What are the typical radiological findings of primary central nervous system (CNS) lymphoma?

Radiological Findings of Primary CNS Lymphoma

Primary CNS lymphoma (PCNSL) typically presents on MRI as hypointense lesions on T1-weighted images, isointense to hypointense on T2-weighted images, with reduced apparent diffusion coefficient (ADC), variable surrounding edema, and homogeneous strong enhancement after contrast administration. 1

Characteristic Imaging Features

Location and Distribution

• Most common locations:

  • Frontal lobe and brain hemispheres (38%)
  • Thalamus or basal ganglia (16%)
  • Corpus callosum (14%)
  • Periventricular regions (12%)
  • Cerebellum (9%)
  • Meninges (16%)
  • Spinal cord (1%)
  • Cranial and spinal nerves (<1%) 1

• Pattern of lesions:

  • Solitary lesions in approximately 80% of patients
  • Multiple lesions in about 20% of patients 2
  • Approximately 58% of lesions abut the ventricular system 3

Signal Characteristics

• T1-weighted images: Hypointense or isointense 1, 2
• T2-weighted images:
  • Only about 40% are hyperintense 2
  • Often isointense to hypointense 1
  • May show mixed signal intensity 4
• Diffusion-weighted imaging (DWI):
  • Restricted diffusion with reduced ADC values 1, 5
  • Median minimum ADC values range: 0.65-0.71 × 10^-3 mm²/s 4
  • Median mean ADC values range: 0.79-0.84 × 10^-3 mm²/s 4

Enhancement Pattern

• Nearly all lesions enhance after contrast administration 2
• Enhancement characteristics:
  • Homogeneous enhancement in 76% of lesions 3
  • Marked enhancement in 79% of lesions 3
  • Strong enhancement pattern 1

Other Features

• Edema: Variable surrounding edema 1
• Mass effect: Typically mild 2
• Density on CT: Most lesions (92%) are hyperdense or isodense 2
• Uncommon findings:
  • Calcification, hemorrhage, or necrosis are rare 2
  • Meningeal or ventricular enhancement is uncommon but suggestive of PCNSL 2

Atypical Radiological Presentations

In approximately 25% of cases, PCNSL may present with atypical radiological features 4:

• Central non-enhancing regions (40% of atypical cases)
• Susceptibility artifacts suggesting hemorrhage (56% of atypical cases)
• Multifocal lesions with mixed T2 signal intensity 4

Differential Diagnosis

The main differential diagnoses to consider include:

• High-grade glioma
• Pseudotumoral demyelinating disease 5
• In immunocompromised patients: neurotoxoplasmosis, progressive multifocal leukoencephalopathy, and cerebral abscess 5

Imaging Protocol Recommendations

• Contrast-enhanced cranial MRI is the recommended imaging modality for patients with PCNSL [II, A] 1
• The International PCNSL Collaborative Group (IPCG) protocol based on 3T or 1.5T MRI is recommended [V, A] 1
• Diffusion and perfusion-weighted sequences should be included 5

Clinical Pitfalls and Caveats

• Avoid corticosteroid administration before biopsy whenever clinically possible 1

  • Corticosteroids can dramatically reduce enhancement and may lead to false-negative biopsies
  • If steroids have been administered, consider stopping them and repeating MRI before biopsy

• Diagnostic delay is common

  • A delay in diagnosis of weeks to months following symptom onset is common 1
  • Atypical radiological presentations (25% of cases) often lead to delayed diagnosis 4

• When to suspect PCNSL despite atypical imaging:

  • Low ADC values in atypical lesions should prompt consideration of early biopsy 4
  • Periventricular location and homogeneous enhancement are highly suggestive features 5, 3

Remember that while imaging is crucial for diagnosis, histopathological confirmation through stereotactic biopsy remains the gold standard for definitive diagnosis of PCNSL 1, 5.