Most PHEOs and PGLs are characterized by excessive production of catecholamines, and thus, biochemical evidence of catecholamine production is an elementary step in diagnosis. Historically, biochemical diagnosis of PHEO/PGL relied on the measurement of urinary and plasma catecholamines (epinephrine and norepinephrine) together with measurement of urinary levels of catecholamine metabolites and vanillylmandelic acid. These tests can often lead to false negatives due to fluctuating levels of catecholamine release in many PHEOs/PGLs [10, 28]. Since PHEOs/PGLs often secrete catecholamines episodically, plasma or urinary levels of catecholamines may be normal. Approximately 30% of PHEOs/PGLs do not secrete catecholamines, even if they still synthesize them or they do not secrete catecholamines in amounts sufficient enough to produce the classical clinical presentation of a tumor with positive test results [52, 53]. Moreover, catecholamines are normally produced by the adrenal medulla and sympathetic nerves. Thus, high catecholamine levels are present in multiple different diseases and conditions and are not specific for these tumors [53].

On the other hand, metanephrines, the O-methylated metabolites of catecholamines, are produced continuously within PHEO/PGL cells, and their production is independent of catecholamine release [54, 55]. Therefore, diagnostic evaluation of plasma-free or urine-fractionated (i.e., normetanephrine and metanephrine measured separately) metanephrines is preferred and is currently the most sensitive diagnostic test (97% sensitivity and 93% specificity for measurement for plasma-free metanephrines) [8, 56–63]. Plasma metanephrines are usually measured in the free form. Metanephrines in urine are measured after deconjugation, although measurement of urine-free metanephrines is also possible [64, 65].

When interpreting the results, differentiating between a mild and high increase in catecholamine or metanephrine levels is very important. In patients with biochemically active tumors, an increase is usually two to four times higher than the upper reference limit. Mildly elevated levels of catecholamines are mostly due to interfering medications [10] (Table 12.6). If it is difficult to distinguish an increased catecholamine release due to sympathetic activation or from the presence of PHEO/PGL, a clonidine suppression test can be performed [66, 67]. Under physiologic conditions, clonidine suppresses release of neuronal norepinephrine (and so normetanephrine). A decrease in elevated plasma normetanephrine levels by ≥40% or within the reference limits after clonidine is administered indicates that sympathetic activation is the cause of elevation. Failure to depress plasma normetanephrine supports the presence of PHEO/PGL [67]. The clonidine suppression test has a high diagnostic sensitivity when combined with measurement of plasma normetanephrine responses to suppression. False positive elevations in plasma normetanephrine levels can be accurately identified with the combination of these tests. However, the reliability of the test can be compromised by tricyclic antidepressants and diuretics [42], as well as in patients with normal or only mildly elevated plasma catecholamine levels, despite the presence of PHEO/PGL [8].

In addition to measurement of metanephrines, recent evidence suggests that plasma 3-methoxytyramine is a biomarker for dopamine-producing tumors. Although it is currently only available in certain research centers, measurements of this biomarker are valuable for detecting very rare, exclusively dopamine-producing tumors (due to the lack of dopamine β-hydroxylase), which can be easily overlooked by solely measuring metanephrines [68, 69]. Moreover, methoxytyramine can also serve as an indicator of malignancy [4]. Exclusively dopamine-secreting tumors can also be detected by measuring serum levels of dopamine. Measurement of urinary dopamine levels is not useful, since it reflects dopamine production in the renal tubules, not in a potential tumor [27].

A nonspecific biomarker of neuroendocrine tumors, chromogranin A , is often measured in PHEO/PGL patients. Chromogranin A is commonly secreted by chromaffin cells, and its levels are elevated in 91% of patients with PHEO/PGL [70]. Despite its nonspecificity, chromogranin A , in combination with catecholamine measurement, can facilitate the diagnosis of PHEO/PGL, especially in tumors related to mutations in succinate dehydrogenase (SDH) subunit B gene [71, 72]. Chromogranin A is also a helpful diagnostic tool in patients with biochemically silent tumors and in disease monitoring [73, 74].

In very rare cases, PHEOs/PGLs can co-secrete other hormones, for example, ACTH or cortisol. These patients often present with the clinical picture of Cushing disease in addition to PHEO/PGL [75–77].

Determining the biochemical phenotype of PHEO/PGL can also be helpful in navigating further investigation and treatment, specifically localization of the tumor by imaging studies, genetic screening, determining the presence of metastatic disease, and an appropriate adrenergic blockade. Based on the type of catecholamines secreted, PHEOs/PGLs can be divided into three basic biochemical phenotypes: (a) adrenergic (epinephrine/metanephrine), (b) noradrenergic (norepinephrine/normetanephrine), and (c) dopaminergic (dopamine/methoxytyramine). Mixed phenotypes are common, and in such cases, PHEO/PGL-producing metanephrine and normetanephrine are considered adrenergic, and those secreting normetanephrine and methoxytyramine are considered dopaminergic. Since epinephrine/metanephrine are produced almost exclusively (99%) in the adrenal gland, adrenergic biochemical phenotype is typical for PHEO (Table 12.5).

Although PHEOs/PGLs are rare tumors, a large number of patients are tested for these tumors in the process of differential diagnosis for secondary hypertension as well as other diseases. Because of this, false-positive results are expected, and they may outnumber true-positive results, even when tests with high specificities are used. This requires follow-up biochemical testing in patients with initially positive results, to confirm or rule out PHEO/PGL. However, when judging the likelihood of a PHEO/PGL from a single test, the degree of initial clinical suspicion or pretest probability of the tumor should be taken into account, which impacts the posttest probability of a tumor [7]. Moreover, patients with known hereditary syndromes associated with PHEO/PGL or with a history of tumors should periodically undergo screening. Biochemical testing is also used to confirm the success of surgical treatment and to evaluate activity of the disease in patients with metastases.

To ensure the reliability of biochemical test results, it is crucial to guarantee certain conditions during blood sample collection . Before collection of blood for measurements of plasma-free metanephrines, patients should be lying supine in a quiet room for at least 20–30 min with a previously inserted intravenous line (to minimize sympathoadrenal activation associated with venipuncture or upright posture) [53, 78]. Alternatively, with a higher risk of false-positive results, the sample may be collected from a seated patient, provided that upper reference limits obtained after supine rest are used [79]. If seated test returns back positive, it should be repeated after rest in supine position to rule out false positivity of initial test [8].

Although 24-h urine collection seems to solve the problem with the rigid conditions needed for blood sampling, it is not that simple. Twenty-four-hour urine results are not always accurate because of unreliable collection from the patient. Samples are also often influenced by diet and the activation of sympathoneuronal and adrenal medullary systems (e.g., during physical activity or changes of posture). To ensure more controlled conditions for urine collection, some investigators advocate spot or overnight urine collections with normalization of output catecholamines or metanephrines against urinary creatinine excretion [8, 80].

Blood samples should be stored on ice immediately after collection and separated plasma at −80 °C upon analysis. Urine samples should be refrigerated during the collection period while using HCl as a preservative. Urine sample aliquots should be stored frozen at −80 °C to minimize auto-oxidation and deconjugation [53].

When evaluating a patient for possible PHEO/PGL, it is necessary to ask the patient about their current medications. Certain compounds can increase catecholamine levels or interfere with the diagnostic analysis and, thus, result in catecholamine/metanephrine false positives [78]. The major source of interference is tricyclic antidepressants, which can lead to significant elevation of plasma or urinary metanephrines due to inhibition of catecholamine reuptake. Acetaminophen, a drug commonly used for pain and fever, as well as mesalamine and sulfasalazine, can interfere with high-performance liquid chromatographic (HPLC) assays used for measurement of catecholamines [67, 81]. An anxiolytic agent, buspirone, can cause falsely elevated levels of urinary metanephrine in some HPLC assays [67]. Other compounds that may distort catecholamine/metanephrine measurements are listed in Table 12.6.

Anatomical imaging of PHEO/PGL should initially focus on the abdomen and pelvis, followed by the chest and neck if abdominal and pelvic scans are negative [59]. Computed tomography and MRI are widely used in the diagnostic workup for PHEO/PGL, and these modalities have been reported to have similar diagnostic sensitivities [10], although MRI may be superior to CT in detecting extra-adrenal tumors in certain locations (e.g., cardiac) [8]. Ultrasound is not recommended for initial PHEO/PGL localization. Exceptions include ruling out tumors in children and pregnant women, when MRI is not available.

Excellent spatial resolution, wider availability, and a relative low cost suggest a CT scan of the abdomen, with or without contrast, as an initial PHEO/PGL localization method [28]. Computed tomography can be used to localize tumors 1 cm or larger. The sensitivity of CT is approximately 95%, with specificity roughly 70% [83]. Use of intravenous contrast media is preferred to enhance the specificity of the method. However, the CT scan may fail to localize recurrent PHEOs/PGLs because of postoperative anatomical changes and the presence of surgical clips.

An MRI with or without gadolinium enhancement is a very dependable imaging method with sensitivity >95% and specificity similar to CT (70–80%) [10, 84, 85]. MRI has a high sensitivity in detecting adrenal lesions (93–100%) and is a good imaging modality for the detection of intracardiac, juxtacardiac, and juxtavascular PGLs. Moreover, MRI offers feasibility of multiplanar imaging and superior assessment of the relationships between tumor and surrounding vessels. This is important in the evaluation of patients with tumors in the adrenal and cardiac areas and for ruling out vessel invasion. The sensitivity of MRI for detection of extra-adrenal, metastatic, or recurrent PHEOs/PGLs is around 90%. Thus, MRI is preferred in patients with head and neck PGLs and metastatic disease and in patients with CT contrast allergies or in whom radiation exposure is contraindicated (pregnant women, children, patients with known germline mutations, patients with recent excessive radiation exposure) [10, 28].

Functional imaging plays an important role in PHEO/PGL workup. Specificity of anatomical imaging studies for PHEO/PGL is not sufficient. Thus, functional studies are needed to confirm the presence of a PHEO/PGL. Functional imaging may also help detect primary and/or metastatic tumors that could be missed on anatomical studies. It is also used to characterize the metabolic activity of the tumors in vivo and for restaging aggressive tumors following treatment completion [86]. Functional imaging studies are enabled by the presence of the cell membrane and/or vesicular catecholamine transport systems in PHEO/PGL cells. Functional imaging modalities used to confirm PHEO/PGL and/or metastatic disease include ¹²³I-metaiodobenzylguanidine (¹²³I-MIBG) scintigraphy, 6-¹⁸F-fluorodopamine (¹⁸F-FDA), ¹⁸F-dihydroxyphenylalanine (¹⁸F-DOPA), ¹¹C-hydroxyephedrine, and ¹¹C-epinephrine (not used anymore) positron emission tomography (PET) [87–93]. Currently, these methods are not widely available, and if needed, patients are referred to specialized centers.

In metastatic PHEO/PGL, tumor dedifferentiation may lead to loss of specific neurotransmitter transporters, resulting in difficulties with its localization. In such cases, ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET imaging or somatostatin receptor scintigraphy may be required. Metastatic PHEOs/PGLs often express somatostatin receptors, which enables somatostatin scintigraphy with the somatostatin analogue octreotide (octreoscan) or DOTA peptides analogues (⁶⁸Ga-DOTA(0)-Tyr(3)-octreotate (DOTATATE) PET/CT) [94–97].

Immediately after diagnosis, all patients with biochemically active PHEO/PGL should be placed on sufficient adrenoceptor blockade to control symptoms and reduce the risk of hypertensive crises and organ damage mediated by the effects of released catecholamines [6]. There is no consensus regarding the drugs recommended for preoperative management because of wid e-ranging practices, international differences in available or approved therapies, and a lack of studies comparing different medications. However, α-adrenoceptor antagonists, calcium-channel blockers, and angiotensin-receptor blockers are recommended [28, 141]. Drugs that can be used in symptom management and presurgical blockade, with suggested doses, are listed in Table 12.8.