Intracranial infections - 2 - Diffuse Infections

Diffuse infections are those infections of the brain which affect large regions of the brain or affect the brain diffusely. This includes meningitis, encephalitis, and ventriculitis.
This lecture is the second in a series of 5 about imaging intracranial infection and covers diffuse brain infections. The series of videos will cover:
1) General considerations
2) Diffuse infections
3) Focal infection
4) Immunocompromised patients
5) Other considerations
Meningitis is infection centered in the surfaces of the brain, particularly the pia and subarachnoid space. This can be caused by bacteria, viruses, or other unusual pathogens like tuberculosis or fungi. Imaging findings include incomplete FLAIR suppression and leptomeningeal enhancement. Basilar meningitis is a special subset of meningitis affecting the spaces around the brainstem and skull base. It is special because it is more likely to be an unusual pathogen. Sarcoidosis and leptomeningeal metastases can also mimic an infectious meningitis.
Encephalitis is similar to meningitis, although it is centered in the brain parenchyma. There is a great deal of overlap between these conditions and they can often be seen together (meningoencephalitis). Compared to meningitis, encephalitis is even more likely to be viral. The medial temporal lobes are commonly involved, and when they are a diagnosis of herpes encephalitis should be considered. This encephalitis caused by HSV can be rapidly debilitating or fatal. Encephalitis can also be autoimmune or inflammatory, mimicking infection.
Finally, ventriculitis is infection within the CSF of the ventricles themselves. This is often seen by abnormal FLAIR or diffusion in the ventricles, sometimes with periventricular enhancement. This can be from a primary pathogen with sparing of the parenchyma or as a complication of meningitis or abscess. Ventriculitis also has somewhat poor prognosis.
The level of this lecture is appropriate for radiology residents, radiology fellows, and trainees in other specialties who have an interest in neuroradiology or may see patients with CNS infections.
Check out this video and additional content on www.learnneuror...

[@caiyu538]

Excellent tutorials and keep on learning.

[@LearnNeuroradiology]

More to come!

[@doctorzhan]

Good job! Interesting lecture.

[@LearnNeuroradiology]

Thanks! There are a couple more pieces of the lecture I'll try to get posted soon so stay tuned.

[@drEAmzZzza]

so much knowledge.. i want to ask, what happens when bacteria enter the brain parenchyma, is it cerebritis? and does cerebritis always lead to an abscess? or can it spread through the entire brain like encephalitis? thanks doc

[@LearnNeuroradiology]

That's an interesting question. Most bacterial infections of the brain are either meningitis (infection of the subarachnoid space) or hematogenously spread into the parenchyma. Meningitis can spread to the parenchyma and cause a cerebritis without forming an abscess, which is well-formed and walled off, but probably some bacteria are there. Similarly, hematogenously spread infection can probably irritate the brain and cause a cerebritis without forming abscess, although this may often be the long term consequence if untreated.

[@drEAmzZzza]

@@LearnNeuroradiology thanks alot for the reply, i believe this is what happened to me (from an infected tooth with a huge abscess in my jaw that disapeared and went somewhere..) as over the course of 3 months i lost 90% of my memories, intellect/knowledge, cognition, balance, vision and alot more.. but the bacteria wouldnt of died on its own so i have no idea anymore what happened (ive seen 4 neurologist and no one knows) would this be possible from oral infection? im literally bedbound and disabled 2 years. it would mean the world to me if you had an answer. thanks so much

[@caiyu538]

At 2:30, Is there any image sign that indicate stroke is caused by meningitis if there is any ( update. I saw at beginning, you mentioned most of them, imaging finding in meningitis will be normal , good to know that).

[@LearnNeuroradiology]

Mostly it's related to the clinical picture. If you see someone who has multifocal infarcts or unexplained infarcts who has clinical signs of meningitis (fever, neck stiffness, leukocytosis), then you really should be thinking of either septic emboli or meningitis. Sometimes you'll have imaging findings, like leptomeningeal enhancement, FLAIR non-suppression, or reduced diffusion material in the CSF, but that's less common.

[@Gragon]

Sorry for the silly question but the main differential point when ddx ischemia from encephalitis is contrast enhancement? Because otherwise both are bright on T2 and both are restrictive on DWI?

[@LearnNeuroradiology]

Depending on the stage, it can sometimes be hard to differentiate infarction from encephalitis. The best clue is that infarction corresponds to a vascular territory and the patient has vascular risk factors. The degree of diffusion reduction tends to be greater with infarction as well. It tends to be very bright on DWI whereas encephalitis is usually mild to moderate. Finally, the timing and pattern of enhancement. Usually infarcts enhance only days to weeks after onset and it usually has a pretty distinct gyriform pattern. These are some clues you can use.

[@Gragon]

@@LearnNeuroradiology thank you. Ive been watching all your videos, youre doing great work, please continue

[@RockerzzzXRave]

distracting vocal fry, but a good lecture nonetheless

[@LearnNeuroradiology]

Glad you enjoyed the video regardless of any audio shortcomings!