Preliminary Diagnosis: Central Nervous System Toxoplasmosis

I. What imaging technique is first-line for this diagnosis?

  • MRI of the brain with IV contrast

II. Describe the advantages and disadvantages of this technique for diagnosis of CNS toxoplasmosis.

  • Very suggestive of the diagnosis given the appropriate clinical scenario

  • Able to localize the anatomic area of abnormality and the extent of edema, thus predicting any specific neurological compromise

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  • Able to evaluate for secondary complications such as cerebral mass effect, midline shift, or hemorrhage

  • Does not use any ionizing radiation

  • Expensive

  • Time-consuming imaging modality

  • Requires significant patient cooperation to minimize motion artifact

  • MRI with IV contrast requires that the patient has good renal function (i.e., GFR >30).

III. What are the contraindications for the first-line imaging technique?

  • MRI is contraindicated in patients with non-MR-compatible metallic hardware or foreign bodies.

  • Decreased renal function (GFR <30); caution in patients with GFR between 30 and 60.

IV. What alternative imaging techniques are available?

  • CT with and without intravenous contrast

  • Thallium-201 SPECT nuclear medicine imaging

V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of CNS toxoplasmosis.

CT with and without intravenous contrast
  • May be performed more quickly than MRI, requires less patient cooperation, and is less susceptible to motion artifact than MRI

  • More specific than MRI with respect to diagnosis of lymphoma, a common mimicker of CNS toxoplasmosis

  • CT exposes the patient to nonionizing radiation.

  • CT has less anatomic detail and contrast resolution than MRI.

Thallium-201 SPECT Imaging
  • Useful tool in differentiating CNS toxoplasmosis from lymphoma due to high specificity in detecting lymphoma

  • Can be used in patients with contraindications to MRI

  • Available only in specialized centers

  • Provides limited anatomic detail

  • Primarily used as a supplement to CT/MRI when distinction is uncertain

VI. What are the contraindications for the alternative imaging techniques?

CT with and without contrast

CT is contraindicated in a pregnant patient, especially during the first two trimesters.

Thallium-201 SPECT

None known