It is common for radiologists to be asked to distinguish between cerebral toxoplasmosis and primary CNS lymphoma (PCNSL) in patients with HIV/AIDS. Treatment is clearly different and thus accurate interpretation of CT and MRI is essential.
In many instances, the imaging appearance is classic and differentiation is not problematic; however, in 50-80% of cases the appearances can be very similar 1. Below are helpful distinguishing features.
Primary CNS lymphoma typically demonstrates subependymal spread, whereas toxoplasmosis tends to be scattered through 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.
On CT and MRI, both entities enhance following administration of contrast. Lymphoma may solidly enhance, whereas toxoplasmosis usually demonstrates ring or nodular enhancement 1,2.
However, in the setting of HIV/AIDS, primary CNS lymphoma may also demonstrate ring enhancement. Thus, the pattern of enhancement may not be helpful.
Haemorrhage does not happen typically in PCNSL before treatment, but may be seen occasionally in toxoplasmosis.
- both entities demonstrate increased lactate and lipids, although this tends to be less marked in lymphoma
- lymphoma typically demonstrates marked increase in Cho, whereas it is reduced in toxoplasmosis 1,2
- both lesions demonstrate decreased Cr and NAA; however, this finding 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. However, rCBV is reduced in the perilesional oedema of both lesions.
Thallium 201 Chloride SPECT demonstrates increased uptake in lymphoma, because thallium serves as a potassium analogue and is avidly taken up by hypermetabolic tumor cells 6. By contrast, thallium activity is decreased in toxoplasmosis because there is no cellular correlate 2.
Features that favour primary CNS lymphoma include:
- single lesion
- subependymal spread
- solid enhancement
- no haemorrhage before treatment
- Thallium SPECT positive
- MRS: increased choline (Cho)
- MR perfusion: increased rCBV
Features that favour cerebral toxoplasmosis include:
- multiple lesions
- scattered though basal ganglia and corticomedullary junction
- ring or nodular enhancement
- haemorrhage occasionally occurs mostly in periphery of lesion
- Thallium SPECT negative
- MRS: decreased choline (Cho)
- MR perfusion: decreased rCBV
- 1. Gupta RK, Lufkin RB. MR Imaging and Spectroscopy of Central Nervous System Infection. Springer Verlag. (2001) ISBN:0306465515. Read it at Google Books - Find it at Amazon
- 2. Chang L, Cornford ME, Chiang FL et-al. Radiologic-pathologic correlation. Cerebral toxoplasmosis and lymphoma in AIDS. AJNR Am J Neuroradiol. 1996;16 (8): 1653-63. Pubmed citation
- 3. Kornienko VN, Pronin I. Diagnostic Neuroradiology. Springer. (2009) ISBN:3540756523. Read it at Google Books - Find it at Amazon
- 4. Ernst TM, Chang L, Witt MD et-al. Cerebral toxoplasmosis and lymphoma in AIDS: perfusion MR imaging experience in 13 patients. Radiology. 1998;208 (3): 663-9. doi:10.1148/radiology.208.3.9722843 - Pubmed citation
- 5. Trenkwalder P, Trenkwalder C, Feiden W et-al. Toxoplasmosis with early intracerebral hemorrhage in a patient with the acquired immunodeficiency syndrome. Neurology. 1992;42 (2): 436-8. Pubmed citation
- 6. Kessler LS, Ruiz A, Donovan Post MJ, Ganz WI, Brandon AH, Foss JN. Thallium-201 brain SPECT of lymphoma in AIDS patients: pitfalls and technique optimization. (1998) AJNR. American journal of neuroradiology. 19 (6): 1105-9. Pubmed
- manifestations of HIV/AIDS
- CNS manifestations
- pulmonary manifestations
- cardiovascular manifestations
- gastrointestinal manifestations
- hepatobiliary manifestations
- genitourinary manifestations
- musculoskeletal manifestations
- AIDS defining illnesses
- HIV associated neoplasms
- immune reconstitution inflammatory syndrome (IRIS)
- AIDS embryopathy