Toxoplasmosis vs lymphoma
It is a relatively common occurrence for radiologists to be asked to distinguish between cerebral toxoplasmosis and primary CNS lymphoma patients with HIV / AIDS. Treatment is clearly different and thus accurate interpretation of CT and MRI is essential.
In many instances appearances are classic and pose little problem, however in 50 - 80% of cases the appearances can be very similar requiring careful interpretation 1.
Below are helpful distinguishing features.
Primary CNS lymphoma typically demonstrates sub-ependymal spread, whereas toxoplasmosis tends to be scattered thought the basal ganglia and at the corticomedullary junction 1.
HIV lymphoma also is far more frequently a solitary lesion, whereas toxoplasmosis is usually multifocal (86%) 2-3.
Following administration of contrast, on both CT and MRI, both entities enhance, however typically lymphoma is solid whereas toxoplasmosis demonstrates ring or nodular enhancement 1-2. It should be noted however that it is in patients with HIV / AIDS that primary CNS lymphoma may demonstrate ring enhancement also.
Thallium 201 Chloride SPECT demonstrates increased uptake in lymphoma whereas it is decreased in toxoplasmosis 2.
Although both entities have increased lactate and lipids, this tends to be less marked in lymphoma. Lymphoma typically demonstrates marked increase in Cho, whereas it is reduced in toxoplasmosis1-2. Both demonstrate decreased Cr and NAA. However, this pattern is variable.
MRS should be performed with both long and short TE sequences 1.
A decrease in cerebral blood volume (rCBV) centrally within lesions suggests toxoplasmosis, whereas it is increased in lymphoma 1. Unfortunately it is reduced in the perilesional edema of both lesions.
Features that favor primary CNS lymphoma include:
- single lesion
- subependymal spread
- solid enhancement
- Thallium SPECT positive
- MRS : increased choline (Cho)
- MR perfusion : increased rCBV
Features that favor cerebral toxoplasmosis include:
- multiple lesions
- scattered though basal ganglia an corticomedullary junction
- ring or nodular enhancement
- Thallium SPECT negative
- MRS : decreased choline (Cho)
- MR perfusion : decreased rCBV