SAT-196 The Use of 11C-metomidate PET-CT to Detect Unilateral Primary Hyperaldosteronism

Background Identifying causative adrenal lesions presents a significant diagnostic burden for physicians and radiologists. We describe the use of radiolabelled metomidate to lateralise primary hyperaldosteronism. Case presentation A 52-year old Chinese man with a 5-year history of hypertension was referred for hypokalemia [K 2.7 mmol/L (3.6 - 5.0)]. He had been on Telmisartan 80 mg and Amlodipine 10 mg daily and blood pressure at home ranged 110-120 / 70-80 mmHg. There was no history of poor oral intake, persistent diarrhea or vomiting, and he was not on any other prescription or alternative medications. There was no significant family history of hypertension or sudden cardiac death. Clinic blood pressure was 140/84 mmHg. There were no features suggestive of Cushing’s syndrome. Repeat biochemical tests confirmed hypokalemia (K 3.1 mmol/L), and associated raised bicarbonate 37.3 mmol/L [19 - 29]. Magnesium and creatinine were normal. Aldosterone-renin Ratio was elevated at 8.1 (serum Aldosterone 611 pmol/L [97.3 - 834.0], active renin 2.7 pg/ml [1.8 – 59.4]). Post-saline infusion, non-suppressible serum aldosterone levels of 1137 pmol/L was demonstrated, consistent with autonomous aldosterone production. A computed tomography of the adrenal revealed a 2.3 cm x 1.9 cm nodule on the left adrenal gland consistent with lipid rich adenoma. Adrenal vein sampling (AVS) under continuous synacthen infusion was performed. Adrenal to peripheral cortisol ratio was ≥10 for either adrenal veins, confirming cannulation of the adrenal veins. Aldosterone-cortisol ratios showed lateralization to the left adrenal gland (lateralization ratio of 10.35). There was contralateral suppression of the right adrenal gland with ratio of 0.41. 11C-Metomidate PET-CT scan demonstrated a maximum standardised uptake value (SUVmax) of 26.8 over the left adrenal nodule, while the SUVmax of the right adrenal gland was 16.2. Ratio of the left to right adrenal gland SUVmax was 1.65 (above the threshold of 1.25); and was concordant with AVS. This confirmed that the patient had a left functional adrenal adenoma responsible for hyperaldosteronism. Our patient underwent a left adrenalectomy, and histology was consistent with adrenal cortical adenoma. Prior to surgery he required 72 mmol/l of potassium supplementation daily to maintain K levels of 3.3 – 4.0 mmol/L. Two weeks post-operatively, he was normokalemic (K 4.9 mmol/L) without potassium supplementation. Serum aldosterone normalized to 159.3 pmol/L (active renin 9.3 pg/ml). Blood pressure is well controlled on amlodipine 5mg daily. Conclusion Targeted molecular imaging such as 11C-Metomidate PET-CT could aid localisation of functional adrenal disease to guide definitive surgical management. In the future, this could obviate the need for invasive and technically complex procedures like AVS.