An unusual collision tumor comprising a prolactinoma and a plasmocytoma originating from the sellar region

A 58-year-old previously healthy man presented with diplopia of rapid onset over a few days. Examination demonstrated bilateral sixth and right fourth cranial nerve palsy. MR imaging showed a large sellar mass with significant destruction of the pituitary fossa. Laboratory tests revealed very high serum prolactin (2,483 ng/dl, reference range 3–13 ng/dl). Dopamine agonist therapy was initiated with significant decline in PRL levels; however, nausea, fatigue, and anorexia developed. Within a few weeks the patient developed renal failure and hypercalcemia. Urine protein electrophoresis revealed large free monoclonal kappa peaks while extensive plasmocytosis was evident in bone marrow aspirates. On bone scan numerous lytic lesions were present. A transsphenoidal excisional biopsy was performed which demonstrated two distinct populations of cells, corresponding to a plasma cell tumor and a lactotroph adenoma. Treatment for multiple myeloma was initiated along with radiotherapy for the sellar tumor. Only a few cases of solitary plasmocytomas of the pituitary region have been reported. Few cases of prolactinomas coexisting with other sellar tumors has been described. We discuss in this report possible pathogenic and functional connections between these two tumors. We suggest that in the presence of extensive cranial nerve involvement, atypical imaging findings for a pituitary adenoma and severe hyperprolactinemia, the possibility of a collision tumor should lead the physician to consider excisional tumor biopsy or surgery in addition to dopamine agonist therapy.