What are the typical MRI findings in a patient with suspected tuberculosis (TB) meningitis?

MRI Findings in Tuberculous Meningitis

MRI with and without IV contrast is the imaging modality of choice for tuberculous meningitis, demonstrating characteristic basal meningeal enhancement, hydrocephalus, tuberculomas, and cerebral infarctions—findings that are critical for early diagnosis and management of this life-threatening infection. 1

Primary MRI Findings

Basal Meningeal Enhancement

• Basal meningeal enhancement is the most sensitive finding in TB meningitis, present in 82-89% of cases, appearing as thick, nodular enhancement along the basal cisterns and Sylvian fissures on post-contrast T1 and T2 FLAIR sequences 2, 3, 4
• Enhancement extends along the basal cisterns, involving the suprasellar, interpeduncular, and ambient cisterns, and may extend into the spinal subarachnoid spaces 3
• T2 FLAIR sequences are particularly sensitive for detecting meningeal enhancement and should be included in the imaging protocol 1

Hydrocephalus

• Hydrocephalus occurs in 29-77% of TB meningitis cases, resulting from obstruction of CSF flow by thick basal exudates 2, 5, 3
• Communicating hydrocephalus is more common than obstructive hydrocephalus in TB meningitis 3
• The presence of hydrocephalus is significantly associated with cerebral infarction (p=0.0019) and portends worse outcomes 5

Tuberculomas

• Tuberculomas develop in 74-100% of patients during treatment, appearing as ring-enhancing lesions with central hypointensity on T2-weighted images 2, 6, 3
• Multiple tuberculomas are more common (61%) than solitary lesions 3
• Tuberculomas are associated with prolonged fever but not necessarily with poor clinical outcome or relapse 2
• These lesions can appear paradoxically during appropriate treatment and should not be interpreted as treatment failure 2

Cerebrovascular Complications

Infarction Patterns

• Cerebral infarcts occur in 27-58% of TB meningitis cases, with the basal ganglia being the most common site of involvement 2, 5, 3
• Infarcts involve perforators from the lateral lenticulostriate arteries (50%) and posterior cerebral/basilar artery perforators (50%), followed by medial lenticulostriate arteries (23%) 5
• Diffusion-weighted imaging (DWI) is essential for detecting early cytotoxic edema from acute infarction, showing restricted diffusion in affected territories 1, 6
• Infarcts can occur in "tubercular zones" (basal ganglia, thalamus, internal capsule) in 13% of cases, "ischemic zones" (cortical territories) in 35%, or both zones in 15% 5

Vasculitis

• Vascular involvement is present in 43% of cases on MR angiography, showing arterial narrowing, irregularity, and beading 5
• The middle cerebral artery is most frequently involved (76%), followed by anterior cerebral artery (38%), internal carotid artery (31%), and posterior cerebral/basilar arteries 5
• Diffuse narrowing with paucity of distal vessels can occur in severe cases 5
• Cerebral infarction is significantly associated with vasculitis (p<0.001) 5

Advanced MRI Techniques

Diffusion Tensor Imaging

• Diffusion tensor imaging parameters (mean diffusivity and fractional anisotropy) are abnormal in regions of infarction, particularly in the basal ganglia 6
• These parameters may normalize in late subacute to chronic infarcts but remain abnormal in acute settings 6

Perfusion Imaging

• Arterial spin labeling demonstrates reduced cerebral blood flow in the basal ganglia region, which can detect early ischemic changes before frank infarction develops 6
• This finding is significant (p<0.05) compared to controls and may predict subsequent infarction 6

Magnetization Transfer Imaging

• Magnetization transfer imaging is helpful in visualizing hyperintense thickened meninges in basal cisterns and Sylvian fissures on pre-contrast imaging 6
• This technique enhances detection of subtle meningeal abnormalities that may not be apparent on conventional sequences 6

Optimal Imaging Protocol

Sequence Selection

• MRI with and without IV contrast should include T1-weighted, T2-weighted, T2 FLAIR, diffusion-weighted imaging, and post-contrast T1 and T2 FLAIR sequences 1
• T2 FLAIR is sensitive for vasogenic edema and meningeal enhancement 1
• DWI is sensitive for cytotoxic edema from acute infarction 1
• Post-contrast sequences are essential for detecting meningeal enhancement and tuberculomas 1

Timing Considerations

• MRI should be performed as soon as possible, ideally within 24 hours of hospital admission, but certainly within 48 hours 1
• MRI obtained within 48 hours of admission is abnormal in approximately 90% of TB meningitis cases 1
• Serial MRI at 60 days and 270 days is valuable for monitoring treatment response and detecting complications 2

Critical Diagnostic Considerations

MRI Superiority Over CT

• MRI is significantly more sensitive than CT in detecting early cerebral changes of TB meningitis, as CT may be normal or show only subtle abnormalities early in the disease course 1
• MRI better demonstrates the extent of meningeal inflammation, identifies early infarction, and detects tuberculomas that may be missed on CT 1, 3

Special Populations

• In immunocompromised patients, particularly those with HIV and low CD4 counts, MRI is essential as clinical presentations are often atypical 1
• Pregnant women should undergo MRI when TB meningitis is suspected, as the benefits outweigh theoretical risks, especially after the first trimester 1

Common Pitfalls

• Do not rely on a normal CT scan to exclude TB meningitis—proceed to MRI if clinical suspicion remains high 1
• The absence of tuberculomas on initial imaging does not exclude TB meningitis, as they frequently develop during treatment 2
• Paradoxical worsening on imaging (new tuberculomas or increased enhancement) during appropriate treatment is common and should not prompt treatment discontinuation 2
• Infarcts may be hemorrhagic in some cases, which can be mistaken for other pathologies 3

Treatment Monitoring

Response Assessment

• Dexamethasone treatment reduces hydrocephalus and prevents infarction, with fewer patients showing hydrocephalus at 60 days compared to placebo (p=0.217) 2
• The proportion of patients with infarction at 60 days is halved in the dexamethasone group (27% vs 58%, p=0.130) 2
• Serial MRI helps assess resolution of meningeal enhancement, reduction in hydrocephalus, and development of complications 2