= characterized by egress of CSF from intracranial cavity through abnormal communication between subarachnoid space and pneumatized structure within skull base (= osteodural defect)

Cause:

1. CONGENITAL: encephalocele
2. ACQUIRED
   1. traumatic (80–90% of all cases)
      • 2% of all head injuries develop CSF fistula
   2. nontraumatic:
      • infection
      • tumor (esp. those arising from pituitary gland)
   3. spontaneous: idiopathic intracranial hypertension

• rhinorrhea / otorrhea (may be exacerbated by Valsalva maneuver)
• “serous otitis media” with conductive / sensory hearing loss
• presence of β-2 transferrin (= polypeptide specific for CSF) / β-trace protein

Technique:

1. invasive techniques (time-consuming, poorly tolerated)
   1. Radionuclide cisternography
   2. CT cisternography
   • Contraindicated in active meningitis / elevated intracranial pressure!
     Disadvantage:
     • requires poorly tolerated lumbar puncture
     • time-consuming
     • slight risk of complications (low-tension headache, infection, bleeding at puncture site)
     • hypersensitivity reaction to contrast
     • high dose of radiation
     • requires active CSF leak
2. noninvasive techniques (best used in combination)
   1. Multidetector CT (92% sensitive, 100% specific)
      • bone defect / dehiscence at skull base
      • adjacent prominent arachnoid granulations
      • air-fluid level / opacification of contiguous sinus / middle ear / mastoid
      • pneumocephalus
      • lobular / nondependent area of soft-tissue opacification (meningocele, meningoencephalocele)
        DDx: mucosal reaction, cholesteatoma, granulation tissue, cholesterin granuloma
   2. MR cisternography (87–100% sensitive, 57–100% specific, 78–89% accurate)
      • hyperintense CSF fistulous tract
      • CSF collection = meningocele
        DDx: inflammatory paranasal secretions
      • extradural brain = meningoencephalocele
      • secondary gliosis of herniated brain
      • dural enhancement in stalk of meningoencephalocele