Ectopic pituitary adenomas (EPAs) are most likely tumors developing from the cellular remnants following the migration of Rathke's pouch. We present the case of a 54-year-old female diagnosed with Cushing's syndrome. Magnetic resonance imaging (MRI) identified an ectopic microadenoma located in the median wall of the cavernous sinus. Microscopic transsphenoidal surgery was performed and the lesion was completely removed without any postoperative surgical complications. Based on characteristic microscopic and immunohistochemical features and on recent clinicopathological prognostic classifications, the histopathological diagnosis was non-proliferative, non-invasive corticotroph pituitary neuroendocrine tumor, grade 1a. Complete remission of disease was achieved postoperatively and was maintained for one year following surgery. MRI showed complete resection, without tumor recurrence at one and two years. Occurrence of an ectopic intracavenous adrenocorticotropic hormone (ACTH)-secreting adenoma is extremely rare and poses difficulties both in the identification, surgery, histopathological grading, and adequate endocrinological treatment and follow-up.