Imaging

Brain metastases

Preliminary Diagnosis: Brain Metastases

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

  • MRI imaging of the brain with intravenous contrast

II. Describe the advantages and disadvantages of this technique for diagnosis of brain metastases.

Advantages

  • Highly suggestive of etiology in appropriate clinical situation

  • Able to localize exact anatomic area of disease and as a result predict any current or potential neurologic compromise

  • Can assess for secondary complications such as mass effect, midline shift, hemorrhage, etc

  • Does not utilize ionizing radiation

Disadvantages

  • Expensive

  • Time consuming and requires significant patient cooperation

  • Very susceptible to motion artifact

  • MRI with IV contrast requires a renal function of at least 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 body.

IV. What alternative imaging techniques are available?

  • Enhanced and nonenhanced CT

  • PET/CT

V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of brain abscesses.

Enhanced (intravenous contrast) and nonenhanced CT

Advantages

  • May be performed much quicker than MRI

  • Can be performed on unstable patients

  • Associated with less motion artifact

Disadvantages

  • Often misses lesions unless hemorrhagic, calcified, or associated with significant vasogenic edema

  • Demonstrates less anatomic detail and contrast resolution compared with MRI

  • Exposes the patient to ionizing radiation

PET/CT

Advantages

  • High sensitivity and specificity for detecting tumors

  • Often used to distinguish between neoplasm and radiation necorsis, a common mimicker

  • Can often differentiate benign versus malignant lesions based on hypermetabolism

  • Ability to detect distant disease affecting staging and therapy

Disadvantages

  • High degree of radiation exposure to patient

  • Cannot detect small lesions (i.e. less than 1.5 cm)

  • Limited anatomic detail

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

Enhanced and nonenhanced CT imaging

  • Contraindicated in pregnant patients. especially within the first two trimesters

  • IV contrast is relatively contraindicated in patients with contrast or iodine allergy. If IV contrast is necessary, the patient must be prepped with antihistamines and corticosteroids.

  • Relative contraindication in patients with renal dysfunction

PET/CT

  • Contraindicated in pregnant patients especially within the first two trimesters

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