What type of CT (Computed Tomography) scan is recommended for suspected mastoiditis?

CT Imaging for Mastoiditis: Recommendations and Protocols

For suspected mastoiditis, a high-resolution temporal bone CT scan with contrast is the recommended first-line imaging modality to assess bone destruction, identify complications, and guide surgical planning.

Optimal CT Protocol for Mastoiditis

• Type of CT scan: High-resolution temporal bone CT
• Contrast: With intravenous contrast (preferred when available)
• Timing: Should be performed when:
  • Clinical diagnosis of mastoiditis is made and surgical intervention is being considered
  • Patient fails to improve after 48 hours of IV antibiotics 1
  • Signs of complications are present (altered mental status, auricular proptosis, fluctuance) 2

Rationale for CT as First-Line Imaging

1. Superior bone visualization: CT excels at depicting cortical bone, periosteal reaction, bone destruction, and sequestra formation 3
2. Surgical planning: Provides essential anatomical detail for mastoidectomy, showing the extent of mastoid air cell involvement and relationship to critical structures (facial nerve, sigmoid sinus) 1
3. Complication detection: Effectively identifies:
   • Subperiosteal abscess
   • Bone erosion/coalescence
   • Sinus thrombosis
   • Intracranial extension 3, 1

When to Add MRI

MRI should be considered as a complementary study (not a replacement) when:

• Intracranial complications are suspected
• Soft tissue extension needs better characterization
• Venous sinus thrombosis is suspected (MRV may be superior) 3

The American College of Radiology notes that "both CT and MRI of the sinuses, including evaluation of the adjacent brain and orbits, may be needed to fully define the extent of disease and orbital or intracranial extension" 3.

Clinical Algorithm for Imaging

1. Initial presentation with suspected mastoiditis:

   • Begin with high-resolution temporal bone CT with contrast

2. If CT shows complications or patient has neurological symptoms:

   • Add MRI brain/face with and without contrast

3. For suspected venous sinus thrombosis:

   • Consider CT venography (CTV) or MR venography (MRV) 3

Common Pitfalls to Avoid

• Delayed imaging: Failure to obtain appropriate imaging when clinical improvement doesn't occur within 48 hours may miss developing complications 1, 4
• Inadequate protocol: Standard head CT is insufficient; specific temporal bone protocol is required for proper evaluation 2
• Radiation concerns: While temporal bone CT requires higher radiation dose, its benefits outweigh risks in suspected mastoiditis with potential complications 2
• Over-reliance on negative CT: A negative CT does not exclude early mastoiditis; clinical correlation is essential 4

Evidence-Based Considerations

Research shows that 51% of patients with suspected mastoiditis who underwent temporal bone CT ultimately required surgery 2. CT findings of temporal bone absorption beyond the mastoid area (squama and/or petrous bones) are indicative of more severe disease requiring aggressive intervention 5.

In a study of children with acute mastoiditis, CT imaging was reserved for those with suspected complications, with the most common indications being suspected subperiosteal abscess (45%), lack of improvement despite adequate medical therapy (35%), and focal neurological signs (20%) 4.

The high-resolution capabilities of CT make it particularly valuable for detecting the rarefying osteitis, coalescence of air cells, and subperiosteal abscess characteristic of coalescent mastoiditis 6.