CSF rhinorrhoea can follow a head injury.
CSF from anterior cranial fossa reaches the nose by way of cribriform plate, ethmoid air cells or frontal sinus.
CSF from middle cranial fossa reaches the nose via sphenoid sinuses.
Sometimes, injuries of the temporal bone result in leakage of CSF into the middle ear and thence via the Eustachian tube into the nose [otorhinorrhoea].
The meninges are torn and cerebrospinal fluid leaks down the nose.
Ascending infection may cause meningitis
Reference: Dhingra’s ENT,5th ed.,p-178