SUN-619 Thyroid Carcinoma Masquerading as Pituitary Tumor: A Rare Diagnosis Not to Miss in the Evaluation of a Sellar Mass

Background Metastatic disease constitutes 1-2% of sellar masses. The majority of pituitary metastases are secondary to lung or breast cancer. Rarely thyroid cancer metastasizes to the pituitary gland setting off diagnostic and therapeutic challenges. We present such a case in a patient with no known history of thyroid cancer. Clinical case A 73 year old woman with history of right breast ductal carcinoma in situ, presented with headaches and left sided vision loss. MRI scan showed a large 6.5 x 3.5 x 4.6 cm sellar mass extending into the clivus, nasal cavity and maxillary, sphenoid and cavernous sinuses with bilateral optic nerve compression. Biopsy of the nasal mass revealed malignant clusters of follicles with scattered intranuclear pseudoinclusions and grooves and immunostaining was positive for thyroid transcription factor 1 and thyroglobulin, consistent with metastatic thyroid carcinoma. PET scan showed a hypermetabolic left hemithyroid mass, the large hypermetabolic destructive skull base mass and a few suspicious right sided cervical lymph nodes. She had a palpable left sided thyroid nodule, seen on ultrasound as 2.9 cm lobulated, rim calcified nodule that was positive for papillary thyroid cancer on fine needle aspiration biopsy. Preoperative thyroglobulin level was >30,000 ng/ml (normal 1.6-55 ng/ml). She underwent a combined endonasal transsphenoidal partial resection of the large sellar mass and total thyroidectomy. Postoperative thyroid pathology was consistent with angioinvasive follicular thyroid cancer (FTC), and surrounding lymph nodes were negative for malignancy. She has recovering vision in both eyes. The residual sellar tumor was treated with fractionated external beam radiation therapy. This was followed by adjuvant radioactive iodine ablation for stage IVc FTC. Conclusion In patients found to have an extensive sellar mass, prompt workup should be done to identify etiology, keeping an open mind to rare pathologies. Pituitary metastases more commonly present with symptoms related to mass effect in the sella than hormone deficiencies. Usually patients with thyroid cancer pituitary metastases already have known thyroid cancer, often with additional metastases. This case is unique in that the patient presented with signs and symptoms of mass effect from an extensive sellar mass. In scenarios with coexisting sellar mass and thyroid nodule it is very important not to miss the possibility of thyroid cancer with metastases to the pituitary gland.