What are the best CT scan requirements for diagnosing cavernous sinus thrombosis?

Optimal CT Protocol for Diagnosing Cavernous Sinus Thrombosis

Contrast-enhanced MRI with coverage through the cavernous sinuses is the test of choice for suspected cavernous sinus thrombosis, but when CT is required, contrast-enhanced CT with thin sections through the skull base is the optimal protocol. 1, 2

Primary Imaging Recommendations

CT Protocol Requirements

• Contrast-enhanced CT of the head/maxillofacial region with:
  • Thin sections (1-2 mm) through the skull base
  • IV contrast administration
  • Coverage including paranasal sinuses, orbits, and cavernous sinuses
  • Post-contrast imaging to identify filling defects within the cavernous sinus

Key CT Findings to Evaluate

• Filling defects within the cavernous sinus (>7 mm filling defects are highly suspicious) 3
• "Empty delta" sign (central hypodensity surrounded by contrast enhancement) 1
• Expansion of the cavernous sinus
• Dilation of tributary veins, particularly the superior ophthalmic vein 4, 5
• Associated sinusitis (particularly sphenoid and ethmoid)
• Orbital complications (proptosis, orbital edema)
• Bone erosion suggesting invasive fungal sinusitis

Limitations of CT for Cavernous Sinus Thrombosis

• CT has approximately 87% accuracy for detecting intracranial complications compared to 97% for MRI 1
• Detection of cavernous sinus thrombosis, meningitis, and early cerebritis is more difficult on CT compared to MRI 1
• Only approximately one-third of cases demonstrate direct signs of hyperdense dural sinus on non-contrast CT 1

Alternative and Complementary Imaging

MRI Protocol (Preferred When Available)

• MRI head/orbits without and with IV contrast
• Coverage through cavernous sinuses
• T2*-weighted/gradient echo/susceptibility-weighted sequences
• Diffusion-weighted imaging to detect restricted diffusion
• MR venography

When to Consider Additional Vascular Imaging

• CTA or MRA should be added if there is suspicion for:
  • Vascular invasion
  • Pseudoaneurysm formation (particularly with fungal disease) 1
  • Carotid artery involvement

Clinical Scenarios Requiring Special Consideration

Suspected Invasive Fungal Sinusitis

• Lower threshold for imaging in immunocompromised patients
• Look for bone erosion, cavernous sinus invasion, and carotid artery involvement 1
• Consider both CT (for bone detail) and MRI (for soft tissue involvement)

Sinonasal Disease with Orbital/Intracranial Extension

• CT maxillofacial with contrast is often the first-line examination 1
• Add contrast-enhanced CT head for increased coverage of suspected intracranial complications
• Follow with MRI if available, especially with neurological symptoms

Pitfalls to Avoid

• Misinterpreting normal anatomic variants as thrombosis (asymmetric sinuses occur in 49% of population) 2
• Relying solely on non-contrast CT (only 30% show abnormalities in cerebral venous thrombosis) 2
• Confusing arachnoid granulations or intrasinus septa for thrombosis
• Failing to administer contrast, which is essential for diagnosis

Remember that while CT is often the first imaging modality due to availability, MRI provides superior diagnostic accuracy for cavernous sinus thrombosis and should be obtained when possible, especially in cases with equivocal CT findings or progressive symptoms despite treatment.