FRI351 Pituitary Stalk Epidermoid Cyst: A Rare Cause Of Diabetes Insipidus

Disclosure: J.T. Batch: None. F. Warda: None. P. Natter: None. R. Makary: None. G.Y. Gandhi: None. Introduction: Epidermoid cysts are benign squamous epithelial cysts filled with keratin. They are rarely found in the central nervous system, constituting 0.2-1.8% of intracranial masses, with the majority located in the cerebellopontine angle. Case Report: A 34-year-old female presented with blurred vision, debilitating headaches, milky breast discharge, and no menstrual periods for three years. Prolactin was mildly high on two occasions at 40.3 and 52.8 ng/mL (3.0-30.0 ng/mL). Estradiol was low at 15 pg/ml in the setting of inappropriately normal FSH (10.1 mIU/mL) and LH (5.8 mIU/mL). ACTH, cortisol, TSH, free thyroxine, and IGF-1 were in the normal range. A pregnancy test was negative. A 1:100 diluted prolactin did not detect the hook effect. MRI revealed a 1.8 x 1.4 x 1.4 cm suprasellar mass centered along the pituitary stalk with peripheral enhancement and central cystic vs. necrotic components. It caused a mass effect on the optic chiasm. Formal visual field testing revealed a left inferior temporal defect. Subsequently, the patient reported increased thirst (consuming 4-5 L of water daily) and urination (confirmed with a 24-hour urine output of 4 L). Following 12 hours of overnight water deprivation, morning labs confirmed diabetes insipidus with high serum sodium of 146 mmol/L, high serum osmolality of 306 mOsm/kg, and low urine osmolality of 204 mOsm/Kg. Initiation of oral DDAVP 0.1 mg nightly resulted in a resolution of nocturia and dramatic improvement in thirst. The patient underwent transsphenoidal resection, during which the neurosurgeon identified a suprasellar cystic lesion with classic epidermoid pearl white material. The lesion and capsule were resected, and patient started on dexamethasone 6 mg IV every 6 hours to prevent chemical meningitis. Pathology was consistent with an epidermoid cyst. Prolactin stained several cells, possibly from compression of the pituitary stalk by the epidermoid cyst. Postoperatively, the patient had severe headaches, and photophobia thought to be associated with chemical meningitis. Lumbar puncture revealed elevated CSF neutrophils and aseptic culture. The patient was continued on dexamethasone with slow taper upon discharge. DDAVP was increased to 0.1 mg twice daily as polyuria and polydipsia worsened. Discussion: There have been six reported cases of epidermoid cysts involving the pituitary stalk. Visual disturbance and headaches are common, while galactorrhea and amenorrhea are uncommon. Preoperative polyuria can be a frequent presenting symptom that can evolve into permanent postoperative diabetes insipidus. Surgical resection is the treatment of choice. It may be difficult to achieve complete excision due to the adherence of the cyst wall to the adjacent structures. The most common complications after resection include chemical meningitis (noted in our patient), hydrocephalus, infectious meningitis, and cranial nerve palsies. Presentation: Friday, June 16, 2023