Continuing Education Activity
Pneumocephalus, also known as pneumatocele or intracranial aerocele, is defined as the presence of air in the intracranial space. Pneumocephalus can occur following trauma, cranial surgeries, or spontaneously. It is classified as simple or tension pneumocephalus and can also be classified as acute, or less than 72 hours, or delayed, or greater than 72 hours old. This activity reviews the evaluation and management of pneumocephalus and highlights the role of interprofessional team members in collaborating to provide well-coordinated care and enhance patient outcomes.
- Identify the epidemiology of pneumocephalus.
- Describe the evaluation of pneumocephalus.
- Outline the treatment and management options available for pneumocephalus.
- Explain interprofessional team strategies for improving care coordination and communication to advance the management of pneumocephalus and improve outcomes.
Pneumocephalus (also known as pneumatocele or intracranial aerocele) is defined as the presence of air in the epidural, subdural, or subarachnoid space, within the brain parenchyma or ventricular cavities. Lecat first described this condition in 1741, but the term "pneumocephalus" was coined independently by Luckett in 1913 and Wolff in 1914. The term "tension pneumocephalus" (TP) was proposed in 1962 by Ectors, Kessler, and Stern.
Pneumocephalus can occur following trauma, cranial surgeries, or spontaneously. It is classified as simple or tension pneumocephalus. It can also be classified as acute (less than 72 hours) or delayed (72 hours or more).
It has to be differentiated from the following terms:
- Pneumorrhachis denotes intraspinal air.
- Pneumocele is focal or diffuse enlargement of any paranasal sinus (usually frontal) associated with thinning of its bony walls and hyperpneumatization
- Pneumosinus dilatans is the same as pneumocele, but the walls of the sinus are intact and normal.
- Skull base defects
- Tegmen tympani defect
- Most common cause
- Fractures involving the skull base with breach of the dura
- Fractures of air sinuses
- Penetrating head injuries with a dural laceration
- Meningitis or ventriculitis produced by gas-forming organisms
- Chronic otitis media and sinusitis
- Dermoid cyst rupture
- Tumor eroding the skull or skull base like osteoma, epidermoid or pituitary adenoma
- Trans-cranial surgeries (especially posterior fossa surgeries in a prone position and following chronic subdural hematoma evacuation in supine position)
- Transsphenoidal surgeries
- Following lumbar puncture or spine surgeries
- Following the development of spontaneous cerebrospinal fluid rhinorrhea
- Secondary to CSF leakage from myelomeningocele
The incidence of pneumocephalus depends on the etiology and is seen in almost all post-craniotomy cases. The incidence following head injury varies depending on the series from 1% to as high as 82%.
During head injury or following cranial surgeries, dura may be opened or torn with or without injury to arachnoid. In all these cases, air can get inside the cranial cavity. There are two theories about the mechanism for the development of pneumocephalus:
- Ball valve theory of Dandy: Unidirectional movement of air from the outside environment into the cranial cavity
- Inverted-soda-bottle effect of Horowitz and Lunsford: Excessive loss of cerebrospinal fluid (CSF) due to drainage in a physiological way during Valsalva or via lumbar drain leads to low intracranial pressure (ICP) and trapping of air in the vacuum created inside the cranium
The presence of air is a source of infection, which can lead to the development of meningitis. Also, it can cause seizures by irritating the cerebral cortex.
History and Physical
The following features of the patient's history should make clinicians suspicious that the patient has pneumocephalus:
- CSF leak from nose, ear, or surgical site
- Persistent headache after cranial or spinal surgery
- Seizures following surgery
- Postoperative meningitis
- Frontal lobe syndrome
Pneumocephalus is a difficult diagnosis clinically. Rarely, some patients may describe a splashing sound on head movement (known as bruit hydro-aerique), which can be auscultated as well. TP can lead to deterioration in sensorium and papilledema. The same features in the posterior fossa may cause brainstem signs, respiratory irregularities, and cardiac arrest. Even paraplegia and hemiplegia have been reported following TP.
X-rays have been used in the past to identify the pneumocephalus, but it will miss small quantities of air.
Head Plain Computed Tomography (CT)
This is the gold standard investigation in the diagnosis of pneumocephalus. It can detect even 0.55 ml of intracranial air, whereas a skull radiograph requires at least 2 ml. Air has a Hounsfield coefficient of -1000. There are two signs which were identified as characteristic of TP by Ishiwata et al.
- "Mount Fuji sign" (named after Mount Fuji, the highest volcano mountain in Japan) formed by the accumulation of air in the frontal region, with separation of tips of two frontal lobes, in a patient in the supine position is diagnostic of tension pneumocephalus.
- "Air bubble sign" denotes the presence of multiple air bubbles scattered in several cisterns
"Peaking sign" denotes bilateral compression of frontal lobes without separation of the tips. It shows a less severe condition compared to the Mount Fuji sign.
Brain Magnetic Resonance Imaging (MRI)
MRI may also be useful, but not as sensitive as CT scan in the diagnosis of pneumocephalus. Moreover, air may be mistaken for flow voids or blood products, and it appears dark in almost all sequences.
Treatment / Management
Initial treatment of any head injury should follow the Advanced Trauma Life Support (ATLS) protocol.
Treatment of simple pneumocephalus:
Usually conservative. It involves the following steps:
- Bed rest
- Placing the patient in 30 degrees Fowler position
- Avoiding Valsalva maneuver like nose-blowing, coughing, and sneezing
- Analgesics and antipyretics
- Osmotic diuretics, if indicated
- High flow oxygen therapy should be given (5 L per minute for five days at least) via a face tent or 100% non-re-breather mask with absolute avoidance of positive pressure. The air is composed of 78% nitrogen and 21% oxygen. The rate of nitrogen absorption from pneumocephalus depends on the partial pressure of nitrogen in the blood, which is inversely proportional to the FiO2. When clinicians supplement oxygen, the nitrogen concentration in blood and brain tissue is reduced, increasing the nitrogen concentration gradient for absorption between the air collection and surrounding brain tissue. Slowly pneumocephalus will be replaced by oxygen, which has got high solubility within brain tissue and blood, which, in turn, facilitates its absorption leading to the final resorption of pneumocephalus.
Indications for surgical intervention:
- Symptomatic pneumocephalus
- Recurrent pneumocephalus
- Persistent traumatic pneumocephalus lasting more than one week
TP following cranial surgery can be treated by introducing a needle through the bur hole of the previous craniotomy and aspirating the air with a syringe. Other cases of TP may require a fresh frontal bur hole and aspiration or insertion of a subdural drain connected to an underwater seal followed by the closure of the dural defect, or insertion of saline primed Camino bolt.
Intracranial fat, although having a much higher density (-90 HU) compared to air (-1000 HU), can appear hypodense on CT scans and can be mistaken for pneumocephalus.
In MRI, pneumocephalus may be mistaken for blood products or flow voids.
Simple pneumocephalus is a condition that usually resolves by itself with conservative therapy. Sometimes it can produce seizures and meningitis. Prognosis is usually good even with tension pneumocephalus, provided timely treatment is given.
The following complications are likely to occur in a patient with pneumocephalus:
- Brain abscess
- Brain herniation secondary to TP
Deterrence and Patient Education
Prevention of Pneumocephalus
The following methods can be done to prevent the development of pneumocephalus after neurosurgical procedures:
- Filling of the surgical site with saline at the time of closure of the dura
- Administering Valsalva maneuver before taking the last bite of a suture through the dura, during its closure, to allow air to escape outside
- A smaller gauge spinal needle makes a smaller dural perforation and prevents cerebrospinal fluid leakage. Hence, such needles should be used while doing the lumbar puncture.
- Keeping the patient in the supine position with no head end of bed elevation following chronic subdural hematoma evacuation
- Positioning the head during dural closure in such a way that the last part of the dural defect becomes the highest point to facilitate the escape of residual air while filling the subdural space with saline
- Nitrous oxide (N2O), an anesthetic agent, had been previously proposed to cause pneumocephalus unless it is discontinued before the time of dural closure. But based on a randomized control trial, such an adverse effect of N2O on intracranial pressure was not noticed.
Neurosurgical procedures can result in residual intracranial air and can also result in a continuous entry of air into the cranial cavity. Hence the patient is advised to wait for at least seven days before taking a flight as the cabin pressure changes can introduce air inside the skull.
There is no proper evidence to support the prophylactic administration of ceftriaxone for preventing meningitis in patients with traumatic pneumocephalus.
Enhancing Healthcare Team Outcomes
All patients with head injuries and post-craniotomy status should be strictly monitored for the development of pneumocephalus. Nurses should monitor the sensorium and should be careful regarding the positioning of patients and give instructions to avoid a Valsalva maneuver. They should contact a physician if there is a serious change. [Level 5] If the patient develops TP, which leads to a drop in sensorium, basic supportive care, including maintenance of airway, breathing, and circulation, followed by definitive management, should be provided.