Massive, mixed, cystic lesion of the mandibular midline

CLINICAL PRESENTATIONA 37-year-old white man presented to the emergencyclinic of a teaching hospital complaining of a“swelling” of his chin of 5 months’ duration. While hewas playing with his daughter, she accidently hit hischin, resulting in increasing size, numbness, and painduring eating. The patient had no signiﬁcant medicalhistory, but he had smoked cigarettes (1 pack per day)since his teenage years. Clinically, the chin mass waslarge (7 6 4 cm), with a slight asymmetry of thesymphysis region. No skin changes, fever, or purulentdischarge were observed.Intraorally, there were multiple carious teeth, themandibular left canine was missing, and the remainingteeth from right second mandibular premolar to left sec-ond premolar exhibited class III mobility; many werehaphazardly displaced. There was slight pain duringpercussionofmostmandibularteeth.Thelesionappearedto be intraosseous, with a considerably expanded cortexthat wasnontender andpliable on both labialand lingualsurfaces.A panoramic radiograph showed a well-circum-scribed radiolucency extending from the right ﬁrstmandibular molar to the left ﬁrst molar, with animpacted left canine displaced to the inferior border.Lateral oblique radiographs helped to further charac-terize the lesion (Figure 1). The lesion had causeddisplacement and considerable external root resorptionof overlying teeth, as well as thinning, expansion, andslight scalloping of the inferior mandibular cortex.There was a thin sclerotic rimming on the left.Conventional computed tomography imaging (softtissue window, with contrast) conﬁrmed the well-circumscribed nature of the lesion and also showedirregularly dense regions of mild opacity, consistentwith soft tissue proliferations, along the lesional pe-riphery and occasionally more centrally (Figure 2);some of these regions had enough density to suggest atleast mild calciﬁcation. The bulk of the lesion wasrepresented by a mildly and diffusely gray haze, sug-gesting a ﬂuid content. There were several small, moreradiopaque densities of the posterior portions, and theoverlying cortex was very thin, with occasional perfo-rations not evident on other radiographs. The lesionconsiderably expanded toward the labial, but alsoshowed expansion of the lingual aspect of the mandible.DIFFERENTIAL DIAGNOSISThe massive size of this lesion, with its multiple corticalperforations and associated paresthesia, suggested anaggressive intraosseous neoplasm. However, the well-demarcated borders, cortical expansion, scleroticrimming, and resorbed tooth roots suggested a benignneoplasm or cyst and almost certainly ruled out primarymalignancy or metastatic disease. It was thought thatthe perforations might be explained by palpation traumain such an unusually thinned cortex, or that perhaps the“perforated” areas were merely regions where the cor-tex was so thin that it could not be detected bycomputed tomography technology.The paresthesia would be more difﬁcult to accept fora benign entity if the paresthesia were not bilateral,suggesting a common pressure or ischemic phenome-non from tumor expansion.Three additional and signiﬁcant features of the lesionprovided important clues to its identity: (1) it was not asolely pericoronal lesion, despite its association with animpacted tooth; (2) it was slightly multilocular, as sug-gested by scalloping of the inferior border; and (3)although basically a cystic radiolucency, it containedscattered radiopacities. The fact that it extended beyondthe cementoenamel junction (see Figure 1, C) broadenedour differential diagnosis and ruled out at least oneexpansile radiolucency, the dentigerous cyst. Addition-ally, the multilocular appearance suggested a number ofclassical lesions, such as ameloblastoma, odontogenickeratocyst (keratocystic odontogenic tumor), glandularodontogenic cyst, odontogenic myxoma, ameloblasticﬁbroma, central giant cell granuloma, aneurysmal bonecyst, intraosseous mucoepidermoid carcinoma, and cen-tral hemangioma.