This is the most interesting of jaw cysts. Unlike other cysts, it has a high recurrence rate estimated to be about 30%. Radiographically, OKC is a great mimic and may resemble dentigerous cyst, periapical cyst, traumatic bone cyst, and tumors such as giant cell granuloma and ameloblastoma. It is so named because of the prodigious production of keratin by the lining epithelium, so much that the cyst lumen may be virtually filled with keratin. The OKC may be discovered on routine dental radiographs or by the appearance of unexplained swelling. The radiographic characteristics are not diagnostic but the histomorphology is. The lining epithelium has a flat basement membrane, basal epithelial cells are frequently columnar or cuboidal and aligned-like dominos, a feature referred to as basal cell palisading. The surface of the epithelium is frequently undulating with a thin layer of keratin or parakeratin. Orthokeratin is sloughed into the cyst lumen where it appears as lamellated, eosinophilic strands that on gross examination may resemble toothpaste. Small daughter cysts may be found in the cyst wall. The keratocyst may be sporadic or a part of the nevoid basal cell carcinoma syndrome (Gorin's syndrome). The syndrome is transmitted as an autosomal dominant trait and is characterized by the early onset of multiple cutaneous basal cell carcinomas, multiple keratocysts, bifid ribs, calcified falx cerebri, and medulloblastoma, and a host of other lesions. The gene has been mapped to 9q22.3 and is the human equivalent of the transmembrane-patched protein involved in the determination of segment polarity in Drosophila. Mutations in this gene have been found in the Gorin syndrome, sporadic cutaneous basal cell carcinoma, medulloblastoma, and the epithelial cells in both sporadic and syndromic OKCs. The gene behaves as a tumor suppressor gene. OKCs are ordinarily treated by curettage but also respond to marsupialization. Peripheral osteotomy has also been advocated. In this approach, following curettage, a round bone bur is used to enlarge the bony cavity to eliminate remnants of the cyst that may be the source of a future recurrence. Chemical cautery of the cyst bed using topical application of Carnoy's solution has been recommended as an alternative to surgical osteotomy. Carnoy's solution, a mixture of absolute alcohol, chloroform, glacial acetic acid, and ferric chloride, is not readily available in the United States. A third approach using application of liquid nitrogen either by direct spray or cryoprobe followed by immediate bone grafting using cancellous bone and marrow has been used to reduce the risk of recurrence of a variety of aggressive bone lesions including OKCs.
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