Ipilimumab cystic hypophysitis mimicking metastatic melanoma

Ipilimumab is an immunotherapeutic agent used in the treatment of metastatic melanoma, and is known to cause hypophysitis in some patients. Magnetic resonance imaging of ipilimumab-induced hypophysitis typically shows diffuse enlargement of the pituitary gland with variable enhancement or enlargement of the infundibulum. This often produces a diagnostic dilemma as melanoma not uncommonly metastasizes to the pituitary gland due to the rich vascular plexus of the hypophyseal portal system, and has a similar imaging appearance to autoimmune hypophysitis. We present a case of a 49-year-old man with a Clark level 4 melanoma of the left calf with inguinal nodal metastases that was treated with resection and 2 cycles of ipilimumab, and subsequently developed a “cystic” pituitary mass. To our knowledge, all of the described cases of ipilimumab-induced hypophysitis to date have shown solid enhancement on imaging. Because metastatic melanoma to the pituitary gland often has internal hemorrhage that produces a “cystic” appearance, and ipilimumab-induced hypophysitis is typically a solidly enhancing abnormality, this presented a significant diagnostic and therapeutic dilemma. Our patient's symptoms, although significant, did not necessitate immediate surgical intervention, and a conservative approach of withholding the ipilimumab and administering therapeutic corticosteroids was pursued. The patient's symptoms abated and follow-up magnetic resonance imaging 1 month later showed near complete resolution of the pituitary abnormalities. As such, this is a unique case of ipilimumab-induced hypophysitis presenting as a “cystic” pituitary mass.