Pituitary hyperplasia refers to non-neoplastic growth or enlargement of pituitary gland cells without qualitative changes in cell biology, which include physiological, pathological, syndrome-related (such as Addison disease, Klinefelter syndrome, and Turner syndrome) and idiopathic subtypes.[9] Pituitary hyperplasia caused by primary hypothyroidism is due to the loss of thyroxine feedback inhibition to the hypothalamus, which can induce the overproduction of TRH and hyperplasia of lactotrophs. Here, TRH is linked to Turner syndrome.