Continuing Education Activity

An intracranial subdural empyema is a loculated collection of pus in the intracranial subdural space, the region between the dura and arachnoid mater covering the brain. This serious condition often starts from an infection spreading from nearby structures, such as the paranasal sinuses, mastoid air cells, or the middle ear. Subdural empyema may also arise following trauma, neurosurgical procedures, or complicated meningitis. The disease is more prevalent in immunocompromised individuals and requires prompt recognition due to its potential for rapid neurological deterioration.

Evaluation of subdural empyema involves a combination of clinical assessment and imaging studies, with magnetic resonance imaging considered the most sensitive tool for early detection. Treatment is urgent and typically involves a combination of surgical drainage and antibiotic therapy. The choice of antibiotic agent depends on the suspected or identified pathogens, and the surgical approach varies based on the empyema's size and location. Early intervention is critical to prevent complications, such as seizures, brain abscesses, or permanent neurological deficits.

This activity for healthcare professionals is designed to enhance learners' proficiency in evaluating and managing subdural empyema. Participants gain a broader grasp of the condition's etiology, pathophysiology, and best diagnostic and treatment approaches. Greater competence enables healthcare professionals to collaborate effectively within an interprofessional team caring for patients with this condition.

Objectives:

• Identify early signs and symptoms of subdural empyema, including nonspecific neurological changes.

• Differentiate subdural empyema from other causes of neurological deterioration, such as meningitis or brain abscess.

• Screen high-risk patients, such as those with recent sinusitis, head trauma, or neurosurgical procedures, for potential subdural empyema.

• Apply effective strategies to improve care coordination among interprofessional team members to facilitate positive outcomes for patients with subdural empyema.

Introduction

Intracranial subdural empyema is a loculated pus collection in the intracranial subdural space, the area between the dura and arachnoid mater surrounding the brain.[1][2] The condition was referred to as "subdural abscess," "cortical abscess," "purulent pachymeningitis," "phlegmonic meningitis," or "subdural suppuration" before 1943.[3] Focal intracranial infections can be classified as a brain abscess, epidural abscess, or subdural empyema. If bacterial infections were to be taken into consideration, the spectrum of infections of the central nervous system would also include more generalized or diffuse infections like pyogenic meningitis or ventriculitis.[4]

This activity focuses on intracranial subdural empyema. The subdural space is continuous and has no anatomic barrier. Thus, subdural empyemas can spread over the brain convexities between both cerebral hemispheres and, in some cases, to the opposite hemisphere or even the posterior fossa.[5] The condition is considered a potentially dangerous but treatable entity. Intracranial subdural empyema can lead to severe symptoms, or even death, by direct brain compression and injury due to the skull being a confined cavity. Prompt diagnosis and adequate treatment can, in most cases, prevent these types of complications, resulting in better outcomes. History and physical examination should direct the clinician to the suspected diagnosis. Imaging techniques often reliably confirm the condition.

Etiology

The etiology of subdural empyema can be multifactorial. However, some of the predisposing factors associated with the development of this condition include prior cranial surgery, head trauma with open skull fractures or penetrating injury, infected hematoma or subdural effusion, and improperly treated ear and sinus infections.[6][7] The literature reports that between 40% to 80% of patients with subdural empyema have otorhinologic infections, especially of the paranasal sinuses. Up to 20% of subdural empyemas occur following head trauma or cranial surgical procedures.[8]

The most frequently recovered microorganisms are anaerobes, aerobic streptococci, staphylococci, Haemophilus influenzae, Streptococcus pneumoniae, and other gram-negative bacilli. However, the most commonly reported microbial agents in cases of paranasal sinusitis-related subdural empyema are anaerobic and microaerophilic streptococci (Streptococcus milleri and Streptococcus anginosus).[9] Meanwhile, Staphylococcus aureus is the most common organism in cases arising from cranial trauma or surgical procedures. Coagulase-negative Staphylococci, anaerobes, and gram-negative organisms may also be found in these patients. Many infections are polymicrobial.[10][11]

Subdural empyema is usually a complication of purulent meningitis in young children.[1] In contrast, the condition is commonly secondary to direct extension from contiguous foci in older children.[12] Intracranial empyema can develop in children following COVID-19 infection and is often associated with cerebral sinus thromboses.[13] The pathophysiological mechanism in infants involves the infection of sterile, reactive subdural effusions from meningitis.[14] Subdural empyema due to bacterial meningitis is rare in adults.

Epidemiology

Intracranial subdural empyema usually affects children and young adults.[15] Male individuals are more commonly affected, with a male-to-female ratio of 3:1. Subdural empyemas can also develop in the spinal canal, though cases are rarely reported in the literature.[16] Intracranial subdural empyemas are much less common than brain abscesses.

Pathophysiology

Subdural empyema most often occurs from the direct extension of local infection, which can spread to the intracranial compartment due to the valveless diploic veins of Breschet. Consequently, blood may flow in either direction, causing intracranial bacterial infection to spread.[17] The lesions can also appear after a cranial surgical procedure due to the inoculation of microorganisms into the subdural space.

History and Physical

Subdural empyema initially presents with signs and symptoms of infection but may also be asymptomatic.[18] Manifestations may include fever, headache, nausea, vomiting, focal neurological deficits, seizures, and mental status changes. Fever and headache are usually present, and seizures occur in about half of patients; meningeal irritation signs may also be seen.

Most cases are gradually progressive; however, some patients can rapidly deteriorate, becoming drowsy, stuporous, and eventually comatose—or even die. Rapid progression may be due to increased intracranial pressure from the expanding pus collection. A recent head and neck infection, trauma, or surgery is often elicited.

Physical examination may show unstable vital signs, including fever, tachycardia, and respiratory compromise, which could all correlate with sepsis. The Cushing triad of hypertension, bradycardia, and bradypnea may be observed in severe cases. Other physical examination findings related to the neurological exam include meningismus, contralateral hemiplegia, cranial nerve palsies, anisocoria, and papilledema.[19]

A subdural empyema must be considered in a patient diagnosed with sinusitis or otitis who develops a fever, headache, and cranial pain. This disease should also be suspected in a patient who has recently undergone subdural hematoma drainage and presents with a fever, seizure, and new neurological deficits. Significant neurological deficits may occur due to localized brain edema and infarction associated with cortical thrombophlebitis.

Evaluation

History and physical examination should help tailor case evaluation and diagnosis. However, cranial imaging should be performed in all patients with suspected subdural empyema. The lesion appears as a hypodense area over a cerebral hemisphere or along the falx on a computed tomography scan. The collection margins are better delineated with the infusion of intravenous contrast dye. Depending on the extent and size of the subdural empyema, mass effects associated with the shifting of midline structures can also be seen. However, the diagnostic imaging study of choice for intracranial subdural empyema is magnetic resonance imaging (MRI) with intravenous gadolinium enhancement.

Contrast-enhanced MRI demonstrates sharp images of small collections and interhemispherically localized lesions. Subdural empyema is usually described in T1-weighted image findings as a "crescent-shaped" or "elliptical area" of hypointensity underneath the skull or adjacent to the falx cerebri. MRI diffusion-weighted imaging has proven to be more sensitive than routine MRI sequences and, therefore, should be performed.[20][21]

Laboratory workup can add evidence to the suspected diagnosis. The complete blood count often demonstrates leukocytosis, indicating an active infectious process, although this change may not always be found in immunosuppressed patients. Depending on the patient’s immune response, bacterial infections can cause a leftward shift with associated neutrophilia. Further laboratory testing, including serum inflammation markers like the erythrocyte sedimentation rate and C-reactive protein, could add evidence as these modalities are considered acute-phase reactants. Clinicians suspecting an infection may recommend blood culture samples to direct antibiotic therapy early in the disease course. However, the etiological agent is often difficult to identify due to the infection's encapsulated nature.[22][23] Spinal puncture does not help with diagnosis. The procedure can also be dangerous in patients with increased intracranial pressure and empyemas, which cause mass effects.

Treatment / Management

The treatment of cranial subdural empyema is multimodal, including medical and surgical interventions. Infectious disease and neurosurgery specialist involvement is indispensable. Monotherapy with antibiotics is rarely prescribed but may be considered in patients with mild presentations, no major neurological deficits, small pus collections on imaging, and documented early treatment response. However, such patients need close monitoring with serial clinical exams and neuroimaging studies. Longer antimicrobial therapy courses may be required. 

A prompt and accurate diagnosis, directly influenced by the clinician's suspicion based on the patient's history, physical examination, laboratory results, and imaging, often leads to a more favorable outcome. Treatment options, including multiple burr holes with drainage or a craniotomy for drainage and debridement, have been previously described in the literature. A craniotomy usually offers better results and fewer recurrences. Infants are treated with a burr hole, multiple subdural taps through the anterior fontanelle, or a craniotomy.

Preoperative imaging accurately localizes the pus collection, guiding the surgical approach. Once selected, multiple burr holes are made over the collection, allowing for incision of the dura mater, pus drainage, and irrigation of the cavity with saline solution. A large skin incision and wide craniotomy are required if a craniotomy is performed. Endoscopic evacuation of panhemispheric subdural empyemas may also be effective.[24]

A wide craniotomy is usually recommended for adequate exposure, thorough exploration, and complete evacuation of the subdural purulent collection. The dura is carefully opened to reveal the empyema, which typically presents as a collection of frank pus. A sample should be sent for both aerobic and anaerobic cultures.

The patient is started on antibiotics based on the results of Gram staining and the infection's pathogenesis until cultures are reported; broad-spectrum antibiotics should be initiated if Gram staining is negative or unavailable. Culture results guide the adjustment of antibiotic therapy. However, operative cultures can be negative, with no microorganisms reported in 7% to 53% of cases—often due to the frequent use of preoperative or preculture antimicrobial therapy.

Intravenous antibiotic therapy, coordinated by the infectious disease team for 3 to 6 weeks, is required. Longer treatment periods are warranted in patients with osteomyelitis. Infant subdural empyema is often secondary to meningitis, requiring 6 to 8 weeks of antibiotic administration.[25]

Laboratory testing is critical for further monitoring and follow-up. The recommended imaging approaches include a repeat head computed tomography scan or brain MRI. Antiepileptic drugs should be given because of the high incidence of preoperative and postoperative seizures.

Differential Diagnosis

The differential diagnosis of intracranial subdural empyema includes conditions with features of infection and neurologic dysfunction, such as the following:

• Epidural abscess
• Brain abscess
• Brain tumor
• Leptomeningeal disease
• Subdural hematoma
• Meningitis
• Cerebritis
• Subdural hygroma

A thorough evaluation, including the appropriate use of imaging tests, can help guide treatment approaches.

Prognosis

The clinical outcome of subdural empyema depends on the preoperative level of consciousness, timing of intervention, and aggressiveness of the treatment. Awake and alert patients have a good prognosis in most cases, while stupor and those in a comatose state bear a high mortality risk. Older patients have the worst prognosis, and up to half of the patients have permanent residual neurological deficits. Further, late seizures may occur despite the use of antiepileptic medications, and those with brain herniation often have an unfavorable prognosis.

Complications

Subdural empyema's complications include seizures, cerebritis, cerebral abscess, cerebral edema, cortical venous thrombosis with cerebral venous infarction, cavernous sinus thrombosis, sepsis, septic shock, electrolyte imbalances, hydrocephalus, cranial osteomyelitis in adjacent cranial bones, osteomyelitis of the craniotomy bone flap, and residual neurological deficits.

Deterrence and Patient Education

Individuals treated for sinusitis or otitis should be instructed to return immediately to their primary physician for reevaluation if they develop headaches, nausea, seizure, or disorientation. Patients on antiepileptic medication should continue treatment if recommended to avoid seizure recurrences.

Pearls and Other Issues

The most important points to remember in the evaluation and management of subdural empyema include the following:

• Subdural empyema is a medical and surgical emergency. Time is of utmost importance when this pathology is encountered, and early recognition and management are required.
• Attempts to identify the causative agent and tailor further therapy accordingly should be prioritized during evaluation and treatment. 
• The choice of antibiotics should be guided by the patient’s age, likely pathogen, predisposing conditions, and local resistance patterns.

Preventive measures include counseling and monitoring of at-risk individuals, especially patients who recently received treatment for head and neck conditions.

Enhancing Healthcare Team Outcomes

Managing intracranial subdural empyema is complex, and most cases need emergent treatment to avoid complications and unfavorable prognosis. Subdural empyema requires the services of an interprofessional team that includes a neurosurgeon, infectious disease specialist, critical care intensivist, neurologist, and physiatrist. Pharmacists review antibiotic and antiseizure medications to check for interactions and contraindications. Emergency, critical care, and neuroscience nurses provide care and update the interprofessional team on changes in patient status.

A good level of suspicion is needed to avoid delaying therapy. Once the infection resolves, many patients require long-term antiepileptic medications and physical therapy to return to premorbid function. Inpatient or outpatient rehabilitation may be needed for physical, occupational, or speech therapy.