Magnetic Resonance Venography (MRV) of the Brain
Magnetic resonance venography of the brain will provide the definitive diagnosis in this postpartum patient with suspected cerebral venous thrombosis. 1
Clinical Context Supporting CVT Diagnosis
This patient presents with the classic triad of risk factors and symptoms for cerebral venous thrombosis:
- Postpartum state (strongest risk factor, accounting for 77.94% of CVT cases in recent studies) 2
- Progressive severe headache with vomiting (present in 98.53% of CVT cases) 2
- Focal neurological deficits (cranial nerve VI palsy causing diplopia, numbness, seizure with obtundation) 3
- Seizure activity (occurs in 70.59% of CVT presentations) 2
The postpartum period confers hypercoagulability and represents the most significant modifiable risk factor for CVT, particularly in the first few weeks after delivery 3, 2.
Why MRV is the Definitive Diagnostic Study
The American College of Radiology designates MRI with MR venography as the preferred imaging modality for diagnosing cerebral venous sinus thrombosis, combining both noncontrast time-of-flight (TOF) and contrast-enhanced sequences for optimal diagnostic accuracy 1.
Diagnostic Performance
- MRI is more sensitive than CT at each stage after thrombosis for detecting cerebral venous thrombosis 1
- Gradient-echo T1-weighted postcontrast MRI demonstrates 92.5% sensitivity and 100% specificity compared to unenhanced MRV (89.6% sensitivity, 91.8% specificity) 1
- T2-weighted susceptibility imaging combined with MRV are considered the most sensitive sequences* 3, 1
Optimal Protocol
The optimal diagnostic approach combines MRI brain with both noncontrast TOF-MRV and contrast-enhanced MRV, as this combination provides complementary information that maximizes sensitivity and specificity 1.
Why Other Options Are Inadequate
D-dimer
- D-dimer is raised in most CVT patients but normal D-dimers do not rule out CVT, particularly in patients who present with isolated headache 4
- D-dimer is a screening tool, not a definitive diagnostic test 4
EEG
- EEG confirms seizure activity but does not identify the underlying etiology (CVT versus other causes)
- Cannot visualize venous thrombosis 3
Lumbar Puncture
- Lumbar puncture is contraindicated in suspected CVT with mass effect or increased intracranial pressure (this patient has obtundation suggesting elevated ICP) 3
- Does not provide definitive visualization of venous thrombosis 3
Noncontrast CT of the Brain
- Noncontrast CT is essential in initial evaluation but has limited sensitivity for CVT diagnosis 3
- The primary usefulness is to evaluate for hemorrhagic complications and alternative etiologies, not to definitively diagnose CVT 3
- Hyperdense dural sinus or cortical vein on noncontrast CT is present in only one-third of cases 1
- CT may show the "cord sign" but this is neither sensitive nor specific enough for definitive diagnosis 3
Alternative When MRI Unavailable
If MRI is not readily available, contraindicated, or in emergency settings, CT with CT venography (CTV) is an acceptable alternative 3, 1.
- Multidetector CTV demonstrates 95% sensitivity and 91% specificity compared to digital subtraction angiography 3, 1
- CT/CTV is as accurate as MRV for diagnosing cerebral venous thrombosis 1
Critical Management Pitfall
A negative plain CT or MRI does not rule out CVT. A venographic study (either CTV or MRV) should be performed in suspected CVT if the plain CT or MRI is negative or to define the extent of CVT if the plain CT or MRI suggests CVT 3.
Immediate Next Steps After Diagnosis
Once CVT is confirmed by MRV:
- Initiate therapeutic anticoagulation immediately with low molecular weight heparin (LMWH) or unfractionated heparin (UFH), even in the presence of intracranial hemorrhage 5
- Anticoagulation is recommended even with hemorrhagic complications, as the benefits of preventing thrombus progression outweigh bleeding risks 5
- Monitor for signs of increased intracranial pressure requiring osmotic therapy or surgical decompression 5