Hypodensity in Left Hemipons: Acute Ischemic Stroke Until Proven Otherwise
A hypodense area in the left hemipons on CT most likely represents an acute ischemic stroke in the posterior circulation, and you should immediately initiate acute stroke protocols including consideration for reperfusion therapy if the patient presents within the appropriate time window.
What the Finding Indicates
A hypodense lesion in the pons on non-contrast CT indicates:
- Acute ischemic stroke (most common in adults presenting acutely)
- The hypodensity reflects cytotoxic edema from ischemic injury
- Posterior circulation involvement, specifically affecting the basilar artery territory
- This finding typically appears within hours of stroke onset, though may be subtle initially
Immediate Management Algorithm
1. Time-Critical Assessment
- Document exact symptom onset time
- Emergency brain imaging is mandatory before any specific therapy 1
- Do not delay treatment to obtain additional imaging sequences if the patient is a candidate for IV thrombolysis 1
2. Reperfusion Therapy Considerations
For IV thrombolysis (tPA):
- Either non-contrast CT or MRI is required to exclude hemorrhage (absolute contraindication) 1
- Intravenous fibrinolytic therapy is recommended even with early ischemic changes on CT, regardless of extent 1
- The critical exception: if frank hypodensity involves more than one-third of the MCA territory, withhold IV tPA due to increased hemorrhage risk 1
- Note: This one-third rule applies to MCA territory; pontine strokes require clinical judgment as the pons is smaller
For endovascular therapy:
- Obtain noninvasive intracranial vascular imaging (CTA or MRA) during initial evaluation if considering mechanical thrombectomy 1
- This should not delay IV tPA administration if indicated 1
- Posterior circulation strokes were underrepresented in major endovascular trials (only 8% in SYNTHESIS) 2, but basilar occlusions are often considered for thrombectomy given poor natural history
3. Imaging Interpretation Timeline
- Brain imaging must be interpreted within 45 minutes of ED arrival by a physician with expertise in neuroimaging 1
- Advanced imaging (CT/MRI perfusion) may be considered for patient selection beyond standard time windows 1
Critical Pitfalls to Avoid
Common diagnostic errors:
- Assuming all hypodensity equals irreversible infarction—early ischemic changes do not preclude treatment 1
- Delaying treatment for additional imaging when IV tPA is already indicated
- Missing basilar artery occlusion, which has devastating outcomes without intervention
Alternative diagnoses to consider (less common):
- Pontine glioma (typically in pediatric patients, with mass effect and possible enhancement) 3
- Demyelinating disease
- Hypoglycemia (can cause transient hypodensity, but resolves with glucose correction) 4
Prognostic Considerations
Pontine strokes carry significant morbidity and mortality due to:
- Critical brainstem structures (cranial nerve nuclei, motor pathways, respiratory centers)
- Basilar artery occlusions have poor outcomes without recanalization
- Even with successful treatment, posterior circulation strokes often result in substantial disability
The presence of hypodensity indicates tissue injury has already occurred, but this does not mean the patient cannot benefit from reperfusion therapy—the goal is to salvage penumbral tissue and prevent extension 1.