What type of computed tomography (CT) scan is recommended for evaluating a hard, immobile, and tender mass located behind the ear?

CT Imaging for a Mass Behind the Ear

For a hard, immobile, and tender mass located behind the ear, a high-resolution CT scan of the temporal bone without IV contrast is the recommended imaging modality. 1

Rationale for CT Temporal Bone

High-resolution CT of the temporal bone provides several advantages for evaluating masses in the post-auricular region:

• Excellent delineation of bony structures, air spaces, and soft tissue with high spatial resolution
• Ability to identify inflammatory or neoplastic masses
• Visualization of potential erosion of ossicles or other inner ear structures
• Helpful in surgical planning by demonstrating the relationship between the mass and surrounding structures 1, 2

CT temporal bone is particularly valuable because:

• It can define small inflammatory or neoplastic masses near the ear 1
• It provides excellent contrast between osseous structures, air, and soft tissue 2
• It can identify erosions of the ossicles or bony walls of the mastoid cells 2

Technical Considerations

When ordering a CT temporal bone for a post-auricular mass:

• Request high-resolution CT (HRCT) with thin sections
• Use bone window settings for optimal visualization of bony details
• IV contrast is usually not beneficial for initial evaluation due to the surrounding dense bone 1, 3
• However, IV contrast may be added if there's concern for extraosseous soft tissue extension associated with invasive neoplasms 1

When to Consider Additional or Alternative Imaging

1. If vascular lesion is suspected:

   • Consider CT angiography (CTA) if there's clinical suspicion of a vascular mass such as a paraganglioma 1
   • CTA can help identify vascular variants or pathology 1

2. If soft tissue characterization is needed:

   • MRI with and without contrast may be added if CT findings are inconclusive 1, 2
   • MRI provides superior soft tissue contrast and can help differentiate between inflammatory changes, cholesteatoma, and tumor 2

Common Pathologies to Consider

The differential diagnosis for a hard, immobile, tender mass behind the ear includes:

• Inflammatory processes (mastoiditis)
• Cholesteatoma (which may appear as a white mass behind an intact tympanic membrane) 4
• Neoplasms (benign or malignant)
• Vascular masses (glomus tumors, high jugular bulb) 5

Pitfalls to Avoid

1. Inadequate technique:

   • Standard head CT provides insufficient detail of temporal bone structures 3
   • Ensure thin-section imaging (submillimeter) is performed

2. Missing extension of disease:

   • CT scan is crucial for documenting extension beyond the mesotympanum 4
   • Evaluate for erosion of surrounding structures carefully

3. Overreliance on a single imaging modality:

   • While CT is first-line, MRI may provide complementary information in complex cases 2
   • Consider both modalities when diagnosis remains uncertain after initial imaging

By following this approach, the clinician can obtain the most appropriate imaging to characterize the mass, determine its extent, and plan for potential surgical intervention while minimizing radiation exposure and unnecessary testing.