What is the pathognomonic feature of neurobrucellosis on brain Magnetic Resonance Imaging (MRI)?

Pathognomonic MRI Feature in Neurobrucellosis

The pathognomonic feature of neurobrucellosis on brain MRI is basal meningeal enhancement with gadolinium, particularly involving the basal cisterns. 1, 2

Characteristic Neuroimaging Findings in Neurobrucellosis

Neurobrucellosis presents with variable MRI findings, but several patterns are particularly characteristic:

1. Basal meningeal enhancement - The most distinctive finding, seen as enhancement of the meninges at the base of the brain after gadolinium administration 2, 3

2. White matter changes - Diffuse white matter lesions that may persist even after clinical recovery 2

3. Vascular involvement - Chronic cerebral ischemic changes due to vasculitis 3

4. Inflammatory findings including:

   • Leptomeningeal involvement
   • Cranial nerve enhancement
   • Spinal nerve root enhancement
   • Brain granulomas or abscesses (less common)
   • Arachnoiditis 3

5. Hydrocephalus - Due to inflammatory obstruction of CSF pathways 3

Diagnostic Considerations

The Istanbul-3 study, which evaluated 263 patients with CNS brucellosis, found that approximately 45% of neurobrucellosis patients had abnormal neuroimaging findings, while 54.3% had normal CT or MRI scans 3. This highlights that normal imaging does not exclude the diagnosis.

Factors associated with inflammatory findings on imaging:

• Longer duration of symptoms
• Presence of polyneuropathy and radiculopathy
• High CSF protein levels
• Low CSF/serum glucose ratio 3

Differential Diagnosis

Several conditions may have similar MRI findings:

• Tuberculous meningitis - Also presents with basal meningeal enhancement
• Neurosarcoidosis - Can show leptomeningeal enhancement and the "trident sign" 1
• CNS vasculitis - May present with similar vascular changes 4
• Viral encephalitis - HSV encephalitis typically shows bilateral temporal lobe involvement 5

Clinical Correlation

It's important to note that clinical-radiologic correlation in neurobrucellosis varies widely. Some patients may have positive clinical findings despite normal imaging, while others show various imaging abnormalities reflecting inflammatory processes, immune-mediated processes, or vascular insults 2.

Diagnostic criteria for neurobrucellosis include:

1. Signs and symptoms suggestive of neurobrucellosis
2. Positive Brucella serology or culture in CSF
3. Abnormal CSF findings (lymphocytosis, high protein, low glucose)
4. Characteristic neuroimaging findings 6

Pitfalls and Caveats

• Normal imaging does not exclude neurobrucellosis - More than half of patients may have normal initial imaging 3
• Enhancement patterns may resolve with treatment while white matter and ischemic changes often persist despite clinical recovery 2
• Mimics of other conditions - Neurobrucellosis can mimic primary CNS vasculitis and other inflammatory or infectious conditions 4
• Need for follow-up imaging - To monitor treatment response, though some changes may persist despite clinical improvement

In cases of suspected neurobrucellosis with negative conventional testing, CSF metagenomic next-generation sequencing may be valuable for diagnosis, potentially avoiding unnecessary invasive procedures like brain biopsy 4.