Massive Skull Base Ameloblastic Carcinoma with Intracranial Extension

AbstractAmeloblastic carcinoma (AC) is a rare and aggressive malignant epithelial odontogenic tumor which may arise either from the mandibula (66.6%) or the maxilla (33. %3). Besides being formed de novo the tumor can develop from a pre-existing ameloblastoma or odontogenic cyst. The clinical course of AC is typically aggressive with extensive local destruction. AC has also been reported to spread to various parts of the body through lymphatic system. Skull base location and intracranial extension of this tumor are uncommon. In this case report we present the clinical course, management and follow up of an uncommonly large AC which destructed anterior skull base and extended into the intracranial space.

Key Words: Ameloblastic carcinoma, skull base, intracranial

Introduction:Ameloblastoma is benign, slowly growing, but locally aggressive neoplasm which constitutes about 1–3% of all jaw tumors and cysts (18). Ameloblastic carcinoma (AC) is an exceptionally rare and aggressive malignant epithelial odontogenic tumor with a poor prognosis which may arise de novo or from malign transformation of a long-standing ameloblastomas (9, 13). Two thirds of these tumors arise from the mandible while one third originates from maxilla (12). AC may also present as a benign cystic lesion or as a large tissue mass with ulceration, bone destruction and may cause unstable teeth (1). Contrary ameloblastoma case presentations which are commonly published in the literature AC cases especially arising from mandibula are rare (2, 10). Whether this tumor transforms from ameloblastoma or represents a separate entity is still controversial (10). Likewise, there is still no consensus on the management of AC’s however currently as much widespread surgical excision with or without radiotherapy is the preferable treatment modality (6, 16). In this presentation we demonstrate the clinical course, management and follow up of a particular case that harbors a giant AC extending into the frontal lobe through destructed anterior cranial fossa. While AC’s infrequently seen in this localization this case may contribute to the differential diagnosis of tumors in this area.

Case ReportA 35 year-old male was referred to our institution with the diagnosis of an anterior cranial fossa lesion. He had been suffering consistent headache, numbness in the left half of his face and anosmia for 3 months. There was no facial swelling or asymmetry. He did not express any pain during mastication or any difficulty in jaw movements. His symptoms had rapidly progressed in the last 3 weeks. The patient underwent transsphenoidal biopsy elsewhere before admitting to our clinic of which pathological examination was reported as AC.Patient’s paranasal computed tomography (CT) scan revealed a soft tissue mass that almost completely occupied the ethmoid cells, nasal cavity, sphenoid and left maxillary sinuses and also destructed lamina paprecea, clivus, and cribriform plate with intracranial extension (Figure 1). Cranial magnetic resonance imaging (MRI) displayed the lesion as solid, lobulated mass enhancing heterogeneously with contrast that showed similar extension pattern seen on the CT by means of compressing both basal frontal lobes (Figure 2). A CT-angiography was performed to rule out any vascular involvement such as internal carotid arteries (ICAs) and to identify the vascularity of the tumor. On CT-angiography tumor was found to be considerably vascular and both ICA’s did not showed any displacement or involvement by the tumor. Laboratory findings including tumor markers were in normal range. First, we planned to approach the tumor inferiorly by aiming as much gross total resection as possible. The patient underwent an extended endoscopic endonasal transsphenoidal surgery through binostril route. The tumor was reached easily in the nasal cavity. With the help of suction/coagulation and tumor-forceps’ the tumor was removed piece by piece. All tumor parts invading the nasal cavity, the maxillar sinus, the sphenoidal sinus, and the clivus were gross totally removed. Additionally, the tumor-invaded anterior cranial fossa dura-mater was also excised. Although the tumor was soft in nature its highly vascular intra-structure prevented more extensive removal and the intracranial part was left residue. The dura-mater defect was repaired with autologous graft. Postoperative early cranial MRI showed the remnant in the anterior cranial fossa (Figure 3). Histopathological examination revealed an ameloblastic carcinoma, which was consistent with the previous biopsy evaluation (Figure 4). As the second step a transcranial approach was planned on the third postoperative day for removal of the residual tumor since AC has characteristically a poor prognosis and is locally aggressive. A gross total resection with dura excision was performed through the right subfrontal approach (Figure 5). No CSF leakage or any other complications were observed after both procedures and the patient was discharged on the 4th day after the second operation. The patient received 5000 cGy of local adjuvant radiotherapy. The patient was followed up closely and there was no recurrence in 18 months control (Figure 6).