, osseous destruction of the major ala of the sphenoid and a fine needle aspirate with crystals, osteoblasts, megakaryocytes and irregular cells of varying size. At surgery there was found a tumour consisting of a white, firm gritty material. It progressed to the skull base where material had to be left, because of the presence of the nerves and vessels. A frozen specimen was reported to be benign. Histological examination showed inflammatory cells, macrophages, a chondroid material with embedded metaplastic chondroid cells and giant cells of foreign body type. Crystal examination of X-ray diffraction revealed calcium pyrophosphate dihydrate.