Ectopic sphenoid sinus pituitary adenoma masquerading as metastatic head and neck cancer

A 68-year-old Chinese man was found to have a lobular mass in the sphenoid sinus which extended to the clivus and the roof of the nasopharynx on a staging MRI scan performed for his high-grade parotid salivary duct carcinoma. Further positron emission tomography scan showed that this lesion was fluorodeoxyglucose (FDG) avid. This proved to be a diagnostic dilemma. The patient underwent a total parotidectomy, left selective neck dissection and a transphenoidal biopsy of his nasal lesion. Final histology revealed that this lesion was a synchronous ectopic sphenoid sinus pituitary adenoma (ESSPA). Initial differential diagnoses that were considered included a chordoma, metastatic carcinoma and nasopharyngeal carcinoma. However, an important differential with a neoplastic appearance and a tendency for positive FDG uptake is an ESSPA. It requires dedicated immunohistochemical staining to diagnose, and its mainstay of treatment is surgical excision.