Desmoplastic ameloblastoma.

Desmoplastic ameloblastoma is a relatively rare variety of ameloblastoma and only very few cases have been reported so far. The present case is an elderly man who had reported with a swelling in the anterior mandible which turned up to be desmoplastic ameloblastoma. Proper diagnosis is necessary to report such a case, so that the actual incidence can be noted.

INTRODUCTION

The tumors that arise from odontogenic epithelium are called as ameloblastomas. Its histopathologic types are plexiform, follicular, acanthomatous, granular, and desmoplastic.[1] The desmoplastic variety is characterized by abundant collagenous stroma and small strands of compressed odontogenic type of epithelium. This feature makes it unique among the ameloblastomas.[2] The other rarer variants include basal cell, keratoameloblastoma, papilliferous keratoameloblastoma, and clear cell types.[3]

CASE REPORT

A 55-year-old male patient presented to the Department of Oral Pathology, GITAM Dental College with the complaint of swelling in the right lower premolar region [Figure 1]. The patient had noticed the swelling 5 months back, which had slowly increased to the present size. On extraoral examination, noticeable facial asymmetry was observed due to swelling present on the right side of the mandible. The right submandibular lymph node was also palpable and non-tender. On intraoral examination, there was an ill-defined solitary swelling extending from the mesial aspect of 31 to the mesial aspect of 45, superioinferiorly extending from the superior margin of attached gingival to well beyond the gingival sulcus. Radiographic examination revealed a mixed radiolucency interspersed with radiopacities with ill-defined borders. Occlusal radiographs showed an ill-defined radiolucent lesion interspersed with radiopacities extending from the mesial aspect of 41 to the distal aspect of 45 [Figures 2 and 3]. The lesional tissue after excisional biopsy had gritty or “frozen ice-cream”-like consistency [Figure 4]. The lower border of the mandible was preserved so that the aesthetic and functional work-up could be done [Figure 5]. The cut surface was solid and whitish in most cases. The epithelial tumor islands were very irregular with a pointed stellate appearance or small strand like and discrete. The histopathology was characterized by stromal desmoplasia, small tumor nests and strands of odontogenic epithelium were scattered in the stroma [Figures 6–8].

Figure 1

Intraoral picture of the patient

Figure 2

Intraoral periapical radiograph

Figure 3

Occlusal radiograph of the mandible

Figure 4

Gross picture of the resected area

Figure 5

Postoperative radiograph

Figure 6

Histopathology showing odontogenic epithelium like areas in between dense collagen tissue fibers

Figure 8

20× magnification of the area exhibiting peripheral cells of tumor island columnar cells with reverse polarity. Hypercellularity of spindle-shaped or polygonal cells and microcyst formation is seen focally

40× magnification of the desmoplastic area

DISCUSSION

The gross specimen most often consists of resected portions of jaws. More than 50% show multilocular mixed radiolucent/radiopaque lesions with ill-defined margins. Desmoplastic ameloblastoma represents approximately 4-13% of all ameloblastomas.[3] This lesion most commonly occurs between the ages of 17 and 72 years, with the mean age being 44.7 years and with a male predilection.[4] The prevalence of ameloblastoma in maxilla when compared to mandible is almost close to 1:1. Desmoplastic ameloblastoma s is found predominantly in anterior or premolar regions of the jaws.[5] The chief initial complaint usually is as a painless swelling of the jaw bone. It is smaller in size than other types of ameloblastoma, and occurs mainly in the alveolar region and occupies the tooth-bearing area.[6] The resorption of tooth roots and displacement of teeth is seen frequently. This variant exhibits no typical findings of ameloblastoma. The oxytalan fibers in the stromal tissue suggest that the tumor derived from the epithelial rest of Malassez in the periodontal membrane of a related tooth. The periphery of islands consists of cuboidal cells with hyperchromatic nuclei. The columnar cells with reversed nuclear polarity are rarely conspicuous. The central area consists of swirled, hypercellular, spindle-shaped, or squamous epithelial cells. Microcysts that contain eosinophilic amorphous deposits or appear empty may occur centrally. The stroma has extensive stromal desmoplasia characterized by moderately cellular fibrous connective tissue with abundant thick collagen fibers that seem to compress or “squeeze” the odontogenic epithelial islands from the periphery. Formation of metaplastic osteoid trabeculae (osteoplasia) may be present. Evidence of a capsule is not found. In the immunoprofile, the tumor cells exhibit variable expression of S100 protein and desmin, similar to other types of solid multicystic a meloblastoma (SMA). Keratin immunoreactivity is confined to the tumor cells showing squamous differentiation. Decreased expression of CK19 and high expression of p63 is observed.[7] Vimentin is not expressed by either squamatoid or spindle-shaped cells. Differences in expression are attributed to diverse factors such as dedifferentiation or rate of proliferation of neoplastic cells, inherent cellular potential, or extracellular mediators.[8] Marked immunoexpression of transforming growth factor beta (TGF-β) points to the part played in prominent desmoplastic matrix formation.[9] Compared to the stroma of SMA, the desmoplastic stroma of desmoplastic ameloblastoma shows a strong positive reaction for collagen type VI, fibronectin, and type 1 collagen. Treatment is by resection (77.1%) and, in some cases, by enucleation and/or curettage. Long-term follow-up is a must after initial treatment.[10]

CONCLUSION

As desmoplastic ameloblastoma is an uncommon lesion, it warrants proper diagnosis and treatment.