Normal pituitary hypertrophy as a frequent cause of pituitary incidentaloma: A follow-up study

Enlargement of the pituitary gland is a frequent cause of incidentaloma and of referrals to endocrinologists for hormonal evaluation and therapeutic a dvice. In neuroradiological series, 25-50% of healthy women who are 18-35 y r old have a convex superior pituitary contour, but pituitary height exceed s 9 mm in less than 0.5% of cases. This study was performed to provide thorough clinical and hormonal data and long-term endocrinological and imaging follow-up data on subjects with inc identally discovered pituitary hypertrophy (height > 9 mm). Seven eugonadal nulliparous women, 15-27 yr old, referred between 1989 and 1998 with incid entally diagnosed pituitary gland enlargement (height > 9 mm) and a suspect ed pituitary tumor, were studied. At presentation and at yearly intervals, PRL plasma levels and corticotropic, somatotropic, and thyrotropic pituitar y function were measured; and pituitary dimensions and signal on magnetic r esonance imaging (MRI), before and after iv gadolinium-diethylenetriamine-p entaacetic acid injection, were assessed. PRL plasma levels were normal; and corticotropic, somatotropic, and thyrotr opic pituitary function was considered normal in all cases. In all the wome n, the upper boundary of the pituitary was convex, on MRI, and touched the optic chiasm in four cases. The width and anteroposterior diameter of the g land were normal. The pituitary itself seemed normal, with a homogeneous si gnal, on plain and dynamic studies with iv contrast injection. Despite norm al initial hormone values, two women underwent surgery, by the transsphenoi dal approach, in another center. During surgery, the pituitary seemed norma l in both cases, with no evidence of tumoral or inflammatory processes. Bio psy specimens showed the morphologic characteristics of a normal, nonhyperp lastic pituitary gland. All seven women were seen at yearly intervals for 2 -8 yr (median, 4 yr). Clinical and hormonal status remained stable, as did the structure and size of pituitary, on serial MRI. No tumor formation occu rred, supporting the diagnosis of physiologic hypertrophy of the pituitary gland. In conclusion, these observations suggest that careful examination of MRI r esults may help to distinguish physiologic pituitary hypertrophy from pitui tary tumors and infiltrating lesions. The former diagnosis is confirmed by normal baseline pituitary function in extensive hormonal tests. Correct ide ntification of such patients is important to avoid unnecessary pituitary su rgery and costly MRI surveillance.