What is the diagnostic approach for cavernous sinus thrombosis?

Diagnostic Approach for Cavernous Sinus Thrombosis

MRI with MR venography (MRV) is the preferred first-line imaging modality for diagnosing cavernous sinus thrombosis (CST), as it provides the highest sensitivity and shows both thrombus and parenchymal changes. 1

Clinical Presentation to Guide Suspicion

CST should be suspected in patients presenting with:

• Fever
• Headache
• Ocular manifestations:
  • Chemosis (conjunctival edema)
  • Periorbital edema
  • Ptosis
  • Ophthalmoplegia
  • Vision changes 2
• Cranial nerve involvement (most commonly CN VI causing lateral rectus palsy, but also CN III, IV, and V) 2
• History of recent sinusitis, facial infection, or maxillofacial trauma 2

Diagnostic Imaging Algorithm

First-Line Imaging

• MRI with MRV: Preferred initial imaging due to superior sensitivity for detecting thrombus and parenchymal changes 1
  • Look for: absence of flow void in the sinus, T2 hypointensity suggesting thrombus, and signal evolution over time 1

Alternative First-Line Imaging

• CT with CT venography (CTV): Reasonable alternative when MRI is contraindicated or unavailable (approximately 87% accuracy) 1
  • On non-contrast CT: Look for hyperdense dural sinus in acute thrombosis
  • On contrast-enhanced CT: Look for "empty delta" sign (central isodense lesion with surrounding enhancement)
  • On CTV: Look for mixed density within venous sinuses (high-density contrast in patent segments and low density in thrombosed segments) 1

When Initial Imaging is Inconclusive

• Cerebral angiography: Reserved for inconclusive MRV/CTV results with high clinical suspicion, cases where endovascular treatment is being considered, and suspected isolated cortical vein thrombosis 1

  • Normal cerebral venous structures should opacify within 7-8 seconds after contrast injection
  • Delayed or absent visualization of cerebral venous structures suggests thrombosis 3

• Direct cerebral venography: Typically performed during endovascular procedures

  • Look for filling defects within the lumen (non-occlusive thrombosis) or complete non-filling (occlusive thrombosis)
  • "Cupping appearance" within the sinus indicates complete thrombosis 3

Laboratory Testing

• Complete blood count
• Blood cultures (positive in up to 70% of cases) 2
• Inflammatory markers (typically elevated) 2
• D-dimer: A normal D-dimer level according to a sensitive immunoassay or rapid ELISA may help identify patients with low probability of cerebral venous thrombosis, but a normal result should not preclude further evaluation if clinical suspicion is high 3

Common Pitfalls in Diagnosis

1. Anatomic variants mimicking thrombosis: Sinus atresia/hypoplasia, asymmetrical sinus drainage, and normal sinus filling defects related to arachnoid granulations or intrasinus septa can mimic thrombosis 3

2. Isolated mental status changes: Patients may present with somnolence or confusion without obvious focal neurological abnormalities, especially in elderly patients 3

3. Normal initial CT: Non-contrast CT is often normal in early CST, with abnormal findings in only about 30% of cases 3

4. Signal intensity variations: Thrombus signal can vary depending on age of the clot, making interpretation challenging 3

5. Flow gaps on TOF MRV: These are common and can affect interpretation 3

6. Misdiagnosis due to rarity: Because CST is rare, it is frequently misdiagnosed initially 4

Diagnostic Approach Summary

1. Maintain high clinical suspicion in patients with characteristic symptoms and risk factors
2. Order MRI with MRV as first-line imaging
3. If MRI is unavailable or contraindicated, proceed with CT with CTV
4. Obtain laboratory tests including blood cultures and inflammatory markers
5. Consider cerebral angiography for inconclusive cases with high clinical suspicion
6. Be aware of anatomic variants and imaging artifacts that can mimic thrombosis

Early diagnosis is critical as CST carries high morbidity and mortality rates, with mortality reported as high as 30% even in the antibiotic era 4. Prompt initiation of appropriate treatment including antibiotics and consideration of anticoagulation can significantly improve outcomes 5.