Schwannoma of Right Thigh

Enlarging Painless Right Upper Thigh Mass • Xray of the Week

This 26 y/o male presented with a right upper inner thigh mass for over a year. The mass was painless and growing. What is the differential diagnosis?

(Left) T2 weighted coronal image demonstrating a high signal intensity lobulated medial right thigh mass.

(Right) FSE PD weighted axial image with fat saturation demonstrating the markedly hyperintense mass. (yellow arrows)

Above: T1 weighted coronal image demonstrating a low signal intensity lobulated subcutaneous right thigh mass.

Discussion

Biopsy of this mass demonstrated a schwannoma. The appearance of the mass is non-specific. However, there are multiple ring-like hypointense structures, consistent with the fascicular sign (1, 2,4). Although this mass is not located along the anatomic course of a peripheral nerve, the appearance is suspicious for peripheral nerve sheath tumor due to the presence of the fascicular sign. The fascicular sign is characterized by multiple small ring-like structures with peripheral hyperintensity on T2 weighted images representing the fascicular bundles within the nerves. Other signs of Schwannoma or neurofibroma include the tail, target, bag-of-worms, and split-fat signs. (4) The target sign is characterized by peripheral high T2 signal and central low signal on T2 weighted images. The split-fat sign is visualized as a thin peripheral rim of fat best seen on planes along long axis of the lesion in non-fat-suppressed images.

The vast majority (approx 90%) of schwannomas are solitary. Multiple schwannomas are virtually diagnostic of Neurofibromatosis 2 (NF2). However up to 20% of solitary schwannomas are seen with NF2. Clinical presentation is usually a painless mass; however, there may be symptoms related to local mass effect or dysfunction of the nerve from which the tumor arises.

Differential diagnosis for soft tissue masses is broad (1):

Mesenchymal Tumors: Dermatofibrosarcoma protuberans, Lipoma, Angiomas (hemangioma, lymphangioma), Peripheral nerve sheath tumor (schwannoma, neurofibroma), Malignant fibrous histiocytoma, Liposarcoma, Leiomyosarcoma, Fibromatosis

Skin Appendage Lesions: Epidermal inclusion cyst, Pilomatricoma, Cystadenoma

Metastatic Tumors: Carcinoma, Melanoma, Myeloma

Other Tumors and Tumor-like Lesions: Myxoma, Lymphoma

Inflammatory Lesions: Cellulitis, Fasciitis, Adenitis, Abscess

References:

1. F D Beaman, M J Kransdorf, et al. Superficial Soft-Tissue Masses: Analysis, Diagnosis, and Differential Considerations. RadioGraphics 2007; 27:509 –523

2. F D Beaman, MD, M J Kransdorf, MD. Schwannoma: Radiologic-Pathologic Correlation. RadioGraphics 2004; 24:1477–1481

3. A Chhabra and T Soldatos. Soft-Tissue Lesions: When Can We Exclude Sarcoma? AJR 2012; 199:1345–1357

4. Chandan Kakkar, et al. Telltale signs of peripheral neurogenic tumors on magnetic resonance imaging. Indian Journal of Radiology and Imaging. 2015, Volume 25 Page: 453-458

Phillip Tirman, MD is the Medical Director of Musculoskeletal Imaging at the Renaissance Imaging Center in Westlake Village, California. A nationally recognized expert in the applications of MRI for evaluating MSK and spine disorders, Dr. Tirman is the co-author of three textbooks, including MRI of the Shoulder and Diagnostic Imaging: Orthopedics. He is also the author or co-author on over sixty original scientific articles published in the radiology and orthopedic literature.

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Kevin M. Rice, MD is the president of Global Radiology CME

Dr. Rice serves as the Chair of the Radiology Department of Valley Presbyterian Hospital in Los Angeles, California and is a radiologist with Renaissance Imaging Medical Associates. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field.

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