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.