So, how do the organisms reach the brain?
Well, they reach the brain
in a variety of ways as a result of
a contiguous focus of infection.
For example, otitis media or mastoiditis.
And you would expect the abscess to be nearby
in the temporal lobe or the cerebellum.
Sinusitis can be a cause of a brain abscess,
either frontal or sphenoid sinus,
and you would expect the frontal
lobe to be most likely involved.
And we already talked about penetrating trauma
anywhere in the brain.
Now, after neurosurgery,
brain abscess does occasionally occur.
But more commonly,
it would be the result of hematogenous dissemination
from a lung abscess
and empyema or bronchiectasis.
There is an association
with those pus-containing lung cavities.
We've already mentioned infective endocarditis.
patients who have very low levels of white blood cells
are particularly prone to bloodstream infections.
And abscess in the brain is not that common
and the reason they don't get abscess is because
they don't have much in the way of white cells
to make an abscess.
So, more often in a neutropenic
patient, it would be cerebritis.
Cyanotic congenital heart disease,
these patients can certainly get
more commonly than normal folks do.
And the same thing goes for
hereditary hemorrhagic telangiectasia.
Protozoa, free-living amoeba,
we’ve talked about in helminths.
So, what are then the stages
of brain abscess evolution
if we turn to the pathogenesis.
Well, first of all, in the first three days,
you're going to have simply cerebritis.
You're not going to have a well-formed abscess.
Later on, you have the beginnings of an abscess,
but it takes 10 to 13 days to develop
a reasonable capsule around it
and 14 or more days to get a thickened capsule.
And in terms of where a
neurosurgeon would try to drain it,
they would normally wait until there's a
well-formed capsule after a couple of weeks.
So, you wouldn't want to go in
to the stage of early cerebritis
if you were a neurosurgeon
because it would be hard to define
where the infection actually was.