Pheochromocytoma

Bang Huu Huynh, MD - Case Coordinator
Aaron David Sodickson, MD, PhD - Radiology Discuss
Frank Samuel David, MD, PhD - Pathology Discussion
Pablo R Ros, MD, MPH - Attending Radiologist

October 28, 2002

Presentation

Imaging Findings

The single, non-contrast computed tomography slice demonstrates an apparent soft tissue mass in the left adrenal gland. The image is otherwise unremarkable.

Differential Diagnosis

Diagnosis

Discussion

The left adrenal gland was resected. It measured 5 cm and weighed 47 g. The external appearance was normal. The cross-sectional view reveals an outer rim of normal tissue surrounding a hemorrhagic, white-tan mass. On visual inspection, the mass appeared to be confined to the adrenal gland; this was confirmed by microscopicinspection.

Pheochromocytoma can exhibit a number of microscopic patterns. The trabecular pattern seen in this case is one typical manifestation. The cells are fairly homogeneous, though some pleomorphism is visible. The cells stained positive for several neuroendocrine markers that are diagnostic for pheochromocytoma. Overall, the mass is relatively small and has a relatively low mitotic rate (less than 2/10 HPF). These facts, along with the lack of necrosis, suggest that the mass was not likely malignant.

Radiology Discussion

Paragangliomas are masses that occur in sympathetic neural tissues. The masses consist of chromaffin cells and generally result in elevated serum levels of catecholamines (e.g., adrenaline, epinephrine, dopamine). This can lead to episodic or systemic hypertension, tachycardia, diaphoresis, and/or headache. Initial tests for these masses include the measurement of catecholamine metabolites (VMA and metanephrines) in urine. The majority of paragangliomas (90%) occur in the adrenal medulla, and are called pheochromocytomas. In fact, in common usage, the term ‘paraganglioma’ is applied only to extra-adrenal masses; pheochromocytoma is the more common term. Extra-adrenal masses can occur in any sympathetic neural tissue, but arise most often in the organs of Zuckerkandl (confluence of sympathetic tissue just below the aortic bifurcation), the sympathetic trunk, and the bladder.

Pheochromocytomas are often described according to the "rule of 10’s":

• 10% are extra-adrenal (i.e., 10% would, by common usage, be described as paragangliomas)
• 10% are malignant (15-30% of paragangliomas are malignant)
• 10% are bilateral
• 10% are familial
• 10% are not associated with hypertension (Although hypertension is a common symptom, it is important to note that pheos (and paraganliomas) cause only 0.1% of hypertension cases.)

Other associated factors include multiple endocrine neoplasia (MEN) IIA and IIB, neurofibromatosis type 1, Von Hippel Lindau disease, and familial pheochromocytoma.

Imaging is used for localization of tumors (to guide therapy), rather than for diagnosis. The diagnosis is generally based on history, symptoms, and catecholamine testing. Imaging may, however, be used to search for metastatic disease.

The masses themselves tend to be quite vascular. They may exhibit some focal/partial cystic degeneration. The masses are typically imaged when they are 2-5 cm. On CT, less than 5% have calcifications; larger masses may have a more heterogeneous appearance. If contrast is used (see below), these masses enhance intensely. On MRI, pheochromocytomas typically have a "light bulb" appearance with high signal on T2-weighted images (although this is not universal). Unlike adrenal adenomas, they display no decrease in signal on out-of-phase imaging (due to the relative lack of lipids). In cases where clinical evidence strongly suggests the presence of the pheochromocytoma or paraganglioma but none can be visualized on CT or MRI, MIBG or adrenal vein sampling may be used to localize occult masses.

The use of contrast during imaging is controversial. A number of case reports suggest that hypertensive crises have been induced by anesthesia, surgical intervention, trauma, and/or iodinated contrast/selective angio (4). But the questions of whether iodinated contrast is safe for use in patients with pheochromocytoma and whether a alpha-adrenergic blockade should be given prior to contrast administration are unanswered; formal data are scarce. In a 1984 study (5), six patients were given a alpha-adrenergic blockade and ionic contrast. Although the results were not statistically significant (probably due to the small sample size), five of the six patients had catecholamine levels that (according to the authors) were elevated sufficiently to have induced a hypertensive crisis had the a alpha-adrenergic blockade not been administered. In a 1997 study (6), 10 patients were given nonionic contrast without the a alpha-adrenergic blockade. None of the subjects had elevated catecholamine levels following contrast, and the authors concluded that the a alpha-adrenergic blockade was not necessary. Because the literature does suggest the possibility (however remote) of hypertensive crisis in these patients, and diagnosis is generally possible without the aid of contrast, it is often recommended that contrast be avoided when pheochromocytoma is suspected.

References

1. Wagner, Brent. Adrenal imaging in Adults: Rad-Path Correlation, AFIP notes.

2. Woodward, Paula. Retroperitoneum, AFIP notes.

3. Lee TH, et al, Best Cases from the AFIP, Cystic Pheochromocytoma. Radiographics 2002; 22: 935-940.

4. Gold RE et al, Hypertensive crisis as a result of adrenal urography in a patient with pheochromocytoma. Radiology 1972; 102(3); 597-80.

5. Raisanen J et al, Plasma catecholamines in pheochromocytoma: effect of urographic contrast media. Am. J Roentgenol., 1984; 143(1): 43-6.

6. Mukherjee JJ et al, Pheochromocytoma: effect of nonionic contrast medium in CT on circulating catecholamine levels. Radiology 1997; 202(1); 227-31.

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