Pancoast tumour with Horner's syndrome and brachial plexus involvement
A 61-year-old smoker presents with right shoulder pain radiating down the ulnar aspect of the arm, a 2 cm right apical lung mass abutting the chest wall, and a partial Horner's syndrome with ptosis and anhidrosis. MRI shows the tumour extending into the superior sulcus with contact with the C8 and T1 nerve roots and the stellate ganglion. There is no mediastinal nodal uptake on PET and no distant disease. He is referred for neoadjuvant chemoradiotherapy followed by resection. The team must define the target volume and decide whether the brachial plexus and stellate ganglion are to be included in the high-dose volume.
1. Describe the anatomy of the superior sulcus and explain which structures the tumour is likely invading to produce this clinical picture.
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The superior sulcus is the groove on the lateral aspect of the first rib, bounded by the subclavian artery and vein, the brachial plexus, the stellate ganglion and the T1 nerve root. The C8 and T1 roots emerge from the lower trunk of the brachial plexus, which lies on the first rib and scalene muscles; invasion produces ulnar-sided pain and hand weakness. The sympathetic chain runs along the heads of the ribs and the stellate ganglion lies at the level of C7–T1, so involvement causes Horner's syndrome.
The tumour is therefore likely invading the lower trunk of the brachial plexus and the sympathetic chain, with the subclavian vessels at risk. This makes it a T4 tumour by invasion of mediastinal structures, and the anatomical proximity to the vertebral body and intervertebral foramina means the spinal canal and cord are at risk if the tumour tracks medially.
2. How would you define the target volume, and what dose constraints apply to the brachial plexus and spinal cord?
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The GTV is the apical mass plus any involved nodes, with a 1–1.5 cm CTV margin constrained by anatomical boundaries: medially by the vertebral body and spinal canal, laterally by the chest wall, superiorly by the lung apex and inferiorly by the first rib. The brachial plexus should be included in the CTV because it is radiologically involved, but the high-dose volume should be limited to the gross disease.
The brachial plexus constraint is commonly Dmax < 66 Gy (or V66 < 1 cc) to avoid plexopathy, and the spinal cord Dmax should be < 45–50 Gy. Because the tumour abuts the plexus, achieving both target coverage and these constraints may require IMRT or proton therapy. If the plexus cannot be spared, document the risk of grade 2–3 neuropathy and consider whether surgery would be more appropriate first.
3. After 45 Gy, the patient develops worsening arm weakness and new sensory loss. What is the differential diagnosis and how does it alter your plan?
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The differential includes tumour progression into the brachial plexus, radiation-induced plexopathy (usually later, after 60 Gy), and cord compression from vertebral body involvement. Worsening weakness during radiotherapy is more likely progression or oedema, and an urgent MRI of the brachial plexus and cervical spine is required to distinguish them.
If there is progression, the plan should be reviewed for geographic miss, and the field may need to be extended to cover the intervertebral foramina and epidural space. If there is cord compression, dexamethasone and neurosurgical review are needed, and the radiation plan must respect cord tolerance. If it is radiation plexopathy, the dose to the plexus should be reduced for the remaining fractions, accepting a compromise in target coverage.