Multinodular Epithelioid Osteoblastoma of the Mandible

Abstract

Multinodular epithelioid osteoblastoma is a rare variant of osteoblastoma characterized by numerous nodules of epithelioid osteoblasts surrounding bony trabeculae as well as clusters of epithelioid osteoblasts without osteoid formation. It commonly occurs in gnathic bones of the face and spine, and has a male predominance. To date, only 26 cases of multinodular epithelioid osteoblastoma have been reported in the literature. Here, we add an additional case to those previously reported. An 18-year-old male patient presents with a periapical radiolucency in the region of vital tooth #30. The surgeon’s differential diagnosis for this radiolucent lesion was ameloblastoma versus cyst. An incisional biopsy of the lesion revealed well-vascularized fibrous connective tissue containing a multinodular tumor composed of collections of epithelioid cells with osteoblastic differentiation surrounding zones of hyalinization and bony trabeculae. Multinucleated giant cells and rare mitotic figures were noted. Additionally present within the tumor were clusters of epithelioid osteoblasts without bony trabeculae. Residual immature viable bone trabeculae were noted surrounding the tumor. A diagnosis of multinodular epithelioid osteoblastoma was rendered. In this paper, we present a rare case of multinodular osteoblastoma of the mandible and a review of the literature. We will highlight the unique histological features that help differentiate this tumor from tumors classified as conventional osteoblastoma, aggressive osteoblastoma, epithelioid osteoblastoma and most importantly, low-grade osteosarcoma.