Radiography
Findings
Conventional radiography has no role in the diagnosis of APA.
Computed Tomography
Findings
Axial enhanced CT scan in a 32-year-old woman who presented with hypertension shows a low-attenuating 2.8-cm suprarenal mass (A) (same patient as in Image 1 in Multimedia). Histologic results obtained after surgery confirmed a tumor due to Conn syndrome.
Axial nonenhanced CT scan through the adrenal glands in 56-year-old man shows multiple nodules in both glands, although biochemical results indicated primary aldosteronism. The patient received medical treatment.
Axial enhanced CT scan in a 56-year-old man shows no enhancement of the adrenal masses (same patient as in Image 3 in Multimedia).
Axial nonenhanced CT scan through the adrenal glands in a 60-year-old patient who presented with hypertension and hypokalemia shows a bilobulated tumor in the right adrenal gland.
Axial enhanced CT scan through the adrenal glands in a 60-year-old patient who presented with hypertension and hypokalemia shows minor tumor enhancement (same patient as in Image 5 in Multimedia). Note the normal left adrenal gland.
A 59-year-old man was referred for renal ultrasonography as a part of the workup for newly diagnosed hypertension. The sonogram depicted a 3-cm right adrenal mass, which was regarded as an incidentaloma (not shown). Axial enhanced CT scan through the adrenal gland shows minor patchy enhancement in a right adrenal tumor.
After a diagnosis of hyperaldosteronism has been established clinically and biochemically, dedicated CT scanning of the adrenal glands is performed using thin (3-mm) collimation. Nonenhanced and enhanced CT scans are obtained.6,7,9,12,13
The mean attenuation level in adrenal adenomas is -2.2 HU. Among hyperfunctioning adenomas, aldosteronomas have the lowest attenuation levels. In patients with primary hyperaldosteronism, CT scan findings may be normal, or scans may show nodular or multinodular glands.
Degree of Confidence
CT scanning has a sensitivity of 60-80% in detecting APAs. CT appears more reliable at revealing tumors larger than 1 cm. Conversely, 20% of tumors may be missed. In one series, the average diameter of an APA was 18 mm, and 20% tumors were smaller than 1 cm. With earlier-generation CT scanners, the sensitivity for detecting APAs was 50-70%. The sensitivity of current scanners has been improved to 82-88%. The specificity of CT scanning in the detection of APAs is 77%.6,7,12,13
False Positives/Negatives
CT scan findings of ipsilateral or contralateral, nonfunctioning adenomas lead to a false-positive diagnosis of adrenal hyperplasia. CT scanning is not reliable in distinguishing hyperplasia from adenoma in patients with multiple, bilateral nodules.
Magnetic Resonance Imaging
Findings
Early experience with MRI in the diagnosis of APA has been encouraging. APAs are iso-intense or hypo-intense relative to the liver on T1-weighted images; they are slightly hyperintense on T2-weighted images. Chemical-shift imaging is a useful method for the characterization of adrenal masses. It is based on the principle that fat protons precess faster than do water protons. Chemical-shift MRI is highly sensitive and specific for the differentiation of benign from malignant adrenal tumors, because benign adrenal tumors contain fat, while malignant adrenal tumors rarely do. With chemical-shift imaging, the signal intensity has been found to decrease on out-of-phase images in 86% of patients with APAs and in 89% of patients with bilateral adrenal hyperplasia.8,9,10,11
Degree of Confidence
A sensitivity of 70-100% and a specificity of 64-100% have been reported in the detection of APAs with MRI.8,9,10,11
False Positives/Negatives
False-positive diagnoses have occurred in cases of idiopathic hyperaldosteronism, bilateral nodular hyperplasia, primary hypertension, and primary hypertension associated with nonfunctioning adrenal adenoma.
Ultrasonography
Findings
Longitudinal sonogram through the left kidney in a 32-year-old woman who presented with hypertension shows a 3-cm hypoechoic but solid mass superior to the upper pole of the kidney. Initially, the mass was regarded as a nonfunctioning adenoma unrelated to the patient's hypertension. Subsequently, mild hypokalemia developed. Surgical resection confirmed a tumor due to Conn syndrome.
Ultrasonograms may reveal a significantly sized APA, but because APAs tend to be small, the overall sensitivity of ultrasonography is poor. Compared with the adrenal tumors in Cushing disease, larger APAs are easier to identify, because neither retroperitoneal nor subcutaneous fat is obtrusive, as it is with Cushing disease.
Degree of Confidence
Ultrasonographic findings contribute little to the diagnosis unless the adrenal tumor is large, which is seldom the case. However, ultrasonography is an excellent modality for the investigation of hypertension.
False Positives/Negatives
The exact sensitivity of ultrasonography in the diagnosis of APA is not known, but it appears to be low. Similar to other types of cross-sectional imaging, ultrasonography may incidentally demonstrate nonfunctioning masses in the adrenal glands.
Nuclear Imaging
Findings
Scintigram obtained by using iodine-131-6β-iodomethylnorcholesterol (NP-59) in a 59-year-old man with hypertension shows fairly intense radionuclide uptake in the right adrenal tumor (same patient as in Image 7 in Multimedia). At surgery, a Conn tumor was confirmed.
Iodine-131-6 β -iodomethylnorcholesterol (NP-59) is a cholesterol analog that binds to low-density lipoprotein receptors of the adrenal cortex and is the primary radionuclide used to image the adrenal cortex.12 Imaging is usually performed after dexamethasone suppression to reduce high background tracer uptake by the zona fasciculata. The normal glands (which show uptake of the radionuclide) are identified on day 5 or thereafter. Early, bilateral depiction of the glands (that is, before day 5) implies adrenal hyperplasia, whereas early, unilateral early depiction implies an APA. Detection rate of APA can be improved by using single-photon emission CT (SPECT) scanning.13
Degree of Confidence
CT scanning is an excellent modality for the detection of APAs; bilateral hyperplasia is usually inferred by the absence of an adrenal tumor. In contrast, NP-59 scanning provides a specific diagnosis of adrenal hyperplasia. Accuracy and sensitivity of 80-95% can be obtained. Smaller adenomas, which are not clearly depicted on CT scans, can be detected on NP-59 scans.13
False Positives/Negatives
Primary aldosteronism must be clinically and biochemically diagnosed before the radionuclide study is performed, because secondary hyperaldosteronism produces bilateral tracer uptake that is indistinguishable from that of primary, autonomous, bilateral hyperplasia. In addition, all drugs that disturb the renin-angiotensin-aldosterone axis must be withdrawn before imaging. The extremely rare mineralocorticoid-secreting carcinoma also demonstrates NP-59 uptake.13
Scintigraphy must be performed in the appropriate clinical setting, because NP-59 uptake has been described in benign, nonsecretory adenoma, as well as in metastatic lung cancer, metastatic colon cancer, lymphoma, myelolipoma, ganglioneuroma, adrenal cysts, and adrenocortical carcinoma. Tracer uptake at extra-adrenal sites also has been reported.13
Angiography
Findings
Because APAs are small and are not usually vascular, selective adrenal angiography is seldom helpful. However, adrenal phlebography has a useful role in the investigation of APA, because the splaying of veins around APAs can help in identifying even small tumors. If contrast medium is refluxed into the veins of the APA, a wheel-spoke pattern is seen in the intratumoral veins. Because APAs are small, a vigorous retrograde venous injection is usually required to detect the tumors; this vigorous injection is not without risk, because extravasation may occur.
Extravasation is a particular problem if the catheter is wedged into the vein. Extravasation can be painful and has been associated with adrenal infarction. Adrenal vein thrombosis is also a known complication of adrenal phlebography, which has been linked to adrenal infarction. Adrenal insufficiency has been described as a result of bilateral adrenal infarction. Adrenal vein thrombosis is more likely to occur if the catheter is wedged in the adrenal vein and left there for several minutes during the procedure.
The most useful technique in the investigation of primary aldosteronism is adrenal venous sampling.7,9,14 Blood samples are obtained from both adrenal veins for aldosterone level analysis; hormone level ratios are compared with each other and with levels in the inferior vena cava below the adrenal veins. In experienced hands, this technique can achieve a high sensitivity; however, it is a time-consuming procedure that necessitates prolonged cannulation of adrenal veins and increases the risk of adrenal vein thrombosis. In addition, the adrenal veins are small, and collecting 7 mL of blood for sampling is not easy. This is particularly a problem when blood is collected from the right adrenal vein, in which a short vein enters the inferior vena cava directly.
Some venous samples thus acquired may be diluted by blood from the inferior vena cava on the right and from the phrenic or renal vein on the left. To overcome the problem of dilution, cortisol levels can be measured from the same samples. A low cortisol level suggests dilution by nonadrenal blood, whereas a high cortisol level indicates a relatively pure sample. When aldosterone and cortisol are measured in blood samples from the same site, an aldosterone-cortisol ratio that corrects the concentration of aldosterone for dilution can be calculated.
Degree of Confidence
An accuracy of 95% and a sensitivity of 75% have been reported with adrenal venous sampling. Adrenal venous sampling is required for the definitive diagnosis of primary aldosteronism and for the detection of laterality of the adrenal lesion.14
Zarnegar and colleagues conducted a study of 59 patients with biochemically diagnosed hyperaldosteronism who subsequently underwent unilateral adrenalectomy.15 Clinical decision in proceeding to surgery was based on CT scanning alone (n=30) or on CT scanning and adrenal venous sampling (n=29). The authors found that in the 2 groups, adrenalectomy had similar clinical effects. CT scanning can be used to reliably diagnose adenomas larger than 1.0 cm. The authors recommended that adrenal venous sampling be reserved for cases in which CT scan findings are equivocal or in which both of the patient's adrenal glands are abnormal.
False Positives/Negatives
The dilution of blood from the inferior vena cava on the right and from the renal or phrenic vein on the left can lead to erroneous results in adrenal venous sampling.
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 Imaging: Hyperaldosteronism |
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Further Reading
Keywords
primary hyperaldosteronism, primary aldosteronism, Conn syndrome, aldosterone hypersecretion, adrenal adenoma, adrenal gland tumor, adrenal gland hyperplasia, aldosterone-producing tumor, adrenal gland carcinoma, aldosterone excess, aldosterone-producing adenoma, APA, aldosterone-producing adrenal adenoma, aldosteronoma, secondary aldosteronism, idiopathic hyperaldosteronism
