Sinonasal Undifferentiated Carcinoma and Esthesioneuroblastoma Recurring as Nonintestinal Adenocarcinoma

Numerous distinct neoplasms are encountered at the anterior cranial base. Management of these primary tumors and their locoregional recurrences are dictated by the histopathologic diagnosis. We present two unusual cases of extra-axial anterior cranial base malignancies with locoregional recurrence where the recurrent tumor encountered was of a distinct histopathologic type. While rare, this report highlights the possibility of encountering a distinct tumor type in the posttreatment surveillance of patients with anterior cranial base malignancies.