Brain abscess (N)

Question 1

Define brain abscess.

Answer 1

A suppurative (pus-producing) collection of microbes (most often bacterial, fungal or parasitic) within a gliotic capsule occurring within the brain parenchyma

Question 2

What are the different ways a brain abscess is caused? (3)

Answer 2

• spread of an infection e.g. sinusitis, endocarditis, meningitis, otitis media
• trauma or surgery to scalp
• penetrating head injuries

Question 3

What are the most common pathogens causing brain abscess? (2)

Answer 3

• Viridians streptococci (secondary to sinusitis)
• S. aureus

Question 4

In which demographics is brain abscess most common? (2)

Answer 4

• adult men <30y
• children 4-7y

Question 5

Where does a brain abscess most often originate?

Answer 5

Ischaemic white matter adjacent to the cortex, where increased vascular density may facilitate collagen deposition and capsule formation

Question 6

What are the well-characterised stages of brain abscesses? (3)

Answer 6

• 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

Question 7

What do brain abscesses present similarly to?

Answer 7

CNS tumour

Question 8

What are the clinical features of a brain abscess? (6)

Answer 8

• 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)

Question 9

What would you see on examination of brain abscess? (3)

Answer 9

• positive Kernig or Brudzinski sign (meningitis)
• papilloedema (raised ICP)
• neurological deficit - sensory/motor/CN palsy

Question 10

What cranial nerve palsy is most likely in brain abscess (secondary to raised ICP)?

Answer 10

CN VI (abducens) most likely compressed due to raised ICP as it has the longest course

Question 11

What are the features of CN III, IV and VI palsies?

Answer 11

• III: eye down and out
• IV: eye up and out
• VI: eye in

Question 12

What are the features of raised ICP? (4)

Answer 12

• nausea
• vomiting
• seizures
• papilloedema

Question 13

What are the general risk factors for brain abscess? (5)

Answer 13

• 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

Question 14

What are the first-line investigations for brain abscess? (5)

Answer 14

• MRI with contrast
• FBC - elevated WBC
• ESR - elevated
• CRP - elevated
• PT/APTT - for surgical Rx, should be normal

Question 15

What is the best first-line initial test for brain abscess?

Answer 15

MRI with contrast - can see one or more ring-enhanced lesions

Question 16

What investigation confirms a brain abscess?

Answer 16

Biopsy

Question 17

What other scan can we do (in addition to MRI contrast) in brain abscess?

Answer 17

CT head +/- contrast (also see ring-enhanced lesions)

Question 18

What are some differential diagnoses for brain abscess? (6)

Answer 18

• 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

Question 19

What is the first-line general treatment for brain abscess?

Answer 19

Antimicrobials +/- surgery (craniotomy performed and abscess cavity debrided) if severe e.g. bacterial brain abscess >2.5cm

Question 20

How do we manage bacterial (or unconfirmed) brain abscess? (4)

Answer 20

• IV Abx - 3rd generation cephalosporin (ceftriaxone) + metronidazole
• anticonvulsant (phenytoin)
• dexamethasone (raised ICP)
• urgent surgical decompression (risk of ventriculitis)

Question 21

How do we manage parasitic brain abscess? (3)

Answer 21

• toxoplasma: pyrimethamine and sulfadiazine, highly active antiretroviral therapy (HAART) if HIV
• taenia: praziquantel
• naegleria: amphotericin B liposomal

Question 22

How do we manage fungal brain abscess? (1+3)

Answer 22

Antifungal Rx, surgical evacuation, phenytoin:

• candida: amphotericin B liposomal / fluconazole / caspofungin
• cryptococcus: amphotericin B liposomal + fluconazole or flucytosine
• aspergillus or mucormycosis: amphotericin B liposomal

Question 23

How do we manage raised ICP in brain abscess?

Answer 23

Dexamethasone

Question 24

What do we give for seizure prophylaxis in brain abscess?

Answer 24

Anticonvulsants e.g. phenytoin

Question 25

What are some complications of brain abscess? (6)

Answer 25

• 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

Question 26

Describe the prognosis of brain abscess.

Answer 26

Overall mortality <13%; major prognostic factor is patient’s neurological status upon presentation