Subdural Empyema - An Overview

What Is Subdural Empyema?

Subdural empyema is the localized collection of pus between the dura mater (outermost layer of the brain) and the arachnoid space (middle layer of the brain that contains cerebrospinal fluid). As per studies, subdural empyema is an intracranial infection; however, a few cases involving spinal neuraxis (axis of the central nervous system) have been reported. Subdural empyema generally refers to intracranial infection and does not involve spinal neuraxis. The subdural space is a continuous area without anatomic obstructions; hence, the pus formed can spread in the entire cerebrum (the most significant part of the brain). It is a dangerous condition and can result in death.

What Is the Pathophysiology of Subdural Empyema?

Subdural empyema is an intracranial infection that spreads rapidly due to the lack of anatomic barriers in the subdural space. The only border is the specific boundaries defined by the falx cerebri, tentorium cerebelli, the base of the brain, and the foramen magnum. As the lesion progresses, intracranial pressure and intraparenchymal penetration increase. The blood and cerebrospinal flow are disturbed, resulting in increased intracranial pressure, which in turn causes cerebral edema and hydrocephalus. In addition, thrombosis (blood clot) of cortical veins or cavernous sinuses occurs in subdural empyema, which can result in cerebral infarction (decreased blood flow).

In adults, subdural empyema occurs due to complications of inflammation of the paranasal sinus, otitis media (middle ear infection), or infection of the mastoid bone of the ear. Subdural empyema occurs due to meningitis in young children and infants. If the infection enters via frontal or ethmoid sinus spaces, the intracranial spread is through thrombophlebitis in the venous sinus. The infection passes directly to the cranium through a mastoid bone or frontal sinus tear. In rare cases, the infection spreads from the lungs or as a complication of surgery or trauma via blood.

What Is the Etiology of Subdural Empyema?

Head injury and cranial surgery are major predisposing factors associated with subdural empyema. In addition, ear and sinus infections, infected hematoma (pooling of blood), and skull fractures result in subdural empyema. Subdural empyema infection is polymicrobial, i.e., anaerobic and aerobic (Streptococci, Staphylococci, Haemophilus influenzae) microorganisms are present in subdural empyema.

What Is the Epidemiology of Subdural Empyema?

• Frequency- Subdural empyema is one of the leading causes of intracranial infection. Infection of the sinus and ears are the primary cause of subdural empyema.

• Mortality and Morbidity Rate- Early diagnosis, medical intervention, imaging technique, and histopathological examination have declined the death rate. Neurological defects are primarily due to the short follow-up period and low death rate.

• Age and Sex- Subdural empyema usually affects children and young adults and is mainly seen in the male population.

What Are the Signs and Symptoms of Subdural Empyema?

Patients present with the signs and symptoms of infection. Few cases are asymptomatic. Common symptoms are fever, headache, vomiting, and neurological symptoms like seizures and changes in the patient's mental status. In addition, patients show unstable vital signs, tachycardia (increased heart rate), and respiratory distress. Due to infection, few patients show rapid signs of degradation and become severely ill and can even die. Patients must be evaluated for subdural empyema if they have an infection and inflammation of the sinus and middle ear. A patient's chance of developing subdural empyema increases if they present with fever, seizure, and drainage of subdural hematoma.

What Are the Diagnostic Tests for Subdural Empyema?

Laboratory Test

• Complete blood count shows leucocytosis.

• Inflammatory markers like C-reactive protein and erythrocyte sedimentation rate are increased.

• A blood culture is done to identify the presence of microorganisms.

• Other routine blood tests like electrolyte and liver function tests are performed if surgery is considered.

Imaging Test- Cranial imaging is done in all the patients where subdural empyema is suspected.

• Cranial CT Scan (Computed Tomography) - It is a less commonly used technique due to the availability of MRI scans. Subdural empyema is seen as a less dense area over the cerebral hemisphere of the brain and along the falx cerebri. Infusion of an intravenous contrast dye helps in the demarcation of the margins. Midline shifts of structures can be seen depending on size.

• Cranial MRI (Magnetic Resonance Imaging) - It is the most preferred imaging technique. Gadolinium contrast medium is injected intravenously for better enhancement of the images. Subdural empyema is seen as crescent-shaped and less intense images below the skull or next to the falx cerebri.

• Cranial Ultrasound - It helps to differentiate between subdural empyema and subdural effusion in infants with meningitis. However, it is the least preferred method of imaging technique.

Other Tests- Echocardiogram (ECG), chest X-ray, computed tomography scan of a paranasal sinus, and sputum culture are advised.

What Is the Treatment of Subdural Empyema?

• Medical care- Proper airway for breathing and oxygen to ensure proper circulation is needed. Intravenous supply is provided for nutrition and antibiotic therapy. In addition, doctors should make arrangements to take care of neurological symptoms like epilepsy and coma.

• Surgical care- Drainage of subdural empyema should be done immediately. A craniotomy is the primary surgical modality. Craniotomy permits a broad exposure of the infected site, thus making it easy for exploration and removal of the pus materials. Drainage and irrigation of the affected area with a stereotactic burr hole is a less popular treatment modality because of incomplete drainage of the pus.

• Medication therapy- Medicines are given to decrease the death rate and improve the outcome of the infection. Intravenous antibiotic therapy is provided for three to six weeks or more, depending on the presence of other conditions. In addition, the antiepileptic drug is given wherever necessary.

What Is the Prognosis of Subdural Empyema?

The death rate is reducing due to advance diagnostic methods and timely medical intervention with antibiotics and surgical drainage.

Poor Prognostic Factors

• Old age or young patients who are less than ten years old.

• Delay in administrating antibiotics.

• Any previous brain disease other than subdural empyema.

• The patient goes into a coma along with subdural empyema.

Good Prognostic Factors

• Early medical intervention with surgery and antibiotics.

• Young age patients who are 10-20 years old.

• Alert, awake, and conscious patient during the clinical presentation.

• Paranasal sinusitis is the primary source of infection.

• Patients in which craniotomy is the preferred surgical modality.

• Presence of streptococci in microbial culture test.

What Are the Complications Of Subdural Empyema?

Complications include cerebral edema and abscess, septic shock, septicemia, hydrocephalus, osteomyelitis of the cranial bone, seizures, and electrolytic imbalance.

Conclusion

Subdural empyema is a medical emergency. Timely medical intervention prevents complications and provides a good outcome for the disease. The medical team consists of neurosurgeons, neurologists, infectious disease specialists, and intensive care unit team. The choice of antibiotic is governed by the patient's age and the pathogens present. A few patients may need the antiepileptic drug. In addition, they may need rehabilitation once recovered.