Recurrent Cushing's disease due to postoperative seeding of tumor cells in the sphenoid sinus: a case report with review of the literature.

Recurrent Cushing's disease is most commonly caused by residual or newly developed pituitary neuroendocrine tumor (PitNET) tissue within the sellar region. Extrasellar recurrence due to postoperative tumor cell seeding is exceedingly rare. We report the unique case of a 30-year-old woman who achieved endocrine remission after gross total resection of an ACTH-secreting PitNET but later developed biochemical and clinical recurrence without radiological evidence of a sellar lesion. Despite long-term medical therapy including cabergoline, metyrapone, and pasireotide, the hypercortisolism gradually progressed. Nearly 10 years after the initial surgery, a reoperation was performed to explore the occult tumor. Intraoperatively, a small soft tumor attached to the posterior surface of the anterior wall of the sphenoid sinus was discovered. Histopathological examination confirmed the presence of a recurrent corticotrophic PitNET. A retrospective review of CT, MRI, and octreotide scintigraphy revealed a subtle lesion that had previously been overlooked. Complete resection resulted in an immediate endocrine remission. This case demonstrates that recurrent Cushing's disease may, although rarely, arise from the implantation of tumor cells that drop into the sphenoid sinus during transsphenoidal surgery. Awareness of this mechanism is crucial for evaluating MRI-negative recurrences. Careful inspection of the sphenoid sinus and meticulous irrigation during surgery may help prevent iatrogenic seeding and improve long-term outcomes.