Synopsis
Recognise pus spreading in the intracranial subdural space, distinguish it from parenchymal abscess and subdural haematoma, and coordinate urgent imaging, drainage, microbiology and source control.
- Subdural empyema is pus between dura and arachnoid, not pus within brain parenchyma; the continuous subdural space permits rapid spread over convexity and falx.
- Sinus and ear disease dominate many community presentations in older children and young adults; infant post-meningitic and postoperative/traumatic empyemas are different populations and microbiological contexts.
- Contrast MRI with DWI is most sensitive, especially for small or interhemispheric collections; urgent contrast CT is appropriate when MRI would delay rescue, and persistent suspicion after equivocal CT requires MRI or repeat imaging.
Key red flags
New focal deficit, seizure, confusion, drowsiness or rapid deterioration during or soon after sinusitis or another head-and-neck infection.
Severe progressive headache with fever, vomiting, meningism or focal signs, especially in a child, adolescent or young adult.
Falling GCS, pupil change, posturing, abnormal breathing or marked midline shift indicates dangerous intracranial pressure and possible herniation.
Fever, seizure or new neurological deficit after cranial trauma, craniotomy or subdural-haematoma drainage raises postoperative empyema.
An initially normal or non-specific CT does not exclude early or interhemispheric empyema when clinical suspicion persists.
Cortical venous thrombosis, venous infarction, cerebritis, abscess and septic shock can coexist and worsen despite initial therapy.
New severe headache, fever, seizure, focal deficit or confusion during sinusitis is an intracranial-complication signal, especially in adolescents and young adults.
Rapidly evolving focal signs, seizures and reduced consciousness reflect spread over cortex and associated oedema or venous injury rather than a single parenchymal focus.
Fever, wound change, seizure or new deficit after cranial surgery or subdural drainage suggests direct inoculation or infected residual fluid and requires the operating service.
Midline shift, pupil change, falling GCS, cortical venous thrombosis and venous infarction increase urgency and may explain abrupt worsening.
Reasoning priorities
Define thin convexity or interhemispheric pus, loculations, cerebritis, abscess, venous injury and mass effect.
Restricted diffusion within a crescentic or parafalcine collection supports empyema. Negative or equivocal early imaging does not overrule progressive clinical suspicion; repeat or alternative imaging may be required.
Worked reasoning
A teenager treated for frontal sinusitis develops fever, severe headache, focal seizure and unilateral weakness.
- Recognise possible subdural empyema with cortical involvement, stabilise airway and circulation, treat the seizure and activate neurosurgery, infection and ENT teams immediately.
- Obtain urgent contrast MRI with DWI; use immediate contrast CT if MRI would delay rescue, and avoid lumbar puncture.
- Take blood cultures if this does not delay treatment, start the locally approved source- and age-appropriate empirical regimen and prepare urgent drainage.
- Send pus for aerobic and anaerobic culture plus directed studies, and coordinate sinus source control rather than treating the cranial collection alone.
- Monitor serial neurology, seizures, inflammatory response and imaging, reassessing for residual loculations, venous complications or need for repeat surgery.