Gliomas versus Brain Abscesses: Diagnosis by Magnetic Resonance Imaging

Introduction

Gliomas and brain abscesses are two serious neurological conditions that can present with similar clinical manifestations, making differential diagnosis challenging. Magnetic resonance imaging (MRI) plays a crucial role in distinguishing between these pathologies, especially with the use of advanced sequences such as diffusion, apparent diffusion coefficient (ADC) mapping, and MR spectroscopy.

Gliomas

History Gliomas are brain tumors that originate from glial cells, which provide support and protection to neurons. The first clinical description of gliomas dates back to the 19th century, and over the decades, technological advances have allowed for a better understanding of their molecular biology.

Classification and Grades The World Health Organization (WHO) classifies gliomas into four grades according to their aggressiveness:

• Grade I: Pilocytic astrocytomas — benign tumors usually found in children.
• Grade II: Low-grade gliomas — grow slowly but may progress to more aggressive forms.
• Grade III: Anaplastic gliomas — malignant tumors with accelerated growth.
• Grade IV: Glioblastoma multiforme (GBM) — the most aggressive and lethal, with a high recurrence rate.

Symptoms Glioma symptoms depend on the tumor's location and size, but may include:

• Persistent headache
• Seizures
• Focal neurological deficits (such as weakness on one side of the body)
• Cognitive and behavioral changes

Treatment Treatment involves a multidisciplinary approach:

• Surgery: maximum tumor removal without compromising vital functions.
• Radiotherapy: used to eliminate remaining cells.
• Chemotherapy: with drugs like temozolomide.
• Targeted therapies and immunotherapy: still under research but promising.

Brain Abscesses

History Brain abscesses were first described in ancient medical literature, but only in the 20th century, with the advent of MRI, was it possible to accurately identify their location and distinguish infections from other lesions.

Causes and Pathogenesis Brain abscesses are encapsulated purulent collections within the brain parenchyma, resulting from:

• Hematogenous spread from distant infections (endocarditis, pneumonia)
• Direct extension from adjacent infections (sinusitis, otitis)
• Head trauma or neurosurgical procedures

Symptoms Symptoms include:

• Severe and persistent headache
• Fever
• Focal neurological signs
• Altered level of consciousness
• Nausea and vomiting

Treatment Treatment includes:

• Intravenous antibiotic therapy: covering aerobic and anaerobic bacteria.
• Surgical drainage: indicated for large abscesses or those with mass effect.
• Corticosteroids: used cautiously to reduce brain edema.

Diagnosis by Magnetic Resonance Imaging

MRI is crucial for differentiating gliomas from abscesses, using techniques such as:

• Diffusion-weighted imaging (DWI) and ADC mapping: abscesses show restricted diffusion (hyperintense on DWI, hypointense on ADC), while gliomas exhibit facilitated diffusion in necrotic areas (hypointense on DWI, hyperintense on ADC).
• MR Spectroscopy: gliomas show increased choline (cell proliferation) and decreased N-acetyl-aspartate (NAA), while abscesses display peaks of amino acids, acetate, and succinate.

Conclusion

Distinguishing between gliomas and brain abscesses is vital for selecting the appropriate therapeutic approach. The use of advanced MRI techniques, such as DWI, ADC, and spectroscopy, enhances diagnostic accuracy, allowing for more targeted and effective treatment.