Toxoplasmosis vs lymphoma

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.

Radiographic features

Distribution

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.

Enhancement

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

Haemorrhage does not happen typically in PCNSL before treatment, but may be seen occasionally in toxoplasmosis.

MR spectroscopy
  • 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.

MRI perfusion

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.

SPECT

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.

Practical points

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
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Article information

rID: 8616
Section: Gamuts
Synonyms or Alternate Spellings:
  • Cerebral toxoplasmosis vs primary CNS lymphoma
  • Cerebral toxoplasmosis vs HIV lymphoma
  • Primary CNS lymphoma vs cerebral toxoplasmosis
  • HIV lymphoma vs cerebral toxoplasmosis
  • Lymphoma vs toxoplasmosis

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Cases and figures

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    Case 1: primary CNS lymphoma
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    Case 2: cerebral toxoplasmosis
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    Periventricular l...
    Case 3: CNS lymphoma - periventricular lesion
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    MR Spectroscopy -...
    Case 3: MRS - primary CNS lymphoma
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    Case 4: MRS - toxoplasmosis
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    Case 5: MRS - PCNSL
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