IMAGING

CT of primary hyperaldosteronism (Conn’s syndrome): the value of measuring the adrenal gland
Lingam RK(1), Sohaib SA(1), Vlahos I(1), Rockall AG(1), Isidori AM(2), Monson JP(2), Grossman A(2),
Reznek RH (1,3)
(1)Department of Diagnostic Imaging, (2)Department of Endocrinology , (3)Academic Department of
Radiology, St. Bartholomew’s Hospital, West Smithfield, London EC1A 7BE, United Kingdom
AJR Am J Roent. 2003; 181: 843-9

• Purpose: The objectives of our study of patients with primary hyperaldosteronism (Conn’s syndrome) were to determine whether the adrenal glands are larger in patients with bilateral adrenal hyperplasia than in those with aldosterone-producing adenomas or in healthy control subjects; and whether a CT criterion based on adrenal gland size can be developed to positively diagnose bilateral adrenal hyperplasia.
• Materials and Methods: A retrospective study of CT scans of 28 patients with primary hyperaldosteronism was performed. The means of two observers’ measurements of adrenal gland size were recorded and compared with published normal values. In addition, a radiologist experienced in adrenal imaging and unaware of the cause of the primary hyperaldosteronism diagnosed either bilateral adrenal hyperplasia or aldosterone-producing adenoma by visual inspection.
• Results: The adrenal glands in patients with bilateral adrenal hyperplasia were significantly (p < 0.05) larger than those in patients with aldosterone-producing adenoma or in healthy control subjects. A sensitivity of 100% was achieved when a mean limb width of greater than 3 mm was used to diagnose bilateral adrenal hyperplasia, and a specificity of 100% was achieved when the mean limb width was 5 mm or greater. Receiver operating characteristic curve analysis showed that the overall performance of the radiologist and the mean adrenal limb width in detecting bilateral adrenal hyperplasia were equivalent.
• Conclusion: In patients with primary hyperaldosteronism, adrenal limb measurements on CT can aid in differentiating bilateral adrenal hyperplasia from aldosterone-producing adenoma because the adrenal glands in bilateral adrenal hyperplasia are larger.
  
  
• Editorial Comment
  Aldosterone-secreting adrenal adenomas are rare tumors, which are responsible for 75% of primary aldosteronism, with adrenal hyperplasia accounting for 25%. Adrenal hyperplasia may be further subdivided into idiopathic (far more common) and primary adrenal hyperplasia. Aldosteronomas are usually small lesions measuring less than 3 cm in diameter and more frequently found on the left side. CT differentiation between adenoma from bilateral adrenal hyperplasia is not an easy task because primary adrenal hyperaldosteronism may be micronodular or macronodular and also because the adrenal glands may appear normal or diffusely thickened. Thus evaluation with CT in patients with primary aldosteronism has its limitations even in the presence of unilateral adenoma. Difficulties increase much more when both adrenals have a nodular appearance. In some patients with hyperaldosteronism the presence of hyperplasic glands may actually contain unilateral aldosteronoma. This report brings to us new and important radiological signs that might help us in the differentiation between bilateral adrenal hyperplasia from aldosterone-producing adenoma. Differentiating between these two distinct causes is fundamental because an aldosteronoma is usually best treated surgically, whereas bilateral adrenal hyperplasia is treated medically. A specificity of 100% was achieved when a mean limb width of greater than 5 mm was used to diagnose bilateral adrenal hyperplasia.

Dr. Adilson Prando
Department of Radiology
Vera Cruz Hospital
Campinas, São Paulo, Brazil