MAGNETIC-RESONANCE-IMAGING MEASUREMENTS OF PITUITARY-STALK COMPRESSION AND DEVIATION IN PATIENTS WITH NONPROLACTIN-SECRETING INTRASELLAR AND PARASELLAR TUMORS - LACK OF CORRELATION WITH SERUM PROLACTIN LEVELS

PROLACTIN (PRL) LEVELS ARE frequently elevated in patients with non-PR L-secreting adenomas or other intrasellar and parasellar diseases (''p seudoprolactinomas''). This phenomenon is believed to result from a lo ss of dopaminergic inhibition on pituitary lactotrophs and is known as the ''stalk-section effect.'' Using magnetic resonance imaging scans and a high-magnification sella technique, we measured a number of para meters indicative of the disruption of normal sellar structures. The i nvestigator was blind to the patient's diagnosis and PRL level while c ollecting the data. Parameters measured were the tumor size, the angul ar deviation of the pituitary stalk, and the degree of compression of the pituitary stalk. Measurements were obtained from 44 patients with pathologically confirmed tumors that had no immunohistochemical reacti vity to PRL. PRL levels were often higher than expected. Four patients (9%) had a PRL level of move than 150 ng/ml, and three patients (7%) had a PRL level of 200 ng/ml or more. One patient with a plasmacytoma eroding the sella floor had a PRL level as high as 504 ng/ml. There wa s no significant correlation of PRL level and the degree of pituitary stalk compression, stalk deviation, or tumor size. PRL levels were fou nd to be markedly elevated in some patients with a tumor causing littl e distortion of the pituitary stalk. Conversely, PRL levels were often normal despite evidence of massive distortion of the stalk. Therefore , magnetic resonance imaging evidence of pituitary stalk distortion ca nnot be used to determine the diagnosis of prolactinoma versus pseudop rolactinoma in most cases. The lack of correlation of PRL level in pat ients with nonprolactinomas is important in view of recent doubts conc erning the role of the ''stalk-section effect.'' A number of illustrat ive cases are presented.