Myxoma

The evidence that myxoma is a tumor of odontogenic ectomesenchyme is circumstantial. The observation that most myxomas occur in tooth-bearing areas of the jaws and are so infrequently encountered in an extragnathic location has been cited as evidence of origin from odontogenic tissue. In one series of 5000 bone tumors, three examples of extragnathic myxoma were identified, all in the femur. This is not an impressive number but does cast doubt on the concept that myxoma is derived from odontogenic ectomesenchyme. Immunoperoxidase stains, usually helpful in identifying cell lineage in so many tumors, is not useful with odontogenic tumors including myxomas. Stains for vimentin and muscle-specific actin are positive but add little regarding histogenesis. Myxoma is a tumor seen principally in the second and third decades. Like many tumors of the jaws, they provoke little symptoms and may grow to a large size before discovery. Radiographically, there are no identifying characteristics, and biopsy is required for diagnosis. They are purely radiolu-cent and may be unilocular or multi-locular. "Wispy" trabeculae of bone may course through the tumor and are highly suggestive of myxoma but they are not pathogno-monic. The microscopic features of myxoma are straightforward, and special stains are ordinarily not required. Seasoned surgeons may recognize the tumor first by the white, slippery, and gelatinous consistency. The tumor is hypocellular. Spindle, angular, or stellate myxoblasts lie randomly arranged in a pale, mucoid matrix comprised of hyaluronic acid and chondroitin sulfate. Occasional islands of odontogenic epithelium may be encountered but they are not an essential part of the tumor. Rests of Malassez may be incidentally incorporated in the tumor. Areas may be encountered in which there is transition to more cellular and collagen rich zones. The term myxofibroma has been used to describe such tumors but the behavior remains unchanged. Myxomas are unencapsulated, locally infiltrating tumors. When small, cure may be achieved by vigorous curettage. Large tumors require complete surgical excision with a margin or normal bone. In this regard, the treatment is essentially the same as for ameloblastoma.

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