CNS Toxoplasmosis

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.

Advantages

• 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

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

• Does not use any ionizing radiation

Disadvantages

• 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

Advantages

• 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

Disadvantages

• CT exposes the patient to nonionizing radiation.

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

Thallium-201 SPECT Imaging

Advantages

• Useful tool in differentiating CNS toxoplasmosis from lymphoma due to high specificity in detecting lymphoma

• Can be used in patients with contraindications to MRI

Disadvantages

• 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