Left brachial plexus schwannoma

Clinical History

A 50-year-old woman presented with left upper limb radicular pain and numbness.

Imaging Findings

MRI of left brachial plexus revealed altered signal intensity lesion in left supra and infraclavicular region along left brachial plexus. The lesion was arising from C8 and T1 nerve roots and then continuing in the lower trunk, anterior division of the lower trunk and medial cord. There was loss of fat planes between lesion and left subclavian artery. On post-contrast study, the lesion showed intense enhancement.
The patient was operated and on histopathology it turned out to be a schwannoma.

Discussion

Brachial plexus tumours are rare tumours of the upper limb. The two most common brachial plexus region tumours are the Schwannomas and the neurofibromas, both of which are benign and arise from the nerve sheath. The most frequent site is in the head and neck and only about 5% of Schwannomas present as brachial plexus tumours. [1]
The most common presentation is a slow-growing mass. Upon palpation, they are slightly mobile except along the long axis of the nerve. Neurological symptoms are usually not seen. [2]
Schwannomas are classically described as “well-circumscribed, encapsulated masses that are attached to the nerve but can be separated from it”. Nerve filaments may be splayed over the surface of the tumour. Microscopically, the tumour shows cellular areas (Antoni A), including Verocay bodies, as well as looser, myxoid regions (Antoni B). Silver stains demonstrate that axons are excluded from the tumour, although they may become entrapped in the capsule.
In contrast, neurofibromas are well-circumscribed but not encapsulated masses. It is not possible to separate the lesion from the nerve. Microscopically they show a haphazard arrangement of fibroblasts, Schwann cells and macrophages. Axons can be demonstrated within the tumour. Electronmicroscopy and immunohistochemical analysis (S-100, Leu-7) are often necessary to diagnose and accurately classify neurogenic tumours.
However, the distinction between Schwannomas and neurofibromas is not always clear cut as one recent report highlighted tumours with both components present within the same specimen. [2]
The MR imaging appearance of the schwannoma is not characteristics. It appears isointense relative to skeletal muscle on T1-weighted images and with increased, slightly heterogeneous signal intensity on T2-weighted images. Unfortunately, these patterns of signal intensity are neither specific for neural tumours, nor do they allow differentiation between benign and malignant nerve sheath tumours. 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).
Distinguishing between neurofibroma and schwannoma should be possible at MR imaging in brachial plexus. Classically, the parent nerve is eccentric to the mass (although within the epineurium) in Schwannoma but central or obliterated by the mass in neurofibroma. [3]
Surgery is indicated for tumours that cause neurological dysfunction or pain or for any rapidly growing tumours with a suspicion of malignancy, and complete resection of these tumours results in cure. [1]

Differential Diagnosis List

Final Diagnosis

Left brachial plexus schwannoma

URL:	https://eurorad.org/case/12021
DOI:	10.1594/EURORAD/CASE.12021
ISSN:	1563-4086