DOI: 10.1148/rg.231025050
(Radiographics. 2003;23:29-43.)
© RSNA, 2003
Neurogenic Tumors in the Abdomen: Tumor Types and Imaging Characteristics1
Sung Eun Rha, MD,
Jae Young Byun, MD,
Seung Eun Jung, MD,
Ho Jong Chun, MD,
Hae Giu Lee, MD and
Jae Mun Lee, MD
1 From the Department of Radiology, College of Medicine, Catholic University of Korea, 505 Banpo-Dong, Seocho-Ku, Seoul 137-040, South Korea. Presented as an education exhibit at the 2001 RSNA scientific assembly. Received March 8, 2002; revision requested April 25 and received June 3; accepted June 4. Address correspondence to J.Y.B. (e-mail: jybyun@catholic.ac.kr).
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Abstract
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There is a broad spectrum of neurogenic tumors that involve the abdomen. These tumors can be classified as those of (a) ganglion cell origin (ganglioneuromas, ganglioneuroblastomas, neuroblastomas), (b) paraganglionic system origin (pheochromocytomas, paragangliomas), and (c) nerve sheath origin (neurilemmomas, neurofibromas, neurofibromatosis, malignant nerve sheath tumors). Abdominal neurogenic tumors are most commonly located in the retroperitoneum, especially in the paraspinal areas and adrenal glands. All of these tumors except neuroblastomas and ganglioneuroblastomas are seen in adult patients. Abdominal neurogenic tumor commonly manifests radiologically as a well-defined, smooth or lobulated mass. Calcification may be seen in all types of neurogenic tumors. The diagnosis of abdominal neurogenic tumor is suggested by the imaging appearance of the lesion, including its location, shape, and internal architecture. Benign and malignant neurogenic tumors are difficult to differentiate unless distant metastatic foci are seen. For malignant tumors, imaging modalities other than computed tomography (CT) and magnetic resonance (MR) imaging may be necessary for staging. However, because most neurogenic tumors in adults are benign, CT and MR imaging can be used to develop a differential diagnosis and help determine the immediate local extent of tumor.
© RSNA, 2003
Index Terms: Nervous system, neoplasms, 87.31, 87.32 • Neurons, 87.3199, 87.364 • Retroperitoneal space, CT, 87.1211 • Retroperitoneal space, MR, 87.1214 • Retroperitoneal space, neoplasms, 87.3199, 87.325, 87.328 • Soft tissues, neoplasms, 80.325
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LEARNING OBJECTIVES FOR TEST 2
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After reading this article and taking the test, the reader will be able to:
- Describe the pathologic characteristics of neurogenic tumors in the abdomen.
- Recognize the typical clinical and imaging findings in these tumors.
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Introduction
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Various types of neurogenic tumors can affect the abdomen. These tumors can be classified as being of ganglion cell origin (ganglioneuromas, ganglioneuroblastomas, neuroblastomas), paraganglionic system origin (pheochromocytomas, paragangliomas), or nerve sheath origin (neurilemmomas, neurofibromas, neurofibromatosis, malignant nerve sheath tumors) (1–3). Abdominal neurogenic tumors usually follow the distribution of the sympathetic ganglia along paraspinal areas or arise from the adrenal medulla or the organ of Zuckerkandl. Occasionally, however, other sites in the abdomen (eg, urinary bladder, bowel wall, abdominal wall, gallbladder) can be involved (3). The urinary bladder is an unusual site of involvement because the trigone of the bladder contains cells of neural crest origin.
The optimal treatment for abdominal neurogenic tumors is surgical removal when they are localized with no evidence of distant metastasis. Recently, laparoscopic surgery has been used (4,5). Thus, accurate preoperative localization and characterization of neurogenic tumor is important in allowing a direct surgical approach. Although all neurogenic tumors have similar clinical and radiologic findings, predominant or specific features are present in each type. In this article, we describe and illustrate the clinical, computed tomographic (CT), and magnetic resonance (MR) imaging features of abdominal neurogenic tumors that can suggest a specific diagnosis or help substantially narrow the differential diagnosis.
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Tumors of Ganglion Cell Origin
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Tumors of ganglion cell origin include ganglioneuroma (benign), neuroblastoma (malignant), and ganglioneuroblastoma (intermediate). The adrenal gland is the most common primary site of involvement for these tumors. Neuroblastoma and ganglioneuroblastoma most often occur in infants and children, whereas ganglioneuroma tends to occur in adolescents and young adults (1–3).
Ganglioneuromas
Ganglioneuromas are rare, benign neurogenic tumors that arise from sympathetic ganglia. The tumors are composed of mature Schwann cells, ganglion cells, and nerve fibers. Ganglioneuromas may arise anywhere along the paravertebral sympathetic plexus and occasionally from the adrenal medulla. The retroperitoneum (32%–52% of cases) and posterior mediastinum (39%–43%) are the two most common locations for a ganglioneuroma, followed by the cervical region (8%–9%) (1–3,6–8). In a series of 46 patients with abdominal ganglioneuroma, the tumor was located in the extraadrenal retroperitoneum in 27 patients (59%) and in the adrenal gland in 19 patients (41%) (3). Patients of all ages are affected, predominantly children and young adults (42%–60% of cases) (6,8,9). The prognosis is excellent, and recurrence is rare after surgical resection.
Ganglioneuromas are often asymptomatic even if they are large. Otherwise, abdominal pain or the palpation of an abdominal mass is the most common clinical feature. Hormonally active forms have been reported, and the secretion of catecholamines, vasoactive intestinal polypeptides, or androgenic hormones explains such symptoms as hypertension, diarrhea, and virilization (8,9).
At CT or MR imaging, retroperitoneal or adrenal ganglioneuromas appear as well-circum-scribed oval, crescentic, or lobulated masses. Interestingly, these tumors tend to partially or completely surround major blood vessels, with little or no compromise of the lumen (Fig 1) (7,8,10). At unenhanced CT, the tumors appear homogeneous, with an attenuation less than that of muscle. At CT, they contain calcification in about 20% of cases. The calcifications are discrete and punctate (Fig 2a) rather than amorphous and coarse as in neuroblastomas (6). Varying degrees of contrast material enhancement in ganglioneuroma have been reported, from slight to moderate to marked. Ichikawa et al (6) reported an interesting contrast enhancement pattern in ganglioneuroma that consisted of delayed heterogeneous uptake (Fig 2b, 2c, 2f–2h). These enhancement features are explained by the presence of an abundance of myxoid matrices in the tumors, resulting in delayed progressive accumulation of contrast material in the extracellular space (6).
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Figure 1. Retroperitoneal ganglioneuroma in a 48-year-old woman. Contrast material-enhanced CT scan shows a relatively homogeneous mass (black arrows) that is hypoattenuating relative to muscle. The mass partially surrounds the inferior vena cava (V) and aorta (A). The right lateral gland (white arrow) is seen lateral to the posterior portion of the mass.
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Figure 2a. Right adrenal ganglioneuroma in a 24-year-old woman. (a) Axial unenhanced CT scan demonstrates a well-defined oval mass (thick arrow) in the right adrenal gland. The mass appears homogeneous, is hypoattenuating relative to muscle, and contains central small punctate calcifications (thin arrow). (b, c) Nephrographic phase (b) and excretory phase (c) contrast-enhanced CT scans show delayed gradual contrast enhancement of the mass (arrow). (d) On an axial T1-weighted MR image, the tumor (arrow) is homogeneous and is hypointense relative to liver. (e) On an axial T2-weighted MR image, the mass (arrow) is heterogeneous and is hyperintense relative to liver. (f-h) Axial contrast-enhanced dynamic T1-weighted MR images obtained 15 seconds (f), 55 seconds (g), and 3 minutes (h) after contrast material injection also show gradual but heterogeneous enhancement of the mass.
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Figure 2b. Right adrenal ganglioneuroma in a 24-year-old woman. (a) Axial unenhanced CT scan demonstrates a well-defined oval mass (thick arrow) in the right adrenal gland. The mass appears homogeneous, is hypoattenuating relative to muscle, and contains central small punctate calcifications (thin arrow). (b, c) Nephrographic phase (b) and excretory phase (c) contrast-enhanced CT scans show delayed gradual contrast enhancement of the mass (arrow). (d) On an axial T1-weighted MR image, the tumor (arrow) is homogeneous and is hypointense relative to liver. (e) On an axial T2-weighted MR image, the mass (arrow) is heterogeneous and is hyperintense relative to liver. (f-h) Axial contrast-enhanced dynamic T1-weighted MR images obtained 15 seconds (f), 55 seconds (g), and 3 minutes (h) after contrast material injection also show gradual but heterogeneous enhancement of the mass.
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Figure 2c. Right adrenal ganglioneuroma in a 24-year-old woman. (a) Axial unenhanced CT scan demonstrates a well-defined oval mass (thick arrow) in the right adrenal gland. The mass appears homogeneous, is hypoattenuating relative to muscle, and contains central small punctate calcifications (thin arrow). (b, c) Nephrographic phase (b) and excretory phase (c) contrast-enhanced CT scans show delayed gradual contrast enhancement of the mass (arrow). (d) On an axial T1-weighted MR image, the tumor (arrow) is homogeneous and is hypointense relative to liver. (e) On an axial T2-weighted MR image, the mass (arrow) is heterogeneous and is hyperintense relative to liver. (f-h) Axial contrast-enhanced dynamic T1-weighted MR images obtained 15 seconds (f), 55 seconds (g), and 3 minutes (h) after contrast material injection also show gradual but heterogeneous enhancement of the mass.
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Figure 2d. Right adrenal ganglioneuroma in a 24-year-old woman. (a) Axial unenhanced CT scan demonstrates a well-defined oval mass (thick arrow) in the right adrenal gland. The mass appears homogeneous, is hypoattenuating relative to muscle, and contains central small punctate calcifications (thin arrow). (b, c) Nephrographic phase (b) and excretory phase (c) contrast-enhanced CT scans show delayed gradual contrast enhancement of the mass (arrow). (d) On an axial T1-weighted MR image, the tumor (arrow) is homogeneous and is hypointense relative to liver. (e) On an axial T2-weighted MR image, the mass (arrow) is heterogeneous and is hyperintense relative to liver. (f-h) Axial contrast-enhanced dynamic T1-weighted MR images obtained 15 seconds (f), 55 seconds (g), and 3 minutes (h) after contrast material injection also show gradual but heterogeneous enhancement of the mass.
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Figure 2e. Right adrenal ganglioneuroma in a 24-year-old woman. (a) Axial unenhanced CT scan demonstrates a well-defined oval mass (thick arrow) in the right adrenal gland. The mass appears homogeneous, is hypoattenuating relative to muscle, and contains central small punctate calcifications (thin arrow). (b, c) Nephrographic phase (b) and excretory phase (c) contrast-enhanced CT scans show delayed gradual contrast enhancement of the mass (arrow). (d) On an axial T1-weighted MR image, the tumor (arrow) is homogeneous and is hypointense relative to liver. (e) On an axial T2-weighted MR image, the mass (arrow) is heterogeneous and is hyperintense relative to liver. (f-h) Axial contrast-enhanced dynamic T1-weighted MR images obtained 15 seconds (f), 55 seconds (g), and 3 minutes (h) after contrast material injection also show gradual but heterogeneous enhancement of the mass.
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Figure 2f. Right adrenal ganglioneuroma in a 24-year-old woman. (a) Axial unenhanced CT scan demonstrates a well-defined oval mass (thick arrow) in the right adrenal gland. The mass appears homogeneous, is hypoattenuating relative to muscle, and contains central small punctate calcifications (thin arrow). (b, c) Nephrographic phase (b) and excretory phase (c) contrast-enhanced CT scans show delayed gradual contrast enhancement of the mass (arrow). (d) On an axial T1-weighted MR image, the tumor (arrow) is homogeneous and is hypointense relative to liver. (e) On an axial T2-weighted MR image, the mass (arrow) is heterogeneous and is hyperintense relative to liver. (f-h) Axial contrast-enhanced dynamic T1-weighted MR images obtained 15 seconds (f), 55 seconds (g), and 3 minutes (h) after contrast material injection also show gradual but heterogeneous enhancement of the mass.
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Figure 2g. Right adrenal ganglioneuroma in a 24-year-old woman. (a) Axial unenhanced CT scan demonstrates a well-defined oval mass (thick arrow) in the right adrenal gland. The mass appears homogeneous, is hypoattenuating relative to muscle, and contains central small punctate calcifications (thin arrow). (b, c) Nephrographic phase (b) and excretory phase (c) contrast-enhanced CT scans show delayed gradual contrast enhancement of the mass (arrow). (d) On an axial T1-weighted MR image, the tumor (arrow) is homogeneous and is hypointense relative to liver. (e) On an axial T2-weighted MR image, the mass (arrow) is heterogeneous and is hyperintense relative to liver. (f-h) Axial contrast-enhanced dynamic T1-weighted MR images obtained 15 seconds (f), 55 seconds (g), and 3 minutes (h) after contrast material injection also show gradual but heterogeneous enhancement of the mass.
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Figure 2h. Right adrenal ganglioneuroma in a 24-year-old woman. (a) Axial unenhanced CT scan demonstrates a well-defined oval mass (thick arrow) in the right adrenal gland. The mass appears homogeneous, is hypoattenuating relative to muscle, and contains central small punctate calcifications (thin arrow). (b, c) Nephrographic phase (b) and excretory phase (c) contrast-enhanced CT scans show delayed gradual contrast enhancement of the mass (arrow). (d) On an axial T1-weighted MR image, the tumor (arrow) is homogeneous and is hypointense relative to liver. (e) On an axial T2-weighted MR image, the mass (arrow) is heterogeneous and is hyperintense relative to liver. (f-h) Axial contrast-enhanced dynamic T1-weighted MR images obtained 15 seconds (f), 55 seconds (g), and 3 minutes (h) after contrast material injection also show gradual but heterogeneous enhancement of the mass.
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At MR imaging, ganglioneuromas are homogeneous with relatively low signal intensity on T1-weighted images (Fig 2d). Interestingly, their T2 signal intensity depends on the proportion of myxoid stroma to cellular components and the amount of collagen fibers in the tumor. Tumors with intermediate to high signal intensity on T2-weighted MR images (Fig 2e) consist of numerous cellular and fibrous components and only a small amount of myxoid stroma. Those with markedly high signal intensity on T2-weighted images (Fig 3) consist of a large amount of myxoid stroma and relatively few cellular and fibrous components. One of the MR imaging characteristics of ganglioneuroma is curvilinear bands of low signal intensity on T2-weighted images, which give the tumor a whorled appearance (Fig 3). These low-signal-intensity bands represent (a) interlacing bundles of longitudinal and transversely oriented Schwann cells that crisscross each other in an irregular fashion and (b) collagen fibers within the tumor. As at contrast-enhanced CT, ganglioneuromas usually demonstrate gradually increasing enhancement rather than early enhancement at contrast-enhanced dynamic MR imaging (Fig 2f–2h) (11).
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Figure 3a. Left retroperitoneal ganglioneuroma in a 20-year-old man. (a) Axial T1-weighted MR image shows a homogeneous, low-signal-intensity tumor (arrow) in the retroperitoneum medial to the left kidney. (b) Axial T2-weighted MR image shows linear and curvilinear low-signal-intensity areas within the markedly high-signal-intensity tumor (arrow), which has a somewhat whorled appearance. (c) On a coronal contrast-enhanced T1-weighted MR image, the tumor is poorly enhanced, except for the central portion (arrow). LK = left kidney.
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Figure 3b. Left retroperitoneal ganglioneuroma in a 20-year-old man. (a) Axial T1-weighted MR image shows a homogeneous, low-signal-intensity tumor (arrow) in the retroperitoneum medial to the left kidney. (b) Axial T2-weighted MR image shows linear and curvilinear low-signal-intensity areas within the markedly high-signal-intensity tumor (arrow), which has a somewhat whorled appearance. (c) On a coronal contrast-enhanced T1-weighted MR image, the tumor is poorly enhanced, except for the central portion (arrow). LK = left kidney.
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Figure 3c. Left retroperitoneal ganglioneuroma in a 20-year-old man. (a) Axial T1-weighted MR image shows a homogeneous, low-signal-intensity tumor (arrow) in the retroperitoneum medial to the left kidney. (b) Axial T2-weighted MR image shows linear and curvilinear low-signal-intensity areas within the markedly high-signal-intensity tumor (arrow), which has a somewhat whorled appearance. (c) On a coronal contrast-enhanced T1-weighted MR image, the tumor is poorly enhanced, except for the central portion (arrow). LK = left kidney.
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Ganglioneuroblastomas and Neuroblastomas
Ganglioneuroblastomas are transitional tumors of sympathetic cell origin that contain elements of both malignant neuroblastoma and benign ganglioneuroma. At histologic analysis, they are malignant tumors that contain primitive neuroblasts and mature ganglion cells. The most common tumor site is the abdomen, followed by the mediastinum, neck, and lower extremity. Ganglioneuroblastomas are most often seen in patients 2–4 years old and are exceedingly rare after the age of 10 years (12). According to Yamanaka et al (13), only 33 cases of retroperitoneal ganglioneuroblastoma in adults have been reported in the English medical literature. Ganglioneuroblastomas occur with equal frequency in boys and girls. Their prognosis and their response to therapy are significantly more favorable than those of neuroblastomas (14).
At gross examination, ganglioneuroblastomas may be partially or totally encapsulated and frequently contain granular calcification (15). Their appearance varies depending on the number of ganglion cells, their degree of differentiation, and their relationship to immature elements (3). Therefore, the reported CT findings in ganglioneuroblastomas also vary, ranging from a predominantly solid mass to a predominantly cystic mass with a few thin strands of solid tissue (15–17).
Neuroblastomas are malignant tumors that consist of primitive neuroblasts and may arise anywhere within the sympathetic plexus or adrenal medulla (15). At histologic analysis, neuroblastomas are composed of small, dark neuroepithelial cells that may show glial or ganglionic differentiation and contain nests of primitive round cells with dark-staining nuclei and scant cytoplasm. They most commonly occur during the first 10 years of life. Boys are more frequently affected than girls. Approximately 80% of these neoplasms are found in children under the age of 5 years, and 35% are found in those under the age of 2 years (15). Two-thirds of neuroblastomas are located in the abdomen, and approximately two-thirds of these abdominal lesions arise in the adrenal gland. The remaining abdominal or pelvic tumors almost always originate in the paravertebral sympathetic chain or presacral area, with an occasional abdominal tumor arising in the celiac axis or organ of Zuckerkandl. Adult-type abdominal neuroblastomas have been reported only very rarely (18). Neuroblastomas tend to metastasize to bone, bone marrow, liver, lymph nodes, and skin. At least 70% of affected patients have disseminated disease at the time of diagnosis (15).
Neuroblastomas are more aggressive than ganglioneuromas; the majority are irregularly shaped, lobulated, and unencapsulated. Sometimes they invade adjacent organs or encase adjacent vessels. Neuroblastomas tend to be inhomogeneous owing to tumor necrosis and hemorrhage (Fig 4). They contain calcification in approximately 85% of cases at CT and in up to 55% of cases at conventional radiography (19). Calcifications in neuroblastomas are usually coarse, amorphous, and mottled in appearance (Fig 5), as opposed to the discrete and punctate calcifications observed in ganglioneuromas. CT and MR imaging are useful for defining the morphologic features of neuroblastoma and precisely assessing tumor extent. They can also help determine tumor extension to the retroperitoneal lymph nodes and liver, around the central vessels, and into the vertebral canal (15).
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Figure 4a. Left adrenal neuroblastoma in an 18-year-old woman. (a) Axial T1-weighted MR image shows a huge heterogeneous mass (arrows) that involves the left side of the retroperitoneum. The anterior portion of the mass has higher signal intensity than the posterior portion, a finding that suggests hemorrhagic necrosis of the tumor. (b) On an axial T2-weighted MR image, the tumor (arrows) demonstrates heterogeneous high signal intensity. (c) Coronal contrast-enhanced T1-weighted MR image also shows a huge suprarenal mass (arrows) with heterogeneous contrast enhancement. The mass displaces the left kidney (LK) inferiorly.
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Figure 4b. Left adrenal neuroblastoma in an 18-year-old woman. (a) Axial T1-weighted MR image shows a huge heterogeneous mass (arrows) that involves the left side of the retroperitoneum. The anterior portion of the mass has higher signal intensity than the posterior portion, a finding that suggests hemorrhagic necrosis of the tumor. (b) On an axial T2-weighted MR image, the tumor (arrows) demonstrates heterogeneous high signal intensity. (c) Coronal contrast-enhanced T1-weighted MR image also shows a huge suprarenal mass (arrows) with heterogeneous contrast enhancement. The mass displaces the left kidney (LK) inferiorly.
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Figure 4c. Left adrenal neuroblastoma in an 18-year-old woman. (a) Axial T1-weighted MR image shows a huge heterogeneous mass (arrows) that involves the left side of the retroperitoneum. The anterior portion of the mass has higher signal intensity than the posterior portion, a finding that suggests hemorrhagic necrosis of the tumor. (b) On an axial T2-weighted MR image, the tumor (arrows) demonstrates heterogeneous high signal intensity. (c) Coronal contrast-enhanced T1-weighted MR image also shows a huge suprarenal mass (arrows) with heterogeneous contrast enhancement. The mass displaces the left kidney (LK) inferiorly.
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Figure 5. Right adrenal neuroblastoma in a 5-year-old girl. Contrast-enhanced CT scan shows a lobulated, inhomogeneous mass with low attenuation that is located in the right suprarenal region and extends across the midline. Dense intratumoral calcifications are also noted (arrows). The tumor displaces the aorta (A) and inferior vena cava (V) ventrally.
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Tumors of the Paraganglionic System
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The paraganglia are widely dispersed collections of specialized neural crest cells that lie adjacent to the sympathetic ganglia and plexuses throughout the body. The paraganglionic system includes the adrenal medulla, the chemoreceptors (ie, carotid and aortic bodies), vagal body, and the small groups of cells associated with the thoracic as well as intraabdominal and retroperitoneal ganglia (3). Tumors that arise from the chromaffin cells of the adrenal medulla are called pheochromocytomas, whereas those that occur in paraganglia at other sites are referred to as paragangliomas.
Although their true prevalence is unknown, pheochromocytomas are thought to be the cause of hypertension in approximately 0.1%–0.5% of patients with newly diagnosed hypertension. These tumors occur with equal frequency in men and women and appear to be more common in the 3rd and 4th decades of life (20).
Pheochromocytomas have been called "ten percent tumors" because approximately 10% are bilateral, 10% are extraadrenal (paragangliomas of the retroperitoneum, mediastinum, or urinary bladder), 10% occur in children, and 10% are malignant. When they occur in children, there often tends to be a high familial prevalence. Pheochromocytomas are associated with multiple endocrine neoplasm (MEN) IIa and IIb or III syndrome, von Hippel–Lindau syndrome, and neurofibromatosis type 1 (NF-1, von Recklinghausen disease, or peripheral neurofibromatosis). MEN IIa syndrome consists of pheochromocytoma, medullary carcinoma of the thyroid gland, and parathyroid hyperplasia, whereas MEN IIb or III syndrome consists of pheochromocytoma, medullary carcinoma of the thyroid gland, ganglioneuromatosis, and multiple mucosal neuromas (20). Pheochromocytomas associated with MEN syndrome tend to be bilateral and are almost always intraadrenal; they also tend to be benign (21).
The clinical manifestations of pheochromocytoma result from the known physiologic effects of catecholamine release. The classic triad of headache, palpitation, and excessive sweating is seen during the paroxysmal hypertensive crisis. Urinary metanephrine or vanillylmandelic acid levels are elevated in over 90% of patients from whom 24-hour urine collections are obtained (21).
If laboratory test results indicate a pheochromocytoma, CT of the adrenal gland is performed first. If no lesion is found, CT is then performed through the organ of Zuckerkandl to encompass all chromaffin cell-bearing tissue along the lower abdominal aorta from the origin of the inferior mesenteric artery to the aortic bifurcation and into the iliac vessels. If there is still no evidence of a lesion, CT is performed on through the bladder, another common site of paraganglioma. At CT, both pheochromocytomas and paragangliomas are usually 3 cm or larger, demonstrate areas of necrosis or hemorrhage (Fig 6), and may even contain fluid-fluid levels except in patients with MEN syndrome, in whom the tumors tend to be small. In MEN syndrome, the adrenal glands can be thickened and nodular without large masses (adrenal medullary hyperplasia) (20). The tumors are hypervascular and exhibit marked enhancement after intravenous administration of contrast material. CT can be performed safely with intravenous administration of low-osmolarity, nonionic contrast material; recent studies have shown no elevation of serum catecholamine levels when such contrast material is used (22).
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Figure 6a. Pheochromocytoma in a 32-year-old woman with hypertension. (a) Contrast-enhanced CT scan shows a 7-cm mass (arrow) in the right adrenal gland with marked contrast enhancement and well-defined internal cystic change. (b) On a coronal T2-weighted MR image, the mass (arrow) demonstrates high signal intensity. (c) Coronal contrast-enhanced T1-weighted MR image shows the right adrenal mass (arrow) with strong contrast enhancement and internal cystic change.
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Figure 6b. Pheochromocytoma in a 32-year-old woman with hypertension. (a) Contrast-enhanced CT scan shows a 7-cm mass (arrow) in the right adrenal gland with marked contrast enhancement and well-defined internal cystic change. (b) On a coronal T2-weighted MR image, the mass (arrow) demonstrates high signal intensity. (c) Coronal contrast-enhanced T1-weighted MR image shows the right adrenal mass (arrow) with strong contrast enhancement and internal cystic change.
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Figure 6c. Pheochromocytoma in a 32-year-old woman with hypertension. (a) Contrast-enhanced CT scan shows a 7-cm mass (arrow) in the right adrenal gland with marked contrast enhancement and well-defined internal cystic change. (b) On a coronal T2-weighted MR image, the mass (arrow) demonstrates high signal intensity. (c) Coronal contrast-enhanced T1-weighted MR image shows the right adrenal mass (arrow) with strong contrast enhancement and internal cystic change.
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If no lesion is found or identified at CT and laboratory test results remain positive, radionuclide imaging with metaiodobenzylguanidine is suggested to identify the occult lesion (Fig 7)(23). This radionuclide imaging study is a more practical way of examining the entire body and is valuable in localizing paragangliomas. MR imaging can also be used to help locate a paraganglioma; however, only about 80% of T2-weighted MR imaging studies will show the characteristic uniform high-signal-intensity image ("light bulb") because the presence of internal hemorrhage may reduce signal intensity (20). Rarely, spontaneous rupture of a pheochromocytoma or paraganglioma can be the cause of lethal retroperitoneal hemorrhage, manifesting as acute abdomen (Fig 8) (24,25).
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Figure 7a. Paraganglioma involving the organ of Zuckerkandl in a 33-year-old woman. (a) Contrast-enhanced CT scan shows a lobulated, inhomogeneous solid mass (arrow) in the left side of the retroperitoneum. (b) Anterior abdominal radionuclide scan obtained 72 hours after injection of 123-iodine metaiodobenzylguanidine demonstrates focal uptake in the left paraspinal area (arrow), a finding that suggests a paraganglioma.
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Figure 7b. Paraganglioma involving the organ of Zuckerkandl in a 33-year-old woman. (a) Contrast-enhanced CT scan shows a lobulated, inhomogeneous solid mass (arrow) in the left side of the retroperitoneum. (b) Anterior abdominal radionuclide scan obtained 72 hours after injection of 123-iodine metaiodobenzylguanidine demonstrates focal uptake in the left paraspinal area (arrow), a finding that suggests a paraganglioma.
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Figure 8a. Spontaneous rupture of a paraganglioma in a 52-year-old man who presented with acute abdominal pain. (a) Contrast-enhanced CT scan shows a retroperitoneal mass (arrow) with strong peripheral enhancement and central low-attenuation necrosis. (b) Contrast-enhanced CT scan obtained caudad to a demonstrates a low-attenuation fluid collection and hazy infiltration (arrows) along the left paraaortic space, findings that mimic rupture of an aortic aneurysm. Surgical findings confirmed a paraganglioma with spontaneous rupture.
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Figure 8b. Spontaneous rupture of a paraganglioma in a 52-year-old man who presented with acute abdominal pain. (a) Contrast-enhanced CT scan shows a retroperitoneal mass (arrow) with strong peripheral enhancement and central low-attenuation necrosis. (b) Contrast-enhanced CT scan obtained caudad to a demonstrates a low-attenuation fluid collection and hazy infiltration (arrows) along the left paraaortic space, findings that mimic rupture of an aortic aneurysm. Surgical findings confirmed a paraganglioma with spontaneous rupture.
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Paragangliomas have a more aggressive course than their adrenal counterparts (Fig 9). Approximately 20%–42% of paragangliomas metastasize, compared with only 2%–10% of adrenal pheochromocytomas (3). Dissemination occurs both lymphatically and hematogenously, with the most common sites of metastasis being the regional lymph nodes, bone, liver, and lung. Because benign and malignant paragangliomas have an identical histologic appearance, their clinical behavior (eg, recurrent or metastatic disease) is the best predictor of the prognosis (3).
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Figure 9a. Malignant paraganglioma with peritoneal seeding in a 73-year-old woman. (a) Contrast-enhanced CT scan shows a large, lobulated mass (T) with central necrosis in the pelvic cavity. (b) Contrast-enhanced CT scan obtained caudad to a shows another solid mass (M) adjacent to the primary mass, a finding that suggests peritoneal tumor seeding. Surgical findings confirmed malignant paraganglioma with peritoneal tumor seeding.
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Figure 9b. Malignant paraganglioma with peritoneal seeding in a 73-year-old woman. (a) Contrast-enhanced CT scan shows a large, lobulated mass (T) with central necrosis in the pelvic cavity. (b) Contrast-enhanced CT scan obtained caudad to a shows another solid mass (M) adjacent to the primary mass, a finding that suggests peritoneal tumor seeding. Surgical findings confirmed malignant paraganglioma with peritoneal tumor seeding.
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Tumors of Nerve Sheath Origin
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Tumors of nerve sheath origin include neurilemmoma, neurofibroma, neurofibromatosis, and neurogenic sarcoma (malignant schwannoma). More than 90% of these tumors are benign (33). The benign lesions are identified in young and middle-aged adults. Neurilemmoma is more common than neurofibroma. Tumors of nerve sheath origin may be multiple in 10% of cases (2).
Neurilemmomas
Neurilemmomas, or schwannomas, are benign neurogenic tumors that arise from the nerve sheaths of peripheral nerves. They tend to be encapsulated, with the nerve fibers stretched around the tumor. Neurilemmomas may occur nearly anywhere in the body but have a predilection for the head, the neck, and the flexor surfaces of the upper and lower extremities. Deeply situated tumors predominate in the retroperitoneum and posterior mediastinum (3). Neurilemmomas comprise 6% of primary retroperitoneal neoplasms (26). They are usually located in the paravertebral regions (Fig 10), adjacent to the kidney (Fig 11), or in the presacral pelvic retroperitoneum (27,28). Occasionally, they occur in the abdominal wall (Fig 12), urinary bladder, or bowel wall. Neurilemmomas are usually less than 5 cm in diameter, but retroperitoneal neurilemmomas may be larger tumors that have been growing slowly over a long period of time. Inadequate blood supply to the center of the tumor sometimes causes secondary degenerative changes such as cyst formation, calcification, hemorrhage, and hyalinization (3). These degenerative tumors are called ancient schwannomas. At histologic analysis, neurilemmomas usually consist of two different components, designated by the Swedish neurologist Nils Antoni as A and B. Antoni type A areas are highly cellular and are composed of spindle cells that often have a palisade or organoid arrangement. In Antoni type B areas, the tumor cells are separated by abundant edematous fluid that may form cystic spaces (29). Neurilemmomas usually occur in young to middle-aged adults, and women are affected twice as often as men. The tumors are generally asymptomatic and therefore discovered incidentally (27).
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Figure 10. Multiple neurilemmomas in a 48-year-old woman. Coronal contrast-enhanced reformatted CT scan shows two lobulated soft-tissue-attenuation masses (arrows) in the left paravertebral space. The lower mass shows prominent cystic degeneration.
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Figure 11. Retroperitoneal neurilemmoma in a 43-year-old woman. Contrast-enhanced CT scan shows a well-defined round mass in the left retroperitoneal space adjacent to the left kidney. The mass appears to have homogeneous low attenuation with a thick rim. Dense peripheral calcifications (arrows) are also seen in the periphery of the mass.
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Figures 12. Neurilemmoma in a 35-year-old man. Contrast-enhanced CT scan shows a tumor with poor contrast enhancement (arrow) in the anterior abdominal wall. The tumor causes splaying of the left rectus abdominis muscle.
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At CT, a neurilemmoma appears as a well-demarcated round or oval mass that frequently demonstrates prominent cystic degeneration and calcification (Figs 10, 11). Calcifications are punctate, mottled, or curvilinear and are seen along the walls of the mass. At contrast-enhanced CT, neurilemmomas demonstrate variable homogeneous or heterogeneous enhancement. Heterogeneous contrast enhancement represents variation in the degree of cellularity. Loose cellularity with diffuse edematous change may result in minimal contrast enhancement. Heterogeneous areas on enhanced CT scans may also be due to cystic and hemorrhagic changes (27,28,30). It is difficult to identify the peripheral nerve from which retroperitoneal neurilemmomas develop.
MR imaging findings in neurilemmoma have been described as masses with low signal intensity on T1-weighted images and with inhomogeneous high signal intensity on T2-weighted images due to alternating Antoni A and B areas and secondary degenerative changes (Fig 13) (31). Contrast-enhanced T1-weighted MR images can clearly depict cystic necrotic areas and well-enhanced peripheral and intervening solid areas of the mass (27,32).
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Figure 13a. Retroperitoneal neurilemmoma in a 38-year-old woman. (a) Contrast-enhanced CT scan shows a well-defined low-attenuation mass adjacent to the right kidney. (b) Axial T1-weighted MR image shows a homogeneous low-signal-intensity tumor (arrow). (c) On an axial turbo spin-echo T2-weighted MR image, the tumor has heterogeneous high signal intensity and is located posterior to the inferior vena cava (V). (d) Axial contrast-enhanced T1-weighted MR image shows the mass with inhomogeneous contrast enhancement (arrow), although it looked like a cystic tumor at CT (cf a).
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Figure 13b. Retroperitoneal neurilemmoma in a 38-year-old woman. (a) Contrast-enhanced CT scan shows a well-defined low-attenuation mass adjacent to the right kidney. (b) Axial T1-weighted MR image shows a homogeneous low-signal-intensity tumor (arrow). (c) On an axial turbo spin-echo T2-weighted MR image, the tumor has heterogeneous high signal intensity and is located posterior to the inferior vena cava (V). (d) Axial contrast-enhanced T1-weighted MR image shows the mass with inhomogeneous contrast enhancement (arrow), although it looked like a cystic tumor at CT (cf a).
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Figure 13c. Retroperitoneal neurilemmoma in a 38-year-old woman. (a) Contrast-enhanced CT scan shows a well-defined low-attenuation mass adjacent to the right kidney. (b) Axial T1-weighted MR image shows a homogeneous low-signal-intensity tumor (arrow). (c) On an axial turbo spin-echo T2-weighted MR image, the tumor has heterogeneous high signal intensity and is located posterior to the inferior vena cava (V). (d) Axial contrast-enhanced T1-weighted MR image shows the mass with inhomogeneous contrast enhancement (arrow), although it looked like a cystic tumor at CT (cf a).
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Figure 13d. Retroperitoneal neurilemmoma in a 38-year-old woman. (a) Contrast-enhanced CT scan shows a well-defined low-attenuation mass adjacent to the right kidney. (b) Axial T1-weighted MR image shows a homogeneous low-signal-intensity tumor (arrow). (c) On an axial turbo spin-echo T2-weighted MR image, the tumor has heterogeneous high signal intensity and is located posterior to the inferior vena cava (V). (d) Axial contrast-enhanced T1-weighted MR image shows the mass with inhomogeneous contrast enhancement (arrow), although it looked like a cystic tumor at CT (cf a).
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Neurofibromas and Neurofibromatosis
Neurofibromas can manifest as a solitary tumor or as a component of neurofibromatosis. In a series by Geschickter, about 90% of neurofibromas were of the solitary type, whereas the remainder were found in the setting of von Recklinghausen disease (3). Neurofibromas originate from the nerve sheath. At histologic analysis, they demonstrate proliferation of nerve sheath cells interspersed with thick, wavy collagen bundles and may show variable degrees of myxoid degeneration (31,33). Although both neurilemmomas and neurofibromas are of nerve sheath origin, each has a characteristic histologic appearance and can occur in different clinical settings (Table). Unlike neurilemmomas, neurofibromas are not encapsulated and lack a clear partition into Antoni A and B areas. Nerve fibers run through neurofibromas; this finding also helps distinguish them from neurilemmomas, in which the nerve fibers diverge and course over the surface of the tumor before reconverging distally to form a normal nerve (34). In addition, in contrast to neurilemmomas, pure neurofibromas are solid tumors at macroscopic analysis. Areas of cystic degeneration, hypocellularity, and xanthomatous material are uncommon in neurofibromas. Neurofibromas often undergo malignant degeneration, particularly in cases of neurofibromatosis, whereas neurilemmomas rarely if ever undergo malignant degeneration. Neurofibromas occur more frequently in men than in women. They are commonly diagnosed in patients in the 2nd to 4th decades of life.
At CT, neurofibromas have a homogeneous, smooth, round appearance with distinct outlines. They have attenuation values of 20–25 HU on unenhanced scans as well as homogeneous enhancement with attenuation values of 30–50 HU on contrast-enhanced scans (35). Kumar et al (36) suggested that the low attenuation of neurofibromas on unenhanced CT scans is attributable mainly to lipid-rich Schwann cells, adipocytes, and entrapment of the surrounding fat. The authors also suggested that the high attenuation on contrast-enhanced scans represents dense bands of collagen (36). Neurofibromas often contain multiple cystic spaces of varying size that are caused by myxoid degeneration (Figs 14, 15) (34). At CT or MR imaging, neurofibromas and schwannomas occasionally demonstrate a target-like enhancement pattern, with different attenuation or signal intensity in the central portion than at the periphery (Fig 16). On T1-weighted MR images, the central portion has higher signal intensity than the periphery, whereas on T2-weighted images the periphery has higher signal intensity. These findings represent nerve tissue centrally and myxoid degeneration peripherally (31).
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Figure 14a. Extraperitoneal pelvic neurofibroma in a 59-year-old man. (a) Sagittal T2-weighted MR image shows a well-defined round tumor in the pelvic cavity with mixed low and high signal intensity due to myxoid degeneration. R = rectum, U = urinary bladder. (b) On a sagittal contrast-enhanced T1-weighted MR image, the tumor has heterogeneous contrast enhancement and indents the urinary bladder (U) anteriorly and the rectum (R) posteriorly.
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Figure 14b. Extraperitoneal pelvic neurofibroma in a 59-year-old man. (a) Sagittal T2-weighted MR image shows a well-defined round tumor in the pelvic cavity with mixed low and high signal intensity due to myxoid degeneration. R = rectum, U = urinary bladder. (b) On a sagittal contrast-enhanced T1-weighted MR image, the tumor has heterogeneous contrast enhancement and indents the urinary bladder (U) anteriorly and the rectum (R) posteriorly.
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Figure 15. Neurofibroma originating from the urinary bladder in a 55-year-old man. Contrast-enhanced CT scan shows a well-enhanced solid mass that abuts the left lateral wall of the urinary bladder (U) and has marked internal heterogeneity due to myxoid degeneration. Occasionally, neurogenic tumors can involve the bladder.
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Figure 16. Neurofibroma in the left iliac fossa in a 34-year-old woman. Contrast-enhanced CT scan shows a mass with a target-like enhancement pattern. The central portion of the mass (nerve tissue) is more hyperattenuating than the periphery (myxoid degeneration).
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Neurofibromatosis is actually a group of heterogeneous diseases that include two distinct types: NF-1 and neurofibromatosis type 2 (NF-2, bilateral acoustic schwannomas, or central neurofibromatosis) (37). NF-1 is an inherited disease that predominantly affects the skin and peripheral nervous system; it is fundamentally characterized by the presence of café-au-lait spots and neurofibromatous nodules along the peripheral nerves (38,39). The classic neurogenic tumors that occur outside the central nervous system include neurofibromas and plexiform neurofibromas. Approximately 30% of patients with solitary neurofibroma have NF-1, and virtually all patients with multiple neurofibromas or plexiform neurofibromas have NF-1 (33). NF-1 with abdominopelvic manifestations may involve numerous ganglia within the abdomen as well as the rich arborization of somatic and autonomic nerve tissue that innervates the abdominal and pelvic organs. These tumors tend to arise in the retroperitoneal, mesenteric, and paraspinal regions (Fig 17). At CT, multiple well-defined neurofibromas that arise from nerves traversing the mesentery or retroperitoneum may be quite extensive and difficult to distinguish from adenopathy. Plexiform neurofibromas within the pelvis may appear as large, extensively infiltrating masses in the presacral or gluteal regions (40). In contrast, the hallmarks of NF-2 are bilateral vestibular schwannomas and multiple meningiomas. NF-2 rarely demonstrates non–central nervous system involvement (37).
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Figure 17. Plexiform neurofibromatosis in a 17-year-old girl. Contrast-enhanced CT scan demonstrates multiple low-attenuation nodular lesions (arrows) along the right paravertebral region. Note the scalloping of the adjacent vertebral body.
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Malignant Nerve Sheath Tumors
Malignant nerve sheath tumors arise in patients with or without associated neurofibromatosis. Tumors that arise in the absence of neurofibromatosis are somewhat more common in large series of malignant nerve sheath tumors (41). Men and women are equally affected by this tumor, which is typically a disease of adulthood: Most tumors occur in patients between 20 and 50 years of age. Imaging criteria are unreliable in differentiating malignant from benign nerve sheath tumors (Fig 18). Irregular infiltrative tumor borders and internal inhomogeneity are more common in malignant nerve sheath tumors but can also be present in benign neurofibromas (42). However, if there is asymmetry in the size or attenuation of bilateral parapsoas masses, the larger lesion is likely to be malignant (43). Progressive enlargement and pain related to the mass are also suggestive of malignant transformation (44).
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Figure 18. Malignant nerve sheath tumor in a 57-year-old man. Contrast-enhanced CT scan shows a well-defined, heterogeneously enhancing solid mass (arrow) in the extraperitoneal pelvic cavity, posterior to the right external iliac vessels. There is no one specific imaging finding that can help differentiate malignant from benign nerve sheath tumors.
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Conclusions
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There is a broad spectrum of neurogenic tumors that involve the abdomen. Most of these tumors are diseases of adulthood, with the exception of neuroblastomas and ganglioneuroblastomas. The diagnosis of neurogenic tumors is suggested by their imaging appearance, including lesion location, shape, and internal architecture. Abdominal neurogenic tumors are most commonly located in the retroperitoneum along the paravertebral sympathetic plexus and in the adrenal glands. Neurogenic tumors commonly manifest radiologically as a well-defined, smooth or lobulated mass. Calcification may be seen in all types of neurogenic tumors. Benign and malignant neurogenic tumors have a similar CT appearance, except that malignant tumors may show distant metastatic foci. Because most neurogenic tumors in adults are benign, the role of imaging is to help develop a differential diagnosis and determine the immediate local extent of tumor. For malignant tumors, other imaging modalities may be necessary for staging.
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Acknowledgments
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We thank Bonnie Hami, MA, Department of Radiology, University Hospitals Health System, Cleveland, Ohio, for editorial assistance in preparing the manuscript.
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Footnotes
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Abstract
LEARNING OBJECTIVES FOR TEST...
