An incidental finding of additional vascular compression of the brachial plexus during ultrasound-guided anterior scalene bupivacaine injection for neurogenic thoracic outlet syndrome: addition of hydrodissection—a case report

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Abstract
Background: Bony, muscular, and fibrous abnormalities in the thoracic outlet are implicated in the pathogenesis of neurogenic thoracic outlet syndrome (nTOS). Compression of the brachial plexus by the dorsal scapular artery (DSA) is rarely reported and is often diagnosed incidentally during cadaveric dissection or surgical decompression. Case presentation: We present the case of a 51-year-old Middle Eastern female who presented with chronic left cervicobrachialgia associated with left-hand paresthesia and weakness. Physical examination supported the diagnosis of nTOS. Imaging revealed an elongated C7 transverse process and aberrant and accessory muscular slips of the anterior scalene muscle. During ultrasound-guided anterior scalene bupivacaine injection, a large blood vessel was observed to dynamically impinge over the C7 nerve root, and hydrodissection using 10 ml of normal saline was added to the intervention. On subsequent computed tomography angiogram and retrospective review of magnetic resonance imaging, this artery was identified as the DSA unusually arising from the first part of the subclavian artery. The patient experienced a dramatic 80% symptom relief 1 week after the intervention. A further 10% relief was experienced following subsequent pectoralis minor bupivacaine injection. nTOS-directed physiotherapy was initiated. Persistence of improvement was observed 3 months after the injections. Recurrence of symptoms occurred starting from the eighth month post-intervention. Conclusions: This case highlights the possible contribution of the DSA to nTOS, the diagnostic value of a dynamic imaging modality, and the incorporation of hydrodissection in the decision-making process. Diagnostic muscle injections using Bupivacaine and neurovascular hydrodissection using normal saline lead in this case to 8 months of symptom relief and allowed us to locate the culprit structures.

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