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A recent preliminary report of a study to determine the patterns of invasion of squamous cell carcinoma to the nonirradiated edentulous mandible indicated that tumor entered mainly through the residual alveolar occlusal ridge.' This study has now been extended and includes both nonirradiated and irradiated mandibles. Of a total of 46 nonirradiated mandibles (10 partially dentate and 36 edentulous) invaded by tumor, 41 were invaded through the occlusal surface. This confirms the findings of the preliminary report. These findings indicate that there is a rational basis on pathologic grounds for adopting a conservative approach to the nonirradiated mandible. In 16 irradiated mandibles, the routes of tumor entry were found to be much more variable than in the nonirradiated mandible, and multiple foci of tumor invasion of the bone were often present wherever tumor in adjacent soft tissues approached the bone. This variability of tumor entry means that a conservative approach to mandibular excision cannot be pursued in the previously irradiated mandible and full-thickness segmental resection is necessary if bone involvement appears likely. HEAD & NECK SURGERY 10: 294-301,1988

The patterns of spread of squamous cell carcinoma within the mandible were investigated in 43 nonirradiated (33 edentulous and 10 partially dentate) and 16 irradiated mandibles. Two modes of spread were identified: (1) spread in relation to the inferior alveolar nerve, and (2) spread in spaces between cancellous bony trabeculae. Although nerve-related spread was significantly more frequent in the edentulous than in the partially dentate nonirradiated mandible, the difference in incidence between all nonirradiated mandibles and irradiated mandibles was not significant. The patterns of spread in cancellous bone in irradiated and nonirradiated mandibles differed little. Spread of tumor within the medulla, deep to an intact cortex beyond the extent of extraosseous soft tissue tumor, was seen infrequently.

Patterns of spread of squamous cell carcinoma to the ramus of the mandible have been studied. In nonirradiated mandibles, tumor in the ramus was found to have spread in continuity from tumor within the body. In 22 of 27 specimens (81.5%) with established invasion of the molar region of the body, tumor spread was either confirmed to the body or to the body and the anterior part of the ramus. The remaining five cases showed extensive spread within the ramus. It was concluded that a more conservative approach to resection of the ramus may be safe on pathologic grounds in the nonirradiated mandible. In postirradiation mandibles, direct invasion through cortical bone was seen in addition to direct spread from the body. Tumor spread to the ramus was seen in nine of 12 specimens (75%), and in each case was both diffuse and extensive. It was concluded that a conservative approach to resection of the ramus is not safe on pathologic grounds after radiotherapy.

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