Pneumocephalus

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Fractures

General information

• AKA
• (Intra)cranial aerocele,
• Pneumatocele,

• The gas may be located in any of the following compartments:
• Epidural
• Subdural
• Subarachnoid
• Intraparenchymal
• Intraventricular

Definition

• Defined as the presence of intracranial gas.

Aetiologies

• Anything that can cause a CSF leak can produce associated pneumocephalus

• Skull defects
• Post neurosurgical procedure
• Craniotomy:
• Risk is higher when patient is operated with surgery in the sitting position
• Shunt insertion
• Burr hole drainage of chronic subdural hematoma:
• Incidence is probably< 2.5%
• Although higher rates have been reported
• Posttraumatic
• Fracture through air sinus (frontal, ethmoid…): including basal skull fracture
• Open fracture over convexity (usually with dural laceration)
• Congenital skull defects: including defect in tegmen tympani
• Neoplasm
• Eg:
• Osteoma
• Epidermoid
• Pituitary tumor
• Usually caused by tumor erosion through floor of sella into sphenoid sinus

• Infection
• With gas-producing organisms
• Mastoiditis

• Post invasive procedure:
• Lumbar puncture
• Ventriculostomy
• Spinal anesthesia

• Spinal trauma (LP could be included here as well)

• Barotrauma: e.g. with scuba diving (possibly through a defect in the tegmen tympani)

• May be potentiated by a CSF drainage device in the presence of a CSF leak

Presentation

• H/A in 38%

• N/V

• Seizures

• Dizziness

• Obtundation

• An intracranial succussion splash is a rare (occurring in ≈ 7%) but pathognomonic finding.

• Tension pneumocephalus may additionally cause signs and symptoms just as any mass (may cause focal deficit or increased ICP).

Tension pneumocephalus

• Intracranial gas can develop elevated pressure in the following settings:
• When nitrous oxide anesthesia is not discontinued prior to closure of the dura
• Nitrous oxide enters the subdural 34 times faster than it diffuses out as nitrogen into the blood stream—creating increased pressure/tension
• When a “ball-valve” effect occurs due to an opening to the intracranial compartment with soft tissue (e.g. brain) that may permit air to enter but prevent exit of air or CSF
• When trapped room temperature air expands with warming to body temperature:
• A modest increase of only ≈ 4% results from this effect
• In the presence of continued production by gas-producing organisms

Diagnosis

• CT
• Pneumocephalus is most easily diagnosed on CT, which can detect quantities of air as low as 0.5 ml.
• Air appears dark black (darker than CSF) and has a Hounsfield coefficient of–1000.
• One characteristic finding with bilateral pneumocephalus is the Mt. Fuji sign in which the two frontal poles appear peaked and are surrounded by and separated by air, resembling the silhouette of the twin peaks of Mt. Fuji

• Plain skull X-rays
• Intracranial gas can be seen

• Difficult to distinguish Tension and simple pneumocephalus
• Brain that has been compressed e.g. by a chronic subdural hematoma may not expand immediately post-op and the “gas gap” may mimic the appearance of gas under pressure.

Treatment

Simple pneumocephalus usually does not require treatment,

• When pneumocephalus is due to gas-producing organisms, treatment of the primary infection is initiated and the pneumocephalus is usually followed.

• Treatment of non-infectious simple pneumocephalus depends on whether or not the presence of a CSF leak is suspected.
• If there is no leak the gas will be resorbed with time, and if the mass effect is not severe it may simply be followed.
• If a CSF leak is suspected, management is as with any CSF fistula

• Treatment of significant or symptomatic post-op pneumocephalus by breathing 100% O2 via a nonrebreather mask increases the rate of resorption (100% FiO2 can be tolerated for 24–48 hours without serious pulmonary toxicity).

Tension pneumocephalus

• Urgent evacuation

• Options
• Needle aspiration on ward via previous burr holes
• Reopen wound and decompress. Fill with saline leave no drain.
• Options include placement of new twist drill or burr holes, or insertion of a spinal needle through a pre-existing burr hole (e.g. following a craniotomy).

• Dramatic and rapid improvement may occur with the release of gas under pressure.

Differential diagnosis (things that can mimic pneumocephalus)

• Although intracranial low-density on CT may occur with epidermoid, lipoma, or CSF, nothing is as intensely black as air

• This is often better appreciated on bone-windows than on soft-tissue windows

• Hounsfield units should be close to -1000.