Carlos Torres, MD - Assistant Professor of Radiology - Program Director - Neuroradiology - University of Ottawa - The Ottawa Hospital Civic and General Campus - 1053 Carling Ave - Ottawa, Ontario K1Y 4E9 Canada - Tel.: 613-798-5555 - Ext:12036 - Fax: 613-761-4476 - E-mail: ac.no.hot@serrotac
Received 2013 Nov 13; Accepted 2013 Nov 22. Copyright © 2013, Centauro S.r.l.Magnetic resonance imaging (MRI) is the imaging modality of choice for the evaluation of the brachial plexus due to its superior soft tissue resolution and multiplanar capabilities. The evaluation of the brachial plexus however represents a diagnostic challenge for the clinician and the radiologist. The imaging assessment of the brachial plexus, in particular, has been traditionally challenging due to the complexity of its anatomy, its distribution in space and due to technical factors. Herein, we describe a modified technique used in our institution for the evaluation of the brachial plexus which led to a substantial decrease in scanning time and to better visualization of all the segments of the brachial plexus from the roots to the branches, in only one or two images, facilitating therefore the understanding of the anatomy and the interpretation of the study. To our knowledge, we are the first group to describe this technique of imaging the brachial plexus. We illustrate the benefit of this modified technique with an example of a patient with a lesion in the proximal branches of the left brachial plexus that was clinically suspected but missed on conventional brachial plexus imaging for six consecutive years. In addition, we review the common and infrequent benign and malignant pathology that can affect the brachial plexus.
Keywords: magnetic resonance imaging, brachial plexus, diagnosis, modified technique, anatomy, pathology
The brachial plexus is a major neural structure that provides sensory and motor innervation to the upper extremity. Different imaging modalities can be used to study the brachial plexus, including magnetic resonance imaging (MRI), computed tomography (CT) and ultrasound (US) 1 , however MRI is the imaging modality of choice for the evaluation of the brachial plexus due to its superior soft tissue resolution and multiplanar capabilities 1-4 . There is a wide range of disease processes that can involve the brachial plexus including primary and secondary tumors, radiation fibrosis, trauma and inflammatory processes. Clinically, a brachial plexopathy represents a diagnostic challenge as the symptoms are often non-specific and adequate localization of lesions along the course of the plexus is difficult. Although electromyography can help clarify whether a lesion is central (preganglionic) or peripheral (postganglionic) based on the pattern of involvement of the plexus, it is not useful for a more exact localization 1 . MR imaging plays an essential role in differentiating preganglionic injuries from postganglionic lesions, a differentiation that is crucial for determining the management of brachial plexus injury, predominantly in the setting of trauma.
The imaging assessment of the brachial plexus, however, has been traditionally challenging due to the complexity of its anatomy and distribution in space. Another important limitation is the prolonged scanning time the patients have to endure. This is particularly problematic in the clinical setting of trauma or neoplastic involvement of the plexus since the patients are in pain and therefore move during the study, resulting in inadequate images for interpretation.
Given our institution is a referral center for trauma and oncology patients, we found a solution to decrease the amount of time a patient spends in the magnet by modifying the way we image the brachial plexus without compromising the diagnostic quality of the study. Herein, we describe the protocol that we use at our institution for the evaluation of the brachial plexus, illustrating the normal anatomy and the benefits of using this modified technique. As an unexpected result, we were able to visualize and follow all the segments of the brachial plexus from the roots to the branches in only one or two images, facilitating the understanding of the anatomy and the interpretation of the study. To our knowledge, we are the first group to describe this technique of imaging the brachial plexus. We illustrate the benefit of this modified technique with an example of a patient with a lesion in the proximal branches of the left brachial plexus that was clinically suspected but missed on conventional brachial plexus imaging for six consecutive years.
All the patients are scanned on a 1.5 Tesla system (Twinspeed Excite HD, General Electric) using the eight-channel neurovascular coil. Our standard protocol includes a three-plane localizer followed by T1W FSE (TR/TE: 500/10, FOV:22-28 cm, matrix : 320×224 mm) in the axial oblique, coronal oblique and sagittal oblique planes, a T2W FSE sequence (TR/TE: 4000/110), FOV: 22-28 cm, matrix: 384×256 mm) in the axial oblique plane, and a coronal T2 FSE STIR sequence to suppress the fat signal. The slice thickness is 3 mm with a 1mm interslice gap. Gadolinium is not routinely used and could be added to better characterize a neoplastic process. When the comparison between the symptomatic and the normal side is necessary, images with a larger field of view (FOV) could be obtained in order to include the bilateral brachial plexus, using a body coil. A similar protocol could be obtained in a 3T system using a surface coil, without interslice gap.
Due to the complex anatomy of the brachial plexus, it is difficult to follow its segments in a continuous fashion on the true axial and true coronal images when using the conventional technique. Since the brachial plexus runs obliquely from superomedial to inferolateral in the coronal plane 3 , we decided to acquire axial oblique and coronal oblique images instead. In order to do that, we increased the number of slices in the coronal localizer (Figure (Figure1) 1 ) which allowed us to better identify the segments of the brachial plexus in that plane (Figure (Figure2 2 ).
The number of slices in the localizer sequence has been increased to improve visualization of the nerve roots. Conventional localizer (A), modified localizer (B).
