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DOI:10.2214/AJR.05.0492
AJR 2006; 187:1309-1311
© American Roentgen Ray Society

Case Report

Incidental Pheochromocytoma Mimicking Adrenal Adenoma Because of Rapid Contrast Enhancement Loss

John K. Yoon1, Erick M. Remer1 and Brian R. Herts1

1 All authors: Department of Radiology, Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, OH 44195.

Received March 20, 2005; accepted after revision April 26, 2005.

 
Address correspondence to E. M. Remer (remere1{at}ccf.org).

Keywords: adenoma • adrenal gland • Barrett's esophagus • CT • MRI • nonadenoma • PET/CT • pheochromocytoma


Introduction
Top
 Introduction
Case Report
 Discussion
 References
 
The characterization of adrenal masses using noninvasive imaging has been the focus of much interest, with the goal of easily differentiating between benign and malignant lesions. A large body of literature exists on the subject of characterizing adrenal lesions found during the staging of patients with known extraadrenal primary malignancy. Signal loss on opposed-phase gradient-echo MR images compared with in-phase images and mean attenuation values of less than 10 H on unenhanced CT are both specific for differentiating adenomas from nonadenomas. Each method exploits the abundance of intracytoplasmic fat typically present in adenomas. Another well-studied characteristic of adenomas is their relatively rapid enhancement and washout on delayed contrast-enhanced images when compared with nonadenomas [1-3]. A recent study [4] suggests that the enhancement loss in pheochromocytomas and adrenocortical carcinomas is similar to that seen in adrenal metastases but is significantly less than that seen in adrenal adenomas, so an absolute washout 10 minutes after contrast medium injection of greater than 50% is highly specific for adenomas. We present a pathologically proven case of an incidental adrenal pheochromocytoma with an absolute contrast medium washout of 72%.


Case Report
Top
 Introduction
 Case Report
Discussion
 References
 
A 50-year-old man presented 9 years ago with a complaint of heartburn and was diagnosed with gastroesophageal reflux disease and Barrett's esophagus. He underwent regular surveillance with annual or biannual esophagogastroduodenoscopy, and a recent such examination identified high-grade dysplasia in a distal esophageal nodule. Contrast-enhanced CT of the chest, abdomen, and pelvis showed a 2-cm incidental right adrenal nodule. A PET/CT examination, performed with 11.1 mCi (410.7 MBq) 18F-FDG IV, showed increased 18F-FDG uptake (with a standardized uptake value of 4.9) in the right adrenal nodule (Fig. 1A), but not in the esophagus. A differential diagnosis of metastatic disease, primary neoplasm such as pheochromocytoma, or benign cause was given.


Figure 1
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  		Fig. 1A —50-year-old man with Barrett's esophagus and esophageal dysplasia on biopsy undergoing staging before esophagectomy. 18F-FDG coronal PET image shows focal, marked uptake in right suprarenal region (arrow). Uptake is also present in urinary tract and heart.

 
Adrenal CT was then performed, with unenhanced, 60-second enhanced, and 15-minute delayed imaging. All scans were obtained at 0.75-mm collimation, 120 kV, and 200 mAs (Sensation 16, Siemens Medical Solutions). Images were reconstructed at a 3-mm slice thickness at 3-mm intervals and reviewed on a PACS workstation (MV1000, Siemens Medical Solutions). The right adrenal nodule measured 2.0 x 1.9 cm in maximum axial dimensions. Region of interest measured 37 H on the unenhanced images (Fig. 1B), 127 H on the 60-second contrast-enhanced images, and 62 H (Fig. 1C) on the 15-minute delayed images (Fig. 1D), representing 72% absolute contrast enhancement washout. This is calculated as follows:

Formula
where E is the enhanced attenuation value, D is the delayed enhanced value, and U is the unenhanced value [5].


Figure 2
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  		Fig. 1B —50-year-old man with Barrett's esophagus and esophageal dysplasia on biopsy undergoing staging before esophagectomy. Unenhanced CT shows 2-cm right adrenal nodule. Region of interest (circle) shows mean attenuation of 37 H.

 

Figure 3
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  		Fig. 1C —50-year-old man with Barrett's esophagus and esophageal dysplasia on biopsy undergoing staging before esophagectomy. Contrast-enhanced CT image obtained 60 seconds after contrast administration shows region of interest (circle) with enhancement to 127 H.

 

Figure 4
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  		Fig. 1D —50-year-old man with Barrett's esophagus and esophageal dysplasia on biopsy undergoing staging before esophagectomy. Contrast-enhanced CT image obtained 15 minutes after contrast administration shows region of interest (circle) with washout to 62 H.

 
The patient denied headaches, palpitations, shortness of breath, and diaphoresis. Blood pressure was 142 over 90 mm Hg; the patient was being treated with antihypertensive medication, Norvasc (amlodipine besylate, Pfizer), 5 mg orally per day, and he had no evidence of episodic hypertension. A biochemical profile performed 1 month later revealed elevated 24-hour urinary metanephrine of 1,087 µg (normal range, 52-341 µg) and 24-hour urinary normetanephrine of 1,069 µg (normal range, 88-444 µg). The urinary vanillylmandelic acid was at the upper limit of normal, measuring 4.0 mg/g creatinine. Urinary aldosterone and cortisol levels were also normal (18 µg/24 h and 64.1 µg/24 h, respectively).

The patient underwent a laparoscopic right adrenalectomy 6 weeks later, and the diagnosis of right adrenal pheochromocytoma was pathologically confirmed. The patient subsequently had an esophagectomy, and the pathology results confirmed adenocarcinoma within Barrett's mucosa with high-grade dysplasia.


Discussion
Top
 Introduction
 Case Report
 Discussion
References
 
Although adrenal masses are common and pheochromocytomas are considered rare, the true incidence of pheochromocytoma is unknown [6]. A retrospective study from the Mayo Clinic reported that a diagnosis of pheochromocytoma was made at autopsy in 45% of patients [7]. Although it has long been thought that approximately 10% of pheochromocytomas are incidental, several series suggest that more than 50% of pheochromocytomas may be discovered incidentally [8-10].

It is generally accepted that the diagnosis of an adrenal adenoma in the setting of a known primary malignancy can be noninvasively confirmed in most cases with both inphase and opposed-phase MRI or through a combination of unenhanced and contrast-enhanced washout CT characteristics. The literature is still emerging as to the best approach to incidental adrenal masses in asymptomatic patients without a known primary cancer. This is because, in most of the existing reports, discriminating adenomas from nonadenomas has been based primarily on series of adenoma and adrenal metastases. In one series, Szolar and Kammerhuber [11] included six pheochromocytomas in the nonadenoma group, and all six showed delayed contrast enhancement and percentage of contrast enhancement loss values in the range of nonadenoma values. Szolar et al. [4] reported 100% sensitivity and specificity for the diagnosis of adrenal adenomas compared with both adrenocortical carcinomas and pheochromocytomas using a threshold value of greater than 50% for absolute contrast enhancement loss and 40% for relative contrast enhancement loss. This retrospective study of 67 patients with 73 adrenal masses included 17 pheochromocytomas. Regarding the high specificity, however, the authors note that their study may not have had enough statistical power. Our case of pheochromocytoma with 72% washout reinforces that further study is needed.

Our technique differs from that of Szolar et al. [4] in that we performed delayed imaging after 15 minutes rather than after 10 minutes. This might in part account for a higher percentage of washout in our patient than was shown in pheochromocytomas in their series. In 166 adrenal masses imaged by Caoili et al. [12], a single pheochromocytoma had washout in excess of 60% at 15 minutes. Also, two pheochromocytoma cases have been reported with both absolute and relative attenuation washout of greater than 60% at 10 minutes by Blake et al. [13]. Unlike our patient, these two patients were symptomatic. As suggested by Szolar et al., all pheochromocytomas may not behave like those in their series.

The only region of increased 18F-FDG metabolism on the PET study was in the right adrenal gland and not in the esophageal adenocarcinoma. Fluorine-18 FDG has been previously described as accumulating in pheochromocytoma in seven (58%) of 12 benign lesions and in 14 (82%) of 17 malignant lesions [14]. Perhaps PET/CT can play a role in detecting occult pheochromocytoma.

This case of an incidental pheochromocytoma showing contrast medium washout greater than 50% on delayed imaging reiterates the importance of performing a biochemical profile in any patient with an incidentally discovered adrenal mass, regardless of clinical signs and symptoms. It also suggests the need for further studies evaluating the delayed contrast-enhanced CT features of masses other than adenomas and metastases because this patient would have been misdiagnosed using the recently reported criteria.


References
Top
 Introduction
 Case Report
 Discussion
 References
 

  1. Korobkin M, Brodeur FJ, Francis IR, et al. CT time-attenuation washout curves of adrenal adenomas and nonadenomas. AJR 1998; 170:747 -752[Abstract/Free Full Text]
  2. Pena CS, Boland GW, Hahn PF, Lee MJ, Mueller PR. Characterization of indeterminate lipid-poor adrenal masses: use of washout characteristics at contrast enhanced CT. Radiology 2000;217 : 798-802[Abstract/Free Full Text]
  3. Szolar DH, Kammerhuber FH. Quantitative CT evaluation of adrenal gland masses: a step forward in the differentiation between adenomas and nonadenomas. Radiology 1997;202 : 517-521[Abstract/Free Full Text]
  4. Szolar DH, Korobkin M, Reittner P, et al. Adrenocortical carcinomas and adrenal pheochromocytomas: mass and enhancement loss evaluation at delayed contrast-enhanced CT. Radiology 2005;234 : 479-485[Abstract/Free Full Text]
  5. Dunnick NR, Korobkin M. Imaging of adrenal incidentalomas: current status AJR 2002;179 : 559-568[Free Full Text]
  6. Francis IR, Korobkin M. Pheochromocytoma. Radiol Clin North Am 1996; 34:1101 -1112[Medline]
  7. Beard CM, Sheps SG, Kurland LT. Occurrence of pheochromocytoma in Rochester, Minnesota, 1950 through 1979. Mayo Clin Proc 1983; 58:802 -804[Medline]
  8. Miyajima A, Nakashima J, Baba S, et al. Clinical experience with incidentally discovered pheochromocytoma. J Urol1997; 157:1566 -1568[CrossRef][Medline]
  9. Cheah WK, Clark OH, Horn JK, Siperstein AE, Duh Q-Y. Laparoscopic adrenalectomy for pheochromocytoma. World J Surg2002; 26:1048 -1051[CrossRef][Medline]
  10. Motta GA, Remer EM, Herts BR, Gill IS, Hamrahian AH. Comparison of CT findings in symptomatic and incidentally discovered pheochromocytomas. AJR 2005; 185:684 -688[Abstract/Free Full Text]
  11. Szolar DH, Kammerhuber FH. Adrenal adenomas and nonadenomas: assessment of washout at delayed contrast-enhanced CT. Radiology 1998;207 : 369-375[Abstract/Free Full Text]
  12. Caoili EM, Korobkin M, Francis IR, et al. Adrenal masses: characterization with combined unenhanced and delayed enhanced CT. Radiology 2002;222 : 629-633[Abstract/Free Full Text]
  13. Blake MA, Krishnamoorthy SK, Boland GW, et al. Low-density pheochromocytoma on CT: a mimicker of adrenal adenoma. AJR 2003; 181:1663 -1668[Abstract/Free Full Text]
  14. Shulkin BL, Thompson NW, Shapiro B, Francis IR, Sisson JC. Pheochromocytomas: imaging with 2-[fluorine-18]fluoro-2-deoxy-D-glucose PET. Radiology 1999;212 : 35-41[Abstract/Free Full Text]

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