What is Pneumocephalus (Pneumatocele)?
The skull, also referred to as the cranium, is the bony structure that forms the head, and it is made up of two main parts. The first part is the ‘neurocranium’, which protects the brain, and the second part is the ‘facial skeleton’, which constitutes the front part of the skull, including the face.
The neurocranium is further divided into:
- Frontal bone (Forehead)
- Parietal bones (Sides of Skull)
- Temporal bones (Temple Area)
- Occipital bone (Back of Skull)
- Sphenoid bone and Ethmoid bone (Behind the Eyes)
The facial skeleton consists of various bones including:
- Lacrimal bones and Nasal bones (Nose Area)
- Maxillae and Zygomatic bones (Upper Jaw and Cheekbones)
- Palatine bones and Inferior nasal conchae (Roof of the Mouth)
- Mandible (Lower Jaw)
- Vomer (part of the Nasal Cavity)
Underneath the skeleton of the head, there’s an area called the scalp, which has different layers can be remembered by the acronym “SCALP”: Skin, Connective tissue (a type of tissue that supports and binds other body tissues and organs), Aponeurosis (a type of soft tissue), Loose Connective tissue, and Pericranium (the outer layer of the skull).
Deep within the skull, there are three layers that protect the brain, known as the meninges. These include the dura mater (outer layer), arachnoid mater (middle layer), and pia mater (inner layer). There are spaces between these layers that can potentially fill with fluid during certain medical conditions.
One such condition is Pneumocephalus, where air gets trapped in these spaces inside the skull or within the brain itself. This condition can happen spontaneously, due to trauma or following skull or brain surgery. There is a variety of this condition named “tension pneumocephalus” that indicates a more severe form involving increased pressure inside the skull due to the accumulation of air, which can potentially compress vital areas of the brain.
It is essential to distinguish Pneumocephalus from other medical conditions involving air in different parts of the body, such as Pneumorrhachis (air within the spine), Pneumocele and Pneumosinus dilatans (air in the sinuses), and Pneumoventricle (air in the chambers within the brain).
What Causes Pneumocephalus (Pneumatocele)?
Pneumocephalus is a condition where air or gas gets into the brain area. It happens for lots of different reasons and the most typical reason is damage to the head or face. The air can find its way into the brain through cracks in the skull caused by this damage.
Let’s explain the different causes in simple language:
If it’s trauma-related, it might include skull fractures that damage the protective covering of the brain, fractures of air-filled spaces in the skull, injuries that penetrate the head and tear this brain cover, damage to the eye caused by high pressure, or even a kind of leak between the brain’s covering and the chest.
If it’s infection-related, it might be because of ‘gas-forming’ infections like meningitis or an infection that affects the brain ventricles (the brain’s ‘communication system’). It can also be caused by a long-lasting ear or sinus infection.
If it’s tumor-related, it might be because a cyst (a pocket of fluid in the body) in the skin ruptures, or tumors that wear away at the skull, like bone tumors, tumors in the outer layer of the skin, or tumors in the pituitary gland (a small gland at the base of the brain).
If it’s iatrogenic, meaning it’s caused by medical procedures, it might be after brain surgery, especially if the patient is located prone (face-down) or if chronic subdural hematoma (an ‘old’ blood clot on the brain) is drained while the patient is supine (on their back). Other examples may be surgeries carried out through the nose, or after a lumbar puncture (where a needle is inserted into the lower part of the spine) or a spinal surgery, among other causes.
If it’s spontaneous, it could occur due to a sudden leakage of cerebrospinal fluid (the fluid found in and around the brain and spinal cord) to the nose and mouth, leakage from a birth defect called myelomeningocele (a type of spina bifida which is a condition where a baby’s spine doesn’t form correctly during pregnancy), or when there’s an unexpected connection between the brain space and an air-filled area of the temporal bone (the bone at the side and base of the skull).
If it’s congenital, meaning the person is born with it, it might be due to defects in the bottom of the skull or a specific part of the temporal bone.
Lastly, if it’s miscellaneous, it might be due to barotrauma, injury caused by a change in air pressure.
Pneumocephalus can vary in seriousness, and the symptoms can range from mild headaches to more severe neurological deficits that affect the nervous system. Treatment depends on what is causing it and the patient’s overall health condition.
Risk Factors and Frequency for Pneumocephalus (Pneumatocele)
Pneumocephalus, or air in the cranial cavity, occurs due to various reasons. After brain surgery, it’s nearly always present. However, when it happens after a head injury, it ranges widely – from 1% to a massive 82% according to different studies. In fact, head trauma causes about 74% of all pneumocephalus cases.
- Pneumocephalus is often seen after brain surgery.
- The occurrence of pneumocephalus after head injury can vary from 1% to 82% based on different studies.
- Head trauma is responsible for roughly 74% of all pneumocephalus cases.
Signs and Symptoms of Pneumocephalus (Pneumatocele)
Pneumocephalus, or air in the brain, is a serious medical condition that can present in many ways. Initial assessment of the patient should include checking their airway, breathing, circulation, level of consciousness, and looking for any injuries. If someone is unconscious with no breath or pulse, immediate resuscitative actions should be taken. After the initial needs are addressed, further evaluations may begin.
The patient’s history could indicate a recent trauma that caused a skull fracture. The symptoms vary significantly based on how much air is in the brain and which parts of the brain are affected. Although many patients may not show any symptoms, those who do may experience nausea, vomiting, memory loss, speech or sensory changes, fluid leak from the nose or ear, seizures, headaches, and muscle weakness.
In rare cases, patients may hear a ‘splashing’ sound when moving their head, which is a definitive sign of pneumocephalus. In extreme situations, patients could exhibit altered consciousness, unusual breathing patterns, or even experience a heart or respiratory arrest. In individuals with no recent trauma, the possibility of pneumocephalus may arise from a recent neurosurgery, spinal procedure, infection symptoms, signs of intracranial mass, or a history of ventilator use or birth defects.
An examination might reveal injuries on the scalp or skin, signs of a skull fracture, bloody fluid in the nose or external ear canal, or a ruptured eardrum. In severe trauma cases, symptoms might include difficulty breathing, low blood pressure, elevated heart rate, rigid abdomen, bloody urine, and fractures in the appendages. If the patient previously experienced pressure injuries, certain signs might be apparent, such as unilaterally decreased breath sounds or a characteristic crunching sound heard in rhythm with the heartbeat.
The symptoms and signs that should make doctors suspect pneumocephalus include:
- Fluid leak from the nose, ear, or a surgical wound
- Constant headache following head or spine surgery
- Seizures after surgery
- Postoperative meningitis
- Behaviour consistent with frontal lobe syndrome
- A ‘flapping’ sign on the scalp
- Failure of eye movement function
- Swelling of the optic disc
- Ringing in the ears
In severe cases, pneumocephalus can cause brainstem symptoms, irregular breathing, and cardiac arrest. There have even been reports of paralysis and motor weakness on one side of the body resulting from severe pneumocephalus.
Testing for Pneumocephalus (Pneumatocele)
If someone is in unstable health, it’s important to keep track of their vital signs and heart activity constantly. For those who are unconscious, a simple sugar test is performed to make sure low blood sugar isn’t causing the unconsciousness. Oxygen levels in the blood need to be monitored for individuals who are getting extra oxygen.
If someone has experienced some form of trauma and might need emergency surgery, immediate lab tests are conducted. These tests could include a complete blood count, which details the different types of cells in the blood, a coagulation profile that looks at how well your blood clots, blood typing to know the patient’s blood group, a complete metabolic panel to measure the health of your kidneys and liver, and a urinalysis to examine your urine. In case of breathing difficulties, the medical team might also consider doing tests involving arterial blood gases and heart monitoring. It is essential to arrange for imaging studies right away.
Plain Films
Although skull x-rays used to be a go-to method for detecting pneumocephalus (air in the head), it’s not very effective at picking up small amounts of air. However, x-rays can still be useful in evaluating patients with several injuries.
Head Computed Tomography Scan Without Contrast
A head CT scan without contrast has become the golden standard to diagnose pneumocephalus. This scan can detect tiny amounts of air in the head, as far down as 0.55 ml, while the skull x-rays need at least 2 ml of air to detect anything.
Specific signs detected through CT scans help define tension pneumocephalus. One is the Mount Fuji sign, where the air accumulates in the front of the brain, pushing apart the tips of the frontal lobes. The other is the “air bubble sign,” which involves several air bubbles scattered throughout the brain’s water-filled spaces. There’s also a less severe condition indicated by “peaking sign”, which signifies squeezing of frontal lobes without separation of the tips.
Calculation of the Volume of Postoperative Pneumocephalus
To figure out how much air is in the brain, there are a couple of methods. You can use computer-assisted volumetric measurement if you have the correct software, or you can measure manually with the ABC/2 formula. The formula involves taking measurements on a selected CT scan slice and multiplying them together, then dividing by two.
ABC/2 Method:
1. Choose a center slice image of the pneumocephalus.
2. Measure “A”, the longest length of the pneumocephalus in millimeters.
3. Measure “B”, the maximum width of the pneumocephalus in millimeters.
4. Measure “C”, the height of the air in millimeters.
5. Then use the formula = A x B x C / 2 to get the volume in milliliters.
This simple formula tends to line up well with more complicated computer methods.
Brain Magnetic Resonance Imaging
MRI scans can also prove helpful, but in the case of pneumocephalus, they are less sensitive than CT scans. MRI can mistake air for other components like flowing blood or blood products, leading to potentially incorrect analysis of the condition.
Treatment Options for Pneumocephalus (Pneumatocele)
The Advanced Trauma Life Support (ATLS) protocol is a step-by-step guide used by medical professionals in treating patients who have experienced trauma. It focuses on delivering crucial treatments during the initial assessment and revival of the patient. If you sustain a head injury, your healthcare team will use this protocol. Once you are stable and necessary tests have been done, the doctors will classify the air in your skull, also known as pneumocephalus, in order to identify the best way to treat you.
A majority of people have simple pneumocephalus. This means they have no signs that pressure inside the skull is increased, and they often feel fine. A head CT scan, an imaging procedure that uses x-rays to create detailed pictures of the head, will show air inside the skull but without tension pneumocephalus indicators, like the “Mount Fuji sign.” This intracranial air typically disappears over time because it gets absorbed into the tissues. In these cases, treatment typically includes:
1. Bed rest
2. Elevating the head of the bed to a 30-degree angle
3. Avoiding sudden forceful straining like blowing your nose, coughing, and sneezing
4. Pain relievers and fever reducers
5. Medicines to aid the removal of body fluids, if needed
6. Breathing in high levels of oxygen for at least five days through a face mask, making sure not to exert any pressure
7. Hyperbaric oxygen therapy, a treatment in which you breathe in pure oxygen in a pressurized environment.
Air in the atmosphere contains 78% nitrogen and 21% oxygen. The speed at which nitrogen from the intracranial air gets absorbed depends on the pressure of nitrogen in the blood, which decreases as the fraction of oxygen breathed in increases. Providing supplementary oxygen reduces the levels of nitrogen in the blood and brain, thus, increasing the difference in nitrogen levels between the pneumocephalus air and the brain around it. Over time, nitrogen gets replaced by oxygen, which gets absorbed easily by the brain tissues and blood and helps in getting rid of pneumocephalus over time. Doctors might get periodic CT scans to supervise the progression of the condition.
Despite pneumocephalus potentially increasing the risk of an infection inside the skull, studies have shown that giving antibiotics as a preventive measure in patients with traumatic pneumocephalus does not necessarily provide an advantage.
Surgery might be needed in certain conditions like:
– Symptomatic pneumocephalus: Pneumocephalus that causes symptoms
– Tension pneumocephalus: Air trapped in the skull causing increased pressure
– Recurrent pneumocephalus: Pneumocephalus that keeps coming back
– Persistent traumatic pneumocephalus: Pneumocephalus that continues for more than one week after a traumatic event
– Tension pneumoventricle: Air trapped in ventricles inside the brain causing increased pressure
If tension pneumocephalus arises after brain surgery, it can be handled by using a needle to suck out the air through the hole made in the skull bone during the previous operation.
Different options for surgery to relieve pressure include:
– Using a needle to remove air either with or without the help of an imaging method through existing openings in the skull.
– Controlled pressure relief through a drain, followed by sealing the dural defect, the protective covering of the brain and spinal cord.
– Using a procedure to drain cerebrospinal fluid for air trapped in the ventricles of the brain.
– Emergency pressure relief by creating fresh openings in the skull.
– Decompressive craniectomy: a procedure which removes a part of the skull.
– Placing a saline-filled Camino bolt or placing a venting system known as Subdural Evacuating Port System (SEPS).
Endoscopic endonasal eustachian tube obliteration, a procedure that involves closing off the eustachian tube through the nose, has been used successfully as a treatment for cases of tension pneumocephalus following lateral skull base surgery.
What else can Pneumocephalus (Pneumatocele) be?
If someone exhibits symptoms suggesting pneumocephalus, doctors need to consider several other neurological conditions that might cause similar symptoms. These conditions include:
- Brain concussion
- Primary headache syndromes
- Stroke
- Metabolic encephalopathy
- Hematoma within the skull
- Diffuse axonal injury
- Arteriovenous malformations
- Tumors within the skull
- Infections within the skull
When tests like CT scans or MRIs are done, pneumocephalus can often look like other conditions. For instance, any fat within the skull can look less dense on a CT scan and might be mistaken for pneumocephalus, even though fat actually has a much higher density. When doctors use MRI, pneumocephalus can appear similar to blood products or voids in blood flow. Hence, doctors must be very careful when interpreting these imaging results to avoid misdiagnosis.
What to expect with Pneumocephalus (Pneumatocele)
Pneumocephalus, which is air or gas in the cranial cavity (the space within the skull), usually gets better on its own with non-invasive treatments. However, in rare cases, it might lead to seizures and meningitis – an inflammation of brain and spinal cord membranes. Even when there’s increased pressure due to pneumocephalus (tension pneumocephalus), the chances of recovery are usually good if it’s treated right away.
Having pneumocephalus might indicate a higher risk of chemical meningitis – which is inflammation triggered by non-infectious substances – after a surgical procedure called corpus callosotomy. This procedure involves cutting a part of the brain (corpus callosum) to control severe seizures. The presence of pneumocephalus after surgery can also predict the chances of recurrence of chronic subdural hematoma – pooling of blood on brain surface – after it has been removed surgically. Due to this, pneumocephalus is a part of the Puerto Rico Recurrence Scale, which is used to assess the likelihood of recurring medical conditions.
Possible Complications When Diagnosed with Pneumocephalus (Pneumatocele)
Pneumocephalus, or air in the skull, can lead to several serious issues including brain inflammation (meningitis), convulsions (seizures), a collection of pus in the brain (brain abscess), brain displacement due to a serious chest injury (tension pneumothorax), and in extreme cases, even death. However, with early medical intervention, these complications can be avoided and the patient’s chances of recovery can be significantly improved.
Potential Complications:
- Brain inflammation (meningitis)
- Convulsions (seizures)
- Collection of pus in the brain (brain abscess)
- Brain displacement due to a serious chest injury (tension pneumothorax)
- Death in extreme cases
Preventing Pneumocephalus (Pneumatocele)
To avoid the presence of air in the brain space (pneumocephalus) during or following surgery, certain practices can be helpful:
– The spots worked on in surgery can be filled with a liquid, saline, during the closing of the dural (outer membrane covering of the brain and spinal cord).
– Performing the Valsalva maneuver (forcefully exhaling against a closed airway) during closing the dural can allow trapped air to escape.
– A thin spinal needle for the lumbar puncture can create a small hole and minimize leakage.
– After a recurring brain blood clot (subdural hematoma) is removed, the patient should lie flat (in supine position).
– Position the head during dural closure in a way that allows air to escape as the brain’s outer covering (subdural space) is filled with saline.
– Instead of air, use saline to identify the epidural space (outside the dural sac) when giving an epidural injection.
Strive to avoid high airway pressure and quick breathing during mechanical ventilation (using a machine to assist with breathing).
Contrary to past beliefs, nitrous oxide, an anesthetic gas, does not significantly increase air buildup in the brain. Even if given after surgery, it does not notably contribute to pneumocephalus.
Ceftriaxone, an antibiotic, is not recommended to prevent brain infection (meningitis) in patients with traumatic pneumocephalus.
Brain surgeries can result in trapped air and constant air entry into the brain. Patients should avoid air travel for at least a week after surgery as changes in cabin pressure can introduce air into the brain.
To avoid pneumocephalus complications on a flight:
– Choose low-level flights or maintain ground-level cabin pressure.
– Avoid frequently changing cabin pressure.
– Find a position that reduces leaks.
– Use additional oxygen.
– Take decongestants before the flight.
– Avoid forceful exhalation (Valsalva maneuvers).
– Avoid slow breathing and carbon dioxide buildup if on a ventilator.
– Get imaging studies before the flight to check the existing air in the brain and rule out irregular connections.
Reduce strains caused by acceleration changes, noise, or low oxygen levels.
It is advised to avoid air travel for 2 to 8 weeks after intracranial (within the brain) surgery.
