Brain abscess (N) Flashcards
Define brain abscess.
A suppurative (pus-producing) collection of microbes (most often bacterial, fungal or parasitic) within a gliotic capsule occurring within the brain parenchyma
What are the different ways a brain abscess is caused? (3)
- spread of an infection e.g. sinusitis, endocarditis, meningitis, otitis media
- trauma or surgery to scalp
- penetrating head injuries
What are the most common pathogens causing brain abscess? (2)
- Viridians streptococci (secondary to sinusitis)
- S. aureus
In which demographics is brain abscess most common? (2)
- adult men <30y
- children 4-7y
Where does a brain abscess most often originate?
Ischaemic white matter adjacent to the cortex, where increased vascular density may facilitate collagen deposition and capsule formation
What are the well-characterised stages of brain abscesses? (3)
- early cerebritis - lasts approx 3 days: local inflammation, tissue necrosis, neutrophilic infiltrate, activation of microglia and astrocytes
- late cerebritis - occurs on days 4-9: increased organisation where lymphocytic and microglial infiltration is seen
- frank abscess formation - after day 10: encapsulation and suppurative collection
What do brain abscesses present similarly to?
CNS tumour
What are the clinical features of a brain abscess? (6)
- meningismus (on rupture)
- dull persistent headache (sudden worsening on rupture)
- CN palsy - 3 or 6 (more common) secondary to raised ICP
- fever
- infarcts - increased head circumference (infants), bulging fontanelles
- features of raised ICP (nausea, vomiting, seizures, papilloedema)
What would you see on examination of brain abscess? (3)
- positive Kernig or Brudzinski sign (meningitis)
- papilloedema (raised ICP)
- neurological deficit - sensory/motor/CN palsy
What cranial nerve palsy is most likely in brain abscess (secondary to raised ICP)?
CN VI (abducens) most likely compressed due to raised ICP as it has the longest course
What are the features of CN III, IV and VI palsies?
- III: eye down and out
- IV: eye up and out
- VI: eye in
What are the features of raised ICP? (4)
- nausea
- vomiting
- seizures
- papilloedema
What are the general risk factors for brain abscess? (5)
- ENT infections e.g. otitis media, sinusitis
- other infections e.g. meningitis, endocarditis
- anything predisposing to infections e.g. dental procedures, recent surgery, congenital heart disease, HHT, DM, HIV, IVDU, chronic granulomatous disease, haemodialysis, birth prematurity
- male sex
- age <30y
What are the first-line investigations for brain abscess? (5)
- MRI with contrast
- FBC - elevated WBC
- ESR - elevated
- CRP - elevated
- PT/APTT - for surgical Rx, should be normal
What is the best first-line initial test for brain abscess?
MRI with contrast - can see one or more ring-enhanced lesions
What investigation confirms a brain abscess?
Biopsy
What other scan can we do (in addition to MRI contrast) in brain abscess?
CT head +/- contrast (also see ring-enhanced lesions)
What are some differential diagnoses for brain abscess? (6)
- primary CNS neoplasm (chronic presentation, no infection)
- metastatic lesion
- recurrent tumour/radiation necrosis in post-surgical patient
- MS (chronic, Lhermitte’s sign = transient electric-like shocks down spine, Uhthoff’s sign = episodic transient obscuration of vision)
- acute disseminated encephalomyelitis
- ischaemic stroke
What is the first-line general treatment for brain abscess?
Antimicrobials +/- surgery (craniotomy performed and abscess cavity debrided) if severe e.g. bacterial brain abscess >2.5cm
How do we manage bacterial (or unconfirmed) brain abscess? (4)
- IV Abx - 3rd generation cephalosporin (ceftriaxone) + metronidazole
- anticonvulsant (phenytoin)
- dexamethasone (raised ICP)
- urgent surgical decompression (risk of ventriculitis)
How do we manage parasitic brain abscess? (3)
- toxoplasma: pyrimethamine and sulfadiazine, highly active antiretroviral therapy (HAART) if HIV
- taenia: praziquantel
- naegleria: amphotericin B liposomal
How do we manage fungal brain abscess? (1+3)
Antifungal Rx, surgical evacuation, phenytoin:
- candida: amphotericin B liposomal / fluconazole / caspofungin
- cryptococcus: amphotericin B liposomal + fluconazole or flucytosine
- aspergillus or mucormycosis: amphotericin B liposomal
How do we manage raised ICP in brain abscess?
Dexamethasone
What do we give for seizure prophylaxis in brain abscess?
Anticonvulsants e.g. phenytoin
What are some complications of brain abscess? (6)
- seizures (give phenytoin/carbamazepine/valproate)
- hydrocephalus (CSF diversion, external ventricular drain)
- hyponatraemia (cerebral salt wasting/SIADH)
- ventriculitis (rupture into ventricular system, give intrathecal Abx)
- cognitive dysfunction
- death
Describe the prognosis of brain abscess.
Overall mortality <13%; major prognostic factor is patient’s neurological status upon presentation
