Mandibular Intraosseous Pseudocarcinomatous Hyperplasia: A Histologic Mimic of Squamous Cell Carcinoma.

Pseudocarcinomatous hyperplasia is a benign reactive squamous proliferation which may mimic well-differentiated squamous cell carcinoma, particularly when present in association with deep tissues such as bone. We report a case of a 65-year-old man who presented with left lingual mandibular pain and spontaneous lingual cortical sequestration with exposed root surfaces and a massive periapical abscess identified on CT scan. The clinical differential diagnosis included osteonecrosis, osteomyelitis, primary or metastatic malignancy, periodontitis or odontogenic lesions. Histologic examination of the left mandible debridement specimen revealed proliferative squamous epithelium within the marrow space of bone, which was involved by extensive acute osteomyelitis, osteonecrosis, and Actinomyces organisms. No squamous atypia or features of malignancy were identified. P53 immunostaining showed wild-type staining pattern within the squamous epithelium, and GMSF stain was negative for fungi. The findings were consistent with mandibular intraosseous pseudocarcinomatous hyperplasia. The patient was treated with a six-week course of high dose oral (500 mg) amoxicillin and experienced a favorable post-operative course. Recognition of this process is essential to avoid misdiagnosis and unnecessary aggressive treatment, as this histologic mimic to carcinoma within bone can present a significant diagnostic challenge for clinicians and pathologists.