ODP333 Mucosal-Associated Lymphoid Tissue Lymphoma: a Rare Condition in the Differential Diagnosis of a Parasellar Mass

The differential diagnosis for sellar and parasellar masses is broad and includes pituitary tumors, inflammatory lesions, meningioma, and lymphoma. In rare cases, the latter can manifest as extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT)-subtype. We report a case of MALT-lymphoma presenting as a parasellar mass. A 68-year-old woman presented with several months of diplopia, cognitive slowing, and progressive balance issues. Brain MRI revealed a 4.6×2.3×1. 0 cm dural skull-based lesion extending from the left tentorium cerebelli to the left cavernous sinus and sella with mass effect on the optic chiasm and pituitary gland. Hormonal assessment revealed elevated prolactin at 93 ng/mL (NR 2.8-29.2) thought to be due to stalk effect. There were no abnormalities in other axes. CSF analysis demonstrated elevated protein (211 mg/dL, NR 15-45) and was negative for malignant cells. Due to the degree of cavernous sinus involvement, the mass was deemed surgically unresectable. Her PCP started dexamethasone 10mg daily for her neurologic symptoms, resulting in subsequent symptomatic improvement, reduction in mass size, and normalization of prolactin. However, she experienced weight gain, glucose intolerance, and fatigue, so dexamethasone was tapered and stopped after a 5-month course. Nine months later, she re-presented with symptoms of a sixth cranial nerve palsy. MRI demonstrated interval increase in mass size, protrusion into the left sella, and possible upward displacement of the pituitary. No pituitary hormone deficiencies were noted. Tumor biopsy and debulking revealed MALT-lymphoma. She received external beam radiation (200 cGy/fraction for 12 fractions) with improvement in symptoms and size of the mass. A PET-CT showed no evidence of other FDG-avid lesions. Follow-up MRI showed resolution of the mass with only minimal thickening along the left cavernous sinus. She continues to follow with Endocrinology post-radiation therapy for hormonal monitoring. Her pituitary axes have remained intact for 7 years. Steroid-responsive sellar and parasellar masses often invoke associations with inflammatory conditions such as sarcoidosis and idiopathic hypertrophic pachymeningitis. Lymphoma, and in particular MALT-lymphoma, also need to be considered in the differential diagnosis for these lesions. MALT-lymphomas of the central nervous system (CNS) tend to occur in women and arise from the dura. In one retrospective analysis, about 50% of cases occurred as primary lymphoma in the CNS while the remaining had systemic disease. Ten out of 13 subjects (77%) in a case series of primary CNS MALT-lymphoma had a complete response to surgery, chemotherapy, and/or radiation therapy. In a separate retrospective analysis, 3 out of 70 subjects (4.3%) experienced a recurrence over a median follow-up of 23 months after treatment. Given the importance of radiation therapy to the management of these tumors, Endocrinologic follow-up is essential given the increased risk of hypopituitarism after intracranial radiation. Presentation: No date and time listed