Epithelioid Multinodular Osteoblastoma of the Mandible: A Case Report and Review of Literature.

Epithelioid multinodular 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 the gnathic bones of the face and spine, and has a male predominance. To date, only 26 cases of epithelioid multinodular osteoblastoma have been reported and described in detail in the literature. Lucas et al. (Hum Pathol 25:117-134, 1994) described 43 cases of a variant of osteoblastoma that he termed epithelioid multifocal osteoblastoma. These both likely represent the same entity. Here, we report another case of this rare variant of osteoblastoma. 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 typical 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 epithelioid multinodular osteoblastoma was rendered. In this paper we present a rare case of epithelioid multinodular osteoblastoma of the mandible, provide a general review of the literature, and highlight the unique histological features that help differentiate this tumor from tumors classified as conventional osteoblastoma, aggressive osteoblastoma, pseudoanaplastic osteoblastoma and, most importantly, low-grade or osteoblastoma-like osteosarcoma.