ODP550 Giant Cell Tumor of Bone: A Diagnostic Consideration of Sellar Lesions

BACKGROUND: Giant cell tumor of bone (GCTB) is a skeletal neoplasm that most commonly occurs in long bones and rarely in the skull. These tumors are considered benign but tend to be locally aggressive and carry a high rate of local recurrence. True malignant transformation is rare and even metastatic disease carries a rather benign course. Clinical manifestations depend on tumor location and are mostly due to mass effect into the surrounding tissues. We describe a patient with a GCTB, located at the sellar-suprasellar region which resulted in optic chiasm compression and panhypopituitarism. CLINICAL CASE: Case of a 28-years-old female who initially presented with recurrent headaches for which brain imaging was done and a suprasellar mass was noted. It initially measured2.3x 3.2x 2. 0 cm. The mass was invading the left cavernous sinus and displacing the pituitary gland and infundibulum to the right. At that time no optic chiasm compression was noted, and no pituitary hormonal excess or deficiency was identified. The mass was treated conservatively with gamma knife radiation, with reduction in size. About 10 months later, patient complained of visual problems for which brain imaging was repeated and noted with interval increase in tumor size. Patient was started on dexamethasone due to mass effect and referred to ER. Review of systems at that time was remarkable for oligomenorrhea and decreased peripheral vision. Patient denied general malaise, dizziness, galactorrhea, weight changes, palpitations, dry skin or striae, bowel changes, polyuria, increased thirst nor changes in shoe or ring size. Physical examination showed unremarkable vital signs. Upon confrontation there was evidence of bitemporal hemianopsia confirmed on formal visual field testing. Laboratory studies showed mildly elevated prolactin, low-normal TSH with mildly low FT4 suggesting overt central hypothyroidism and suppressed morning cortisol. Patient was scheduled for craniotomy, which resulted in an overall decrease of tumor bulk. After the surgery, patient developed DI requiring desmopressin administration. Currently, patient continues with panhypopituitarism treated with hormonal replacement. Pathology report was compatible with a GCTB. On follow up MRI about 6 months after surgery, there was mild interval increase in size, no distant metastases identified. Treatment with denosumab was started as recommended by oncology service in an attempt to control tumor growth. At this time, patient has tolerated denosumab well and has not developed further headaches or visual symptoms. Follow up imaging is pending to assess response to treatment. CONCLUSION: GCTB of the sella-suprasellar region, albeit rare, have been described and always should be included in the differential diagnosis of sellar lesions. Imaging alone is insufficient to make a definitive diagnosis of these tumors and tissue sampling either by biopsy or surgical resection should be considered in order to determine treatment alternatives. Presentation: No date and time listed