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Abscess

Definition

Suppurative infections involving CNS and its coverings, most commonly caused by bacteria.

Pathogenesis

Spread From Contiguous Meningeal Or Parameningeal Site

Most Frequently Implicated Sites
  • Paranasal sinuses
  • Middle ear cavities
  • Mastoids2
  • Pathogenesis imprecisely defined:
    • commonly held to be retrograde thrombophlebitic carriage of organisms into cranial cavity via emissary veins
  • Organisms most often isolated:
    • aerobic or microaerophilic streptococci:
      • especially Streptococcus intermedius ‘milleri’ group
    • aerobic Gram-negative bacilli:
      • Proteus
      • Escherichia coli
      • Klebsiella–Enterobacter
      • Haemophilus spp.
      • Bacteroides spp.
    • commonly mixed infection
Other Local Suppurative Processes
  • Dental sepsis
  • Pyogenic infections of face and scalp:
    • usually:
      • Staphylococcus aureus
      • cavernous sinus thrombosis
  • ‘Odontogenic’ abscesses:
    • typically follow:
      • tooth extraction
      • other dental manipulation
    • mixed aerobic and anaerobic populations dominated by:
      • Fusobacterium spp.
      • Bacteroides spp.
      • Streptococcus spp.
  • Mandibulofacial actinomycosis4
  • Intramedullary abscesses:
    • predisposing factors:
      • spinal anomalies
      • tumors of spinal neuraxis5

Hematogenous Seeding From Distant Foci Of Infection

Sources
  • Commonly chronic suppurating pulmonary disorders, e.g.:
    • lung abscess
    • bronchiectasis2
  • Less commonly:
    • bacterial endocarditis:
      • characteristically acute
    • empyema
    • osteomyelitis
    • infections of deep pelvic organs or abdominal viscera
Additional Risk Factors
  • Impaired filtering function of lung's capillary bed e.g.:
    • pulmonary arteriovenous fistula
    • cyanotic congenital heart disease complicated by right-to-left shunt:
      • tetralogy of Fallot
      • patent foramen ovale
      • ventricular septal defect
      • transposition of great vessels
  • Secondary polycythemia:
    • may promote development from infective emboli by causing microcirculatory sludging and regional brain hypoxia
  • Similar mechanisms may account for significant risk of cerebral abscess in hereditary hemorrhagic telangiectasia6
Iatrogenic Causes
  • Instrumentation of esophagus:
    • to relieve caustic strictures
    • to treat varices by endoscopic injection of sclerosing agents7
  • Microbiology complex:
    • Fusobacterium, Bacteroides, and streptococci:
      • most commonly recovered from brain abscesses associated with:
        • pulmonary sepsis
        • actinomycosis4
        • nocardial8 lesions:
          • often in debilitated and immunosuppressed
  • streptococci and Haemophilus spp.:
    • typical offenders in cases related to congenital heart disease
  • S. aureus:
    • dominates isolates from examples complicating acute bacterial endocarditis
Direct Inoculation By Penetrating Cranial Trauma Or Neurosurgery2

Gross Pathology

Spread From Contiguous Meningeal Or Parameningeal Site
  • Typically solitary
  • Stereotyped topographic presentations:
    • frontoethmoid sinusitis:
    • anterobasal frontal lobes
    • ‘otitic’ examples (including those associated with chronic mastoiditis):
    • usually temporal lobes or cerebellar hemispheres
    • sphenoid sinusitis:
    • frontal and temporal regions
    • ‘odontogenic’:
    • usually frontal
Hematogenous Seeding From Distant Foci Of Infection
  • Usually:
    • multiple
    • within territories subtended by middle cerebral arteries
    • germinate at junction of cortical mantle and underlying white matter
    • may also involve:
    • cerebellum
    • basal ganglia
    • thalami
    • brainstem

Histopathology

  • Begin as ill-defined zone:
    • most commonly in white matter immediately subjacent to cortical ribbon or at gray–white junction2 of:
      • bacterial multiplication
      • polymorphonuclear leukocytic infiltration (cerebritis)
  • With time, proliferating fibroblasts:
    • surround central mass of fibrinopurulent debris
    • fashion collagenous capsule (Fig. 1
      Cerebral abscess. The lesion's purulent contents are separated from neighboring white matter by a granulation tissue-like zone of angioblastic and fibroblastic activity.

      Fig. 1: Cerebral abscess. The lesion's purulent contents are separated from neighboring white matter by a granulation tissue-like zone of angioblastic and fibroblastic activity.

      ):
      • bordered by edematous, chronically inflamed, and gliotic brain tissue:
        • may be foci of acute cerebritis
      • rate of encapsulation and completeness vary:
        • usually less developed if due to hematogenous bacterial seeding from distant sites
        • nocardial lesions are known for poor encapsulation
        • capsular organization typically most advanced along superficial, juxtacortical perimeter:
          • reflected in tendency of ‘daughter’ lesions to:
            • bud from deep aspects
            • rupture into ventricular system rather than subarachnoid space:
              • often fatal

Other investigations

CT or MRI
  • Characteristic appearance:
    • may be shared by malignant neoplasms and occasionally demyelinating disease:
    • central hypodensity
    • ‘ring’ enhancement
    • surrounding edema (Fig. 2
      Cerebral abscess. Ring enhancement of developing pseudocapsules, budding of ‘daughter’ lesions, and marked hypodensity of adjacent white matter reflecting severe edema are all characteristic of cerebral abscesses on CT or MR study. This example complicated mandibulofacial actinomycosis.

      Fig. 2: Cerebral abscess. Ring enhancement of developing pseudocapsules, budding of ‘daughter’ lesions, and marked hypodensity of adjacent white matter reflecting severe edema are all characteristic of cerebral abscesses on CT or MR study. This example complicated mandibulofacial actinomycosis.

      )

Diagnosis

  • A diagnostic challenge due to nonspecific presentation and neuroradiology

Differential Diagnosis

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References

1 Chun CH, Johnson JD, Hofstetter M, Raff MJ. Brain abscess. A study of 45 consecutive cases. Medicine (Baltimore). 1986;65:415–431.

2 Wispelwey B, Dacey RG, Scheld WM. Brain abscess.  Scheld WM,  Whitley RJ,  Durack DT editor. Infections of the central nervous system. ed. 2. Philadelphia: Lippincott-Raven; 1997.

3 Renier D, Flandin C, Hirsch E, Hirsch JF. Brain abscesses in neonates. A study of 30 cases. J Neurosurg. 1988;69:877–882.

4 Smego RA. Actinomycosis of the central nervous system. Rev Infect Dis. 1987;9:855–865.

5 Thomé C, Krauss JK, Zevgaridis D, Schmiedek P. Pyogenic abscess of the filum terminale. Case report. J Neurosurg. 2001;95:100–104.

6 Hall WA. Hereditary hemorrhagic telangiectasia (Rendu-Osler-Weber disease) presenting with polymicrobial brain abscess. Case report. J Neurosurg. 1994;81:294–296.

7 Schlitt M, Mitchem L, Zorn G, Dismukes W, Morawetz RB. Brain abscess after esophageal dilation for caustic stricture. Report of three cases. Neurosurgery. 1985;17:947–951.

8 Mamelak AN, Obana WG, Flaherty JF, Rosenblum ML. Nocardial brain abscess. Treatment strategies and factors influencing outcome. Neurosurgery. 1994;35:621–631.

9 Berenson CS, Bia FJ. Propionibacterium acnes causes postoperative brain abscesses unassociated with foreign bodies: case reports. Neurosurgery. 1989;25:130–134.

10 Ekseth K, Boström S. Late complications of Silastic duraplasty. Low-virulence infections. Case report. J Neurosurg. 1999;90:559–562.

Last updated: 30 Dec 2006

Abscess

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