12612 Chiasmal Herniation - A Rare Complication Of Prolactinoma Treatment

Abstract Disclosure: A. Syeda: None. V. Kantorovich: None. Introduction: Primary treatment of symptomatic prolactinomas is medical therapy with dopamine agonists (DA). Herniation of optic chiasm is a rare complication of tumor shrinkage induced by DA therapy which causes secondary deterioration in visual fields. Case:A 26-year-old man presented to our hospital after a syncopal episode. He had headaches and blurry vision in the left eye for the past 4 months. He was diagnosed with a 4 cm x 3.6 cm x 2.6 cm pituitary macroprolactinoma compressing the optic chiasm, his prolactin (PRL) was 4700 ng/mL (N: 4.0-15.2 ng/mL) and testosterone was suppressed to 10 ng/dL (N: 249-836 ng/dL). Other hormonal workup was unremarkable. Ophthalmologic evaluation was consistent with left optic nerve pallor and neural rim thinning suggestive of a guarded prognosis. Immediate neurosurgical intervention was deemed unnecessary. Cabergoline 0.25 mg twice a week was initiated. Subsequently, the PRL levels improved but remained elevated to 414.2 ng/mL and cabergoline dose was increased to 0.5 mg twice a week. MRI Brain after 10 months revealed significant tumor reduction to 2.1 cm x 2.1cm x 1.2 cm. He was inconsistent with his endocrinology follow up appointments and was also non-adherent to cabergoline intermittently. After 14 months of starting DA therapy, he presented with worsening blurriness in his left eye. A repeat brain MRI showed stable appearance of the large pituitary macroadenoma with inferior bowing of the optic chiasm. Significant distortion, tented appearance, and attenuation of the left prechiasmatic optic nerve was also noted. He was evaluated by neuro ophthalmology and a diagnosis of secondary visual deterioration due to optic chiasmal herniation was made. Cabergoline therapy was promptly discontinued. Two weeks post-cabergoline cessation, he underwent trans-sphenoidal resection reporting vision improvement pre-surgery. Post-operative MRI depicted changes with no residual tumor and improved optic chiasm position. Discussion:Various theories explain chiasmal herniation with dopamine agonist (DA) treatment for prolactinomas. Pre-existing chiasm-tumor tethering may exacerbate downward pull during tumor reduction caused by DA therapy. Some case series have suggested that not all patients with chiasmal herniation have visual field defects and that despite improvement in visual fields with decrease in DA dosage, there are no appreciable radiographic changes/reversal of chiasmal herniation. One of the explanations for this lack of correlation is that visual impairment is rather a consequence of vascular compression. This case underscores the need for regular perimetry in macroprolactinoma patients on medical treatment. Adjusting dopamine agonist dosage to allow controlled tumor regrowth, monitored closely with frequent visual field and prolactin assessments, is crucial for relieving optic chiasm tension. Presentation: 6/3/2024