Primary hyperaldosteronism: discordant imaging and adrenal venous sampling results

L Rich, K Bradley, D Wynick acknowledging J Jackson and K Meeran

1Musgrove Park Hospital, Taunton. 2University Hospitals, Bristol.

Primary hyperaldosteronism (PA) is more prevalent than once thought. It is estimated to occur in over 10% of hypertensive patients, with normokalaemia being more common than coexisting hypokalaemia. It is characterised by hypertension due to excessive and vastly autonomous production of aldosterone and is due to bilateral idiopathic hyperaldosteronism in 60% of cases and an aldosterone producing adenoma in 35%. It is important to diagnose as patients with PA have an increased risk of cardiovascular disease and mortality compared to age and blood pressure matched controls and curative intervention or effective treatment is often possible.

We present a case of PA in a 48 year old man with a 10 year history of drug resistant hypertension with a potassium level between 3.1 and 4.2 mmol/L. He was obese but had no other significant past medical history or family history. His aldosterone: renin ratio, whilst on an ACE inhibitor, was >3800 making PA highly likely. He subsequently underwent confirmatory testing with a saline infusion test in which the aldosterone failed to suppress thus confirming the diagnosis of PA.

In line with current guidance he had imaging in the form of an adrenal CT with contrast which revealed a left sided 6 mm adrenal nodule with 97% absolute washout. The imaging characteristics were in keeping with an adrenal adenoma. Adrenal vein sampling (AVS) was carried out at the Hammersmith hospital and the cortisol levels in all the adrenal vein samples indicated correct siting of the catheter. The left adrenal vein aldosterone: cortisol ratio (A/C) was suppressed (aldosterone 1560 pmol/L, cortisol 482 nmol/L, A/C 3.2) whilst the right adrenal vein ratio was markedly elevated (aldosterone 30000 pmol/L, cortisol 942 nmol/L, A/C 31.8). The cortisol-corrected aldosterone lateralisation ratio from the right adrenal to the left was approximately 10:1 thus indicating predominantly unilateral secretion of aldosterone from the right adrenal and not the left adenoma containing gland. The patient is currently awaiting a laparoscopic resection of the right adrenal gland.

The Endocrine Society clinical practice guidelines 2008, give detailed recommendations for the management of PA. It is well recognised that imaging alone is insufficient to localise the site of aldosterone excess and AVS should be attempted in all patients being considered for surgery. The sensitivity and specificity of AVS for detecting unilateral aldosterone hypersecretion is 95% and 100% respectively, compared to adrenal CT (78% and 75% respectively). Evidence has shown that imaging misdiagnoses the cause of PA in approximately 40% of patients. In the majority of cases AVS was able to lateralise the site of production when CT was not, thus preventing patients from being excluded from potentially curative surgery. As was the case with our patient around 15% to 20% of cases had discordant findings with AVS demonstrating aldosterone excess from the imaging defined normal gland.

Our case and the evidence above highlight the importance of using all the resources available when considering surgical treatment for primary hyperaldosteronism.