Background: Although, the diagnostic accuracy of magnetic resonance imaging (MRI) has increased in recent years, it may fail to detect secretory adenoma in a few patients with GH excess. Managing such patients with acromegaly can be challenging. We present a case where 11C-methionine PET/CT co-registered with SPGR/volume MRI proved to be helpful in identifying GH secreting pituitary adenoma.
Case history: A 42-year-old male was referred by surgeons with clinical features of acromegaly. He was 192 cm tall with large hands, significant prognathism and shoe size of 13. His only complaint was hyperhidrosis. He was normotensive with normal glucose tolerance. Visual field was intact and echocardiogram showed borderline LVH. Biochemical tests confirmed GH excess with random GH values between 2030 μg/l and IGF1 103 nmol/l (reference range 1337 nmol/l). Oral GTT confirmed autonomous growth hormone production (nadir GH 27.5 μg/l). Rest of the pituitary function tests were unremarkable. Post-contrast pituitary MRI, undertaken at two centers and reviewed at two others, revealed an enlarged, partially empty sella with no obvious surgical target. Medical management was initiated. Dopamine agonists did not have any significant impact. Prior to commencement of long-term somatostatin analogues, further imaging was arranged at a specialist center. 11C-methionine PET/CT co-registered with SPGR/volume MRI detected a resectable pituitary adenoma. He underwent endoscopic removal of the tumor. Immunochemistry confirmed somatotroph adenoma. Results of post operative IGF1 and dynamic GH testing are awaited.
Conclusion: This case highlights the utility of complex imaging modalities in localization and treatment of secretory adenomas of the pituitary gland which are not identified routinely by conventional techniques. In addition to possibility of achieving a cure, this approach has significant cost benefit bearing in mind that this gentleman in his 40s would have been committed to long term somatostatin analogue treatment.