Differential diagnosis of submandibular cystic lesions by computed tomography.

A retrospective analysis of 35 submandibular cystic lesions was undertaken to assess the usefulness of CT in their differential diagnosis. Lesions were analysed on the basis of extent, shape and density. It was found that all those lesions that extended into both the sublingual and the anterior part of the submandibular spaces could be diagnosed as ranulas (10/10) and all those limited to the posterior part as lateral cervical cysts (8/8). Those lesions that extended to the sublingual, but not the anterior part of the submandibular space, were dermoid cysts if they had a smooth margin (2/2), and probably ranulas when it was concave (4/5). Those lesions that extended into the anterior part of the submandibular but not the sublingual space were ranulas on the basis of a multilocular or concave margin (3/3), but if they had a smooth margin (3/7) they could not be differentiated from dermoid cysts (4/7). Although CT density was less valuable for the differential diagnosis, both ranulas and dermoid cysts could be excluded if it was similar to that of muscle.