Brain Abscess

Question 1

Give two sites of primary infection that can sometimes give rise to a brain abscess (2)

Answer 1

Otitis media, sinusitis, lung abscess (maybe secondary to an infected traumatic compound fracture of the skull)

Question 2

Name two organisms that are commonly associated with this type of infection and give the gram stain appearance for each organism (4)

Answer 2

• Streptococci (viridans, beta-haemolytic, S milleri etc) - gram-pos cocci in chains
• Anaerobes (Bacteroides - gram-neg bacilli
  Peptostreptococci - gram-pos cocci)
• Enterobacteria (Proteus, Klebsiellas, E.coli etc) - gram-neg bacilli
• Staphylococci - gram-pos cocci in clusters

Question 3

A three-year-old girl, Mary Smith presents to the emergency department with a 4-day history of headache, vomiting and fever. She was seen by her General Practitioner two days ago who diagnosed otitis media and prescribed an antibiotic. She is conscious, alert and complains of pain over the neck area. On examination she cries in pain when her neck is flexed. A lumbar puncture (LP) was performed. A gram stain is negative for bacteria. Culture growth showed a scanty growth of S. pneumoniae. Her headache improved and she appears less ill following the LP.

If Mary had a CT scan and a brain abscess was diagnosed, briefly outline the most likely pathogenesis of this condition in Mary’s case (1)

Answer 3

Mary has otitis media that was untreated and spread locally to brain tissue.

Question 4

The CSF in this case did not grow any bacterial organisms. This is often the case with brain abscesses. Name another reason why there could be no bacterial growth on a cellular CSF (1)

Answer 4

Viral infection or prior antibiotics

Question 5

Name the empiric antibiotics (use generic names) that are used to treat brain abscesses. Assume skull trauma has NOT occurred in this case (2)

Answer 5

Ceftriaxone and metronidazole

Question 6

State the route by which infection is likely to have spread from the decayed tooth to the brain (½)

Answer 6

Haematogenous

Question 7

Give two (2) other common sites from which infection can spread to the brain in a similar way (1)

Answer 7

Lung/ sinuses/ middle ear

Question 8

Give one other route/mechanism by which a brain abscess can develop (1)

Answer 8

Direct implantation related to trauma/contiguous spread

Question 9

Give three (3) types or groups of organisms that can cause brain abscesses and state which antibiotic is usually recommended in South Africa for empiric treatment of that organism (3)

Answer 9

• (viridans) streptococci: ceftriaxone
• Anaerobes: metronidazole
• Enterobacteriacaeae: ceftriaxone
• S. aureus: ceftriaxone/cloxacillin

Question 10

Explain why, in this case, it was preferable to perform a brain scan rather than a lumbar puncture (2)

Answer 10

The history suggests the possibility of a brain abscess which is a space occupying mass and therefore would increase the risk of coning if a lumbar puncture was performed.

Furthermore, unless the abscess had ruptured into a ventricle or into the subarachnoid space the CSF findings would likely be non-diagnostic

Question 11

Name three organism groups that are most often involved in this type of abscess (2)

Answer 11

Streptococci (½) or viridans streptococci (1), gram negative bacilli or enterobacteria (½) and anaerobes (½).