Radiographic stages (Scadding staging)
Although the accuracy and clinical utility of this staging system are debated, historically four stages of the disease process are distinguished:
- Stage I: isolated lymphadenopathy.
- Stage II: lymphadenopathy combined with parenchymal opacities.
- Stage III: parenchymal opacities only (without lymph node enlargement).
- Stage IV: development of pulmonary fibrosis.
The lower the disease stage, the better the prognosis, though the diagnosis always requires histological confirmation.
Lymphadenopathy features
In 70–80% of patients, bilateral symmetrical lymphadenopathy is detected at some point. Strictly unilateral involvement is extremely rare.
Hilar lymph nodes can vary from barely perceptible to massive lobulated masses. Paratracheal lymph nodes (especially on the right) and the aortopulmonary window nodes on the left are frequently enlarged.
An interesting feature is lymph node calcification in an eggshell fashion (eggshell fashion) or homogeneous calcification («frosted sugar» appearance). Maximal lymph node enlargement is typically visible on initial radiographs, after which nodes regress over 6–12 months. Relapses are atypical.
Parenchymal changes
Parenchymal opacities appear as lymphadenopathy regresses (in 50–70% of cases on radiographs) and are localized predominantly in the upper and middle zones.
- Nodular pattern (75–90% of cases): rounded or irregular well-defined nodules measuring 2–4 mm.
- Focal consolidation (10–20%): opacities with air bronchograms and ill-defined margins that may break down into small nodules.
In two-thirds of patients, these changes resolve completely. In the remaining third, irreversible fibrotic changes develop: coarse linear opacities, volume loss of the upper lobes, upward displacement of the hila, traction bronchiectasis, and bullae. The fibrotic stage can be complicated by pulmonary hypertension or spontaneous pneumothorax.
HRCT features of sarcoidosis
High-resolution CT (HRCT) is not recommended for initial diagnosis but is indispensable in atypical presentations. The most consistent feature is small (1–5 mm) well-defined or ill-defined nodules with a perilymphatic distribution (along bronchovascular bundles, pleura, and interlobar fissures).
- Galaxy sign (galaxy sign): a macronodule formed by the confluence of smaller lesions, with a scattering of micronodules at the periphery.
- Alveolar sarcoidosis: micronodules coalesce to form areas of ground-glass opacity.
- Air trapping (air trapping): indicates small airway involvement.
- Fibrosis: manifests as honeycombing, linear strands extending from the hilum to the periphery, and traction bronchiectasis in the upper lobes.
Prognosis and activity assessment
HRCT is poorly suited for determining prognosis, as its findings may not correlate with the clinical picture. 18F-FDG PET is used to monitor inflammatory activity and treatment response.
High mortality risk is predicted based on clinical and radiological data: reduced lung function, extent of fibrosis on CT (>20%), and signs of pulmonary hypertension (when the ratio of the pulmonary trunk diameter to the ascending aorta exceeds 1).
Briefly: answers to topical questions
What are the differences between the galaxy sign and alveolar sarcoidosis on HRCT?
The differences between these HRCT patterns lie in the size of the nodules and the nature of their visual confluence.
| Pattern | HRCT description |
|---|---|
| Galaxy sign (galaxy sign) | A cluster of micronodules forming a large opacity (macronodule) with a scattering of smaller nodules at the periphery |
| Alveolar sarcoidosis | Nodules are so small (below the resolution of HRCT) that they coalesce and appear as areas of ground glass |
To memorize Scadding stages, use the "center-to-periphery" logic: initially only lymph nodes react (I), then the process extends to the lung parenchyma (II), after which the nodes "deflate", leaving only the parenchyma (III), which in the worst case scars into fibrosis (IV).
Class and exam questions
This is a specific variant of calcium deposition at the periphery of a uniformly affected lymph node. A similar sign is also found in silicosis and histoplasmosis.
This is a specific variant of calcium deposition at the periphery of a lymph node. A similar sign is also characteristic of silicosis and histoplasmosis.
Which changes in sarcoidosis are reversible and which are not?
Areas of consolidation and ground-glass opacity are usually reversible. Irreversible changes include reticular abnormalities, distortion of lung architecture, and signs of fibrosis (e.g., honeycombing).
Do all patients with suspected sarcoidosis need an HRCT?
No, HRCT is not a primary diagnostic method. It is prescribed for patients with atypical findings on a standard chest radiograph.
What else to study on this topic
- Differential diagnosis of causes of bilateral upper-lobe fibrosis.
- Evaluation of pulmonary hypertension signs on CT (ratio of pulmonary trunk to aortic diameters).
- Use of 18F-FDG PET to detect cardiac sarcoidosis with myocardial uptake suppression.
- Pathogenesis and radiological features of hypersensitivity pneumonitis (as a differential diagnosis).
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