Aggressive granular cell ameloblastoma: Report of a rare case.

Granular cell ameloblastoma is a slow growing odontogenic ectodermal tumor. The tumor shows typical ameloblastoma with the cells showing eosinophilic granularity. This variant of ameloblastoma is aggressive with high recurrence rates. We report a case of aggressive ameloblastoma of granular cell variant.

The ameloblastoma is a true neoplasm of enamel organ type tissue, which does not undergo differentiation to the point of enamel formation. It has been described by Robinson as being a tumor that is “unicentric, nonfunctional, intermittent in growth, anatomically benign and clinically persistent.”[1] It is a slow growing odontogenic epithelial tumor of jaw and accounts for about 1% of all oral tumors and about 18% of odontogenic tumors. Ameloblastoma is primarily seen in adults within third to fifth decade and shows almost equal gender predilection.[2] The mandible appear to be the most commonly affected area (more than 80% of cases) though other areas of the mandible can also be involved. Molar angle-ramus area is involved three times more commonly than are the premolar and anterior regions combined.[1]

The ameloblastoma is said to be of varied origin and they may be originated from cell rests of enamel organ, epithelium of odontogenic cysts, disturbances of developing organ, basal cells of surface epithelium and heterotrophic epithelium in other parts of body.[3]

There are various histological types of ameloblastoma namely follicular, plexiform, acanthomatous, granular cell and less common variants such as clear cell, desmoplastic, [Figure 1] basal cell, papilliferous and keratoameloblastoma.[2] Granular cell ameloblastomas are rare odontogenic tumors accounting for 3.5% of all ameloblastoma cases. The recurrence rate for granular cell ameloblastoma is 33.3%.[4]

Figure 1

Hemimandibulectomy specimen showing extensive destruction

Case Report

An incisional biopsy from mandibular region of a 45-year-old female patient was submitted to our Department of Oral Pathology and Microbiology with the history of pain and swelling in the right lower back teeth region for past 2 months. The clinical details given to us were, swelling in the right lower cheek region extraorally. Intraorally the swelling was extending from right canine to retromolar area and 45 and 46 were mobile. The hematoxylin and eosin stained histopathological stain showed numerous follicular structures within the connective tissue. The follicles were lined by tall columnar ameloblast like cells with reverse polarity and surrounding stellate reticulum like cells. Both peripheral tall columnar cells and central stellate reticulum like cells showed dense granularity. The connective tissue was moderately collagenous with minimum inflammation. The diagnosis of granular cell ameloblastoma was given [Figure 2].

Figure 2

Hematoxylin and eosin stained section showing ameloblastic follicles with granular cells (H and E, ×10)

Following the histopathological diagnosis hemimandibulectomy was done. The hemimandibulectomy specimen showed thinned out buccal cortical plate and perforation of the lingual article plate at multiple locations. Multiple sections were processed for histopathological examination. Anterior and posterior surgical margins were sectioned, and histopathological examination was done after decalcification. All the sections from the excised specimen showed granular cell ameloblastoma while the anterior and posterior surgical margin did not show any residual tumor. Patient had an uneventful recovery. Patient is currently on regular follow-up for the past 22 months and no sign of recurrence.

Discussion

Ameloblastoma sometimes exhibits granular transformation of cytoplasm occurring in central stellate reticulum like cells, and this change often extends to peripheral columnar or cuboidal cells.[5] Hematoxylin and eosin staining and periodic acid Schiff staining showed granular neoplastic cells residing within the tumor follicles.[6]

Light microscopic study of granular cell ameloblastomas shows numerous neoplastic epithelial islands in a scant, mature fibrous stroma. The most striking features of this tumor were that the center of the island had large eosinophilic granular cells, surrounded by tall columnar cells resembling the inner enamel epithelium of the enamel organ. Variations in the size and shape of the granules were noted. Their cytoplasmic granules ranged from fine to coarse and in some cells pink, homogenous rounded masses which resembled inclusion bodies larger than coarse granules. The granular cells nuclei varied in position and often they were crescent shaped. Clear cell outlines and no intercellular bridges were noticed. The peripheral cells lining the islands were tall columnar or cuboidal with nuclei displaced opposite to the base of the cell and many peripheral cells were granular.[7] The granular cells are a transitional or matured phase in the life cycle of ameloblasts, starting with normal stellate reticulum like cells leading to the production of granules and finally resulting in degeneration and the formation of cystic areas.[2]

Ultrastructurally, in the granular cell ameloblastoma the peripheral cells of the tumor islands were separated from surrounding stroma by continuous basement membrane. The most striking cytoplasmic feature is the presence of numerous granules (pleomorphic osmiophilic granules). The granules are round or oval, composed of homogenous amorphous osmiophilic material of different density. Coarse granules were formed by fusion of several smaller granules.[7] The granules were known to be lysosomes, which might play a role of autophagy and of remodeling the cytoplasm, as opposed to the aging or degenerating function.[8] The cytoplasmic granularity in granular cell ameloblastomas might be caused by increased apoptotic cell death of neoplastic cells and associated phagocytosis by neighboring neoplastic cells.[9] Lysosomal aggregation within cytoplasm is caused by dysfunction of either a lysosomal enzyme or lysosome associated protein involved in activation or targeting of the enzyme or lysosomal biogenesis.[3]

The granular cell ameloblastoma is a locally aggressive tumor with a high frequency of recurrence and potential to metastasize.[1011] It shows a slightly higher rate of recurrence of about 33.3% when compared with other common variants.[12] However, very high recurrence rates were reported by Hartman et al. (73%).[12] The presence of tumor cells within the bone beyond the clinical and radiological margins are thought to be responsible for the recurrence when the tumors are treated with enucleation or curettage.[10] The malignant transformation is rare, but the cases with metastasizing granular cell ameloblastoma lymph nodes, lungs and cervical vertebrae have been reported.[131415]

Conclusion

The granular cell ameloblastoma is aggressive tumors with high chances to metastasize. However, further studies with long-term follow-up are necessary for the better understanding of the tumor's diagnosis, prognosis and treatment.