CHONDROID TENOSYNOVIAL GIANT CELL TUMOR OF THE TEMPOROMANDIBULAR JOINT

Abstract

<h3>Background</h3> Tenosynovial giant cell tumor (TGCT) is a locally aggressive tumor arising from the synovium, most commonly associated with the large joints such as the knee, but they may involve the temporomandibular joint (TMJ). Compared to other sites, TGCT of the TMJ more frequently shows chondroid metaplasia and may mimic chondroid neoplasms. <h3>Case Report</h3> A 78-year-old man presented with several months of history of otalgia, tinnitus, and aural fullness. A computed tomographic scan of his brain showed a destructive, lytic lesion in the squamous part of the temporal bone extending into the zygomatic arch. A fine-needle aspiration biopsy produced a blood-stained smear with scattered pigmented histiocytes and multinucleated giant cells. A diagnosis of giant cell tumor was favored. The patient was commenced on denosumab; however, he showed no clinical improvement after 6 months. A core biopsy was then performed at Westmead Hospital, which revealed a cellular neoplasm comprising spindled and epithelioid cells containing hemosiderin pigment, multinucleated giant cells, and chondrocyte-like cells. Focally, calcific deposits were observed with a "chicken-wire" like pattern. The possible differential diagnoses of chondroblastoma and tenosynovial giant cell tumor were suggested. The histiocyte-like cells showed positive immunoperoxidase staining with CD68, while the larger epithelioid cells were positive for podoplanin (D2-40). The cells were negative for S-100 and H3-K36M, thereby confirming a diagnosis of TGCT. <h3>Conclusions</h3> Although rare, TGCTs are known to show chondroid metaplasia, particularly when involving the TMJ, and they may mimic a chondroblastoma. Immunohistochemical markers such as podoplanin, S-100, and H3F3 K36M are useful in distinguishing these entities.