Epithelioid sarcoma presenting as radial mononeuropathy: anatomical, magnetic resonance neurography and diffusion tensor imaging appearances
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- Wadhwa, V., Salaria, S.N., Thakkar, R.S. et al. Skeletal Radiol (2013) 42: 853. doi:10.1007/s00256-013-1591-x
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The authors report an unusual case of radial mononeuropathy caused by epithelioid sarcoma and describe the anatomical 3-Tesla MR neurography and the functional diffusion tensor imaging findings of the case, which were subsequently confirmed on surgical excision and histopathology.
KeywordsMR neurographyDTIADCEpithelioid sarcomaRadial nerve
Radial mononeuropathy is commonly caused by entrapment or trauma . Primary sarcoma of the radial nerve presenting with neuropathic symptoms is unusual . A high degree of suspicion is required on the part of the radiologist to differentiate such tumor from the more common mass-like lesions of the peripheral nerve, namely post-traumatic neuroma in continuity. To the best of our knowledge, a primary radial nerve epithelioid sarcoma has not been reported before. The authors describe the anatomical MR neurography and functional diffusion tensor imaging (DTI) findings of such a case, which were subsequently confirmed on surgical excision and histopathology. The relative values of advanced MR imaging in this unusually rare tumor are discussed.
A 24-year-old naval aviator presented with progressive functional deterioration of the right upper extremity for 2 years with progressive weakness and atrophy of his triceps muscle. This progressed to weakness and atrophy of his wrist and then finally his digital extensors. He also developed numbness in the radial sensory distribution. Physical examination showed total atrophy of the triceps, brachioradialis, and extensor musculature on the dorsum of his forearm, but no atrophy of the hand itself. On manual muscle testing, there was no function of any of the radial nerve innervations, but the median and ulnar musculature appeared to be intact. Sensation in the hand was normal with the exception of the radial sensory distribution along the dorsum of the first web space, where two-point discrimination was absent. A brisk positive Tinel sign could be localized within the axilla itself, while a negative Tinel sign was observed around the spiral groove and more distally in the extremity. The nerve felt relatively firm in this area and palpation was uncomfortable. Electrodiagnostic tests were performed, which limited the problem to the radial nerve without finding any evidence of a generalized brachial plexopathy.
Epithelioid sarcoma is a rare, slow-growing soft tissue tumor that was first described in 1970, occurring most commonly in the forearms and hands of young adults . The tumor often has a nodular, pseudogranulomatous growth pattern. It can be located superficially or deep in the soft tissues. Superficially, the tumor involves the subcutis, presenting as firm nodules that are raised above the surface and can frequently become ulcerated. The more deep seated lesions tend to be larger in size and are usually attached to the tendons, tendon sheaths or the deep fascia. Uncommonly, the tumor may involve the neurovascular bundles and cause pain or tenderness [4, 5]. However, primary growth along a peripheral nerve and presentation as mononeuropathy or a mass-like lesion is extremely rare [6–8]. Because of its slow growth and nodular pattern, it is often mistaken for various other entities . It can present with a relentless clinical course, frequently culminating in regional lymph node and pulmonary metastasis. Similar to our case, the tumor is more prevalent in the age group 10 to 35 years, having a predilection for men over women and is more frequently seen in the upper extremity . Histologically, epithelioid sarcoma is composed of uniform epithelioid cells with pale eosinophilic cytoplasm infiltrating dermal collagen, showing diffuse positivity for epithelial membrane antigen (EMA) and CD34 immunostaining. Characteristically, there is loss of expression of INI1 in the tumor cells as in this case .
Radiologists should be aware of the rare possibility of sarcoma presenting as mononeuropathy. On conventional MR imaging, it shows homogeneous to heterogeneous isointense signal intensity (SI) to the skeletal muscle on T1W images. It may contain areas of hemorrhage or necrosis. On T2W images, it shows iso- to heterogeneously hyperintense signal with intense enhancement on intravenous contrast medium injection . Similar appearance was seen on MR neurography; however, it also mimicked neuroma in continuity (NIC), especially with a history of naval employment. However, the lesion was not located at the typical site for entrapment or injury. Additionally, contrast enhancement is unusual in NIC as they are detected at a subacute stage of evolution . It could be easily distinguished from benign peripheral nerve sheath tumor owing to a lack of fascicular or target sign as well as low ADC values . Other tumors that could mimic this appearance include, synovial sarcoma (T1 hypointense, T2 hyperintense, homogeneous enhancement); malignant peripheral nerve sheath tumor (with or without underlying known neurocutaneous syndrome, isointense on T1W, and homogeneously to heterogeneously hyperintense on T2W images, rapid interval increase in size, internal hemorrhage, perilesional edema, ill-defined margins, local invasion, high SUVmax values (>3–4) on F18 FDG PET scan and a low minimum ADC value, <1.1–1.2 × 10−3 mm/s2 on DTI); lymphoma (with or without underlying known lymphoma, diffuse enlargement of the peripheral nerve or plexus components with multifocal nodularity, heterogeneous hypointensity on T2W images, homogeneous or heterogeneous contrast enhancement of the mass lesion, and increased uptake on F18 FDG PET scan); and fibrosarcoma (mass-like lesion with the nerve fascicles displaced peripherally consistent, with an intraneural process and enhancement on contrast-enhanced images [14–17].
Diffusion tensor imaging has multiple benefits. It selectively shows the lesion by suppressing the vessels and fat as in this case. Most lesions are hyperintense on T2W images making differentiation difficult. DTI allowed interrogation of internal architecture of the nerve infiltrated by the lesion by showing missing tracts in the thickened nerve, indicating internal fascicular disruption by the malignancy, which was confirmed on surgery. Further, low ADC values indicate high cellularity, associated with malignancy, which improved on post-operative imaging following resection of the tumor . Finally, low fractional anisotropy values indicate neuropathy with demyelination and/or axonal degeneration [18–20]. Fractional anisotropy indicates the degree of anisotropy in proton diffusion in the three-dimensional space. Owing to various connective tissue boundaries inherently present within the complex architecture of the nerve, there is a high degree of anisotropy in a normal nerve. The values of anisotropy measure between 0.4 and 0.7 in a normal peripheral nerve. With neuropathy, there is expanded space created by demyelination and/or axonal degeneration, and the anisotropy values decrease (increased isotropy). These values have been shown in the literature to improve as the nerve recovers from pathology on treatment . Although, other malignancies, such as lymphoma or leukemia, could not be excluded from the imaging appearance , high-resolution 3-T MR neurography with anatomical and functional imaging capabilities played a vital role in detecting nerve abnormality, accurate localization of the lesion, confirming the regional muscle denervation changes, and characterization of the lesion as possibly aggressive/malignant. DTI is useful as it adds to the diagnostic confidence and may play a supplemental role, especially if the patient cannot get contrast for renal issues or some other reason.
To conclude, MR neurography with DTI is an excellent technique for the preoperative diagnosis, localization, and characterization of tumor-like lesions of the peripheral nerves. Radiologists should be aware of the rare possibility of sarcoma presenting as mononeuropathy.
Conflicts of interest
Vibhor Wadhwa: The author reports no conflicts of interest.
Safia N. Salaria: The author reports no conflicts of interest.
Rashmi S. Thakkar: The author reports no conflicts of interest.
Dr. Chhabra has received patient research grants from Siemens, Interga Life Sciences and GE-AUR. He also serves as MSK CAD consultant with Siemens.