Brachial Plexus – Lower Trunk Anatomy — SCE Neurology MCQ

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EasyPeripheral Neuropathy & NeuromuscularBrachial Plexus – Lower Trunk AnatomySCE Neurology

A 60-year-old man presents with progressive right arm pain and weakness. He has wasting of the right hand intrinsic muscles and forearm flexors. He also has a right Horner syndrome. Chest X-ray shows a right apical mass. EMG confirms a right lower trunk brachial plexopathy. He is diagnosed with a Pancoast tumour. What nerve roots form the lower trunk of the brachial plexus?

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Correct answer: D — C8, T1

The lower trunk of the brachial plexus is formed by the union of the C8 and T1 nerve roots. It gives rise to the medial cord (via the anterior division) and contributes to the posterior cord (via the posterior division). The lower trunk/medial cord supplies the hand intrinsic muscles (via the ulnar nerve and median nerve C8/T1 components), the long finger flexors (anterior interosseous nerve), and the medial cutaneous nerves of the arm and forearm. Pancoast tumours invade the lower trunk from above, and the stellate ganglion (causing Horner syndrome). A: C5/C6 form the upper trunk. B: C6/C7 do not form a single trunk. C: C7 forms the middle trunk alone. E: T2 is not part of the brachial plexus main trunks.

Reference: Clinical Neuroanatomy; Preston & Shapiro