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Peripheral Schwannoma Lacking Enhancement on MRI

Wake Forest University Baptist Medical Center Winston-Salem, NC 27157-1088

Schwannomas (neurilemmomas) are benign nerve sheath tumors that arise from the epineurium of the peripheral nerves. They most commonly affect patients in their third decade of life and show no preference for occurrence in either sex [1]. Schwannomas are often grouped together with neurofibromas, which are benign nerve sheath tumors arising centrally from a peripheral nerve. The MR appearance of a benign nerve sheath tumor has been well described: a smooth, well-defined, fusiform mass that enters and exits the nerve. Schwannomas generally display intermediate to low signal on T1-weighted images but show a diffuse increase in signal on T2-weighted images. Enhancement on contrast-enhanced T1-weighted images is considered to be a defining feature of schwannomas. The enhancement pattern is typically inhomogeneous, with stronger enhancement peripherally, but it is often homogeneous [2–4].

We report a case of a 23-year-old woman who presented with a slow-growing mass at her elbow. A preoperative MRI was obtained that clearly revealed a lesion in the course of the median nerve, with the classic appearance of a fusiform mass that entered and exited the nerve. The mass was hypointense relative to muscle on T1-weighted images (Fig. 4A, 4B, 4C, 4D) and showed an overall increased signal on T2-weighted images. The contrast-enhanced T1-weighted images, however, revealed no enhancement of the lesion. Findings were interpreted as indicative of a nonenhancing nerve sheath tumor of the median nerve. To our knowledge, the only prior description of a nerve sheath tumor that did not show enhancement was reported by Zbar et al. [5], who described two intralabyrinthine acoustic schwannomas, each smaller than 5 mm. In our patient, the large size of the schwannoma prevented any volume-averaging loss of signal, and there definitely was no enhancement. The 2.7-cm mass was excised; the histologic diagnosis was a schwannoma, including S-100 protein staining. We believe that this schwannoma is by far the largest nonenhancing nerve sheath tumor that has been described as well as the only reported nonenhancing peripheral nerve sheath tumor.

View larger version (133K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A. —23-year-old woman with peripheral nerve sheath tumor of median nerve. T1-weighted image (TR/TE, 400/11) reveals intermediate signal of lesion (asterisk) in expected position of median nerve.

View larger version (129K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B. —23-year-old woman with peripheral nerve sheath tumor of median nerve. Fat-suppressed proton density–weighted image (TR/effective TE, 2000/34) shows homogeneously increased signal of mass.

View larger version (136K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4C. —23-year-old woman with peripheral nerve sheath tumor of median nerve. Contrast-enhanced fat-suppressed T1-weighted image (TR/TE, 300/11) reveals complete lack of enhancement in lesion. Mass is slightly hypointense relative to adjacent muscle. Fat suppression is slightly inhomogeneous but could be expected to affect only small part of periphery of mass.

View larger version (126K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4D. —23-year-old woman with peripheral nerve sheath tumor of median nerve. In gross pathologic specimen obtained during resection, fibers of median nerve (arrow) are displaced by mass, as would be expected with schwannoma.

References

1. Murphey MD, Smith WS, Smith SE, Kransdorf MJ, Temple HT. From the archives of the AFIP: imaging of musculoskeletal neurogenic tumors— radiologic–pathologic correlation. RadioGraphics1999; 19:1253 –1280[Abstract/Free Full Text]
2. Varma DG, Moulopoulos A, Sara AS, et al. MR imaging of extracranial nerve sheath tumors. J Comput Assist Tomogr1992; 16:448 –453[Medline]
3. Soderlund V, Goranson H, Bauer HC. MR imaging of benign peripheral nerve sheath tumors. Acta Radiol1994; 35:282 –286[Medline]
4. Beggs I. Pictorial review: imaging of peripheral nerve tumours. Clin Radiol1997; 52:8 –17[Medline]
5. Zbar RI, Megerian CA, Khan A, Rubinstein JT. Invisible culprit: intralabyrinthine schwannomas that do not appear on enhanced magnetic resonance imaging. Ann Otol Rhinol Laryngol1997; 106:739 –742[Medline]

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This Article Figures Only Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lee, J. A. Articles by Boles, C. A. Search for Related Content PubMed PubMed Citation Articles by Lee, J. A. Articles by Boles, C. A. Social Bookmarking                      What's this?