In a 28-year-old woman with a new unilateral right-sided headache causing vomiting and gait instability, how can I clinically differentiate cerebral venous sinus thrombosis (CVST) from migraine?

Clinical Differentiation of CVST from Migraine

In a 28-year-old woman presenting with unilateral headache, vomiting, and gait instability, you must strongly suspect CVST over migraine and obtain urgent neuroimaging with venography—this presentation contains critical red flags that distinguish CVST from primary headache disorders.

Key Clinical Features That Point to CVST

Red Flags Demanding Immediate Investigation

The combination of vomiting with gait instability in your patient represents focal neurological dysfunction that should never be attributed to migraine without excluding CVST 1. According to AHA/ASA guidelines, CVST presents with two distinct mechanisms:

• Increased intracranial pressure (causing headache, vomiting)
• Focal brain injury from venous ischemia/hemorrhage (causing gait instability, motor deficits)

Your patient has both mechanisms present simultaneously, which is common in CVST but atypical for migraine 1.

Temporal Pattern Distinguishes the Two

• CVST headache: Typically progressive over days to weeks (56% subacute onset >48 hours to 30 days; median 4 days before hospital admission) 1
• Migraine: Usually reaches maximum intensity within hours, rarely persists beyond 72 hours untreated

While CVST can occasionally present with migrainous-type headache 1, 2, the progression pattern and associated neurological signs are the critical differentiators.

Specific Examination Findings

Look for these CVST-specific signs that migraine lacks:

On neurological examination:

• Papilledema (present in >80% with increased intracranial pressure) 1
• Sixth nerve palsy causing diplopia 1
• Focal motor deficits (hemiparesis most common) 1
• Altered consciousness or confusion 1
• Seizures (occur in 40% of CVST patients—virtually diagnostic against migraine) 1

On general examination:

• Scalp edema or dilated scalp veins (particularly with superior sagittal sinus involvement) 1
• Signs of underlying infection (ear discharge, mastoid tenderness for lateral sinus thrombosis) 1

Critical Risk Factor Assessment

Immediately assess for prothrombotic conditions 1:

• Oral contraceptive use (OR 5.59 for CVST; your 28-year-old patient's age makes this highly relevant) 1
• Pregnancy/postpartum state (within 6 weeks) 3
• Recent infection (ear, sinus, dental)
• Known thrombophilia
• Inflammatory conditions (lupus, Behçet's, inflammatory bowel disease)

The presence of any risk factor dramatically increases CVST probability over migraine 1, 4.

Diagnostic Algorithm

Step 1: Clinical Suspicion Threshold

Any headache with:

• Focal neurological signs (your patient's gait instability qualifies) OR
• Progressive worsening over days OR
• Papilledema/sixth nerve palsy OR
• Seizures OR
• Altered consciousness

→ Proceed immediately to imaging 1

Step 2: Imaging Strategy

Plain CT or MRI alone is insufficient and may be normal 1. The AHA/ASA guideline is explicit:

• Obtain CT venography (CTV) or MR venography (MRV) as the definitive test 1
• Do not rely on negative plain CT to exclude CVST 1
• Venography must be performed even if initial CT appears normal 1

Step 3: Laboratory Testing

D-dimer has limited utility 1:

• High sensitivity but poor specificity 1
• Normal D-dimer does NOT exclude CVST 5, 4—multiple case reports document CVST with normal D-dimer 5, 4

Obtain these labs 1:

• Complete blood count
• Chemistry panel
• PT/aPTT
• Screen for prothrombotic conditions (contraceptive use, pregnancy test, inflammatory markers)

Common Diagnostic Pitfalls

Pitfall 1: Attributing Symptoms to "First Migraine Attack"

Multiple case reports document catastrophic outcomes when CVST was misdiagnosed as migraine 6, 7, 3. Never diagnose "first migraine" in the emergency setting without excluding CVST when red flags exist 6, 7.

Pitfall 2: Reassurance from Normal Initial Imaging

25% of CVST patients present with isolated headache without focal signs initially 1, but your patient already has focal signs (gait instability). Plain CT misses many cases 1.

Pitfall 3: Assuming Young Age and Health Exclude CVST

CVST predominantly affects young adults, especially women of reproductive age 7, 3, 8. The median delay to diagnosis is 7 days, often because clinicians don't suspect it 1.

Pitfall 4: Misinterpreting Functional Symptoms

Gait instability and vomiting can be dismissed as anxiety or functional disorder 3. Always obtain objective imaging before attributing neurological symptoms to functional causes 3.

Practical Clinical Decision Rule

For your specific patient:

1. Unilateral headache (can occur in both conditions)
2. + Vomiting (suggests increased ICP in CVST context)
3. + Gait instability (focal neurological sign—CVST until proven otherwise)
4. + Young woman (high-risk demographic for CVST)

→ This combination mandates urgent CTV or MRV 1

Do not treat as migraine without definitive imaging excluding CVST. The mortality risk of untreated CVST (3-15%) 3 and potential for permanent disability 7 far outweigh the inconvenience of neuroimaging.

If venography confirms CVST, immediate anticoagulation is required regardless of hemorrhagic transformation presence 1. If venography is negative, then migraine treatment is appropriate.