80% of post-traumatic CSF leakage occurs within 48 hours after injury. Bone defects in the central part of the anterior cranial fossa imply communication between the sinonasal cavity and the intracranial space. Occult CSF leaks may lead to severe intracranial infections (meningitis, brain abscess, etc.) even years after trauma.
The anterior fossa is formed by the ethmoid bone, sphenoid bone and frontal bone. It is limited anteriorly by the frontal bone and the posterior wall of the frontal sinus, posteriorly by the limen of the lesser wing of the sphenoid bone. The lateral parts form the roof of the orbits. The median (central) part is formed by the crista galli, the cribriform plate of the ethmoid plane and the planum of the sphenoid bone.
Diagnosis of late CSF leak is usually based on imaging. Serial CT-scans of patients having suffered a skull base fracture are critical to prevent late complications. The common finding is a bone defect affecting the posterior frontal sinus wall and usually extending to the anterior part of the cribriform plate.
Late posttraumatic rhinorrhea may occur.
For suspected but not evident rhinorrhea a provocation test (Valsalva maneuver) can be useful. Other tests are:
Double ring sign
Glucose test strip
The gold standard for the radiographic detection of skull base defects is computed tomography.
Specific, very useful CT sequences are:
Non contrast high resolution bone window CT (thin slices 1mm, axial and coronal)