When Cancer Mimics Pain: Maxillary Primary Intraosseous Carcinoma Misdiagnosed as Trigeminal Neuralgia

<b>Background</b>: Primary intraosseous carcinoma (PIOC) is a rare and aggressive odontogenic malignancy that originates within the jaw bones without initial mucosal involvement. Its atypical and nonspecific symptoms frequently lead to diagnostic delays, especially in maxillary presentations. <b>Methods</b>: A 74-year-old male presented with persistent trigeminal-like neuralgic pain along the ophthalmic branch, initially misdiagnosed as secondary trigeminal neuralgia. MRI revealed a 45 × 46 × 34 mm mass occupying the right maxillary sinus with orbital wall destruction and dural invasion. Following histopathological confirmation of malignancy, a multidisciplinary team performed total maxillectomy with orbital exenteration and dural resection, followed by reconstruction using a temporoparietal flap. Adjuvant radiotherapy was administered. <b>Results:</b> Histopathology revealed invasive odontogenic carcinoma with atypical squamous features, dentinoid deposition, and perineural invasion. Postoperative recovery was uneventful, with complete pain resolution. MRI and PET surveillance over 2.5 years demonstrated no local recurrence. <b>Conclusions:</b> Maxillary PIOC may present exclusively with neuropathic pain, mimicking trigeminal neuralgia and leading to delayed diagnosis. In cases of unexplained facial pain with sinus or skull base involvement, odontogenic malignancies should be considered in the differential diagnosis. Early imaging and multidisciplinary management are key to achieving timely diagnosis, effective treatment, and improved quality of life.