Conn syndrome

Conn syndrome (or primary hyperalderosteronism) is a condition of excess of aldosterone production and occurs secondary to adrenal cortical adenoma, bilateral adrenal hyperplasia, or rarely, adrenal carcinoma. Differentiation between the causes is required to avoid unnecessary surgery. 

Clinical presentation

Conn syndrome typically presents with diastolic hypertension, metabolic alkalosis, and hypokalaemia. Other symptoms include muscular weakness, paresthesias, headache, polyuria, and polydipsia. Oedema is rare in these patients. 


Primary hyperaldosteronism is distinguished from secondary hyperaldosteronism by measurement of serum renin:

  • primary: low renin levels
  • secondary: high renin levels

Conn syndrome is due to an autonomous solitary adrenal cortical adenoma in 33% of cases, with the remainder almost entirely due to bilateral adrenal hyperplasia (66%) with adrenal carcinoma being a rare cause 6.

Excess secretion of aldosterone can also occur in renin-related hypertension. 


The aldosterone level tends to increase and the aldosterone:renin retio is also increased.

Biochemical analysis may also demonstrate hypokalaemia, which may be the first clue to the diagnosis of aldosteronoma in a patient being evaluated for hypertension. The baseline plasma aldosterone is usually greater than 20 g/dL.

Radiographic features

Adrenal adenomas in Conn syndrome tend to be unilateral (95%) quite small, often ~ 2 cm (range 1-5 cm) in diameter, and can be a challenge to detect, even by CT or MR imaging.

Selective adrenal arteriography, venous sampling, adrenal phlebography, radionuclide studies and CT scans are helpful in diagnosis. 

  • aldosteronomas are homogeneous and often hypodense, with an attenuation value near that of water (<10 HU)
  • none or minimal contrast enhancement
  • rarely calcify
  • detects 70% of aldosteronomas, although small lesions may be missed
  • if CT findings are negative, selective adrenal venous sampling for aldosterone or a dexamethasone suppressed iodocholesterol adrenal scan may identify the lesion

Adrenal venous sampling to assay aldosterone serum via selective catheterization of both adrenal veins, may still only be helpful in ~50% of cases. 

Treatment and prognosis

If a solitary adrenal mass is detected, surgical adrenalectomy will correct hypertension in 75-90% of cases. Bilateral adrenalectomy in patients with hyperplasia is not usually an effective treatment and results in adrenal insufficiency and is usually treated medically. Thus differentiation between the causes is required to avoid unnecessary surgery. 

History and etymology

It is named after J W Conn, who first described the condition in 1955 4.

See also

Updating… Please wait.


Error Unable to process the form. Check for errors and try again.

Alert_accept Thank you for updating your details.