Pituitary hyperplasia mimicking macroadenoma secondary to primary hypothyroidism

Objective – We aim to emphasize the importance of extensive endocrine workup in cases of pituitary masses. Case report – We report on a case of pituitary thyrotrophic hyperplasia in a 12-year-old girl who was thought to have a pituitary macroadenoma with suprasellar extension. The main complaint was headache, while other symptoms of hypothyroidism were present, but weren’t recognised. Hormonal testing revealed low total thyroxine (<12.8 nmol/l) and high TSH (310.5 mIU/l) levels, and hyperprolactinemia (prolactin level at 1680 mIU/l). Based on the clinical history, laboratory data, and MRI, a diagnosis of pituitary hyperplasia secondary to primary hypothyroidism, consequent to chronic autoimmune thyroiditis, was made. Therapy with levothyroxine was initiated at 50 µg/day and gradually increased to 75 µg daily. After three months of thyroxine replacement, she was clinically and biochemically euthyroid. A follow-up MRI, 4 months after thyroxine replacement was initiated, showed complete resolution of the mass, and normal pituitary gland. Conclusion – Primary hypothyroidism should be considered in the differential diagnosis of pituitary masses. Multidisciplinary assessment in these cases will help to avoid delays in diagnosis and prevent unnecessary surgery.