MON-308 Pituitary Magnetic Resonance Imaging in the Postoperative Follow-Up of Patients with Acromegaly, Less Is More!
Authors: Fernandes Stuti , Varlamov Elena V , Stack Madeleine , Johnson Nathaniel , Cetas Justin S , Dogan Aclan , Yedinak Christine G , Fleseriu Maria 
Published: May 2020

Abstract
Background Patients (pts) with acromegaly (A) require long term follow up, as up to 15% will develop recurrence. Current guidelines for MRI surveillance recommend 12 week post-operative (postop) imaging for all pts and yearly if on pegvisomant (PEG). Many pts with residual tumor postop undergo repetitive imaging even when controlled with pituitary (PIT) directed therapies. However, gadolinium retention and healthcare costs are of increased concern. Aim Assess tumor growth postop and necessity of serial MRI in medically treated A pts. Methods Retrospective, IRB-approved, data analysis of pathology-proven A pts. Included were pts with at least 1 MRI at ≥1 year postop. Initial tumor size, invasion status, pathology, postop remission, MRIs, radiation and medical therapy data were collected. Biochemical (biochem) remission = normal IGF-1 and GH &lt;1 at 3 mo postop. For pts with radiation, data was only collected up to radiation. Stats: t-test, chi-square. Results 83 pts were included; mean age 46±16 years, 45% female, mean follow up 7.9±5.3 years. 55 pts were on PIT-directed therapy (50 on somatostatin receptor ligands (SRL) alone, 1 on cabergoline (Cab) alone, 4 on SRL/Cab), 12 on PEG &gt; 1 year (9 on PEG alone.) 11/83 (13.25%) had tumor growth at median 3.5 years (range 1-11). Tumors that grew were larger at diagnosis (25.21±10.93 mm vs 17.45±8.37 mm, p=0.004), had larger residuals postop (23.83±5.0 mm vs 11.86±7.47 mm, p=0.0003), and tended to be invasive (77.78% (7/9) vs 53.03% (35/66), p=NS). 7/11 were sparsely granulated and 4 mixed GH-PRL. Of 11 that grew, 8 had postop residual tumor, 3 in remission, 4 with discrepant IGF-1/GH, 2 uncontrolled and 2 with no data at 3 months postop. At the time of growth, 9/11 pts were untreated (6 had active A, 1 with discrepant IGF-1/GH and 2 with no IGF-1/GH data), 1 was controlled on pasireotide and one in biochem remission. Only 1/50 (2%) pts on pasireotide had growth and no pts on PEG &gt;1 year. Discussion 86.75% of pts with A did not have tumor growth after surgery. Only one pt on PIT-targeted medications and none on PEG experienced tumor growth. Almost all pts who had growth had large invasive adenomas, majority were sparsely granulated, residual tumor postop, were biochemically uncontrolled and not on medication at the time of growth. A previous metanalysis of SRLs in A showed that tumor increase occurs in 1.4% (follow up 3-36 months). In our study pt follow up was longer and 1.82% (1/55) of pts who were on SRL/Cab had growth. Conclusion We recommend less frequent MRI monitoring for pts treated with PIT-targeted medications. Conversely, pts with residual adenoma not on medical therapy should be closely monitored biochemically and by serial MRIs. Further studies are needed to identify appropriate imaging interval for pts on medications and based on characteristics of aggression (such as sparsely granulated, large residual tumors, lack of biochemical control despite medications).