Carotid Artery Dissection
The most likely diagnosis is carotid artery dissection (Option A), given the classic triad of traumatic mechanism, ipsilateral Horner syndrome (ptosis and miosis), and contralateral hemiparesis following high-speed motor vehicle trauma. 1
Clinical Reasoning
The patient presents with a pathognomonic constellation of findings that strongly indicates left internal carotid artery dissection:
- Left-sided Horner syndrome (ptosis and miosis) indicates disruption of the sympathetic pathway along the left internal carotid artery 1
- Right-sided hemiparesis reflects cerebral ischemia in the left hemisphere from the dissected left carotid artery 1
- Headache and neck pain are the leading symptoms in carotid dissection, occurring in the typical presentation alongside Horner syndrome 1, 2
- High-speed motor vehicle crash provides the traumatic mechanism for cervical artery dissection through sudden or excessive neck movement 3
Why Not the Other Options?
Epidural hematoma (Option B) typically presents with loss of consciousness, a lucid interval, then deterioration—none of which occurred here. The focal neurological signs (Horner syndrome with contralateral hemiparesis) point to vascular rather than mass effect pathology.
Subarachnoid hemorrhage (Option C) would present with sudden severe "thunderclap" headache, often with meningismus and altered consciousness. The combination of Horner syndrome with focal motor deficits is not characteristic.
Subdural hematoma (Option D) usually causes diffuse symptoms from mass effect rather than the specific pattern of ipsilateral Horner syndrome with contralateral focal deficits seen with arterial dissection.
Pathophysiology
Carotid dissection results from an intimal tear initiating an intramural hematoma. 1 The dissection disrupts sympathetic fibers traveling along the internal carotid artery, producing Horner syndrome, while luminal narrowing or thromboembolism causes hemispheric ischemia manifesting as contralateral weakness. 1 After initial warning symptoms (headache, neck pain, Horner syndrome), cerebral or retinal ischemia develops in 50% to 95% of carotid dissection cases. 1, 3
Critical Next Steps
Immediate vascular imaging with CTA of the head and neck is the preferred diagnostic modality with 100% sensitivity for detecting arterial dissection. 4 This should be performed emergently given the high risk of stroke progression.
Antithrombotic therapy should be initiated immediately upon diagnosis confirmation—options include anticoagulation (heparin followed by warfarin with target INR 2.0-3.0) or antiplatelet therapy (aspirin, clopidogrel, or extended-release dipyridamole plus aspirin) for at least 3-6 months. 3, 5 The prognosis is usually favorable with appropriate treatment. 1, 5
Clinical Pearls
Painful Horner syndrome in trauma patients is carotid dissection until proven otherwise. 6, 2, 7 The combination of periorbital/neck pain with Horner syndrome is highly specific for internal carotid artery pathology.
No loss of consciousness does not exclude serious vascular injury. 1 Carotid dissection can present with progressive symptoms rather than immediate catastrophic events.
The pattern of ipsilateral Horner syndrome with contralateral hemiparesis localizes the lesion to the carotid artery on the side of the Horner syndrome, as sympathetic fibers travel with the carotid while motor pathways cross in the brainstem. 1