Pituitary Hyperplasia and Oncocytic Thyroid Neoplasia in a Child With Severe Hypothyroidism

<h2>Abstract</h2><h3>Background/Objective</h3> Severe pediatric hypothyroidism may cause growth failure and pituitary hyperplasia mimicking adenoma. Although thyroid nodules are rare in children, their malignancy risk is higher than in adults. We report a boy with severe hypothyroidism, growth failure, pituitary hyperplasia, and oncocytic thyroid carcinoma, underscoring the need for comprehensive evaluation. <h3>Case Presentation</h3> A 10-year-old boy presented with growth delay, height 105 cm (<1st percentile, –6.7 SD) and weight 21.2 kg (3rd percentile, –2.03 SD). Examination revealed pallor, dry skin, alopecia, Tanner stage I/I, and bitemporal hemianopsia. Laboratory results showed thyroid stimulating hormone >500 mIU/ml (reference 0.45–4.50 mIU/L), free thyroxine <0.30 ng/dl (reference 0.93–1.60 ng/dl), prolactin 102 ng/ml (reference 5–20 ng/ml), and insulin-like growth factor 1 of 8 ng/ml (reference 123–497 ng/ml). Pituitary magnetic resonance imaging demonstrated a homogeneous, isointense sellar lesion with optic chiasma displacement. Thyroid ultrasound showed a 43.9 mm hypoechoic nodule, and fine-needle aspiration classified it as Bethesda category IV. Total thyroidectomy confirmed encapsulated angioinvasive oncocytic carcinoma, followed by radioactive iodine therapy. With levothyroxine and growth hormone treatment, pituitary hyperplasia regressed, and height increased by 15 cm in one year. <h3>Discussion</h3> Pituitary hyperplasia secondary to hypothyroidism is reversible with levothyroxine and must be differentiated from adenomas to avoid unnecessary surgery. Oncocytic thyroid carcinoma is rare in children, and its coexistence with hypothyroidism is unusual. <h3>Conclusion</h3> This case emphasizes the importance of thyroid function testing in children with growth failure and sellar lesions, and vigilance in evaluating pediatric thyroid nodules given their elevated risk of malignancy.