Anatomical anomaly discovered at neurogenic thoracic outlet surgery: a timely reminder

A 38 year old female presented with longstanding symptoms of thoracic outlet syndrome. Symptoms included neck and shoulder pain, forearm and hand paraesthesiae, which impaired hair washing, using clotheslines and high cupboards. Provocative testing was positive. Radiography revealed a prominent transverse process of the 7th cervical vertebrae, but no fully developed cervical rib (see Fig. 1). She proceeded to undergo right brachial plexus exploration and thoracic outlet release. Dissection revealed that the 5th and 6th cervical nerve roots formed separate anterior and posterior divisions (see Figs. 2 and 3), in addition to anomalous scalene muscle passing between plexus elements. The suprascapular nerve originated directly from the 5th cervical root. The divisions of the 5th and 6th cervical roots joined to form more typical anterior and posterior divisions, analogous to those which would usually arise from the absent upper trunk. The remainder of the operation proceeded uneventfully, including resection of compressive scalene muscle and 70 mm of the first thoracic rib. The patient's symptoms were effectively relieved thereafter, including at 12 months follow-up. The conventional anatomy of the brachial plexus is based on studies published by Abram Kerr in 1918.1 Numerous variations have been reported, including pre- and post-fixed plexuses, duplicated or absent plexus elements, and aberrant communications.2-4 Thoracic outlet syndrome is a diverse and complex disorder resulting from compression of the brachial plexus roots and trunks and/or the subclavian vessels as they pass through the cervicoaxillary canal.5-8 Commonly those affected by this condition possess anatomical variations including accessory muscle (‘scalenus minimus' and/or ‘pleuralis’), tendon and fascia, often associated with an elongated transverse process of the seventh cervical vertebra or a variably complete supernumerary cervical rib.5, 6, 9, 10 These anomalies alone may be sufficient to cause symptoms early in life, or only after the superimposed insult of trauma later in life, as has previously been described.5, 6 Anatomical variations of muscle, tendon, bone and nerve clearly play a role in the pathogenesis of thoracic outlet syndrome, though it can be difficult prior to surgery to identify the specific elements in individual patients. In this case, the 5th and 6th cervical nerve roots formed separate anterior and posterior divisions, effectively duplicating upper trunk elements at the level of the scalene muscles, which also demonstrated variant anatomy. These were not the primary cause of the patient's symptoms, though they potentially contributed. This case reminds us of the reality that thoracic outlet syndrome exists in patients with typical symptoms and signs, even when investigations are relatively unremarkable. Radiologic investigations can include but not exclude a diagnosis of thoracic outlet syndrome. Our approach to decompression of the thoracic outlet involves a careful dissection prior to resection of any structures. Surgeons performing dissections of the brachial plexus should be vigilant about possible variations in plexus anatomy. It is important in such surgeries to fully appreciate the anatomy of the entire brachial plexus, both pathologic and normal. This enables an understanding of that patients specific mechanical problems, thereby maximizing the opportunity for surgical remedy. Open access publishing facilitated by Monash University, as part of the Wiley - Monash University agreement via the Council of Australian University Librarians. Adam C. Gascoigne: Investigation; writing – original draft; writing – review and editing. Scott Ferris: Conceptualization; investigation; supervision; writing – review and editing.