T2-weighted MRI signal predicts hormone and tumor responses to somatostatin analogs in acromegaly.

GH-secreting pituitary adenomas can be hypo-, iso- or hyperintense on T2-weighted MRI sequences. We conducted the current multicenter study in a large population of patients with acromegaly to analyze the relationship between T2-weighted signal intensity on diagnostic MRI and hormonal and tumoral responses to somatostatin analogs (SSA) as primary monotherapy. Acromegaly patients receiving primary SSA for at least 3 months were included in the study. Hormonal, clinical and general MRI assessments were performed and assessed centrally. We included 120 patients with acromegaly. At diagnosis, 84, 17 and 19 tumors were T2-hypo-, iso- and hyperintense, respectively. SSA treatment duration, cumulative and mean monthly doses were similar in the three groups. Patients with T2-hypointense adenoma had median SSA-induced decreases in GH and IGF-1 of 88% and 59% respectively, which were significantly greater than the decreases observed in the T2-iso- and hyperintense groups (p<0.001). Tumor shrinkage on SSA was also significantly greater in the T2-hypointense group (38%) compared with the T2-iso- and hyperintense groups (8% and 3%, respectively; p<0.0001). The response to SSA correlated with the calculated T2-intensity: the lower the T2-weighted intensity, the greater the decrease of random GH (p<0.0001, r=0.22), IGF-1 (p<0.0001, r=0.14) and adenoma volume (p<0.0001, r=0.33). The T2-weighted signal intensity of GH-secreting adenomas at diagnosis correlates with the hormone reduction and tumor shrinkage in response to primary SSA treatment in acromegaly. This study supports its use as a generally available predictive tool at diagnosis that could help to guide subsequent treatment choices in acromegaly.