Resistant or multidrug hypertension, hypertension in a young patient, as well as spontaneous hypokalemia in a patient should raise the suspicion for primary hyperaldosteronism. Screening with simultaneous random plasma aldosterone concentration (PAC) to plasma renin activity (PRA) ratio (preferably in the morning after being upright for several hours) showing a value above 20 to 40 suggests positive screening test for primary hyperaldosteronism. Recent meta-analysis, however, raised uncertainty about the screening test characteristics and described lack of standardization [13]. Validated assays for plasma renin and aldosterone have to be used (various centers report a different positive cutoff for positive screening ratios), and medications that severely affect the ratio of measured hormones should be withdrawn. A multicenter study from Italy analyzing PAC/PRA ratios performed under different conditions showed good within-patient reproducibility [14]. A confirmatory test with sodium loading (NaCl tablet, typically 1 g tid × 3 days, or 3 days high-salt diet) and 24-hour urinary collection for aldosterone should follow (urinary aldosterone >14 μg/24 hr has sensitivity of 96% and specificity of 93% for diagnosis of hyperaldosteronism) [15]. A saline infusion test is used very rarely, and a cutoff value of 7 ng/dl for serum aldosterone at the end of infusion gave 100% specificity for diagnosis of primary hyperaldosteronism [16]. Mineralocorticoid deficiency is suspected when hyperkalemia and hyponatremia are present in appropriate clinical situations. No dynamic evaluation is recommended for mineralocorticoid deficiency.

Measurements of catecholamines and their metabolites are essential in the diagnostic evaluation of pheochromocytoma. For physiology and metabolism details, see the pheochromocytoma subchapter.

The utility of various available biochemical tests has been evaluated in various studies. The results of these tests depend on the type of assay used, proficiency, and lack of analytic interference of the particular laboratory and especially normative values for a given reference population. Plasma free fractionated metanephrines have the highest sensitivity (96%—99%) but a lower specificity (85%—89%), depending on the cutoffs a particular laboratory or study uses [17, 18]. Severe stress and various medications could cause false-positive values, but dietary consumption of catecholamine-rich food products did not seem to influence results of measurements of free metabolites compared to deconjugated metabolites [19]. Total urinary metanephrines combined with fractionated free urinary catecholamines have also been reported to have a relatively high sensitivity and excellent specificity for catecholamine tumor diagnosis [20]. The threshold for positive plasma metanephrine test plays a significant role in diagnostic accuracy [21]. Urinary fractionated metanephrine use is limited by lack of specificity (69%), whereas urinary vanillylmandelic acid (VMA) assays lack sensitivity (65%) [17]. Plasma catecholamine use is limited by multiple compounding factors.

Evaluation of adrenal tests for congenital adrenal hyperplasia is beyond the scope of this chapter. There are some excellent reviews available in the literature [22, 23, 24].

Despite their small size, the adrenal glands are visualized in nearly 100% of patients with CT scanning. The V-shaped right adrenal gland is usually seen directly posterior to the inferior vena cava (IVC) and measures approximately 1 × 2 × 0.5 cm. This gland is nearly the same width as the diaphragmatic stripe. The left adrenal gland, which has a similar size and shape, is located anterior to the upper portion of the kidney and directly adjacent to the aorta. Adrenal CT scanning remains an excellent initial study in the patient with adrenal disease, and 1 cm contiguous scans are routinely used to demonstrate the location, size, and tissue characteristics of most adrenal masses. This technique can also identify lymphadenopathy, obvious malignancy, and local invasion or distant metastasis associated with adrenal tumors [30]. Thinner scans using 3- to 5-mm slices are often necessary to detect and evaluate smaller functional tumors such as
aldosteronomas. Most pheochromocytomas or adrenal adenomas causing CS are 2 to 5 cm in diameter, whereas most aldosteronomas are 8 mm to 2 cm in size. The main limitation of CT scanning is its periodic inability to separate benign from malignant and functional from nonfunctional tumors of the adrenal. Cysts and myelolipomas are the only benign conditions readily identified with CT scanning. An adrenal lesion with a large amount of macroscopic fat is readily identified as a myelolipoma. Most smooth-walled water density adrenal lesions are cysts, but necrotic metastatic adrenal tumors can appear cystic and have higher density [27]. Benign adrenal adenomas are low density, lipid rich, and have an attenuation value of less than 10 Hounsfield units (HU) measured with the region of interest on noncontrast CT images (NCCT) [27]. For adrenal lesions with density greater than 10 HU, the use of IV contrast improves this distinction and benign adrenal adenomas often exhibit more than an absolute washout percentage of 60% measured 15 minutes after initial enhancement using standard contrast-enhanced CT (CECT) imaging of the adrenal gland [31]. A relative washout percentage, calculated when NCCT density is not available, of over 40% is consistent with benign adrenal disease [32]. Although contrast enhancement may increase accuracy, patients with suspected pheochromocytoma should undergo α-adrenergic blockade before contrast administration to eliminate the small risk of contrast agents precipitating a hypertensive crisis. Comparison to prior adrenal CT imaging remains important, as the volume and dimensions of benign adenomas are usually stable and only enlarge very gradually, if at all. Significant growth is frequently associated with malignancy, although adrenal hemorrhage can cause rapid enlargement in benign adrenal tumors [29]. Many surveillance imaging schedules exist for incidentally detected presumed benign adrenal tumors. While some believe this may be excessive, a reliable recommendation is for 6-month, 1-, 2-, and 3-year follow-up cross-sectional imaging to confirm lesion stability and exclude adrenal cortical malignancy. Primary adrenal malignancy should be considered in large adrenal masses with calcification, necrosis, or hemorrhage. CT of the adrenal gland has reported sensitivity, specificity, and accuracy rates of 84%, 98%, and 90%, respectively [4, 11]. Percutaneous biopsy of the adrenal gland is rarely indicated but can be safely performed by using CT guidance techniques. The left adrenal gland is usually more difficult to access for biopsy with this technique because of its posterior location [33].

Magnetic resonance imaging (MRI) is gaining widespread acceptance as the initial study in the evaluation of adrenal masses because of its superb soft tissue contrast, natural enhancement of certain pathologic adrenal masses, and the lack of ionizing radiation. MRI characterizes adrenal tumors by their signal characteristics on different pulse sequences and by their enhancement characteristics. It also allows multiplanar imaging to depict the relation between the adrenal mass and the kidney [34]. MRI accurately identifies benign adrenal adenomas, myelolipomas, adrenal cysts, malignant or metastatic adrenal tumors, and pheochromocytomas and generally augments information obtained with CT [35]. MRI reliably distinguishes between adenoma and metastasis in most cases and allows accurate oncologic staging, limited adrenal biopsies, and initiation of appropriate treatment regimens in the affected patient population. Chemical-shift techniques using breath-hold T1-weighted gradient echo (GRE) images can rapidly and reliably identify benign adrenal adenomas through the accurate detection of their characteristic high intracellular lipid content [34, 36]. Chemical-shift MRI offers little advantage over NCCT, but some continue to recommend this technique to differentiate lipid-rich benign adenomas from their
lipid-poor indeterminate or malignant counterparts [27]. Normal adrenal glands and adrenal tumors larger than 1 cm in diameter can be visualized in more than 90% of patients with these images, but MRI is not able to distinguish functional from nonfunctional cortical adenomas of the adrenal. T2-weighted images, however, can demonstrate unique signal intensities. Hyperintense T2-weighted images suggest the presence of pheochromocytoma, and MRI can also be useful in locating extra-adrenal pheochromocytomas. The MRI signal intensity of adrenal cortical carcinomas is variable, and they generally are heterogeneous on T1- and T2-weighted images. These tumors often appear as large, necrotic, poorly marginated retroperitoneal masses of uncertain origin where MRI fails to identify a normal ipsilateral adrenal gland [37]. These aggressive neoplasms often invade into the renal vein or IVC, and this venous extension can also be demonstrated on MRI. MRI is also an attractive imaging modality for children and pregnant patients with adrenal disease because of its lack of ionizing radiation.

Hormone production in the adrenal cortex begins with cholesterol, and several radiolabeled cholesterol analogs have been developed to allow localization and functional information regarding adrenal cortical tumors. The only one currently approved for use in the United States is [¹³¹I]-⁶β-iodomethylnorcholesterol (NP-59). Unfortunately, NP-59 scanning has been largely abandoned as it is difficult to obtain, expensive, time consuming, and involves significant radiation exposure to the patient. The material, however, is safe to administer, and the accuracy rate of NP-59 to identify and distinguish correctly a Cushing adrenal adenoma or an aldosteronoma from bilateral adrenal hyperplasia approaches 90% [38]. Detection of aldosteronomas with NP-59 requires discontinuation of diuretic and antihypertensive medication, and accuracy rates are increased if the patients are pretreated with dexamethasone.

Metaiodobenzylguanidine (MIBG), a radiolabeled derivative of guanethidine with no pharmacologic effect, was developed in 1980. It is the most frequently used substance to image the adrenal medulla and other sympathetic tissues. It is incorporated into sympathetic nerve cells as a catecholamine precursor. [¹³¹I] MIBG is the most commonly used isotope, but recent studies suggest that¹²³I is more accurate with less radiation exposure to the patient. Single-photon emission computed tomography technology may also improve the sensitivity and accuracy of this imaging tool. MIBG scanning is diagnostic for neoplasms producing excess catecholamine and has successfully detected pheochromocytomas, neuroblastomas, and other neuroendocrine tumors such as paragangliomas, carcinoid tumors, and medullary carcinomas of the thyroid. The most common role for MIBG is in patients with a biochemical diagnosis of pheochromocytoma and normal conventional adrenal imaging studies. MIBG can identify paragangliomas and metastatic pheochromocytomas to guide further imaging. The sensitivity and specificity of MIBG scanning for pheochromocytoma and neuroblastoma are between 80% and 100%. An alternative to MIBG is radiolabeled octreotide [¹¹¹I(indium)]-DTPA (diethylenetriaminepenta-acetate) octreotide, which can detect paragangliomas and neuroendocrine tumors containing cell-surface receptors for somatostatin [39]. Unfortunately, this imaging modality is only 30% sensitive [40]. The use of MIBG may be decreasing with the adoption of positron emission tomography (PET) scanning, which often demonstrates increased FDG activity [41].

Several different radiopharmaceuticals can detect increased cellular activity in hyperfunctional adrenal states more specifically than does conventional imaging. These agents can also target specific adrenal enzymes that are expressed in adrenal tumor cells. As an example, [¹⁸F]fluorodopamine PET scanning allows tumor visualization within minutes of injection of the imaging agent, and spatial resolution is excellent. Malignant cells are frequently glucose avid, and PET scanning with the glucose analog¹⁸F-fluoro-deoxyglucose (¹⁸F FDG) is effective in differentiating benign from malignant and metastatic adrenal lesions with 97% sensitivity and 91% specificity [42, 43]. PET scanning also correctly localizes adrenal and extra-adrenal pheochromocytomas that lack the ability to concentrate MIBG [44, 45]. PET imaging is now frequently combined with CT imaging (CT/PET) to assess both the gross appearance of the lesion and its metabolic activity [27].

Adrenal vein sampling is useful in patients with functional tumors of the adrenal glands such as in patients with CS or primary hyperaldosteronism. These patients have normal or equivocal findings on CT, MRI, or adrenal scintigraphy, and these imaging studies cannot distinguish between a unilateral aldosteronoma requiring adrenalectomy from bilateral adrenal hyperplasia treated medically [46]. Although the left adrenal vein is accessible in nearly all patients, the right adrenal vein can be more difficult to cannulate. Patients with primary hyperaldosteronism receive an infusion of cosyntropin, and blood from both adrenal veins and the distal IVC is measured for both aldosterone and cortisol. Adrenal vein cortisol should be five times greater than IVC cortisol to verify the position of the venous catheter in the adrenal vein. The ratios of aldosterone to cortisol for both adrenal veins are compared, and a ratio of 4:1 or greater reliably identifies a small unilateral aldosteronomas, whereas a ratio of less than 3:1 usually indicates bilateral adrenal hyperplasia [47]. Selective venous sampling in patients with CS is performed in a similar manner without the infusion of cosyntropin. Cortisol levels from both adrenal veins and the IVC are compared to distinguish between bilateral adrenal hyperplasia and adrenal adenoma in patients with CS.

Primary hyperaldosteronism is the excessive autonomous adrenal secretion of aldosterone, resulting in elevation of PAC and suppression of PRA. While the exact cause is unknown, this syndrome results in a rare form of surgically correctable hypertension, polyuria, weakness, hypokalemia, sodium retention, and mild metabolic alkalosis. A small, benign, unilateral, aldosterone-producing adrenal tumor, first described by Jerome Conn in 1955, was historically the most common cause of primary hyperaldosteronism in 70% of patients. Currently though, the contemporary incidence of idiopathic bilateral macronodular or micronodular hyperplasia of the adrenal cortex causing primary hyperaldosteronism has increased to over 50%, largely due to widespread screening of hypertensive patient populations [48, 49]. Other far less common causes of primary hyperaldosteronism include unilateral primary adrenal hyperplasia detected by adrenal venous sampling (AVS), glucocorticoid-suppressible hyperaldosteronism, a rare familial form of hypertension that affects 1% to 3% of patients with primary hyperaldosteronism [50], and aldosterone-producing adrenal carcinoma [51].

The prevalence of primary hyperaldosteronism in unselected patients with hypertension is 0.5% to 2%, but centers routinely obtaining PAC/PRA ratios detected primary hyperaldosteronism in 8% to 15% of their hypertensive patients, representing a 10-fold increase in this diagnosis [52]. Age at diagnosis ranges between 30 and 60 years, and about 1% of all adrenal masses discovered incidentally are found to be aldosterone-producing adrenal adenomas. Aldosteronomas occur more commonly in female patients, by a 2:1 ratio, and are rare in children. Patients with aldosteronomas tend to be younger, have more severe hypertension and hypokalemia, have higher urine and serum aldosterone levels, and respond better to spironolactone than patients with bilateral adrenal disease. Bilateral idiopathic adrenal hyperplasia causing primary hyperaldosteronism is more common in men and usually appears in patients at an older age when compared to aldosteronoma. High blood pressure is present, but this sign is a common medical problem and is not sufficiently specific to identify this endocrinopathy. Although hypertension in these patients is often of moderate severity, multiple medical regimens to control blood pressure are usually unsuccessful, causing the diagnosis of primary hyperaldosteronism to be considered [50].

Aldosterone is the final product in the biosynthesis of mineralocorticoids produced from the zona glomerulosa of the adrenal cortex. Factors stimulating the synthesis and release of aldosterone include angiotensin II, potassium, ACTH, and decreased renal perfusion or circulating blood volume. The clinical manifestations of primary hyperaldosteronism arise from the autonomous production of aldosterone, causing altered sodium and potassium homeostasis. Aldosterone normally enhances the reabsorption of sodium from the distal renal tubules in exchange for potassium and hydrogen excretion. Excessive aldosterone secretion leads to sodium and water retention and increased potassium and hydrogen excretion. The result is volume expansion and hypertension, suppressed PRA, hypokalemia, and metabolic alkalosis [48]. Serum sodium levels usually remain normal because of a parallel increase in the water content of the blood, but mild hypernatremia can be present. Hypokalemia appears to be responsible for most of the clinical symptoms of primary hyperaldosteronism, such as proximal muscle weakness and cramps, polyuria, polydipsia, nocturia, headache, and fatigue.

Exogenous administration of glucocorticoids (iatrogenic or factitious) is the most common cause of CS. Approximately 80% of patients with endogenous CS have ACTH-dependent disease, most frequently caused by pituitary microadenomas (i.e., Cushing disease; see Chapter 1) [69]. Overproduction of ACTH in ACTH-dependent Cushing may also be due to ectopic overproduction of ACTH or corticotropin-releasing hormone (CRH), caused by certain malignancies (Table 3.1) [70]. The excessive ACTH or CRH production leads to overproduction of cortisol by adrenal glands. In ACTH-independent CS (15%—20% of endogenous causes), autonomous increase in cortisol production by adrenal glands is found, resulting in suppression of ACTH. The etiology of this autonomous cortisol overproduction is represented by: adrenal adenomas, adrenal carcinomas, bilateral or unilateral macronodular adrenal hyperplasia, and micronodular adrenal hyperplasia. The expression of certain ectopic promiscuous receptors (gastric inhibitory polypeptide, vasopressin, β-adrenergic receptors, serotonin, and luteinizing hormone receptors) in adrenocortical cells explains some of the causes of macronodular adrenal hyperplasia [71]. Certain conditions such as affective disorders, stress, and obesity can lead to mild elevations in plasma or urinary cortisol levels, the so-called pseudo-Cushing state. The entity of subclinical CS (SCS) is described in the section on adrenal incidentalomas.

The clinical manifestations of hypercortisolism are common to all forms of CS and include hypertension; central obesity; diabetes mellitus [72]; acne; androgenic hirsutism; signs of protein catabolism such as myopathy, osteopenia, or osteoporosis; cutaneous lesions (i.e., wide violaceous striae, tinea versicolor, verrucous vulgaris, ecchymosis); hyperpigmentation; and psychiatric manifestations (depression, cognition, and vegetative function). Increased thrombotic events
were well documented in recent meta-analysis [73].The classic features may not be present in ectopic ACTH production from malignancies, because of shorter duration of hypercortisolemia. Impaired quality of life is seen in patients with CS after remission of CS [74].