Subdural empyema is a localized collection of pus in the subdural space between the dura and arachnoid, most often arising as a complication of sinus, ear, or cranial infection. It is a neurosurgical emergency due to rapid expansion, cortical compression, and high mortality if untreated.

 

Q. What is the pathogenesis of subdural empyema?

 

Infection spreads by direct extension from nearby sources such as paranasal sinuses, mastoid air cells, or middle ear. Spread occurs through valveless diploic veins, cortical veins, or emissary veins leading into the subdural space. The infection causes pus accumulation, venous thrombophlebitis, cortical necrosis, and local cerebritis. May coexist with cerebral abscess in 20–25% of cases.

 

Q. What are the common etiologies?

 

1. Frontal or ethmoidal sinusitis: most common
2. Otitis media and mastoiditis
3. Postoperative or post-traumatic causes (compound fractures, contaminated craniotomies)
4. Meningitis (especially pneumococcal in infants)
5. Septic cortical venous thrombosis or bacteremia

 

Q. What are the common causative organisms?

 

Aerobes: Streptococcus milleri, Staphylococcus aureus, Streptococcus pneumoniae.
Anaerobes: Bacteroides, Peptostreptococcus, Fusobacterium.
Post-surgical / post-traumatic: Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacteriaceae.
Immunocompromised hosts: Aspergillus, Candida, Nocardia.

 

Q. What are the common sites of involvement?

 

70–80% occur over the cerebral convexity.
10–20% are parafalcine (interhemispheric).
Posterior fossa involvement is rare and usually secondary to otitis or mastoiditis.
Empyema may extend rapidly across the convexity due to the lack of barriers in the subdural space.

 

Q. What are the associated and secondary complications?

 

Cerebral abscess (in 20–25% of cases)
Cortical venous thrombosis
Localized cerebritis or extension into brain parenchyma
Spinal subdural empyema (hematogenous dissemination)
Meningitis, seizures, or hydrocephalus

 

Q. How does it differ from epidural abscess and cerebral abscess?

 

Epidural abscess: Between bone and dura; limited by dural attachments.
Subdural empyema: Between dura and arachnoid; spreads freely over convexity.
Cerebral abscess: Within brain parenchyma; encapsulated.

 

Q. What are the clinical features?

 

Fever and severe headache: Rapidly progressive
Focal neurological deficits: Hemiparesis, aphasia, cranial nerve palsies
Seizures: Occur in 40–50% acutely; persistent seizures in up to 34% long-term
Signs of raised ICP: Papilledema, vomiting, altered sensorium, coma
Meningeal signs: Neck stiffness, photophobia.
Rapid deterioration within 24–48 hours is characteristic.

 

Q. What are the laboratory findings?

 

Leukocytosis with left shift
CRP and ESR elevated in almost all cases
Blood cultures positive in 30–40%
Lumbar puncture is contraindicated because of high risk of herniation.

 

Q. What are the characteristic imaging features?

 

CT with contrast:
Crescentic or lentiform hypodense extra-axial collection over convexity or falx.
Enhancing inner margin (arachnoid side) — double arc sign.
Associated sinus or mastoid opacification.
Mass effect, midline shift, compression of sulci.

MRI:
T1: Iso- to hypointense extra-axial collection with enhancing inner rim.
T2: Hyperintense fluid collection with surrounding cortical edema.
DWI: Restricted diffusion (helps differentiate from sterile effusion).
MR venography: may reveal cortical venous or sagittal sinus thrombosis.
MRI is superior to CT for early detection, interhemispheric spread, or posterior fossa lesions.

 

Q. How will you manage a case of subdural empyema?

 

It is a neurosurgical emergency, immediate antibiotics and surgical drainage are mandatory.

 

1. Medical management (initial stabilization)

Empirical IV antibiotics:
Ceftriaxone 2 g IV q12h + Metronidazole 500 mg IV q6h.
Add Vancomycin 15 mg/kg IV q8–12h if postoperative or trauma-related.
If Pseudomonas suspected: Cefepime 2 g IV q8h or Meropenem 2 g IV q8h.
Adjust based on cultures.
ICP management: Head elevation, mannitol.
Anticonvulsants for all patients.
Steroids reserved for massive edema threatening herniation.

 

2. Surgical management

Indications:
- Any established subdural collection
- Clinical deterioration or focal deficits
- Midline shift, mass effect, or radiologic evidence of pus
- Failure of conservative therapy

Techniques:
Emergency craniotomy with evacuation of pus and irrigation of subdural space.
Burr-hole drainage only if the patient is moribund or too unstable for craniotomy, but recurrence rate is higher.
Repeat exploration for reaccumulation (in 10–20%)
Posterior fossa empyema: Suboccipital craniectomy
Simultaneous management of primary focus (sinus drainage, mastoidectomy, or ENT repair).
Contraindications: None absolute except deep coma with absent brainstem reflexes.

 

3. Postoperative and adjunctive care

Continue IV antibiotics for at least 6 weeks or until MRI shows complete resolution.
Serial imaging (MRI preferred) every 3–5 days initially, then weekly.
Seizure prophylaxis for 6–12 months.
Monitor for cortical venous thrombosis clinically and via MRV if deterioration occurs.
Control of primary source (sinus or ear infection) is essential to prevent recurrence.

 

Q. What are the complications?

 

Recurrence or reaccumulation
Cortical venous thrombosis
Localized cerebritis or progression to brain abscess
Spinal subdural empyema
Hydrocephalus, seizures, or permanent focal deficits
Mortality: 10–20% even with timely treatment

 

Q. What is the prognosis?

 

Mortality 10–20% overall
Persistent seizures in 34% of survivors
Neurological deficits in up to 50%
Prognosis excellent with early surgery and appropriate antibiotic therapy

 

Q. What is the follow-up protocol?

 

MRI at 2 weeks, then monthly till resolution.
Continue antibiotics until imaging and CRP normalize.
Continue AEDs 6–12 months.
Evaluate sinus and mastoid cavities for residual infection.

 

Recalls:

 

Frontal or ethmoidal sinusitis is the most common source.
Spread via valveless diploic veins.
70–80% convexity; 10–20% parafalcine.
20–25% associated with cerebral abscess.
Cortical venous thrombosis, localized cerebritis, or spinal SDE → known complications.
CT crescentic collection with enhancing inner margin is the hallmark.
LP is contraindicated.
Craniotomy with evacuation is the treatment of choice.
Mortality 10–20%, and persistent seizures 34%.