DOI: 10.1148/rg.245045001
RadioGraphics 2004;24:1477-1481
© RSNA, 2004
Schwannoma: Radiologic-Pathologic Correlation1
Francesca D. Beaman, MD,
Mark J. Kransdorf, MD and
David M. Menke, MD
1 From the Departments of Radiology (F.D.B., M.J.K.) and Pathology (D.M.M.), Mayo Clinic, 4500 San Pablo Rd, Jacksonville, FL 32224-3899. Received January 5, 2004; revision requested February 10 and received March 17; accepted March 29. All authors have no financial relationships to disclose. Address correspondence to M.J.K. (e-mail: kransdorf.mark@mayo.edu).
Index Terms: Elbow, MR, 42.1214 • Elbow, US, 42.1298 • Nerves, MR, 42.1214 • Nerves, neoplasms, 42.364 • Schwannoma, 42.364
 |
History
|
|---|
A 52-year-old man presented to his primary care physician complaining of a painless mass in the left elbow that had slowly enlarged over a 2-year period. When pressure was applied to the mass, the patient experienced "electrical shocks" that radiated to the left hand.
Physical examination demonstrated a soft, mobile mass in the anteromedial aspect of the left antecubital fossa. The patient’s strength, motion, sensation, and two-point discrimination were normal. A Tinel test was positive, evoking pain and numbness within the left forearm and hand. Nerve conduction velocity studies were normal.
|
Imaging Findings
|
|---|
Radiography of the left elbow revealed soft-tissue prominence in the antecubital fossa (Fig 1). No osseous erosion was present. Magnetic resonance (MR) imaging of the left elbow verified a round, sharply marginated intermuscular mass measuring 5.4 cm in diameter. The mass was in the antecubital fossa, on the ulnar side of the elbow joint line. On spin-echo T1-weighted MR images, the lesion was homogeneous and isointense relative to skeletal muscle (Fig 2). The median nerve was identified as a distinct structure at the proximal and distal aspects of the mass; however, it could not be separated from the body of the mass. Conventional spin-echo T2-weighted MR images demonstrated the lesion to be mildly heterogeneous, with a signal intensity greater than that of fat (Fig 3). No demonstrable enhancement was identified following intravenous administration of gadolinium-based contrast material (Fig 4). The mass abutted but did not directly communicate with the joint, nor was it separable from the median nerve.
View larger version (126K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1. Lateral radiograph of the left elbow shows a subtle soft-tissue mass in the antecubital fossa (small arrows). Note the small foreign body in the superficial subcutaneous tissue (large arrow).
|
|
View larger version (115K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2. Coronal spin-echo T1-weighted MR image (repetition time msec/echo time msec = 460/16) shows the mass to be homogeneous and isointense relative to skeletal muscle. A subtle rind of fat is seen at the inferior margin of the mass. The median nerve is eccentric in relation to the mass, although the course of the nerve becomes indistinct at the superior margin of the mass (arrow).
|
|
View larger version (140K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3. Axial spin-echo T2-weighted MR image (2000/83) shows a well-defined mass within the antecubital fossa. The mass is mildly heterogeneous with a signal intensity greater than that of fat.
|
|
View larger version (120K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4. Axial contrast material-enhanced fat-saturated spin-echo T1-weighted MR image (420/16) shows no appreciable enhancement within the mass. Note, however, the enhancement of the adjacent vessel (arrow).
|
|
Subsequent ultrasonography (US) showed the mass to be well circumscribed with a whorled echogenic internal architecture. The course of the median nerve was well seen up to and abutting the margins of the mass, a finding that suggested an intimate relationship between the mass and the nerve (Figs 5, 6). Although the exact nerve-mass relationship could not be definitively established with US, the nerve appeared to be eccentric relative to the mass. Doppler US showed no appreciable vascularity.
|
Pathologic Evaluation
|
|---|
The patient underwent surgical excision of the mass performed with an anteromedial approach to the antecubital fossa. The mass was located eccentrically within the epineurium of the median nerve, which was carefully dissected from the mass without incident (Fig 7). A small, serpiginous vessel was located superficially on the surface of the mass, a finding that is often present in benign neural tumors. The small caliber of the vessel precluded its being identified at imaging. The mass was removed in toto, hemostasis was achieved, and the wound was irrigated, after which a primary closure was performed.
View larger version (107K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7. Intraoperative photograph shows the median nerve schwannoma. Arrows indicate the proximal median nerve, and blue sutures indicate its distal extent. The brachial margin of the mass is very slightly lobulated. Note the corkscrew-shaped vessel on the surface of the lesion. Drain extends around the brachial artery.
|
|
Gross pathologic evaluation demonstrated a well-circumscribed, xanthochromic, rubbery mass 5.0 x 3.8 x 3.5 cm in size with an appearance that suggested a lipoma (Fig 8). Microscopic evaluation confirmed the diagnosis of schwannoma, demonstrating Antoni A areas (densely cellular, arranged in short bundles or interlacing fascicles) and Antoni B areas (less cells, organized with more myxoid component) (Fig 9). The tumor was S-100 positive. Antoni A areas constituted approximately 5% of tumor volume.
View larger version (170K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 9a. (a) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) reveals that the tumor consists of focal cellular (Antoni A) areas (white *) and hypocellular (Antoni B) areas with vacuolar degeneration (black *). (b) Higher-power photomicrograph (original magnification, x400; hematoxylin-eosin stain) of an Antoni A area shows a dense, whorled proliferation of nerve sheath cells.
|
|
View larger version (173K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 9b. (a) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) reveals that the tumor consists of focal cellular (Antoni A) areas (white *) and hypocellular (Antoni B) areas with vacuolar degeneration (black *). (b) Higher-power photomicrograph (original magnification, x400; hematoxylin-eosin stain) of an Antoni A area shows a dense, whorled proliferation of nerve sheath cells.
|
|
|
Discussion
|
|---|
Solitary benign peripheral nerve sheath tumors are divided into two major groups: schwannoma (neurilemoma) and neurofibroma. Both schwannomas and neurofibromas contain cells that are closely related to normal Schwann cells. Schwannomas are slightly less common than neurofibromas, although each lesion constitutes about 5% of all benign soft-tissue tumors (1).
At pathologic analysis, a schwannoma has a true capsule composed of epineurium (2–4). When large nerves are affected, the mass is characteristically eccentric with respect to the affected nerve, with the nerve displaced to the periphery of the mass. This finding is helpful when present and may be identified at imaging but is usually not seen in small nerves. Growth of schwannoma within the epineurium creates encapsulation, which allows successful resection. In contrast, neurofibroma arises from the nerve fascicle, is centrally located, is rarely encapsulated, and cannot be separated from the involved nerve.
The vast majority (90%) of neurofibromas are solitary and are not associated with neurofibromatosis 1 (von Recklinghausen disease). Neurofibromas that are present in the setting of neurofibromatosis 1 are almost invariably multiple, with visceral and deep nerve involvement and an increased risk of malignant transformation (1–4).
The malignant counterparts of these benign lesions, malignant peripheral nerve sheath tumors, account for approximately 6% of all sarcomas, with approximately one-half occurring in the setting of neurofibromatosis 1 (1,5). Benign soft-tissue tumors are estimated to occur 100 times more frequently than sarcomas; thus, malignant peripheral nerve sheath tumors are relatively uncommon statistically. Similar to schwannomas, malignant peripheral nerve sheath tumors usually arise from major nerve trunks (commonly in the proximal extremities and torso), often containing prominent areas of hemorrhage and necrosis (2,6,7). These tumors are generally high-grade sarcomas, and although they have no specific imaging features, their aggressive biologic behavior may be suggested by indistinct margins, the infiltrative nature of the lesion within the nerve and adjacent structures, and lesion heterogeneity (7).
The MR imaging appearance of the schwannoma in this case is similar to that of others reported in the literature (ie, isointense signal relative to skeletal muscle on T1-weighted images and increased, slightly heterogeneous signal intensity on T2-weighted images) (5–9). Unfortunately, these patterns of signal intensity are neither specific for neural tumors, nor do they allow differentiation between benign and malignant nerve sheath tumors (1,5,7). In many cases, however, imaging characteristics help identify the neurogenic origin of a mass. Distinctive features that suggest a peripheral nerve sheath tumor include a location in the region of a major nerve, depiction of the nerve entering or exiting the mass, and the presence of certain signs (split fat sign, fascicular sign, target sign). These features are summarized in the Table.
In this case, the lesion was readily identified as intermuscular and associated with the neurovascular structure. As such, a fine rind of fat (split fat sign), typical of that seen around neurovascular structures, was identified at the periphery of the mass. Both MR imaging and US also showed the continuity of the lesion with the median nerve. Identification of such a nerve entering and exiting a mass is virtually pathognomonic for a peripheral nerve sheath tumor (7,8,10).
Ideally, distinguishing between neurofibroma and schwannoma should be possible at MR imaging in a nerve as large as the median nerve. Classically, the parent nerve is eccentric to the mass (although within the epineurium) in schwannoma but central or obliterated by the mass in neurofibroma. This distinction has been reported to be accurate in 65% of cases (8) but could not be confidently established in this case.
The target and fascicular signs were not seen in this case. The target sign has been described at T2-weighted MR imaging of neurogenic tumors. It is characterized by low signal intensity centrally and high signal intensity peripherally, findings that correspond to central fibrous components and peripheral myxomatous elements seen at pathologic analysis. The target sign is seen more frequently in neurofibromas, although it may be seen in schwannomas as well. The term fascicular sign refers to the appearance of the fascicular bundles in neurogenic tumors and normal nerves. The target and fascicular signs are typically seen in benign lesions, although they may occasionally be seen focally in malignant peripheral nerve sheath tumors.
As in this case, patients typically present with the complaint of a slowly enlarging, painless mass. Pain with paresthesia may be elicited in the distribution of the affected nerve upon percussion over the site of swelling (Tinel sign) (7,11,12), again as in this case. The most unusual features in this case were the absence of tumor enhancement following contrast material administration and the obliteration of the median nerve by the mass.
In summary, there are certain imaging characteristics that may aid the radiologist in establishing a focused preoperative diagnosis of a peripheral nerve sheath tumor. These characteristics include association with a peripheral nerve, intermuscular location, and certain specific MR imaging signs (split fat sign, fascicular sign, target sign).
|
References
|
|---|
- Kransdorf MJ, Murphey MD. Neurogenic tumors. Imaging of soft tissue tumors. Philadelphia, Pa: Saunders, 1997; 235-273.
- Harkin JC, Reed RJ. Tumors of the peripheral nervous system. Atlas of tumor pathology, fasc 3, ser 2. Washington, DC: Armed Forces Institute of Pathology, 1969; 29-120.
- Stout AP. The peripheral manifestations of the specific nerve sheath tumor (neurilemmoma). Am J Cancer 1935; 24:751-796.
- Weiss SW, Goldblum JR. Benign tumors of the peripheral nerves. Enzinger and Weiss’s soft tissue tumors. 4th ed. St Louis, Mo: Mosby, 2001; 1111-1207.
- Hems TE, Burge PD, Wilson DJ. The role of magnetic resonance imaging in the management of peripheral nerve tumours. J Hand Surg [Br] 1997; 22:57-60.[Medline]
- Weiss SW, Goldblum JR. Malignant tumors of the peripheral nerves. Enzinger and Weiss’s soft tissue tumors. 4th ed. St Louis, Mo: Mosby, 2001; 1209-1263.
- Stull MA, Moser RP, Kransdorf MJ, Bogumill GP, Nelson MC. Magnetic resonance appearance of peripheral nerve sheath tumors. Skeletal Radiol 1991; 20:9-14.[Medline]
- Cerofolini E, Landi A, DeSantis G, Maiorana A, Canossi G, Romagnoli R. MR of benign peripheral nerve sheath tumors. J Comput Assist Tomogr 1991; 15:593-597.[Medline]
- Katsumi K, Ogose A, Hotta T, et al. Plexiform schwannoma of the forearm. Skeletal Radiol 2003; 32:719-723.[CrossRef][Medline]
- Suh JS, Abenoza P, Galloway HR, Everson LI, Griffiths HJ. Peripheral (extracranial) nerve tumors: correlation of MR imaging and histologic findings. Radiology 1992; 183:341-346.[Abstract/Free Full Text]
- Silver M, Patel MR, Vigorito V. Preoperative diagnosis of a forearm peripheral schwannoma. Orthop Rev 1993; 22:714-716.[Medline]
- Phalen GS. Neurilemmomas of the forearm and hand. Clin Orthop 1976; 114:219-222.
This article has been cited by other articles:
|
|
|
|
 
W.-C. Tsai, H.-J. Chiou, Y.-H. Chou, H.-K. Wang, S.-Y. Chiou, and C.-Y. Chang
Differentiation Between Schwannomas and Neurofibromas in the Extremities and Superficial Body: The Role of High-Resolution and Color Doppler Ultrasonography
J. Ultrasound Med.,
February 1, 2008;
27(2):
161 - 166.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. P. Valencia and M. Castillo
Congenital and Acquired Lesions of the Nasal Septum: A Practical Guide for Differential Diagnosis
RadioGraphics,
January 1, 2008;
28(1):
205 - 223.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
F. D. Beaman, M. J. Kransdorf, T. R. Andrews, M. D. Murphey, L. K. Arcara, and J. H. Keeling
Superficial Soft-Tissue Masses: Analysis, Diagnosis, and Differential Considerations
RadioGraphics,
March 1, 2007;
27(2):
509 - 523.
[Abstract]
[Full Text]
[PDF]
|
|
|
Top
History
Imaging Findings
