Brain Abscess: Etiology

00:01 In our continuing discussion of central nervous system infections, we turn now to brain abscess.

00:09 50% of cases are due to contiguous suppurative spread.

00:15 In other words, there's a focus of pus somewhere near the brain.

00:19 For example, from osteomyelitis of the frontal sinus or the sphenoid sinus.

00:27 Trauma accounts for about 10% of the cases, which allow organisms direct access via a skull fracture.

00:35 And I want to tell you about an interesting patient I saw that was involved on a baseball team and one of his jobs was helping to clean up the baseball diamond.

00:49 And he had a small electric cart that he was driving around that had some utensils like rakes on it to rake up the grass and rake up the dirt and he tried to drive that cart through a narrow gate.

01:06 And when he did that, it set the rake up into the air flipping end over end and the rake – the tines of the rake impaled him in the side of the head, penetrated his skull bone and gave him a brain abscess due to soil born organism.

01:26 I thought that was an extremely strange and interesting occurrence.

01:30 But trauma is responsible for about 10% of the cases.

01:34 25% of the cases are the result of organisms – microorganisms getting into the bloodstream from another focus.

01:43 Say, from infective endocarditis.

01:45 And by the way, if somebody has a brain abscess due to an organism that is a common cause of endocarditis, a careful evaluation for endocarditis should be done.

02:00 Lung abscess can also be responsible for bacteria getting into the bloodstream and alighting in the brain HIV and IV drug use.

02:13 15% of the cases, we’re not exactly sure how the organisms got to the brain.

02:20 Bacteria are by far the most common causes of brain abscess and frequently involve other streptococci which colonize mucosal surfaces.

02:34 And these are normal flora.

02:36 But because the mucosal surfaces also are teeming with other organisms, you would expect mixed infections in a lot of patients.

02:46 Staph aureus is responsible for about 10 to 20% of brain abscesses and these are usually not large brain abscesses.

02:57 Anaerobic organisms, I think I have mentioned in other presentations that life on human beings is predominantly anaerobic, especially on mucosal surfaces where anaerobes outnumber the aerobes from 10 to 1 to 1000 to 1.

03:14 And here's an example of Prevotella, which is an anaerobic organism, gram-negative rod that you find frequently in the oropharynx.

03:24 Nocardia is a soil-born organism, but you particularly can encounter this organism who don't handle it well in immunocompromised patients.

03:36 So, it may get into the lungs in immunocompromised patients and from there disseminate.

03:42 And what you're seeing in this particular slide is a very filamentous, elongate, beaded, acid fast rod of Nocardia.

03:56 Fungi can cause brain abscess and the ones that cause it most commonly are these, Candida.

04:05 And what you're seeing in this particular view is an elongate bud, which is called a pseudohypha with yeast budding from it.

04:17 Classic for Candida.

04:21 Aspergillus is a filamentous organism.

04:25 And what you should notice about this particular organism is that it tends to look like it's flowing in one direction and that's because the organisms as they divide, one trunk divides into two, so-called dichotomous branching, and that's why the organisms in a tissue section appear to be flowing.

04:50 And Aspergillus accounts for 10% to 20% of all cases of invasive brain abscesses.

05:02 Rhizopus, one of the bread molds, is also responsible for brain abscess and it’s usually in a person with ketoacidosis.

05:13 And the classic, of course, is a diabetic in ketoacidosis.

05:19 And there are other bread molds, but the spores from these bread molds are ubiquitous.

05:26 All of us inhale them daily, but we have a normal immune system and we do not have ketoacidosis.

05:34 If you provide an acidic environment, these organisms can invade blood vessels.

05:43 Scedosporium apiospermum is an organism that you frequently find in freshwater.

05:51 And that's why it has an association not only with neutropenia, but with near-drowning accidents.

06:01 I'm familiar with a patient I saw that was in a boat that apparently capsized and he was essentially submerged head first in mud at the bottom of a river.

06:19 And he developed a Scedosporium brain abscess.

06:24 This organism is also known as Pseudoallescheria boydii and we actually sent out some investigators from the University of Georgia to culture the silt at the bottom of this river.

06:41 And sure enough, we isolated this organism from the riverbed.

06:47 But the association of near-drowning is an important factor if somebody develops this kind of a brain abscess.

06:57 And then the classic endemic fungi, like histoplasmosis.

07:02 And what you're seeing in this particular picture is a macrophage that is stuffed full of these little tiny budding yeast.

07:14 I think you can see that they appear to have a capsule around them.

07:18 They don't really – that's an artifact of the staining, but that's where the name came from, Histoplasma capsulatum.

07:25 And the filamentous form of the organism is actually a mold that you find in the Ohio and Mississippi River valleys.

07:36 Coccidioides immitis is also a mold that you find in the desert Southwest, and so areas like the San Joaquin Valley in California.

07:49 The soil is actually teeming with some of these fungi.

07:55 And you inhale the tiny arthroconidia and when it gets into the lungs at 37°, it becomes this huge spherical structure called a spherule.

08:11 And this certainly can cause brain abscess in this endemic area, especially among immunocompromised individuals.

08:20 Not terribly common as a cause of brain abscess, but more of skin infections is Blastomyces dermatitidis.

08:29 And this is characterized by these very large budding yeast and with broad-based buds.

08:38 The way I remember it is B for blasto B for broad-based budding yeast, if you want to get alliterative about it.

08:47 And then parasites can cause brain abscess.

08:51 Among the most common would be protozoa, specifically Toxoplasma gondii and this is acquired by ingesting rare or raw meat.

09:06 And just as an aside, if you and I were to go out for a steak dinner, my steak would look like Joe DiMaggio's baseball glove from the 38 World Series.

09:21 It is dark and hard as about 25% of raw meat contains living protozoa of Toxoplasma gondii.

09:31 So, I'm not eating that stuff.

09:34 You may like it rare, but I choose not to eat rare meat.

09:39 And it’s particularly problem in patients with HIV infection with depressed immunity.

09:45 And when their CD4 count gets less than 100, they are very susceptible to Toxoplasma encephalitis and brain abscess.

09:54 And so are patients who have reticuloendothelial malignancies.

10:00 Trypanosoma cruzi, Chagas disease that you find in South America and Central America.

10:09 Entamoeba histolytica, also found in developing countries, normally causes gastroenteritis and maybe a liver abscess, but every once in a while a brain abscess.

10:23 And then, also associated with swimming in freshwater would be the free living amoeba that belong to the Naegleria and Acanthamoeba species.

10:38 So, swimming and diving, particularly diving, in freshwater rivers, ponds and lakes, free living amoeba.

10:47 And you can see these large organisms present in the brain parenchyma in this particular image.

10:56 Worms can also do it.

10:58 Helminths.

10:59 Among the most common would be the pork tapeworm Taenia solium.

11:05 Not the beef tapeworm so much.

11:08 The pork tapeworm seems to cause a disorder in humans called cysticercosis, whereas the beef tapeworm doesn't usually cause that disease in human beings.

11:22 And you get this cysticercosis by ingesting the egg from one of these worms, from contaminated food or water.

11:33 Schistosomiasis can certainly cause abscess anywhere and the worms can migrate anywhere via the bloodstream and every once in a while will be the cause of the brain abscess.

11:48 But, personally, I've never seen a patient with a Schistosoma brain abscess.

11:54 And this is also acquired by wading or swimming in freshwater in developing countries.

12:03 Also found in the Far East is Paragonimus, which is from the consumption of freshwater crustaceans, once again something you won't find me ingesting.