A 49-year-old male with no history of head trauma suffered cerebrospinal fluid (CSF) discharge from the left nostril for one month. Coronal computed tomography (CT) showed lateral extension of the sphenoid sinus on both sides and CSF collection on the left side. CT cisternography could not identify the site of CSF leakage. Heavily T2-weighted magnetic resonance (MR) imaging (MR cisternography) in the coronal plane clearly delineated a fistulous tract through the sphenoid bone into the sphenoid sinus. Patch graft with muscle fragment completely relieved the CSF rhinorrhea. Postoperative three-dimensional CT showed the two bone defects identified during surgery. Small bony dehiscences in the sphenoid bone and lateral extension of the sphenoid sinus predisposed the present patient to CSF fistula formation. MR cisternography in the coronal and sagittal planes is superior to CT scanning or CT cisternography for detection of the site of active CSF leakage.