25th June 2023

False localising signs

A neurological sign is described as a false localising sign if it reflects dysfunction distant from the actual pathology. It commonly arises due to space-occupying lesions and diseases that cause raised intracranial pressure, including idiopathic intracranial hypertension. Extracranial false localising signs arise mainly due to spinal cord lesions.

Some anatomical considerations to consider are:

• Cranial nerve with the longest intracranial course is CN 4 – more vulnerable to head trauma
• Cranial nerve with the longest intradural course is CN 6 – most likely to be affected by raised intracranial pressure, vulnerable to stretching, classic example of false localising signs
• CN 3 passes close to the tentorium and is vulnerable to uncal herniation/pressure effects at that level – vulnerable to false localisation

Not necessarily related to false localising signs but of interest :

• Cranial nerve with the longest intraosseous course is CN 7 – making it vulnerable to infection, trauma and congenital conditions with craniofacial craniosynostosis. Note its descent in the petrous part of the temporal bone which makes it vulnerable to facial fractures
• Cranial nerve with longest extracranial course is CN 10 –vulnerable to traction and compression in the cervical area
• Cranial nerves in the cavernous sinus are CN 6, CN 3, CN 4, CN 5a – targets for cerebral venous sinus thrombosis