Pituitary microadenomas exhibit slow growth and may require less frequent MRI surveillance

1. In this retrospective cohort study, two-thirds of incidental pituitary microadenomas remained unchanged or decreased in size over a median follow-up of 4.91 years.

2. Smaller (less than or equal to 4mm) and larger (greater than 4mm) pituitary microadenomas were more likely to increase and decrease in size over time, respectively.

Evidence Rating Level: 2 (Good)

Study Rundown: Current guidelines, published in 2011, recommend pituitary magnetic resonance imaging (MRI) after initial pituitary microadenoma diagnosis. Further, it is recommended this be followed by annual or biannual imaging for the next three years. No updated guidelines have been proposed, likely due to the paucity of new evidence in this area. In this retrospective cohort study, patients with pituitary microadenomas identified at the Mass General Brigham, Boston, Massachusetts, between 2003 and 2021 had their imaging analyzed. Microadenoma size resulted in minimal change, with two-thirds of cases having stable or decreased size over time. Tumors with a baseline size of 4mm or less were more likely to increase in size during follow-up. Conversely, those with a baseline tumor size of more than 4mm tended to decrease in size. Less than 2% of the total microadenomas progressed to macroadenomas. In terms of limitations, this study used a retrospective design, and there were large variabilities in MRI study intervals and follow-up durations between patients.

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In-Depth [retrospective cohort study]: In this retrospective cohort study, patients (n=414) diagnosed with a pituitary microadenoma (tumor size ≤10 mm) from the Mass General Brigham, Boston, Massachusetts, between 2003 and 2021 were included. The patient median follow-up time was 4.91 years (95% Confidence Interval [CI], 3.88 to 5.32 years). In total, 44%, 19%, and 28% of microadenomas remained unchanged, decreased, or increased in size, respectively. A small proportion of microadenomas (1.7%) progressed to macroadenomas (adenomas over 10 mm). A mixed model linear regression analysis was used to estimate the pituitary microadenoma size trajectory over time. For all patients, the estimated slope was 0.016 mm/year (CI, -0.038 to 0.069). For tumors sized 4mm or less, the size tended to increase (estimated slope 0.09 mm/year; CI, 0.020 to 0.161). For tumors over 44mm, the size tended to decrease (estimated slope -0.063 mm/year; CI, -0.141 to 0.015). This study supports revised guidelines recommending increasing the time interval between pituitary MRIs in patients with pituitary microadenomas of limited size.

Image: PD

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