Radiological staging
Sarcoidosis staging is traditionally performed using chest radiography (modified Scadding classification). Although the initial stages statistically have a more favorable prognosis, the clinical value of this categorization is currently considered questionable.
- Stage I: Isolated enlargement of intrathoracic lymph nodes (lymphadenopathy).
- Stage II: Combination of lymphadenopathy and focal parenchymal opacities in the lungs.
- Stage III: Isolated parenchymal changes (without lymph node enlargement).
- Stage IV: Development of pulmonary fibrosis.
Lymphadenopathy and parenchymal changes on radiography
Lymphadenopathy: A typical presentation is bilateral symmetrical enlargement of the pulmonary hilar and paratracheal lymph nodes. The roots acquire a dense, lobulated, and well-demarcated outline. Asymmetry is observed in only 1–5% of cases, and strictly unilateral involvement is extremely atypical. An interesting feature is node calcification: it can form in an "eggshell fashion" (eggshell fashion) or have a homogeneous character—"icing sugar" (icing sugar). Lymphadenopathy usually resolves within 6–12 months, and relapses are rare.
Parenchymal changes Detected on imaging in 50–70% of patients. An important distinction from lymphoma is that lung lesions appear as lymph nodes decrease. The main pattern (75–90% of cases) is small (2–4 mm) well-defined nodules in the peribronchovascular regions of the middle and upper zones. Less commonly (10–20%), focal consolidation is observed — poorly defined opacity areas that may contain air bronchograms.
Computed tomography (HRCT) findings
HRCT (High-Resolution Computed Tomography, HRCT) is not a primary screening method and is generally ordered for patients with atypical chest radiographs.
Basic HRCT patterns of sarcoidosis:
- Perilymphatic distribution: Well-defined micronodules cluster along the bronchovascular bundles, pleura (including interlobar fissures), and interlobular septa. Irregular, beaded interface boundaries are visualized.
- Galaxy sign (galaxy sign): Multiple micronodules merge into a single large macronodule, surrounded at the periphery by a scatter of smaller satellite lesions.
- Ground-glass opacity pattern (ground glass): In so-called alveolar sarcoidosis, nodules are smaller than the resolution limit of the tomograph. They visually merge, creating the effect of a translucent decrease in aeration.
- Air trapping (air trapping): A frequent sign correlating with small airway involvement.
Fibrotic stage and prognostic evaluation
About a third of parenchymal changes do not resolve but progress to fibrosis. Consolidation and ground-glass areas are usually reversible, whereas reticular patterns and architectural distortion remain permanent.
Classic HRCT signs of fibrosis:
- Coarse linear opacities radiating laterally from the lung hilum.
- Volume loss of the upper lobes, upward displacement of the hila, and displacement of the interlobar fissures (fissural displacement).
- Traction bronchiectasis and honeycombing (honeycombing) in the upper zones.
HRCT is less informative for prognosis, as its results often do not correlate with the clinical presentation. The gold standard for determining inflammatory activity and predicting the deterioration of pulmonary function is 18-FDG PET (18-FDG PET). Clinical and radiological predictors also indicate a high risk of mortality: extent of fibrosis >20% and pulmonary trunk enlargement (ratio to ascending aorta >1), which directly points to pulmonary hypertension.
To memorize the Scadding stages, use the «L-P-F» rule: Stage 1 — Lymph nodes only; Stage 2 — Lymph nodes + Parenchyma; Stage 3 — Parenchyma only; Stage 4 — Fibrosis.
Class and exam questions
In which parts of the lungs are changes in sarcoidosis most pronounced?
Predominant involvement of the middle and upper lobes is characteristic, unlike many other interstitial lung diseases that affect the basal regions.
Is HRCT the first-line method when sarcoidosis is suspected?
No, standard chest radiography is the primary and sufficient method in typical cases. HRCT is ordered to clarify the diagnosis when the radiographic picture is atypical.
Which parenchymal changes in sarcoidosis are considered completely reversible?
Air-space consolidation and ground-glass opacity patterns can usually resolve completely, whereas reticular changes and architectural distortion (bronchiectasis, honeycomb lung) are irreversible.
How to differentiate the dynamics of pulmonary changes in sarcoidosis from lymphoma?
In sarcoidosis, lung parenchymal lesions appear as lymph nodes regress (decrease in size), whereas in lymphoma, lymph node and lung tissue involvement progresses simultaneously.
What else to study on this topic
- Assessment of inflammatory activity in sarcoidosis using 18-FDG PET
- Specifics of the galaxy sign and its morphological basis
- Differential diagnosis of sarcoidosis and chronic berylliosis
- Causes of bilateral upper lobe fibrosis: tuberculosis, ABPA, histoplasmosis
- Complications of the fibrotic stage: pulmonary hypertension, mycetomas, and bullous disease
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