Approach to HRCT interpretation:
- Dominant pattern?
– High attenuation eg ground glass opacity, consolidation
– Low attenuation eg cystic, emphysema
- Nodules in secondary lobules
- Distribution in lung
Reticular pattern (septal thickening)
- Regular: interstitial pul.edema, lymphangitic carcinomatosis
Regular septal thickening in interstitial pul.edema
- Irregular: lymphangitic carcinomatosis, sarcoidosis, silicosis
Focal thickening in lymphangitic carcinomatosis
- Centrilobular nodules: hypersens.pneumonitis, infectious bronchiolitis (eg RSV), adenocarcinoma in situ
Centrilobular nodules in hypersens.pneumonitis
– Tree in bud: nodular branching structure; represents dilated and impacted (mucus or pus-filled) centrilobular bronchioles. Narrows differential to infectious eg TB, ABPA and CF.
Tree in bud pattern in TB
- Perilymphatic nodules (located in subpleural or peribronchovascular locations): lymphangitic carcinomatosis, sarcoidosis, silicosis
Example of sarcoidosis
- Random: miliary TB, metastasis, fungal infection
- Hazy increase in lung opacity without obscuration of underlying vessels (consolidation = obscuration of underlying vessels).
- Zone predominance can help lower the differential diagnosis:
– Upper zone: Respiratory bronchiolitis, PCP
– Lower zone: most of the interstitial lung diseases, drug related pneumonitis etc
- Extensive GGO is known as crazy paving pattern.
GGO in adenocarcinoma in situ.
- basically when your alveoli are filled with pus, cells or fluid.
Eg pneumonia, neoplasm, alveolar edema, hemorrhage
Mosaic attenuation pattern
- Small airway obstruction: bronchiolitis, CF
– Mosaic attenuation pattern is seen when expiratory CT is done in cases of small airway obstruction. it represents air trapping.
– Abnormal areas are the low attenuation areas
- Vascular occlusion: chronic PE
– Also known as mosaic perfusion pattern
– Abnormal areas are the low attenuation areas (areas of oligemia)
- Parenchymal changes – basically represent GGO
Mosaic attenuation pattern in CF
Low attenuation pattern
- Cystic, cavitation
- Traction bronchiectasis
- Bronchiectasis (signet ring sign)
Cystic lung diseases – cysts are radiolucent areas with a wall thickness of less than 4mm (if >4mm are called cavities)
- Langerhans cell histiocytosis
Cysts in Langerhans cell histiocytosis
- Autoimmune eg WG, RA
- Vascular eg septic neoplasm
- Trauma eg pneumotocele
- Youth eg bronchogenic cyst, pulmonary sequestration
- presence of small cystic spaces lined by bronchiolar epithelium with thickened walls composed of dense fibrous tissue
- typical feature of UIP
- areas of low attenuation WITHOUT visible walls, sparing peripheral lungs
- centrilobular: smoking, panlobular: alpha-1 antitrypsin (especially genotype SZ and ZZ), paraseptal
Centrilobular emphysema sparing the periphery lung regions
- Do you see those thick black lines inside the yellow circle)?
- Those are airways being tugged open. The lung surrounding those airways retracts as it scars, and as it retracts, the walls of those airways are pulled toward the scar…this is happening on all sides of the airway, and thus, their diameters increase.
- A lot can cause traction bronchiectasis
- Differential diagnosis: CHADO
CF, hypogammaglobulinemia, alpha 1 antitrypsin, after infection, ciliary dyskinesia, obstruction
- Represents localized bronchial dilatation with bronchial wall thickening.
- Signet rign sign: an axial cut of a dilated bronchus (ring) with its accompanying small artery (signet)
- 4 main types
Cystic and cylindrical bronchiectasis
Upper vs lower
Upper: CASSET P
- Lower: drug induced pneumonitis, asbestosis, interstitial lung diseases
Central vs peripheral
- Central: sarcoidosis, pulmonary edema, PJP (batwing)
- Peripheral: chronic eosinophilic pneumonia, COP, adenocarcinoma in situ, contusion and vasculitis
Peripheral consolidation in chronic eosinophilic pneumonia