Table 1. Anatomical pathway, pathological processes, and localising clinical features.

Neuronal order	Location	Pathology	Associated clinical signs
First order (central)	Posterior hypothalamus	Pituitary tumour
	Brainstem	Stroke—Wallenberg syndrome, pontine haemorrhage Demyelination	Vertigo Altered facial sensation Contralateral CN IV palsy Crossed motor/sensory signs
	C-spine Intermediolateral grey substance C8-T2	Arnold-chiari Cervical spondylosis Syringomyelia Neck trauma	Radicular signs
Second order (intermediate)	C8–T2 ventral nerve roots	Cervical rib	Neck/arm pain and weakness
		Brachial plexus injury
	Apex of the lung	Tumours  - Pancoast tumour  - mesothelioma	Signs of lung disease
	Mediastinum	Cardiothoracic procedure Aortic aneurysm or dissection
	Cervical sympathetic chain	Subclavian artery aneurysm Thyroid tumour Post neck dissection	Vocal cord paralysis Anhydrosis of face and neck
Third order (post ganglionic)	Superior cervical ganglion at C2-3	Jugular venous ectasia
	Carotid artery	Carotid  - dissection  - aneurysm  - arteritis	Facial pain Stroke Ocular ischaemia
	Cavernous sinus	Base of skull tumours	Abducens palsy
		Inflammatory mass
	Orbit	Herpes zoster