What laboratory tests should be ordered for a suspected brain mass?

Laboratory Tests for Suspected Brain Mass

For suspected brain mass, the most appropriate initial laboratory workup should include a non-contrast head CT followed by MRI brain with and without contrast, with additional targeted tests based on clinical presentation and suspected primary malignancy.

Initial Imaging Studies

First-Line Imaging

• Non-contrast head CT
  • Serves as the initial screening test for patients with suspected brain mass 1
  • Can identify acute hemorrhage, significant mass effect, hydrocephalus, and large lesions 1
  • Provides rapid assessment in unstable patients or those with acute neurological deterioration

Second-Line Imaging (Definitive)

• MRI brain without and with IV contrast
  • Gold standard for comprehensive evaluation of suspected brain masses 1
  • Superior to CT for detection of small lesions, posterior fossa abnormalities, and characterization of mass lesions 1
  • Essential sequences include:
    • T1-weighted pre- and post-contrast
    • T2-weighted and/or FLAIR
    • Diffusion-weighted imaging (DWI)
    • Susceptibility-weighted imaging (for hemorrhage detection) 1

Laboratory Testing Algorithm

Basic Laboratory Tests

• Complete blood count (CBC)
• Comprehensive metabolic panel (CMP)
• Coagulation studies (PT/INR, PTT)

Based on Clinical Suspicion

1. For suspected metastatic disease:

   • Chest CT with contrast (detects primary lung malignancies, which account for 82% of brain metastases) 2
   • The combination of brain MRI and chest CT identifies the diagnostic biopsy site in 97% of patients with newly detected brain masses 2

2. For suspected infectious etiology:

   • Blood cultures
   • HIV testing
   • Serum cryptococcal antigen
   • Consider lumbar puncture if no significant mass effect on imaging

3. For suspected primary CNS lymphoma:

   • LDH
   • Serum protein electrophoresis
   • Consider lumbar puncture for cytology if safe

Special Considerations

Imaging Technique Optimization

• MRI should be performed with at least 1.5-Tesla field strength 1
• Three-dimensional acquisition is preferred for thinner slices and better detection 1
• Contrast agent should be administered 10 minutes before data acquisition at a dose of 0.1 mmol/kg 1

Common Pitfalls to Avoid

1. Delaying definitive imaging: The average time to biopsy for patients with brain tumors is 4.7-6.0 days; early neurosurgical consultation after initial imaging can reduce time to diagnosis by at least 10% 2

2. Performing extensive workup before biopsy: This can lead to unnecessary expense and delay in diagnosis 2

3. Relying solely on non-contrast imaging: Contrast-enhanced studies are essential for proper characterization of brain masses 1

4. Missing leptomeningeal disease: When evaluating for brain masses, also assess for leptomeningeal enhancement which may indicate leptomeningeal metastasis 1

By following this structured approach to laboratory and imaging studies for suspected brain masses, clinicians can efficiently reach a diagnosis while avoiding unnecessary testing and delays in treatment.