Pituitary Hyperplasia: To Operate or Not to Operate, That Is the Question

Pituitary hyperplasia is defined as an absolute increase in the number of one or more adenohypophyseal cell subtypes, manifesting radiologically as pituitary enlargement beyond what is considered normal. It has been noted in certain physiological conditions like pregnancy however can also be seen in pathological conditions with end organ insufficiency like severe hypothyroidism. 21- year old female with a past medical history of Primary Hypothyroidism secondary to Hashimoto’s thyroiditis presented initially for evaluation of worsening headache and blurry vision. She was diagnosed with hypothyroidism at 10 years of age and had an extensive family history of hypothyroidism. At the time of presentation, she was 11 months post- partum and had been on and off her levothyroxine supplementation, having stopped it completely for a few months after delivery. MRI brain showed an 18 mm homogeneously enhancing intrasellar mass with suprasellar extension. She was referred to Neurosurgery for further evaluation. Workup revealed a TSH >100 (0.27 - 4.2 mIU/L) and FT4 <0.4 (0.8 - 2 ng/dL). In the context of severe untreated hypothyroidism and MRI findings consistent with pituitary hyperplasia with abutment but no mass effect on the optic apparatus, initial plan was to treat the hypothyroidism medically and observe closely. Patient was started on levothyroxine supplementation. Her TSH improved to 3.367 (0.550 - 4.780 uIU/mL) and FT4 to 2.00 (0.89 - 1.76 ng/dL), ηοωεϖερ she continued to have worsening of visual symptoms. Surgery was considered to decompress the optic nerve, but pre-operative MRI showed a significant decrease in size of the pituitary gland with decreased suprasellar bulging and no mass effect on the optic chiasm. Surgery was subsequently cancelled. Prolonged primary hypothyroidism leads to pituitary hyperplasia due to loss of negative feedback from lack of circulating T4 and T3, leading to excessive TRH secretion from the hypothalamus. The high TRH can lead to thyrotroph as well as lactotroph hyperplasia. Subsequently patients can present with headache, vision changes along with signs and symptoms of hypothyroidism and increased prolactin secretion. It is important to differentiate hyperplasia from other sellar lesions like pituitary macroadenoma or hypophysitis. Patients with hypothyroidism, who have pituitary enlargement diagnosed on brain imaging, should be promptly diagnosed and treated with thyroid hormone replacement. With a higher frequency and improved quality of imaging techniques, we are increasingly coming across scenarios of abnormal findings on imaging. Correlation of radiographic imaging results with a thorough history and biochemical testing is essential prior to proceeding with surgical intervention.