The Joint Annual Scientific Meetings of the Endocrine Society of Australia and the Society for Reproductive Biology 2018

False positive Iodine-123 (123-I) metaiodobenzylguanidine (MIBG) scintigraphy in large adrenocortical neoplasm (#286)

Ayanthi A Wijewardene 1 , Kathy Tucker 1 , Ivan Ho-Shon 1 , Sue Mei Lau 1
  1. Department of Endocrinology, Prince of Wales Hospital, Randwick, NSW, Australia

 Iodine-123 (123-I) metaiodobenzylguanidine (MIBG) scintigraphy has a high sensitivity of 85-96%  and specificity of 95-100% for the detection of phaeochromocytoma.  False positive result can occur in younger patients with small adrenal lesions with moderate, often bilateral uptake. Only four reported cases have described a false positive MIBG study in large adrenocortical adenoma. Our case describes an example of a false positive MIBG in a large adrenocortical neoplasm.

 An 18yo male was found to have a large incidental adrenal mass. He had a background of left frontal anaplastic oligodendroglia managed previously with surgical resection, chemotherapy and radiation therapy at the age of 8. Computed tomography showed a left suprarenal mass measuring 78x 56x 17mm. The mass has numerous vessels coursing through it towards a central necrosis. There was washout of the lesion in the delayed scan. These features were suggestive of phaechromocytoma. Blood pressure remained within normal parameters . The adrenal mass was non-functioning with normal plasma metanephrines and normetanephrines, 24 hour urine metanephrines and normetaphrines. Aldosterone to renin ratio was also normal. MIBG scan showed an irregular, intense tracer accumulation localised to the large left adrenal mass, also suggestive of pheochromocytoma. Left adrenalectomy was undertaken after two weeks of alpha blockade. Histology revealed an  85 x 80 x 60mm mass with yellow friable areas suggestive of central necrosis. The tumour was composed of large epithelioid and polygonal cells with pleomorphic nuclei. Immunohistochemistry stained positively for Calretinin, Melan A, CAM5.2 and AE1/AE3 and was negative for Synaptophysin, Chromogranin A, SOX10, PAX8, Inhibin and HepPAR1. The overall  Ki67 proliferation index was approximately 2% with the focal area approaching 5%. These findings were consistent with adrenal cortical neoplasm and not pheochromocytoma. MLH1 mutation was detected on genetic testing which is associated with Lynch syndrome related cancers.