DOI: 10.1148/rg.235035022
(Radiographics. 2003;23:1279-1286.)
© RSNA, 2003
Best Cases from the AFIP
Paraganglioma of the Organs of Zuckerkandl1
Daniel P. Saurborn, MD,
Jonathan B. Kruskal, MD, PhD,
Isaac E. Stillman, MD and
Sareh Parangi, MD
1 From the Departments of Radiology (D.P.S., J.B.K.), Pathology (I.E.S.), and Surgery (S.P.), Beth Israel Deaconess Medical Center and Harvard Medical School, 1 Deaconess Rd, West 203B, Boston MA 02215. Received January 28, 2003; revision requested February 26 and received April 2; accepted April 4. Address correspondence to J.B.K. (e-mail: jkruskal@bidmc.harvard.edu).
Index Terms: Paraganglioma, 89.3199
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History
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A 32-year-old man with human immunodeficiency virus presented with a fever of 102°F, left lower quadrant pain radiating to the back, diarrhea, and a 15-pound weight loss over the previous 5 months. The patient was undergoing antiretroviral therapy and had a CD4 count of 400. He described having experienced several similar episodes over the previous 2 years, which had resolved spontaneously. None of the prior episodes was formally evaluated. At physical examination, the patient was normotensive (he was receiving atenolol), with point tenderness in the left lower quadrant. Notable laboratory findings included urinary and serum norepinephrine levels that were eight times greater than normal, normal urinary and serum epinephrine levels, an elevated urinary vanillylmandelic acid (VMA) level of 19.9 mg/24 h (normal, 2–10 mg/24 h), elevated serum calcitonin levels of 12 pg/mL (normal, <8 pg/mL), and an elevated serum chromogranin A level of 111 ng/mL (normal, <14.3 ng/mL). The patient’s family history was notable for a younger brother who had had a pheochromocytoma removed at 15 years of age. In addition, the patient’s own medical history was notable for hypertension of several years duration, which had been adequately controlled with atenolol. Three years prior to the current presentation, he had undergone emergency computed tomography (CT) for evaluation of right flank pain associated with leukocytosis; CT revealed a low-attenuation filling defect in the distal right ureter, a finding consistent with indinavir crystals. CT also revealed an "incidental" 4.5 x 4.5-cm left paraaortic mass associated with a small focus of peripheral calcification and heterogeneous enhancement. Although the radiologist recommended further evaluation, no follow-up was pursued.
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Imaging Findings
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Unenhanced and contrast material–enhanced helical CT of the abdomen and pelvis was performed with 150 mL of nonionic contrast material. CT was initially ordered to exclude obstructive uropathy. There was no history or laboratory findings to suggest a pheochromocytoma. CT urography was performed with data acquired during both the parenchymal and excretory phases according to a standardized protocol. Notably, there were no adverse side effects following contrast material administration.
CT revealed a 6 x 6-cm left paraaortic mass at the level of the origin of the inferior mesenteric artery. On the unenhanced scans, the mass was relatively homogeneous and similar in attenuation to the adjacent psoas muscle (Fig 1a). The mass contained a single linear focus of calcification. Contrast-enhanced arterial and venous phase scans both demonstrated avid peripheral enhancement that paralleled aortic enhancement, a finding that suggested a highly vascular tumor (Fig 1b). A stellate area was seen centrally in the lesion whose enhancement did not change after contrast material administration. This finding was consistent with central necrosis. At CT, the lesion could not be distinguished from the aortic wall. Both adrenal glands were well visualized and entirely normal in size and appearance. At that time, a differential diagnosis that included lymphoma, necrotic lymph node, and primary retroperitoneal tumor was considered.
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Figure 1a. (a) Unenhanced abdominal CT scan demonstrates a 6 x 6-cm soft-tissue mass adjacent to the aorta, just superior to the bifurcation. Note the small focus of peripheral calcification (arrow). (b) Contrast-enhanced arterial phase CT scan demonstrates prompt peripheral enhancement with central nonenhancement. Note the thin slip of enhancing tissue just anterior to the aortic wall (arrow); this tissue is not readily distinguishable from the aorta.
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Figure 1b. (a) Unenhanced abdominal CT scan demonstrates a 6 x 6-cm soft-tissue mass adjacent to the aorta, just superior to the bifurcation. Note the small focus of peripheral calcification (arrow). (b) Contrast-enhanced arterial phase CT scan demonstrates prompt peripheral enhancement with central nonenhancement. Note the thin slip of enhancing tissue just anterior to the aortic wall (arrow); this tissue is not readily distinguishable from the aorta.
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Findings at magnetic resonance (MR) imaging performed the following day with a 1.5-T imager confirmed the presence of a 7 x 5 x 5-cm paraaortic mass. T1-weighted MR images demonstrated a slightly heterogeneous lesion with a slightly hyperintense rim and a central region that was slightly hypointense relative to muscle (Fig 2a). On T1-weighted out-of-phase MR images, no lipid elements were identified (Fig 2b). T2-weighted volumetric interpolated breath-hold excitation images demonstrated a relatively hyperintense stellate center and a rim that was only slightly hyperintense relative to the hepatic parenchyma (Fig 2c). Contrast-enhanced T1-weighted images helped confirm the intense peripheral enhancement and central nonenhancement seen at CT (Fig 2d). Although there was the suggestion of a thin capsule, a discrete plane of separation from the aorta could not be visualized. No lymphadenopathy, adrenal masses, or hepatic lesions were evident. A differential diagnosis of lymphoma, metastatic disease (such as from a testicular neoplasm), chronic infection, and primary soft-tissue or smooth muscle tumor was offered. Despite the lack of typical hyperintensity on T2-weighted images, the biochemical abnormalities made the diagnosis of paraganglioma most likely. Imaging with iodine-123 metaiodobenzylguanidine (MIBG) was not performed.
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Figure 2a. (a) Axial unenhanced in-phase T1-weighted MR image shows a heterogeneous mass that is both slightly hyperintense and hypointense relative to the adjacent psoas muscle. (b) Axial out-of-phase T1-weighted MR image shows no appreciable lipid component. (c) Coronal T2-weighted MR image demonstrates the mass with a stellate hyperintense center. Note that the mass adheres closely to the aorta but does not directly invade the lumen. Note also that the viable tumor rim lacks the typical T2-weighted hyperintensity of most paragangliomas. (d) On a contrast-enhanced arterial phase T1-weighted MR image, the mass demonstrates prompt peripheral enhancement with central nonenhancement.
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Figure 2b. (a) Axial unenhanced in-phase T1-weighted MR image shows a heterogeneous mass that is both slightly hyperintense and hypointense relative to the adjacent psoas muscle. (b) Axial out-of-phase T1-weighted MR image shows no appreciable lipid component. (c) Coronal T2-weighted MR image demonstrates the mass with a stellate hyperintense center. Note that the mass adheres closely to the aorta but does not directly invade the lumen. Note also that the viable tumor rim lacks the typical T2-weighted hyperintensity of most paragangliomas. (d) On a contrast-enhanced arterial phase T1-weighted MR image, the mass demonstrates prompt peripheral enhancement with central nonenhancement.
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Figure 2c. (a) Axial unenhanced in-phase T1-weighted MR image shows a heterogeneous mass that is both slightly hyperintense and hypointense relative to the adjacent psoas muscle. (b) Axial out-of-phase T1-weighted MR image shows no appreciable lipid component. (c) Coronal T2-weighted MR image demonstrates the mass with a stellate hyperintense center. Note that the mass adheres closely to the aorta but does not directly invade the lumen. Note also that the viable tumor rim lacks the typical T2-weighted hyperintensity of most paragangliomas. (d) On a contrast-enhanced arterial phase T1-weighted MR image, the mass demonstrates prompt peripheral enhancement with central nonenhancement.
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Figure 2d. (a) Axial unenhanced in-phase T1-weighted MR image shows a heterogeneous mass that is both slightly hyperintense and hypointense relative to the adjacent psoas muscle. (b) Axial out-of-phase T1-weighted MR image shows no appreciable lipid component. (c) Coronal T2-weighted MR image demonstrates the mass with a stellate hyperintense center. Note that the mass adheres closely to the aorta but does not directly invade the lumen. Note also that the viable tumor rim lacks the typical T2-weighted hyperintensity of most paragangliomas. (d) On a contrast-enhanced arterial phase T1-weighted MR image, the mass demonstrates prompt peripheral enhancement with central nonenhancement.
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Pathologic Evaluation
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The patient was prepared for surgery with atenolol beta-blockade and phenoxybenzamine alpha-blockade. The aorta was exposed in the midline with an anterior approach. The tumor was palpable at this location, starting just below the infrarenal aorta, and was larger than anticipated from the imaging findings, measuring approximately 10 x 8 cm in diameter. There was a prominent surrounding desmoplastic reaction that caused tumoral adherence to the aorta (Fig 3a). The left ureter also adhered to the tumor but was easily freed with surgical dissection. The tumor enveloped the aorta and the inferior mesenteric artery and vein. During manipulation of the tumor, the patient’s blood pressure surged to levels of 220/120 mm Hg on several occasions, but these episodes were well controlled with appropriate vasodilators. Once the tumor was removed, pressure was artificially maintained with phenylephrine and norepinephrine.
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Figure 3a. (a) Intraoperative photograph demonstrates an extraadrenal paraganglioma (large arrow) that adheres to the aorta (small arrows). (b) Photograph of the gross specimen shows a 9.5 x 7 x 5-cm mass with focal hemorrhage (curved arrow) and an area of tumor necrosis with a pale yellow rim (straight arrow).
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Figure 3b. (a) Intraoperative photograph demonstrates an extraadrenal paraganglioma (large arrow) that adheres to the aorta (small arrows). (b) Photograph of the gross specimen shows a 9.5 x 7 x 5-cm mass with focal hemorrhage (curved arrow) and an area of tumor necrosis with a pale yellow rim (straight arrow).
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The pathologist received a firm, tan mass that measured 9.5 x 7 x 5 cm and weighed 142 g. The mass was serially sectioned to reveal tan parenchyma with focal hemorrhage and a 4 x 3.5-cm area of necrosis with a yellow rim (Fig 3b). Microscopic examination revealed sheets and trabeculae of polygonal cells with granular, mostly eosinophilic cytoplasm (Fig 4). The tumor showed prominent vascularity, and areas of hemosiderin deposition and necrosis were seen (Fig 5a, 5b). Neoplastic cells were positive for synaptophysin (Fig 6) and chromogranin, and there was focal S-100 protein positivity in sustentacular cells. These findings were diagnostic for an extraadrenal paraganglioma.
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Figure 4. Photomicrograph (original magnification, x40; hematoxylin-eosin [H-E] stain) of the paraganglioma shows a population of cells with abundant cytoplasm and indistinct cell borders (arrow).
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Figure 5a. (a) Photomicrograph (original magnification, x40; H-E stain) demonstrates hemosiderin deposition (arrow) within the neoplasm, a finding that indicates prior hemorrhage. (b) Photomicrograph (original magnification, x40; H-E stain) shows coagulative necrosis with pyknotic nuclear debris (arrow) and neutrophils (arrowhead).
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Figure 5b. (a) Photomicrograph (original magnification, x40; H-E stain) demonstrates hemosiderin deposition (arrow) within the neoplasm, a finding that indicates prior hemorrhage. (b) Photomicrograph (original magnification, x40; H-E stain) shows coagulative necrosis with pyknotic nuclear debris (arrow) and neutrophils (arrowhead).
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Figure 6. Photomicrograph (original magnification, x40; immunoperoxidase stain for synaptophysin, a neuroendocrine marker) shows diffuse positive staining of the cytoplasm. Note the negatively staining blood vessels (arrow).
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Discussion
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Clinical Characteristics
Pheochromocytomas are rare primary neoplasms of the adrenal medulla that may produce catecholamines. Subsets of this tumor family that arise from tissue of the extraadrenal sympathetic nervous system are referred to as paragangliomas. Paragangliomas constitute only about 10% of pheochromocytomas and are therefore even rarer. Pheochromocytomas occur mainly in adults and are usually benign. The signs and symptoms can be related to excess catecholamine secretion and include paroxysmal hypertension accompanied by anxiety, sweating, a throbbing headache, and either facial pallor or flushing during the attack. A classic triad of symptoms that includes headache, sweating, and palpitations has been described in functional tumors. Rarely, if a paroxysm is sufficiently severe, a hypertensive crisis or myocardial infarction may occur, resulting in death. Additional recognized clinical features include orthostatic hypotension, weight loss, and visual and psychiatric disorders. Cardiac enlargement may be identified at physical examination. Recognized biochemical abnormalities include an elevated erythrocyte sedimentation rate, hyperglycemia, and glycosuria, which may occur during the attack. Although pheochromocytomas are known to cause elevated blood pressure, they are responsible for less than 0.1% of cases of hypertension (1). In fact, a strong clinical suspicion of pheochromocytoma is seldom borne out at subsequent investigation. Approximately 10% of pheochromocytomas and paragangliomas are discovered incidentally at imaging performed to evaluate patients with unrelated symptoms (2), as in this case.
Biochemical Findings
In patients who present with symptoms suggestive of excess catecholamine production, laboratory tests can help detect active tumor secretion of epinephrine and norepinephrine by measuring catecholamines and related metabolites in the plasma and urine. In this case, the major metabolic product of catecholamines, urinary VMA, was more than twice the normal level, a finding that is diagnostic for catecholamine-secreting tumors, and serum and urinary norepinephrine were eight times the normal levels. In one biochemical study of 858 subjects, the most sensitive test (99%) was the plasma free metanephrine level, whereas the urinary VMA level yielded the most specific results at 95% (3). If the hypertension is paroxysmal, urine is best collected during and immediately after the attack, which may be the only times during which increased excretion can be detected. Care should be taken when interpreting the results of these tests because several medications and foodstuffs may produce false-positive results, including the beta-blocker labetalol, which may be prescribed for a presumptive diagnosis of essential hypertension in these same patients. Although chromogranin A is secreted along with catecholamines (and yielded positive results in this patient that were 10 times normal), it is generally considered to be less sensitive and specific than other available tests.
Genetics
A recent study by Neumann et al (4) demonstrated that the previously quoted genetic-associated prevalence of 10% of all pheochromocytomas is underestimated. In a series of 271 patients with pheochromocytomas, 25% were found to have germline mutations of recognized genes, including those for von Hippel–Lindau disease; RET (rearranged during transfection) genes; and the SDHD or SDHB genes (succinate dehydrogenase subunits D and B). We recommend routine genetic analysis for these four mutations in any patient who presents with pheochromocytoma. Genetic forms of pheochromocytoma and paraganglioma are inherited in an autosomal dominant fashion. Familial pheochromocytoma may be inherited alone or in combination with multiple endocrine neoplasia (MEN) type 2 syndromes (MEN-2A, MEN-2B) (50% of cases), von Hippel–Lindau disease (20%), or neurofibromatosis type 1 (<5%). When pheochromocytoma is linked to these genetic syndromes, there is a significantly higher prevalence of bilateral tumors.
Because of the patient’s family history of a brother with pheochromocytoma, a genetic syndrome was suspected, but genetic analysis was negative for MEN-2 syndrome. This familial syndrome is characterized by the additional presence of medullary carcinoma of the thyroid gland and neurofibromatosis.
Imaging Features
The frequency with which a pheochromocytoma is diagnosed at abdominal CT performed for indications unrelated to adrenal disease is considerably lowered by the high prevalence of so-called adrenal "incidentalomas" (5). At abdominal CT, irrespective of whether intravenous contrast material is used, there are no unique imaging characteristics that are specific for paragangliomas (6). Functional tumors tend to be smaller than nonfunctional tumors, in part because the symptoms caused by tumor-associated hormone secretion often lead to clinical and imaging evaluation at an earlier stage of the disease. This smaller size may occasionally make detection at CT difficult, especially at unenhanced CT. Although this patient did not suffer side effects from contrast-enhanced CT (originally ordered to evaluate for obstructive uropathy), it is a common policy at many institutions not to use intravenous contrast material for CT requested to "rule out pheochromocytoma" for fear of inciting a hypertensive crisis. Use of intravenous contrast material remains controversial given reports of reactions, especially induction of a hypertensive crisis. This concern frequently results in abdominal MR imaging being performed instead. Hypersensitivity reactions can be aggravated in patients on beta-blockers, and these patients may be refractory to standard treatment with beta agonists.
In patients with known elevated catecholamines and normal appearing adrenal glands, the entire sympathetic chain must be evaluated for the presence of an extraadrenal paraganglioma. Although 90% of paragangliomas are contained within the adrenal gland as pheochromocytomas, the remaining 10% are located elsewhere along the sympathetic chain, including the skull base and neck (5% of cases), thorax (10%), aorta (75%), and bladder (10%) (7). When a paraganglioma is suspected, CT may help identify the responsible tumor as a soft-tissue mass (usually 
3 cm) along the retroperitoneal path of the sympathetic nervous system. Of the paraganglionic tissues adjacent to the aorta, the organs of Zuckerkandl are the most common site of involvement. The organs of Zuckerkandl are located along the aorta, beginning cranial to the superior mesenteric artery or renal arteries and extending to the level of the aortic bifurcation or just beyond. The highest concentration is typically seen at the origin of the inferior mesenteric artery. The organs of Zuckerkandl are not often visualized radiologically unless they are involved by a pathologic process.
MR imaging may be used to evaluate an adrenal or extraadrenal mass suspected to be a pheochromocytoma. Because of its high sensitivity, full-body MR imaging has been advocated as a first-line test to evaluate for functioning paragangliomas (8). At T2-weighted imaging, pheochromocytomas tend to be hyperintense relative to the hepatic parenchyma, whereas most other adrenal masses tend to be isointense (9). It is virtually impossible to distinguish between nonfunctioning and functioning paragangliomas at MR imaging because they both demonstrate T2-weighted hyperintensity and intense contrast enhancement. It is important for the radiologist to realize that, although the majority of paragangliomas are hyperintense at T2-weighted MR imaging, a smaller but significant number are not, as in this case. It is suspected that a relatively higher concentration of fibrous tissue within the fibrovascular matrix may be responsible for tumors that demonstrate only mild T2-weighted hyperintensity, based on previous reports that document a subset of pheo-chromocytomas with relatively low T2-weighted signal intensity (10,11).
MIBG or Octreoscan (indium-111 pentetreotide) are both avidly taken up in adrenergic tissues. Nuclear scintigraphy with either of these markers may be useful in locating multiple primary tumors, tumors outside the usual locations, metastases, or smaller extraadrenal tumors that are below the threshold for CT and MR imaging. However, there is a 10% false-negative rate with MIBG scanning, which has led some authors to recommend abdominal CT or MR imaging if a high clinical suspicion of pheochromocytoma exists but a causative tumor is not identified with MIBG uptake. Positron emission tomography with 18F-fluorodeoxyglucose may also be useful in evaluating for metastatic disease, but larger clinical studies are still required before accurate comparisons can be made between positron emission tomography with 18F-fluorodeoxyglucose and MIBG scanning in terms of sensitivity and specificity.
Before image-guided biopsy is performed on indeterminate adrenal or retroperitoneal masses, correlation with biochemical markers should be made to exclude the possibility of a paraganglioma. Indiscriminate biopsies may result in hypertensive crisis or even death. For this reason, only those individuals who are well versed and knowledgeable in the pharmaceutic management of catecholamine blockade should attempt these procedures. Thus, a team approach including anesthesiologists and endocrinologists may be most appropriate if and when percutaneous biopsy is required.
Pathologic Characteristics
Paragangliomas are tumors that arise from paraganglionic tissue and are further classified on the basis of anatomic origin. Paragangliomas of the adrenal medulla are known as pheochromocytomas. The majority of paragangliomas of the head and neck are nonfunctioning tumors of the parasympathetic system that are often brought to clinical attention by symptoms of mass effect rather than excess catecholamine. Paragangliomas that arise from the jugulotympanic body are known as chemodectomas because of the specialized cells at this location, which are sensitive to changes in blood gas levels. Paragangliomas of the carotid body are simply called carotid body tumors. Tumors below the neck are more frequently functional and associated with the sympathetic system.
There are several important clinical differences between adrenal pheochromocytomas and extraadrenal paragangliomas, particularly tumors that arise from the paraaortic sympathetic chain. First, sporadic adrenal pheochromocytomas will often affect patients in the 5th to 7th decades of life, with a slight female predilection. Extraadrenal paragangliomas will affect patients in the 2nd or 3rd decade of life, with genetic tumors having a male predilection. Second, familial forms are far more likely to be bilateral than are sporadic tumors. Finally, extraadrenal tumors are more likely to be multifocal than are adrenal lesions.
At gross examination, paragangliomas range from 1 to 6 cm in diameter, with malignant tumors tending to be slightly larger (12). They are firm, encapsulated masses that adhere to adjacent structures. On cut section, paragangliomas are tan-red, with or without areas of necrosis. Microscopic analysis demonstrates neuroendocrine cells arranged in clusters called zellballen and interspersed with fibrovascular stroma. It is this vascular component that produces intense contrast enhancement at CT or MR imaging. Functional tumors contain neurosecretory granules that give the tumor a granular appearance with silver stain. When catecholamines are oxidized by potassium dichromate solution, a dark brown staining results. This "chromaffin reaction" is used to distinguish tumors of sympathetic origin from parasympathetic neural tumors. Specific antibodies for neuroendocrine markers such as synaptophysin and chromogranin, as well as S-100 protein, may also be used to confirm the diagnosis. Overall, the appearance may be impossible to distinguish from that of an adrenal pheochromocytoma without knowledge of tumor location.
Treatment
Treatment invariably involves surgical excision to reduce the symptoms of excess catecholamine. Angiographic arterial embolization has been used to debulk tumor burden in multicentric tumors, although it may be necessary to use chronic pharmacologic blockade if the lesions cannot be eliminated entirely. Chemotherapy has also been advocated but is used infrequently due to inconsistent response rates (13). Metastatic lesions have a poor prognosis, with a 5-year survival rate of 36% according to one study (14). Fortunately for this patient, there was no evidence of metastatic disease 2 years after tumor removal, and he no longer requires antihypertensive medications.
Although 10%–40% of extraadrenal paragangliomas are malignant, there are few pathologic or radiologic features that can help reliably predict benignity. Neither local tissue invasion, nuclear pleomorphism, nor mitotic activity necessarily implies malignancy. Unfortunately, it is only by the presence of metastases, seen at the time of initial discovery or as many as 15 years after surgical excision, that a diagnosis of malignancy can be confirmed.
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Footnotes
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Abbreviations: H-E = hematoxylin-eosin,
MEN = multiple endocrine neoplasia,
VMA = vanillylmandelic acid
Editor’s Note.—Everyone who has taken the course in radiologic pathology at the Armed Forces Institute of Pathology (AFIP) remembers bringing two beautifully illustrated cases for accession to the Institute. In recent years, the staff of the Department of Radiologic Pathology has judged the "best cases" by organ system, and recognition is given to the winners on the last day of the class. With each issue of RadioGraphics, one or more of these cases are published, written by the winning resident. Radiologic-pathologic correlation is emphasized, and the causes of the imaging signs of various diseases are illustrated.
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- Dunnick NR, Korobkin M. Imaging of adrenal incidentalomas: current status. AJR Am J Roentgenol 2002; 179:559-568.[Free Full Text]
- Lenders JW, Pacak K, Walther MM, et al. Biochemical diagnosis of pheochromocytoma: which test is best? JAMA 2002; 287:1427-1434.[Abstract/Free Full Text]
- Neumann HP, Bausch B, McWhinney SR, et al. Germ-line mutations in nonsyndromic pheochromocytoma. N Engl J Med 2002; 346:1459-1466.[Abstract/Free Full Text]
- Erickson D, Kudva YC, Ebersold MJ, et al. Benign paragangliomas: clinical presentation and treatment outcomes in 236 patients. J Clin Endocrinol Metab 2001; 86:5210-5216.[Abstract/Free Full Text]
- Hayes WS, Davidson AJ, Grimley PM, Hartman DS. Extraadrenal retroperitoneal paraganglioma: clinical, pathologic, and CT findings. AJR Am J Roentgenol 1990; 155:1247-1250.[Abstract/Free Full Text]
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- Bravo EL. Evolving concepts in the pathophysiology, diagnosis, and treatment of pheochromocytoma. Endocr Rev 1994; 15:356-368.[CrossRef][Medline]
- Baker ME, Blinder R, Spritzer C, et al. MR evaluation of adrenal masses at 1.5 T. AJR Am J Roentgenol 1989; 153:307-312.[Abstract/Free Full Text]
- Kier R, McCarthy S. MR characterization of adrenal masses: field strength and pulse sequence considerations. Radiology 1989; 171:671-674.[Abstract/Free Full Text]
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- Mikhail RA, Moore JB, Reed DN, Jr, Abbott RR. Malignant retroperitoneal paragangliomas. J Surg Oncol 1986; 32:32-36.[Medline]
- Sclafani LM, Woodruff JM, Brennan MF. Extraadrenal retroperitoneal paragangliomas: natural history and response to treatment. Surgery 1990; 108:1124-1129.[Medline]
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History
Imaging Findings
