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AJR Teaching File: Incidental Adrenal Mass and Hypertension

¹ University of Alabama School of Medicine, Birmingham, AL.
² Department of Radiology, Brooke Army Medical Center, MCHE-DR, 3851 Roger Brooke Dr., Fort Sam Houston, TX 78234.

Received May 26, 2005; accepted after revision August 18, 2005.

 
This Teaching File article is available for SAM credit and CME credits when completed with the additional educational material provided in "Imaging of Pheochromocytoma and Incidental Adrenal Lesions: Self-Assessment Module." See page S467 for details.

The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as representing the views of the Department of the Army, the Department of the Air Force, or the Department of Defense.

Address correspondence to K. P. Banks (Kevin.Banks{at}cen.amedd.army.mil).

Keywords: abdominal imaging • cancer • CT • MRI • pheochromocytoma

Clinical History

Top Clinical History Radiologic Description Laboratory and Pathologic... Differential Diagnosis Diagnosis Commentary Objective Conclusion References

 
A 71-year-old woman presents with an indeterminate left adrenal mass found incidentally during chest CT angiography performed for chest pain. Physical examination is remarkable only for hypertension and tachycardia. Three-phase adrenal CT is recommended for further evaluation.

Radiologic Description

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Unenhanced abdominal CT (Fig. 1A) illustrates a well-defined, 3.9-cm left adrenal mass with mixed iso- and hypodensity. No calcifications are associated with the lesion, and no adenopathy is seen. The contralateral adrenal gland is normal. The average attenuation of the lesion is 27 H, prompting further evaluation with contrast material. Arterial phase CT (Fig. 1B) shows heterogeneous enhancement with a mean attenuation of 44 H. Axial CT images delayed 15 minutes after administration of contrast material (Fig. 1C) exhibit no substantial washout (< 50%), and the average attenuation is 40 H. Attenuation greater than 10 H on unenhanced CT and the lack of washout on delayed images suggests a malignant rather than a benign process.

View larger version (135K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A —71-year-old woman with indeterminate left adrenal mass discovered incidentally during chest CT angiography performed for chest pain. Unenhanced abdominal CT scan illustrates well-defined 3.9-cm left adrenal mass with mixed iso- and hypodensensity. No calcifications are associated with lesion, and no adenopathy is seen. Contralateral adrenal gland is normal. Average attenuation of lesion is 27 H, prompting further evaluation with contrast material.

View larger version (117K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B —71-year-old woman with indeterminate left adrenal mass discovered incidentally during chest CT angiography performed for chest pain. Arterial phase CT scan shows heterogeneous enhancement with mean attenuation of 44 H.

View larger version (142K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C —71-year-old woman with indeterminate left adrenal mass discovered incidentally during chest CT angiography performed for chest pain. Axial CT scan delayed 15 minutes after administration of contrast material exhibits no substantial washout (< 50%), and average attenuation is 40 H.

View larger version (71K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1D —71-year-old woman with indeterminate left adrenal mass discovered incidentally during chest CT angiography performed for chest pain. Reconstructed tomographic image from PET illustrates increased glucose metabolism from left adrenal mass; standard uptake value is 10.5. Normal glucose metabolism is evident in kidneys, bladder, and heart. Subsequent iodine-131 metaiodobenzylguanidine (MIGB) scan (not shown) shows minimal uptake.

View larger version (103K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1E —71-year-old woman with indeterminate left adrenal mass discovered incidentally during chest CT angiography performed for chest pain. Avid activity (arrowhead) is shown in reconstructed tomographic image from indium-111 octreotide scan. Liver, spleen, and kidneys exhibit normal physiologic activity. Because tumor lies anterior to left kidney, activity associated with tumor and normal activity of upper role are superimposed on this coronal view.

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Differential Diagnosis

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For a unilateral solid adrenal mass, the differential diagnosis includes the benign conditions adenoma, pheochromocytoma, myelolipoma, granulomatous disease, and hemorrhage, and the malignant entities adenocortical carcinoma, neuroblastoma or ganglioneuroma, and metastasis.

Diagnosis

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The final pathologic diagnosis in this patient was pheochromocytoma.

Commentary

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The differential diagnosis for adrenal masses is broad, which makes definitive diagnosis by cross-sectional imaging alone extremely difficult. Through careful consideration of the lesion's various imaging features and the clinical context, the list of potential diagnoses may be dramatically reduced or even a definitive diagnosis achieved, as in this patient.

By far the most commonly encountered solid adrenal lesion is a benign adrenal adenoma. They are found in approximately 1% of individuals undergoing abdominal CT examinations [1]. These lesions are typically small (< 4 cm) and smoothly marginated with homogeneous attenuation [2]. Visually, they commonly appear similar in density to normal adrenal tissue; however, their high intracellular lipid content typically yields a density similar to that of water (< 10 H) on unenhanced studies. As with attenuation, MRI can take advantage of the typical lipid-rich nature of adenomas; lesions show decreased signal attenuation that results from chemical shift artifacts on out-of-phase imaging.

In patients in whom the adenoma is a lipid-poor variant, the characteristic washout of contrast material during CT may serve as an additional noninvasive means of evaluation. Malignant lesions typically have a washout rate of less than 40% at 15 minutes, whereas adenomas and other benign lesions normally have a washout rate greater than 40% [3] (other authors use a figure of 50% washout [4]). When both attenuation and morphology are considered, the specificity of CT for adrenal adenoma approaches 100% [2].

The myelolipoma, a rare cause of adrenal masses, can be dismissed in this patient. These benign tumors are composed of bone marrow elements and generally contain a large amount of macroscopic fat that is easily recognized on CT or on MRI with fat saturation.

Granulomatous disease is another consideration. Although granulomas can have a varied appearance ranging from a soft-tissue mass to a cystic lesion with associated calcifications, they are most often bilateral and are rarely unilateral [1]. This feature makes the diagnosis of granulomatous disease unlikely in this patient, particularly in the absence of calcifications.

Hemorrhage is a known cause of adrenal lesions. In the absence of trauma, hemorrhage is usually associated with anticoagulation therapy or the presence of an underlying blood dyscrasia [1]. Unilateral adrenal hemorrhage, as in this patient, is most commonly the result of blunt trauma, with the right gland affected more often than the left. On the basis of the appearance, density, enhancing characteristics, and lack of known predisposing factors or a supporting history, hemorrhage should not be a consideration in this patient.

Although uncommonly encountered, ganglioneuromas and neuroblastomas can both be seen in the adrenal gland. Their appearance is nonspecific, seen on CT as soft-tissue masses revealing homogeneous or mildly heterogeneous enhancement. On MRI, ganglioneuromas and neuroblastomas are usually less intense than the liver on T1-weighted sequences and show heterogeneous signal intensity on T2-weighted imaging. Unlike in children, neuroblastomas in adults less commonly contain calcifications. Although the absence of disseminated disease helps exclude a neuroblastoma, ganglioneuromas can have an identical CT and MRI appearance and must be differentiated by other means, such as laboratory analysis or nuclear scintigraphy.

Although rare, one of the most worrisome lesions encountered in the adrenal gland is adenocortical carcinoma. When discovered, they are almost always greater than 6 cm, with a heterogeneous appearance on CT and MRI due to hemorrhage and necrosis. Invasion of the renal vein may be seen [5].

Pheochromocytoma is an uncommon catecholamine-secreting tumor arising from the chromaffin cells of the adrenal medulla. Up to 10% of cases are clinically silent, which, when combined with the increased use of abdominal CT, has led to an increased rate of incidental finding. Varying pathologic degeneration can complicate radiographic evaluation of pheochromocytomas; the presence of necrosis, calcification, fibrosis, cystic degeneration, or intracellular lipid degeneration makes pheochromocytoma difficult to distinguish from other solid adrenal masses. However, a noninvasive method of diagnosis is critical because of the fatal hypertension and arrhythmias that these tumors can precipitate if they are manually disturbed [3].

Pheochromocytoma can be clinically characterized by the rule of 10%: 10% are bilateral, 10% are extraadrenal, 10% are malignant, 10% are hereditary, and 10% are nonfunctioning [3, 6]. The diagnosis is often suspected in the young patient who presents with paroxysmal hypertension and palpitation. Despite this, less than 1% of all hypertension is caused by a pheochromocytoma [3]. Other presenting signs and symptoms include headaches, sweating, and tachycardia, which, when combined with hypertension, have a 91% sensitivity and 94% specificity for the tumor [6].

The workup of a suspected pheochromocytoma should begin with measurement of appropriate biochemical markers, particularly plasma catecholamine levels and 24-hour urine vanillylmandelic acid and metanephrine levels. For those patients in whom the clinical and laboratory suspicion of pheochromocytoma is strong, initial radiologic evaluation is centered on CT [2]. On CT, pheochromocytoma exhibits a wide range of heterogeneity, calcification, and cystic components, so identification is chiefly dependent on attenuation, with most having an unenhanced attenuation greater than 10 H. With contrast administration, a pheochromocytoma rapidly and avidly enhances to greater than 40 H, an indication of the tumor's rich network of capillaries. Once again, contrast-enhanced characterization relies principally on attenuation.

If a mass is not identified on CT, then MRI may prove helpful. Pheochromocytoma usually shows low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. In addition, most pheochromocytomas enhance intensely on MRI with contrast administration. However, T2-weighted intensity is highly variable, leading to as many as 35% of pheochromocytomas being misclassified. Therefore, high signal intensity on T2-weighted images should not be used exclusively to imply or to exclude the diagnosis [3, 5]. In rare instances, pheochromocytomas may contain sufficient intracellular lipid to show signal dropout on opposed phase imaging, mimicking benign adrenal adenomas [3].

In patients in whom neither CT nor MRI is decisive, several radio-nuclide imaging techniques may be beneficial. Iodine-131 MIBG is a structural analogue of norepinephrine, a commonly secreted product of pheochromocytomas. Whole-body imaging performed at 24-72 hours after the administration of MIBG has 80-90% sensitivity and 90-100% specificity for the detection of pheochromocytoma. Indium-111 octreotide, a synthetic octapeptide analogue of somatostatin, is a second radionuclide used in the detection of pheochromocytoma. However, conventional doses of octreotide locate fewer than 30% of tumors. In general, ¹³¹I MIBG and ¹¹¹In octreotide should be considered complementary radionuclides because up to 50% of tumors are visualized only with both agents [2, 3].

Lastly, PET has been used in a few instances to identify pheochromocytoma. The most convincing results have been obtained using ¹⁸F-FDG and ¹⁸F-fluorodopamine PET. However, PET cannot distinguish between pheochromocytomas and adrenal metastases [3].

Objective

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The educational objective of this article is to describe the imaging features in a case of adrenal pheochromocytoma.

Conclusion

Top Clinical History Radiologic Description Laboratory and Pathologic... Differential Diagnosis Diagnosis Commentary Objective Conclusion References

 
The highly variable radiologic presentation of pheochromocytoma makes its diagnosis particularly complicated. An approach involving clinical suspicion, laboratory markers, and one or more imaging techniques that would reveal an appropriately located mass is the best method for making the appropriate diagnosis.

References

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1. Dunnick NR, Korobkin M. Imaging of adrenal incidentalomas: current status. AJR 2002;179 : 559-568[Free Full Text]
2. Mayo-Smith WW, Boland GW, Noto RB, Lee MJ. State-of-the-art adrenal imaging. RadioGraphics 2001;21 : 995-1012[Abstract/Free Full Text]
3. Blake MA, Kalra MK, Maher MM, et al. Pheochromocytoma: an imaging chameleon. RadioGraphics 2004;24 [suppl 1]:S87 -S99[Abstract/Free Full Text]
4. Korobkin M. CT characterization of adrenal masses: the time has come. (editorial) Radiology 2000;217 : 629-632[Free Full Text]
5. Elsayes KM, Mukundan G, Narra VR, et al. Adrenal masses: MR imaging features with pathologic correlation. RadioGraphics2004; 24[suppl 1]:S73 -S86[Abstract/Free Full Text]
6. Bravo E, Rodrigo T. Pheochromocytoma: state-of-the-art and future prospects. Endocr Rev 2003;24 : 539-553[Abstract/Free Full Text]

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				F. S. Chew and K. P. Banks Imaging of Pheochromocytoma and Incidental Adrenal Lesions: Self-Assessment Module Am. J. Roentgenol., September 1, 2006; 187(3_Supplement): S467 - S469. [Abstract] [Full Text] [PDF]

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