What are the CT scan differences between Stage II, Stage III, and Stage IV sarcoidosis?

CT Differences Between Sarcoidosis Stages II, III, and IV

Stage II sarcoidosis shows bilateral hilar lymphadenopathy with parenchymal infiltrates (typically perilymphatic nodules and upper lobe infiltrates), Stage III demonstrates parenchymal infiltrates without hilar adenopathy, and Stage IV reveals irreversible pulmonary fibrosis with architectural distortion, fibrocystic changes, bronchiectasis, and hilar retraction. 1, 2, 3

Stage II CT Characteristics

Lymph Node and Parenchymal Features:

• Bilateral hilar and mediastinal lymphadenopathy remains present, distinguishing it from Stage III 2, 3
• Perilymphatic nodular distribution throughout the lungs, appearing along bronchovascular bundles, interlobular septa, and subpleural regions 4, 5
• Upper lobe or diffuse parenchymal infiltrates with symmetrical distribution 4
• Miliary nodules may be diffusely distributed throughout both lungs 6
• Ground-glass opacities representing active alveolitis 2, 7

Prognostic Implications:

• Radiographic remission occurs in 30-80% of Stage II cases 1
• High-resolution CT (HRCT) is particularly valuable in Stage II to discriminate active inflammation (potentially reversible with treatment) from early fibrosis 2, 7

Stage III CT Characteristics

Parenchymal Dominance Without Adenopathy:

• Parenchymal infiltrates present without bilateral hilar lymphadenopathy—this is the defining distinction from Stage II 2, 3
• Upper lobe predominant infiltrates with irregular densities 4, 3
• Peribronchial thickening and architectural distortion beginning to appear 4
• Ground-glass opacities may still be present, indicating potentially reversible disease 2

Prognostic Implications:

• Only 10-40% chance of radiographic resolution, significantly lower than Stage II 1
• HRCT remains valuable to assess whether infiltrates represent active inflammation versus early irreversible fibrosis 2, 7

Stage IV CT Characteristics

Irreversible Fibrotic Changes:

• Advanced pulmonary fibrosis with no chance of resolution 1, 3
• Fibrocystic disease with honeycombing and cystic changes 1
• Bronchiectasis with traction bronchiectasis from fibrotic retraction 1
• Hilar retraction creating distorted mediastinal contours 1
• Architectural distortion with volume loss, typically in upper lobes 1, 3
• Bullae formation in areas of destroyed lung parenchyma 1

• 20% fibrosis on HRCT correlates with highest mortality risk 1

Associated Complications:

• Up to 70% of Stage IV patients develop precapillary pulmonary hypertension 1
• Mortality exceeds 40% at 5 years in patients with significant fibrosis, abnormal pulmonary function, or pulmonary hypertension 1

Critical Diagnostic Pitfalls

Common Misinterpretation Errors:

• Failing to distinguish Stage II (adenopathy + infiltrates) from Stage III (infiltrates alone) leads to incorrect prognostic counseling, as Stage II has 30-80% remission versus Stage III's 10-40% 1
• Relying solely on chest radiographs rather than CT underestimates disease extent and misses early fibrotic changes 2
• Not using HRCT in Stages II-III to differentiate reversible alveolitis from irreversible fibrosis results in inappropriate treatment decisions 2, 7
• Mistaking Stage IV fibrocystic changes for infection or malignancy without recognizing characteristic upper lobe predominance and hilar retraction 1, 3

When HRCT is Essential:

• Stage II or III disease with atypical clinical presentation requiring discrimination of active inflammation from fibrosis 2, 7
• Assessing treatment response when clinical and pulmonary function changes are equivocal 2
• Evaluating for complications such as aspergilloma in fibrocystic cavities 1