What are the MRI findings in a patient with Human Immunodeficiency Virus (HIV) vasculitis causing a pontine infarct?

MRI Findings in HIV Vasculitis Causing Pontine Infarct

In HIV vasculitis causing pontine infarct, MRI will demonstrate acute ischemic changes in the pons on diffusion-weighted imaging (DWI) with corresponding ADC map changes, T2/FLAIR hyperintensity in the affected pontine territory, and may show basilar artery stenosis or irregularity with characteristic vessel wall enhancement on post-contrast sequences. 1, 2

Key MRI Sequences and Findings

Diffusion-Weighted Imaging (DWI)

• DWI is the most sensitive sequence for detecting acute pontine infarction, showing restricted diffusion (hyperintensity) in the affected pontine territory within hours of symptom onset 1
• The pontine lesion pattern typically corresponds to one of five vascular territories: anteromedial (most common at 58%), anterolateral (17%), tegmental (10%), bilateral (11%), or multiple unilateral infarcts (4%) 3
• DWI has 77% sensitivity within the first 3 hours compared to only 16% for CT 1

T2-Weighted and FLAIR Sequences

• T2-weighted and FLAIR images demonstrate hyperintensity in the infarcted pontine region, though these changes may be subtle in the hyperacute phase 1, 4
• FLAIR is particularly useful for distinguishing lacunar infarcts from perivascular spaces 1

Vessel Wall Imaging with Contrast

• Post-gadolinium vessel wall enhancement of the basilar artery is a characteristic finding in HIV vasculitis and helps distinguish it from atherosclerotic disease 2
• This enhancement reflects inflammatory changes in the vessel wall and is highly suggestive of vasculitic etiology 2
• Very high-resolution MRI can directly image vessel wall thickening or enhancement in arteriopathies 1

Magnetic Resonance Angiography (MRA)

• MRA typically shows basilar artery stenosis, irregularity, or beading patterns consistent with vasculitis 1, 5
• In HIV vasculopathy, arterial luminal irregularities and stenosis are common findings 1
• MRA should include both intracranial and cervical vessels, as cerebral arterial abnormalities are found in 25% of unexplained stroke patients 1

Additional MRI Features Specific to HIV Vasculitis

Pattern Recognition

• HIV vasculopathy tends to cause large, cortical hemispheric strokes more frequently than small subcortical infarcts (75% versus 25% in one series), though pontine involvement can occur 5
• Multiple intracranial aneurysms may be present and visible on MRA sequences 6, 7
• The presence of multiple vascular territory involvement or bilateral lesions suggests more severe vasculopathy 3, 7

Susceptibility-Weighted Imaging (SWI)

• SWI may detect microhemorrhages or blood products, though hemorrhagic transformation is less common in HIV vasculitis compared to other etiologies 1
• "Blooming" artifact within vessels on SWI can suggest intravascular thrombus 1

Distinguishing Features from Other Vasculitides

HIV Vasculopathy versus VZV Vasculitis

• VZV vasculitis more commonly presents with small, deep, subcortical ischemic strokes (80% of cases), while HIV vasculopathy shows large cortical hemispheric strokes (75% of cases) 5
• This distinction likely reflects different arterial size involvement: VZV affects smaller penetrating arteries while HIV vasculopathy affects larger vessels 5, 7
• VZV vasculitis requires CSF testing for anti-VZV immunoglobulin G (highest sensitivity), immunoglobulin M, and PCR 1

Vessel Wall Characteristics

• HIV-associated large vessel vasculopathy shows leukocytoclastic vasculitis of vasa vasorum with adventitial inflammation 7
• The basilar artery stenosis with vessel wall enhancement pattern is characteristic of HSV/HIV CNS vasculitis 2

Clinical-Radiological Correlation

Pontine Infarct Patterns

• Anteromedial pontine infarcts (58%) present with motor deficits, dysarthria, and ataxia; MRI shows lesions in the paramedian pontine territory 3
• Anterolateral pontine infarcts (17%) show motor and sensory deficits with tegmental signs; MRI demonstrates lateral pontine involvement 3
• Tegmental pontine infarcts (10%) present with eye movement disorders and vertigo; MRI shows dorsal pontine lesions 3
• Bilateral pontine infarcts (11%) cause tetraparesis and pseudobulbar palsy; MRI reveals bilateral pontine involvement with poor prognosis 3

Common Pitfalls to Avoid

• Do not rely on CT alone, as it has only 16% sensitivity for acute pontine infarcts compared to 77% for MRI in the first 3 hours 1
• Do not assume atherosclerotic disease without vessel wall imaging, as HIV vasculitis requires different treatment with immunosuppression and antiretroviral therapy 1, 6
• Do not overlook multiple aneurysms on MRA, as these are characteristic of HIV-associated large vessel vasculopathy and may require specific monitoring 6, 7
• Do not delay lumbar puncture for CSF analysis if coexistent VZV vasculitis is suspected, as negative VZV PCR does not rule out the diagnosis 1
• Perform MRI within 48 hours of symptom onset for optimal sensitivity, as approximately 90% of cases will show abnormalities within this timeframe 1, 4

Recommended Imaging Protocol

• Obtain brain MRI with DWI, T2/FLAIR, T1 pre- and post-contrast with vessel wall imaging, and MRA of head and neck 1, 2
• Consider perfusion-weighted imaging (arterial spin labeling preferred to avoid contrast) to assess hemodynamic compromise 1
• Transcranial color-Doppler ultrasonography may complement MRI findings 1
• Follow-up MRI is recommended to evaluate treatment response and detect new lesions 4