A Case of Giant Prolactinoma Characterized by a Nasopharyngeal Extension and Diagnosed by Nasal Cavity Biopsy

Abstract Introduction: Giant prolactinomas represent 2-3% of all prolactinomas and less than 0.5% of all pituitary lesions. Uncommon extensions of giant pituitary adenomas to areas such as nasopharynx or paranasal sinuses are even rarer. There are about 50 cases described in the literature. Here, we report a giant prolactinoma case diagnosed by biopsy from the nasal cavity. Case: A 40-year-old male patient applied to the emergency room after falling on ice. Cranial CT revealed a giant sellar mass destroying the clivus and the sphenoid bone corpus. The patient has had frontotemporal headache for 5 years, and also loss of libido and erectile dysfunction. He had right superolateral visual field defect and right-sided ptosis. Pituitary MRI showed a T2-hyperintense sellar mass measuring 58x58x70 mm, with extension to the nasopharyngeal wall, right cavernous sinus, right petrous apex and ethmoid spaces at the base of the skull. A punch biopsy was taken from the vascular mass located in the right nasal cavity, in between the middle concha and the septum. Pathological examination revealed a neoplasm that showed strong diffuse immunostaining with PRL and CK8, and focal staining with GH. Ki-68 proliferation index was 2%. Serum PRL level was 11881 ng/mL, FSH: 1.5 mIU/mL, LH: 1.3 mIU/mL, testosterone: 35.7 ng/dL, GH: 0.5 ng/mL, IGF-1: 520 ng/mL, ACTH: 73 pg/mL, cortisol: 12 mcg/dL, TSH: 0.04 uIU/mL, fT4: 14.2 pmol/L, fT3: 4.9 pmol/L and electrolytes were normal. Five days later, a right pterygonal craniotomy was performed. The mass showed the same immunostaining characteristics as the earlier biopsy specimen, and also included fibrin, monotonous cells with ischemic necrosis and distorted architecture of the reticulin pattern. According to the post-operative MRI, the right cavernous and clival part of the mass was reduced in size. Cabergoline (0.5 mg/w), levothyroxine (100 mcg/d) and testosterone propionate (250 mg/m) were started. The patient received conventional radiotherapy in a total dose of 1250 Gy, because of the residual mass. Sixth months after radiotherapy, the nasopharyngeal part of the tumor was not visualized. Cabergoline was up-titrated to a maximum dose of 3 mg/w. Prolactin levels decreased to 136 and 22 ng/mL at the third and sixth months of the treatment, respectively. Superolateral right-sided visual field defect persisted. Five years after surgery, secondary hypocortisolism has emerged, and 5 mg/day prednisolone was added to the therapy. Eight years after diagnosis, MRI revealed significant reduction in the size of the heterogeneous residual mass lesion. Discussion: Giant macroadenomas extending to nasopharynx are mostly prolactinomas, but other functional or non-functional pituitary adenomas may also have the same presentation. These lesions tend to be surgically hard to excise due to uncommon localizations, as in our case, and radiotherapy may be needed to control the residual mass.