What is the recommended chest Computed Tomography (CT) scan protocol to detect sarcoidosis?

High-Resolution CT (HRCT) Protocol for Detecting Sarcoidosis

For detecting sarcoidosis, a high-resolution computed tomography (HRCT) of the chest is the preferred CT protocol due to its superior ability to characterize both lymph node involvement and parenchymal changes.

Optimal HRCT Protocol for Sarcoidosis Detection

Technical Parameters

• Slice thickness: 1 mm thin sections 1
• Algorithm: High spatial frequency reconstruction algorithm 1
• Viewing windows: Both lung and mediastinal windows must be evaluated 1
• Coverage: Full thoracic scan including all mediastinal compartments

Key Imaging Features to Evaluate

1. Lymph Node Assessment

   • Hilar lymphadenopathy (bilateral is characteristic)
   • Mediastinal lymphadenopathy
   • Maximum Short Axis Diameter (MSAD) >10 mm as cut-off for enlargement 1

2. Parenchymal Evaluation

   • Micronodules (1-4 mm) with perilymphatic distribution (most characteristic finding) 1, 2
   • Macronodules (>5 mm) if present
   • Distribution pattern (typically upper and middle lobe predominance) 1
   • Reticular opacities
   • Fibrotic changes
   • Ground glass opacities
   • Consolidations

Advantages of HRCT Over Conventional Imaging

HRCT is superior to conventional chest radiography for sarcoidosis detection for several important reasons:

• Higher sensitivity for detecting subtle parenchymal lesions 1, 3
• Better characterization of lymph node involvement 1
• Superior assessment of disease activity and staging 1, 4
• Ability to distinguish between active inflammation and irreversible fibrosis 3, 4
• Better correlation with respiratory functional impairment 4

Clinical Correlation and Interpretation

The HRCT findings should be interpreted in the context of:

1. Disease Staging: HRCT findings correlate with Scadding stages 5

   • Stage I: Bilateral hilar lymphadenopathy
   • Stage II: Lymphadenopathy with parenchymal infiltrates
   • Stage III: Parenchymal infiltrates without lymphadenopathy
   • Stage IV: Pulmonary fibrosis

2. Disease Activity Assessment

   • Active inflammation vs. fibrosis can help guide treatment decisions
   • HRCT abnormalities correlate strongly with functional parameters including FEV1, FVC, DLCO, and gas exchange 4

Important Considerations

• While HRCT is highly sensitive, routine CT scanning is not recommended for all cases of suspected sarcoidosis 3
• HRCT is particularly valuable in patients with atypical clinical or radiographic findings 3
• For cardiac sarcoidosis evaluation, cardiac MRI is the preferred first-line imaging modality, with PET-CT as an alternative when MRI is unavailable 5

Pitfalls to Avoid

• Relying solely on chest radiography, which is less sensitive than HRCT 3
• Failing to evaluate both lymph nodes and parenchymal changes
• Not considering atypical manifestations such as masslike opacities, honeycomb-like cysts, miliary opacities, or pleural involvement 2
• Missing complications such as aspergillomas 2

HRCT findings should be correlated with clinical presentation, laboratory findings (including serum calcium, which is strongly recommended for all patients), and when necessary, tissue sampling for definitive diagnosis 5.