Intracranial infections – 4 – Immunocompromise

Immunocompromised patients have special considerations for infection of the brain, including HIV encephalopathy, toxoplasmosis, cryptococcus, and progressive multifocal leukoencephalopathy (PML).

This lecture is the fourth in a series of 5 about imaging intracranial infection and covers special considerations in immunocompromised patients. The series of videos will cover:
1) General considerations
2) Diffuse infections
3) Focal infection
4) Immunocompromised patients
5) Other considerations

HIV encephalopathy is a result of direct infection of the white matter in the brain by the HIV virus. It is bilateral, symmetric, and tends to progress over time. There is usually no enhancement.

Toxoplasmosis is the most common opportunistic infection of the brain in HIV patients. Common imaging findings include multifocal masses and enhancement, often involving the basal ganglia. The “target sign”, or bullseye like appearance of the enhancing lesions, is common. The imaging appearance of toxoplasmosis overlaps a great deal with lymphoma, which tends to be more solidly enhancing and involves the periventricular white matter more. Often a treatment trial for toxoplasmosis is begun with short term follow-up imaging to see if the patient improves.

Cryptococcus is also a common brain infection in immunocompromised patients. It’s most common manifestation is enlargement of the perivascular spaces of the basal ganglia, or gelatinous pseudocysts. This typically does not have much, if any, postcontrast enhancement.

Finally, progressive multifocal leukoencephalopathy (PML) is an infection caused by reactivation of a virus (JC virus) in the brain parenchyma in the setting of immune suppression, either because of HIV or immunosuppressive medications. It is manifested by bilateral, subcortical, asymmetric white matter abnormalities without enhancement. Treatment is restoration of the immune system, but outcomes are poor.

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.

Other videos on the intracranial infection playlist are found here.