Presentation
9-month-old baby boy who was born at 38 weeks gestation by vaginal delivery, complicated by a nuchal cord and bruising of the right arm at the time of delivery, presenting with weakness of the right arm. Physical examination demonstrated right arm internally rotated with the forearm extended and pronated, and significant weakness of the right deltoid, biceps, and brachioradialis. He could grasp with the right hand but weaker than the left.
Patient Data
MRI of the cervical spine without and with IV contrast demonstrates a pseudomeningocele at the level of the right C7-T1 neural foramen. This is T1 hypointense and T2 hyperintense without enhancement.
MRI of the right brachial plexus without and with IV contrast was also performed on the same day as the cervical spine MRI. In addition to the right C8 pseudomeningocele, there is right glenoid dysplasia with glenoid retroversion and posterior subluxation at the right glenohumeral joint.
The brachial plexus is comprised of the C5, C6, C7, C8, and T1 nerve roots. The upper trunk, middle trunk, and lower trunk are slightly thickened / hyperintense in the region of the scalene triangle (in between the anterior scalene and middle scalene muscles). The divisions appear normal in morphology, forming a Christmas tree appearance over the subclavian artery.
The cords (lateral cord, posterior cord, medial cord) are seen more distally and give a paw print configuration over the subclavian artery in this region. The branches of the brachial plexus (including the median nerve, musculocutaneous nerve, ulnar nerve, radial nerve, and axillary nerve) are seen more distally near the level of the coracoid process.
No muscle edema or atrophy is seen in the field of view. There is atelectasis in the posterior right lung.
Case Discussion
Brachial plexus birth injury has an incidence of 0.9 per 1000 live births in the US, with the strongest associated risk factor being shoulder dystocia 1. The classification of injury depends on the severity of the damage to the nerves. Neurapraxia, a relatively mild injury, results from compression or stretching and does not disrupt axonal continuity. The prognosis for a neuropraxic injury is favorable and requires little intervention. Neurotmesis, however, represents complete nerve discontinuity and is the most severe form of this injury with little chance of recovery of affected nerves.
This case involves complete avulsion of the C8 nerve root with associated pseudomeningocele formation. Additional brachial plexus roots and trunks appear thickened and hyperintense, indicating a low-grade injury 2. Glenohumeral dysplasia, characterized clinically by exaggerated internal rotation and diminished external rotation of the shoulder, is a major cause of morbidity related to this class of injury and may be an indication for surgery in children with brachial plexus birth injury 3.
Case co-author: Alec Boyd (Loyola University)
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