Unusual radiographic appearance of ossifying fibroma in the left mandibular angle

Abstract

Ossifying fibroma is usually a unilocular lesion with a well-defined, thinly corticated margin radiographically, although various patterns have been noted. The patient was a 27-year-old woman with a painless radiolucent lesion demonstrated on panoramic radiography to involve the root-apex area of the left lower second and third molars. Radiographically, the lesion had some features of a benign tumour, such as an odontogenic myxoma. However, the deep invaginations towards the interalveolar septa suggested a simple bone cyst, whereas the irregular margin and lack of expansion or mandibular canal displacement were consistent with a malignant lesion. A hard tissue component was confirmed only by soft-tissue mode CT. Although this lesion was histopathologically diagnosed as ossifying fibroma, the conflicting imaging findings were challenging and very intriguing.

Figure 1

Cropped panoramic radiograph showing a radiolucent lesion with an irregular margin and sclerotic rim extending from the left second molar tooth to the mandibular angle

Figure 2

Intraoral radiograph shows deep invaginations toward the interalveolar septa and no displacement of the inferior mandibular canal. A small vesicular space appears in the cervical region, in contact with the distal surface of the left third molar tooth

Figure 3

(a) CT showed no destruction of the buccolingual cortical bone, but invasion of the internal surface of the cortical bone. (b) CT appearance in soft-tissue mode. The CT value of various components of the lesion was 39 HU, 60 HU and 120 HU, compared with 73 HU for the masseter muscle

Figure 4

(a) Cross-sectional cone beam CT image shows the lesion penetrating nearby bone tissue mesially. (b) Sagittal section cone beam CT shows irregular margin and sclerotic rim with no displacement of the inferior mandibular canal. (c) Axial section cone beam CT shows the interior to be homogeneous with no calcification, with thinning of the lingual cortex

Figure 5

(a) The lesion demonstrated well-defined low signal intensity on axial T₁ weighted imaging, time of repetition/time of echo (TR/TE): 579/10; (b) heterogeneously high signal intensity on STIR axial imaging, TR/TE: 3579/60 and (c) enhancement at the margin on axial T₁ weighted imaging after injection of diethylenetriamine-pentaacetic acid (Gd-DTPA), TR/TE: 545/10

Figure 6

High-power view demonstrates the tumour to be composed of cellular and collagenous fibrous stroma with spherical woven bone. The woven bone is lined by osteoblastic cells and equally distributed throughout the tumour (haematoxylin–eosin stain; magnification 100×)