Image of the Month—Diagnosis

The patient underwent transperitoneal laparoscopic left adrenalectomy, which was uncomplicated. Final histologic examination of the left adrenal gland demonstrated cortical hyperplasia involving the zona glomerulosa, fasciculata, and reticularis. There was a nodular proliferation of cells that formed nested groups and trabeculae with round ovid nuclei and vesicular to clear cytoplasm. These features were compatible with adrenal hyperplasia. At a follow-up of 12 months postoperatively, the patient was cured of hypokalemia with a serum potassium concentration of 4.2 mEq/L without supplements. Her hypertension was not cured but she had improved control. Her blood pressure was 130/80 mm Hg with 50 mg of atenolol every morning and 30 mg of nifedipine every morning.

Primary hyperaldosteronism is one of the most common causes of secondary hypertension. It was first described in 1955 by Conn¹as a syndrome characterized by hypertension, hypokalemia, and excessive urinary excretion of aldosterone secondary to an adrenal cortical adenoma. Aldosterone-producing adenoma and bilateral adrenal hyperplasia account for more than 95% of PH cases.²Very rarely, PH is caused by unilateral adrenal hyperplasia (UAH).³According to a recent review of 30 cases,³UAH occurs in patients with a median age of 49 years and affects mainly men (male to female ratio, 1.7:1). However, the results from another recent study of 15 patients demonstrated that the sex distribution was equal (male to female ratio, 7:8).⁴

Adrenal venous sampling is the most accurate test for the detection of UAH and remains the gold standard.³Postural studies are unpredictable, with a sensitivity of only 77%.³Although computed tomography successfully detected a nodule in our case, it generally only has a sensitivity ranging from 40% to 53% in correctly localizing UAH.³Adrenal scintigraphy is equally unreliable in the detection of this pathologic abnormality, with a sensitivity of 50%.³

Unilateral adrenalectomy is the treatment of choice for patients with PH secondary to UAH, as these patients demonstrate excellent outcome after surgery. At a median follow-up of 1 year, more than 95% of patients are completely cured or have improved control of their hypertension and almost all of the patients are cured of hypokalemia.³These excellent results are similar to those of unilateral adrenalectomy for PH secondary to aldosteronoma.⁵

Presently, although it is being increasingly recognized as a unique pathologic cause of PH, the existence of UAH remains controversial. The follow-ups of reported cases have been relatively short, with most cases followed up for less than 2 years.³It remains to be seen whether these cases of UAH will stay cured with longer follow-up or whether they will relapse and thus prove to be cases of bilateral disease. The initial success of unilateral adrenalectomy reported in some cases of bilateral adrenal hyperplasia lends support to the argument that hyperplasia of the adrenal glands in bilateral adrenal hyperplasia may occur at different times.⁶Hence, long-term follow-up in larger numbers of patients is required to determine whether UAH is a truly unique clinicopathologic entity or whether UAH may just represent bilateral adrenal hyperplasia presenting initially with asymmetrical hyperplasia and aldosterone production.

In conclusion, recognition of UAH as a rare cause of PH is important because it is surgically curable. Its existence lends support to the argument that adrenal venous sampling should be performed in patients with PH without localizing signs on cross-sectional imaging, as approximately half of these lesions cannot be detected on imaging.

Correspondence:Brian K. P. Goh, MBBS, MRCS, MMed (Surgery), Department of Surgery, Singapore General Hospital, Outram Road, Singapore 169608 (bsgkp@hotmail.com).

Accepted for Publication:September 12, 2006.

Author Contributions:Study concept and design: Goh. Acquisition of data: Goh, Tan, and Tran. Analysis and interpretation of data: Goh, Tan, Yip, and Cheng. Drafting of the manuscript: Goh. Critical revision of the manuscript for important intellectual content: Goh, Tan, Tran, Yip, and Cheng. Administrative, technical, and material support: Tan, Yip, and Cheng. Study supervision: Goh, Tan, Tran, and Cheng.

Financial Disclosure:None reported.