Nontraumatic cerebrospinal fluid rhinorrhoea from a fistula between the trigeminal cistern and sphenoid sinus.

The radiological appearances of the trigeminal cistern on metrizamide cisternography and metrizamide CT cisternography are described. The frequent demonstration of this cistern on metrizamide cisternography is emphasised. A case of nontraumatic CSF rhinorrhoea produced by a CSF leak between the trigeminal cistern and the sphenoid sinus is described.