Objective: To analyze the difficulty in diagnosis of pituitary hyperplasia secondary to primary hypothyroidism and reasons of misdiagnosis.
Methods: Ten patients with clinical manifestations of primary hypothyroidism, 3 males and 7 females, aged 7 - 26, underwent MR imaging and serum hormone examination before and after thyroid hormone replacement therapy. T1-weighted images without and with contrast material enhancement in sagittal and coronal planes were obtained. Serum free triiodothyronine, free thyroxine, thyrotropic-stimulating hormone and prolactin (PRL) levels were measured.
Results: Obvious symmetrical enlargement of the pituitary gland with homogeneous signal intensity was revealed by MRI in all the patients. The height of the pituitary ranged 1.2 - 2.2 cm. The pituitary glands appeared homogeneously enhanced after Gd-DTPA administration. After 3 - 6 months of L-thyroxin replacement therapy, follow-up MRI showed that the pituitary glands reduced in size markedly in 9 cases, and the plasma thyroxine, TSH, and PRL levels of these 9 cases turned normal. One patient was misdiagnosed as with macroadenoma and was treated with gamma knife, resulting in permanence hypothyroidism.
Conclusion: Symmetrical enlargement of pituitary gland with homogeneously enhancement on MRI has great diagnostic value in pituitary hyperplasia with primary hypothyroidism. Thyroid hormone replacement therapy can cause regression of the enlarged pituitary, thus avoiding unnecessary surgery.