Neurosurgery notes/Infection/Cranial infection/Subdural empyema

Subdural empyema

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Cranial infection

General

  • Empyema is a collection of pus within a normal anatomical space therefore a collection in the subdural space is deemed an empyema
  • Frontal most

Epidemiology (Osborn and Steinberg, 2007).

  • It occurs most commonly in the second decade of life
  • M:F, 3:1
  • Less common than cerebral abscess (ratio of abscess:empyema is ≈ 5:1).
  • Found in 32 cases in 10,000 autopsies.

Pathology

  • Subdural empyema has the propensity to spread rapidly due to lack of fibrin capsule and anatomical barriers in the subdural space
  • Anaerobes
  • Concomitant (Osborn and Steinberg, 2007)
    • Cerebral abscess may occur in 6– 22%
    • Epidural abscess in 9– 17%
  • Location
    • 70–80% are over the convexity,
    • 10–20% are parafalcine.

Pathogen

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  • Most monomicrobial
  • The causative microorganisms vary according to the primary source of infection.
  • Paranasal sinuses
    • Polymicrobial infections (Nathoo et al., 1999).
  • Mastoiditis or sinusitis
    • Aerobic and microaerophilic Streptococci (Miller et al., 1987).
  • Postoperative and post- traumatic subdural empyema
    • Immunocompetent: Staphylococcus aureus
    • Immunocompromised: Klebsiella pneumonia (Greenlee et al., 2003).
  • Other causative microorganisms that have been reported include Escherichia coli and Salmonella species (Munusamy and Dinesh, 2015).
  • The success rate for culturing bacteria from surgically evacuated subdural pus ranges from 54% to 81% (Mauser et al., 1987; Nathoo et al., 1999).
    • Low culture positivity due to
      • Use of broad- spectrum antibiotics as empirical treatment for infection before sampling
      • Difficulties in culturing anaerobic organisms.

Aetiology (Munusamy and Dinesh, 2015).

  • Otitis media, mastoiditis
    • Most common
    • Aerobic and anaerobic streptococci
      • S. aureus was not a common pathogen in sinusitis-related SDE
  • Postcraniotomy infection
    • Staphylococci and Gram-negative species
    • CSDH evacuation
      • Craniotomy > burr hole drainage.
        • Presumably, the relatively simple and limited procedure minimizes tissue trauma and reduces the extent of bacterial inoculation.
      • Propionibacterium acnes, a ubiquitous skin commensal can rarely be implicated with an indolent clinical presentation and course of progression (Gritchley and Strachan, 1996)
  • Posttraumatic (penetrating injuries)
    • Staphylococci and Gram-negative species
  • Paranasal sinusitis
  • Hematogenous dissemination
  • Osteomyelitis of calvarium
  • Purulent bacterial meningitis
  • Organisms in SDE associated with sinusitis
      • Organisms
      %
      Adult cases
      ㅤ
      Aerobic streptococcus
      30–50
      Staphylococci
      15–20
      Microaerophilic and anaerobic strep
      15–25
      Aerobic Gram-negative rods
      5–10
      Other anaerobes
      5–10
      Childhood
      ㅤ
      Organisms are similar to meningitis for the same age group. Antibiotics choice is the same as for meningitis
      ㅤ
    • Sterile cultures occur in up to 40% (some of which may be due to fastidious anaerobes and/or previous exposure to antibiotics).

Complication

  • Cerebral abscess (seen in 20–25% of imaging studies in patients with SDE),
  • Cortical venous thrombosis with risk of venous infarction
  • Localized cerebritis.

Clinical presentation

  • SDE should be suspected in the presence of meningismus + unilateral hemisphere dysfunction.
  • Fever, headache, and altered mental state >>> rapid neurological deterioration.
    • Focal neurologic deficit and/or seizures usually occur late.
  • Seizures
    • occur in up to 63% of patients (Cowie and Williams, 1983).
  • The median time from the onset of symptoms to diagnosis is two days (French et al., 2014).
  • Marked tenderness to percussion or pressure over affected air sinuses is common.31
  • Forehead or eye swelling (from emissary vein thrombosis) may occur.
  • Symptoms are due to mass effect, inflammatory involvement of the brain and meninges, and thrombophlebitis of cerebral veins and/or venous sinuses.
    • Progression into an expanding mass lesion → raised ICP.
    • Disruption of cerebral blood flow or CSF flow. → Cerebral oedema and hydrocephalus
    • Direct spread or septic emboli → Thrombosis of the cortical veins or dural venous sinuses → venous hypertension → may progress to cerebral infarction.
  • Other presenting symptoms will depend on underlying aetiology for example sinusitis, mastoiditis, otitis media, meningitis, postoperative wound infection, systemic infection, or head trauma.
  • Findings on presentation with SDEᵃ
      • Finding
      %
      Fever
      95
      H/A
      86
      Meningismus (nuchal rigidity...)
      83
      Hemiparesis
      80
      Altered mental status
      76
      Seizures
      44
      Sinus tenderness, swelling or inflammation
      42
      Nausea and/or vomiting
      27
      Homonymous hemianopsia
      18
      Speech difficulty
      17
      Papilledema
      9
    • ᵃfrom a review of multiple articles

Evaluation

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LP

  • ❌ potentially hazardous (risk of herniation).
  • Organisms are usually present only in cases originating from meningitis.
  • If no meningitis, usually see findings consistent with a parameningeal inflammatory process
    • Moderate sterile pleocytosis (150–600 WBC/mm3) with PMNs predominating;
  • Glucose normal;
  • Opening pressure is usually high;
  • Protein is usually elevated (range: 75–150mg/dl)

Radiological

  • Radiological features
    • Crescent shaped collection
    • Dense enhancement of medial membrane
    • Crosses suture lines
    • On the surface of the brain
    • Below the cranial vault or adjacent to the falx or tentorium
    • Fq is rim enhancement with administration of contrast media.
  • CT
    • May miss small lesions.
    • Lesion is hypodense (but denser than CSF)
    • Images
        • notion image
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  • CT+C
    • If CT+C show no enhancement due to chronic empyema forming well- organized subdural pus (Moseley and Kendall, 1984; Munusamy and Dinesh, 2015)
  • MRI
    • Low signal on T1WI
    • High signal on T2WI
  • MRI+C
    • More sensitive than CT+C in detecting
      • Chronic organized empyema
      • Empyema located at the skull base, in the posterior fossa, or along the falx cerebri.
  • MRI+DWI: DIffusion restriction
    • High signal intensity on DWI
    • Low signal intensity on ADC maps
    • Can reliably distinguish subdural empyema from subdural hematoma or reactive subdural effusion that may also occur after trauma, surgery, or meningitis (Wong et al., 2004).

Treatment

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  • Almost all need Surgery
    • Antibiotic penetration into subdural space is poor.
  • Nonsurgical management has been reported but rarely done,
    • Indicated if
      • Minimal neurologic involvement,
      • Limited extension
      • Limited mass effect
      • Early favorable response to antibiotics
  • Time to treatment
    • <72HRs disability 10%
    • >72 hrs disability 70%
  • Goal of treatment
    • Bacteriological identification
    • Eradication of the primary foci of infection
    • Adequate antibiotic therapy (Miller et al., 1987).
  • Surgical options

      • Burr hole

      • Indicated for
        • Non-viscous empyema
        • Non-loculated empyema
          • Early in the course, the pus tends to be more fluid and may be more amenable to burr hole drainage; later, loculations develop which may necessitate craniotomy
        • Critically ill patients with localized SDE
      • Advantage
        • Avoid potential surgical complications associated with longer duration or more complex surgery.
      • If Post CSDH Burrhole just reopen and washout but if this is insufficient conversion to craniotomy is mandatory.
      • Usually inadequate if loculations are present
      • Repeat procedures may be needed, and up to 20% will later require a craniotomy

      Craniotomy

      • Indicated for
        • Thicked organized empyema (Munusamy and Dinesh, 2015)
      • Craniotomy to debride and, if possible, drain.
      • A wide craniotomy is often required because of septations.
      • The dura appears white because of pus underneath.
      • Open and wash out subdural space.
      • Do not try to remove material adherent to cortex (may cause infarction)

      Craniectomy

      • Indicated for
        • Thicked organized empyema with significant brain swelling
        • In postoperative setting if there is intraoperative suspicion of osteomyelitis of the bone flap which may act as a devascularized nidus of ongoing infection.

      Burrhole vs craniotomy vs craniectomy: which one is the best

      • Results of all three have been shown to be comparable as long as effective drainage of purulent material and relief of mass effect was achieved (Bok and Peter, 1993).
      • Early studies indicated a better outcome with craniotomy than with burr holes.
      • Recent studies show less difference
  • Treat primary source
    • Exploration and drainage of the primary source (Otologic or extracranial)
  • Anticonvulsants
    • Usually given prophylactically
    • Mandatory if seizures occur
  • Antibiotic
    • Initiation of empirical antibiotic therapy without delay is recommended if the patient is septic and clinically unwell from the subdural empyema.
    • Further antimicrobial therapy should be targeted against the causative microorganisms revealed by
      • Gram stain or special bacterial stains,
      • Positive bacterial culture result
      • Knowledge of the bacterial profile at the primary site of infection.
    • Duration: 4– 6 weeks
      • Depending on the clinical and radiological response (Leys et al., 1986).

Outcome

  • Outcome depends on factors such as age, comorbidities, primary organism, and prompt diagnosis and treatment.
  • Mortality rate of up to 20% and morbidity rate of 50% despite intervention (Le Beau et al., 1973; Nathoo et al., 1999)
    • Fatal cases may have associated venous infarction of the brain.
  • Neurologic deficits
    • Tend to improve following treatment,
    • But were present in 55% of patients at the time of discharge from the hospital.
  • Poor prognostic factors
    • Age≥ 60 years,
    • Obtundation or coma at presentation,
    • SDE related to surgery or trauma (rather than sinusitis)
    • Burr-hole drainage may be associated with a worse outcome than with craniotomy,
      • Might be confounded by the poorer condition of these patients.
  • Outcome with SDE
      • Outcome
      %
      Persistent seizures
      34
      Residual hemiparesis
      17
      Mortality
      10–20
  • Compares patient mortality with level of consciousness at presentation.
    • Those patients presenting awake and alert (grade I) have the greatest chance of survival and those presenting unresponsive to pain (grade IV) are least likely to survive.
    • Patients who are drowsy and disoriented (grade II) or responsive only to painful stimuli (grade III) have intermediate survival statistics.
    • Of the survivors, decreased level of consciousness at presentation correlates with more severe neurologic sequelae (4,7,8).
    • Association of level of consciousness with mortality in SDE
        • Reference
        Grade I (No., Deaths)
        Grade II (No., Deaths)
        Grade III (No., Deaths)
        Grade IV (No., Deaths)
        Bradley and Shaw (1)
        20, 0
        18, 9
        0, 0
        5, 5
        Mauser et al. (4)
        16, 1
        36, 5
        22, 6
        24, 10
        Hodges et al. (7)
        0, 0
        5, 0
        7, 0
        2, 2
        Khan and Griebel (8)
        2, 0
        8, 0
        4, 1
        1, 1
        Hockley and Williams (9)
        7, 1
        22, 1
        0, 0
        13, 5
        Bannister et al. (12)
        22, 2
        30, 10
        6, 1
        8, 6
        Dill et al. (18)
        13, 0
        12, 0
        5, 2
        2, 1
        Morgan and Williams (27)
        1, 1
        4, 1
        0, 0
        2, 2
        Total
        81, 5
        135, 26
        44, 10
        57, 32
        % Deaths
        6%
        19%
        23%
        56%
      • I = awake and alert; II = drowsy and disoriented; III = responsive to painful stimuli; IV = unresponsive to pain.