What is Subdural Empyema (subdural abscess)?
Intracranial subdural empyema is a type of brain infection where pus gathers in the space between the protective layers around the brain, known as the dura mater and the arachnoid. This condition was previously referred to as subdural abscess, cortical abscess, purulent pachymeningitis, phlegmonic meningitis, and subdural suppuration. Brain infections can differ and can be categorized as brain abscess, epidural abscess, and subdural empyema. When we consider bacterial infections, they can lead to more general or widespread infections like pyogenic meningitis or ventriculitis.
This focus is on intracranial subdural empyema because it’s particularly dangerous. Since the space where the pus accumulates is open and continuous, it can easily spread over the brain’s surface and in worst cases, even start impacting other parts of the brain. However, with timely diagnosis and correct treatment, we can avoid these complications and achieve better health results. Given that the skull is a limited space, this brain infection can generate severe symptoms and can even cause death by directly harming the brain.
Doctors identify this condition through its history and physical examination. At this point, if the healthcare provider suspects intracranial subdural empyema, they will use imaging techniques, like CT or MRI scans, to confirm the diagnosis.
What Causes Subdural Empyema (subdural abscess)?
Subdural empyema is a condition where pus collects between the layers of the brain’s protective coverings. It can be caused by several factors, such as previous brain surgeries, head injuries with open fractures or puncture wounds, infected bruises or fluid collections in the brain, and untreated ear or sinus infections. Studies show that 40 to 80% of people suffering from this condition have untreated infections in the ear, nose, or sinuses, especially in the area near the nose. Besides that, up to 20% of these cases are seen after head injuries or brain surgeries.
Various types of bacteria are responsible for subdural empyema. These include anaerobes (organisms that don’t need oxygen to grow), Streptococci, Staphylococci, Haemophilus influenzae, Streptococcus pneumoniae, and other bacteria that are negative on a type of staining called gram staining. If a patient has subdural empyema due to sinusitis (sinus infection), the most common bacteria reported are anaerobic and microaerophilic streptococci. In contrast, if subdural empyema results from brain trauma or surgeries, the most common bacterium is Staphylococcus aureus. Also, some types of bacteria such as coagulase-negative Staphylococci, anaerobes, and gram-negative organisms are found in those cases related to trauma or surgical procedures. Usually, more than one type of bacteria is involved in the infection.
When it comes to infants, subdural empyema is a typical complication of purulent meningitis (an infection that causes the membranes that cover the brain and spinal cord to swell). However, in older kids, it is often a consequence of a direct spread from nearby infected areas. For babies, the infection occurs because of bacteria getting into sterile, reactive brain fluids due to meningitis. In comparison, in adults, subdural empyema due to bacterial meningitis rarely happens.
Risk Factors and Frequency for Subdural Empyema (subdural abscess)
Intracranial subdural empyemas, a type of brain infection, usually impact children and young adults more than other age groups. It’s more common in males, with males being three times more likely to be affected than females. These empyemas can also affect the spinal canal, although this is not often discussed in medical literature. Brain abscesses, another form of brain infection, are more common than intracranial subdural empyemas.
Signs and Symptoms of Subdural Empyema (subdural abscess)
Subdural empyema is an infection that often shows symptoms, although, in some cases, it may not present any. Common symptoms include fever, headache, nausea, vomiting, neurological issues, seizures, and alterations in mental state. A person with subdural empyema can also experience signs of irritation on the meninges, the protective layers over the brain and spinal cord.
During a physical examination, doctors might observe unstable vital signs that suggest possible sepsis, including increased body temperature, rapid heart rate, and breathing difficulties. Subdural empyema tends to develop gradually and can lead to worsened symptoms if unchecked. In severe cases, individuals can become extremely ill in a short timeframe, showing signs of extreme drowsiness, stupor, and even falling into a coma or death. This can result from increased pressure inside the skull due to the infection, leading to Cushing’s triad, a condition characterized by high blood pressure, slow heart rate, and slow breathing.
Other signs that doctors may observe during an examination include stiff neck, weakness or paralysis on one side of the body, issues with cranial nerves, unequal pupil size, and swelling of the optic disc (papilledema). Anyone diagnosed with sinusitis or otitis (ear infection) who suddenly develops fever, headache, and head pain should be evaluated for subdural empyema. Likewise, individuals who have undergone drainage of a blood clot beneath the dura mater (the outermost layer enveloping the brain and spinal cord) who exhibit fever, seizures, and new neurological deficits should be checked for this infection. Severe neurological problems can arise due to brain swelling and stroke associated with inflammation of the vein walls.
- Fever
- Headache
- Nausea
- Vomiting
- Neurological issues
- Seizures
- Alterations in mental state
- elevated body temperature
- Rapid heart rate
- Breathing difficulties
- Extreme drowsiness or stupor
- Coma or death (in severe cases)
- Stiff neck
- Weakness or paralysis on one side of the body
- Issues with cranial nerves
- Unequal pupil size
- Swelling of the optic disc
Testing for Subdural Empyema (subdural abscess)
If your doctor suspects you might have subdural empyema, which is a pocket of pus in the space between your brain and its outermost covering, they will begin by asking about your health history and performing a physical examination. This information helps your doctor understand your symptoms and guides their approach to diagnosing your condition.
However, to make a definite diagnosis, imaging of your brain is required. This is typically done using a technique called computed tomography, or a CT scan. Subdural empyema often appears as a lighter area on the scan, located either over part of your brain or near a connective tissue called the falx. Sometimes, a special dye might be used to make this area easier to see. Depending on the size and location of the empyema, it might also cause parts of your brain to shift, which can also be spotted on the scan.
While CT is useful, the imaging method of choice is usually magnetic resonance imaging (MRI) with a special contrast agent to make the images clearer. This is because MRI can provide a detailed view of even smaller or harder-to-reach pockets of empyema. In these MRI images, the empyema usually appears as a “crescent” or oval-shaped area under the skull and near the falx. For an even better view, your doctor might use a version of MRI that uses motion to create images, called diffusion-weighted imaging.
In addition to imaging, your doctor might also order some blood tests. If your white blood cell count is high, it means your body is fighting an infection, which is a clue that you could have subdural empyema. However, not all patients’ white blood cell count will increase, especially if their immune system is already compromised. Other tests, such as the erythrocyte sedimentation rate and C-reactive protein test, can also indicate if your body is responding to an infection. In some cases, your doctor might also take a blood sample to identify the specific bacteria causing the infection, although this is less common with subdural empyema.
One thing your doctor will avoid is a spinal puncture. This procedure, which involves taking a sample of fluid from your spine, can be dangerous in those with increased pressure in the brain and empyemas that are causing parts of the brain to shift.
Treatment Options for Subdural Empyema (subdural abscess)
The treatment of a condition called cranial subdural empyema, which is an infection that forms a collection of pus between the surface of the brain and its outer covering, requires both medicine and surgery. The specialists involved typically include an infectious disease doctor and a brain surgeon. While antibiotics can be used alone in rare cases when the patient is doing well, doesn’t have significant neurological issues, and the amount of pus is small, these patients must be closely monitored with repetitive health checks and brain scans. They may also need extended courses of antibiotics.
Quick and accurate diagnosis is key to a better outcome. The diagnosis will be based on the patient’s history, a physical examination, lab tests, and imaging results. Treatment options may include creating multiple small surgical holes (burr holes) or performing a larger operation (craniotomy) to drain and clean out the infected area. Studies indicate that a craniotomy usually offers better results and fewer recurrences. In infants, treatment might involve a burr hole, multiple taps through the soft spot on their head (anterior fontanelle), or a craniotomy.
Before surgery, imaging helps the doctors accurately locate the site of the pus collection to determine where the operation needs to be performed. The surgical process involves making holes over the infected area and then draining the pus and washing the area with a saline solution. If a craniotomy is performed, a large skin cut is made followed by a large bone opening. This wide opening helps the surgeon get good access to the infected area for thorough cleaning.
During surgery, samples of the pus will be sent to the lab for testing to identify the type of bacteria causing the infection. The patient will then start on targeted antibiotics depending on the test results. If test results are not yet available, the patient will be put on broad-spectrum antibiotics, which cover a wide range of potential bacteria.
After surgery, the patient will need intravenous antibiotic therapy for 3 to 6 weeks under the supervision of the infectious disease team. This period might be longer if there’s a bone infection (osteomyelitis). In infants, cranial subdural empyema is often due to an infection of the protective membranes that cover the brain and spinal cord (meningitis), and thus, antibiotic treatment may be needed for 6 to 8 weeks.
The patient’s ongoing condition and progress will be monitored with repeated lab tests and scans. Antiepileptic drugs may also be prescribed because of the high risk of seizures before and after surgery.
What else can Subdural Empyema (subdural abscess) be?
When dealing with certain brain or neurological conditions, healthcare professionals may need to consider a variety of possible diagnoses. These might include:
- Epidural abscess (infection in the area between the skull and outer covering of the brain)
- Brain abscess (pockets of pus in the brain)
- Brain tumor (abnormal growth of cells in the brain)
- Leptomeningeal disease (cancer that has spread to the layers covering the brain and spinal cord)
- Subdural hematoma (bleeding on the surface of the brain)
- Meningitis (infection of the membranes covering the brain and spinal cord)
- Cerebritis (inflammation of the brain)
- Subdural hygroma (buildup of clear fluid on the surface of the brain)
Each of these conditions has unique characteristics and requires different treatments, so it is crucial to accurately identify what is happening.
What to expect with Subdural Empyema (subdural abscess)
The outcome of a patient largely depends on their level of consciousness before treatment, how quickly they received treatment, and how intensive the treatment was. Patients who were awake and alert generally have a good prognosis in most cases. Those who were semi-conscious or unconscious have a higher risk of death. Older patients tend to have the worst prognosis.
About half of the patients might experience lasting neurological damage. Even with the use of medications to prevent seizures, some patients may still experience them later on. Cases where the brain is forced out of its normal position, known as brain herniation, often have a poor prognosis.
Possible Complications When Diagnosed with Subdural Empyema (subdural abscess)
Subdural empyema can lead to a variety of complications. These might include seizures, a condition called cerebritis that causes inflammation in the brain, cerebral abscess or brain infections, brain swelling (cerebral edema), blockage of a brain blood vessel leading to brain tissue loss (cortical venous thrombosis with cerebral venous infarction), a rare condition where blood clots form in a cavity at the base of the brain called the cavernous sinus (cavernous sinus thrombosis), severe blood infection (sepsis), life-threatening low blood pressure condition (septic shock), electrolyte imbalances, accumulation of excess cerebrospinal fluid in the brain (hydrocephalus), bone infection near the site of the skull (cranial osteomyelitis) and within the surgical bone flap (osteomyelitis of the craniotomy bone flap), and potential lasting nerve damage (residual neurological deficits).
Complications of Subdural Empyema:
- Seizures
- Cerebritis (brain inflammation)
- Cerebral abscess (brain infection)
- Cerebral edema (brain swelling)
- Cortical venous thrombosis with cerebral venous infarction (blockage of brain blood vessel leading to tissue loss)
- Cavernous sinus thrombosis (blood clot in a cavity at the base of the brain)
- Sepsis (severe blood infection)
- Septic shock (life-threatening low blood pressure condition)
- Electrolyte imbalances
- Hydrocephalus (excess cerebrospinal fluid in the brain)
- Cranial osteomyelitis (skull bone infection)
- Osteomyelitis of the craniotomy bone flap (bone flap infection following surgery)
- Residual neurological deficits (lasting nerve damage)
Preventing Subdural Empyema (subdural abscess)
If you have been treated for sinusitis (inflammation of the sinuses) or otitis (ear infection), it’s important to be aware of certain symptoms. If you start to get headaches, feel sick to your stomach, experience seizures, or become disoriented or confused, make sure to go back to your doctor right away. They will need to reassess your condition.
If you are on medication for epilepsy (a neurological disorder characterized by recurrent seizures), never stop taking it without advice from a medical professional. If you do, you run the risk of having your seizures return.