FINAL DIAGNOSIS
Positive for Neoplasm, consistent with Metastatic Ameloblastoma
DISCUSSION
Ameloblastoma is a rare tumor that is classified as a benign odontogenic neoplasm and constitutes approximately 1% of oral tumors and 13% of odontogenic tumors. It is locally aggressive with high recurrence rate after removal and can rarely metastasize despite of its benign histologic appearance [1]. Ameloblastoma affects males and females equally and has a wide age range of 8-92 years with a peak age of incidence in the fourth to fifth decades of life.
About 80% of the ameloblastomas occur in the mandible, followed by the maxilla especially the posterior region and rarely the sinonasal tract [2]. Clinically, the tumor presents with non-specific symptoms ranging from painless to painful swelling of the involved jaw. However, most of the times, these lesions are detected incidentally on imaging as a multilocular or a unilocular lesion. Ameloblastoma commonly exhibit a slow expansion followed by an accelerated growth later in the disease course, this expansion has been associated with complications including loosening of teeth, malocclusion, paraesthesia, pain, soft tissue invasion, facial deformity, limited mouth opening, difficulty with mastication, and airway obstruction [3].
The current 2019 World Health Organization (WHO) classification of odontogenic tumors divides ameloblastoma into four types, including unicystic, extraosseous/peripheral, and metastasizing ameloblastoma. The most common histologic subtype of ameloblastomas is the follicular type, which is that of odontogenic epithelial islands simulating the stellate reticulum with peripheral palisading columnar cells and hyperchromatic nuclei with reversed nuclear polarity [4], which is the subtype present in our case. The second most common subtype is the plexiform type, which consists of anastomosing strands of ameloblastomatous epithelium with inconspicuous stellate reticulum and cyst-like stromal degeneration. Other histologic subtypes including acanthomatous, granular, and basaloid are less common. Immunohistochemically, almost all ameloblastomas are positive for CK19 which is a marker for odontogenic epithelium, CK13 and calretinin are positive in stellate reticulum cells, while the peripheral cells stain for CK14 and CD56 [5].
At the molecular level, studies have detected that most ameloblastomas harbor gene mutations in the mitogen-activated protein kinase (MAPK) pathway including BRAF V600E, KRAS, NRAS, HRAS, and FGFR2 mutations. Nevertheless, non-MAPK pathway mutations including SMO, SMARCB1, CTNNB1, and others are also very common and tend to co-occur with the MAPK pathway mutations [6].
Radical surgical management appears to be the optimal treatment of choice for most multicystic/solid and advanced unicystic tumors, with long-term follow up due to the possibility of delayed presentation of metastasis and recurrence beyond 10 years [7]. However, given the rarity of metastasizing ameloblastoma, there are no established treatment protocol yet, but the management often includes chemotherapy with wide surgical resection [8].
REFERENCES
Contributed by Raniah Al Amri, MD, Samer Khader, MD