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This phenomenon reflects the presence of air trapping in areas where partial airway obstruction is present. These areas are commonly well-demarcated, reflecting the geometry Table 2. Causes of and association with obliterative (constrictive) bronchiolitis Post-infection – Childhood viral infection (adenovirus, respiratory syncytial virus, influenza, parainfluenza) – Adulthood and childhood (Mycoplasma pneumoniae, Pneumocystis carinii in AIDS patients, endobronchial spread of tuberculosis, bacterial bronchiolar infection) Post-inhalation (toxic fumes and gases) – Nitrogen dioxide (silo filler’s disease), sulfur dioxide, ammonia, chlorine, phosgene – Hot gases Gastric aspiration – Diffuse aspiration bronchiolitis (chronic occult aspiration in the elderly, patients with dysphagia) Connective-tissue disorders – Rheumatoid arthritis – Sjögren’s syndrome Allograft recipients – Bone marrow transplant – Heart-lung or lung transplant Drugs – Penicillamine – Lomustine Ulcerative colitis Other conditions – Bronchiectasis – Chronic bronchitis – Cystic fibrosis – Hypersensitivity pneumonitis – Sarcoidosis – Microcarcinoid tumorlets (neuroendocrine cell hyperplasia) – Sauropus androgynus ingestion Idiopathic of individual or joined lobules.

It reflects abnormal bronchiolar wall thickening and dilatation of the bronchiolar lumen, which is filled with mucus or pus, often associated with peribronchiolar inflammation. The branching pattern of dilated bronchioles and peribronchiolar inflammation give the appearance of a budding tree. Some variants have the same diagnostic value. They include clusters of centrilobular nodules linked together by fine linear opacities, or branching tubular or Yshaped opacities without nodules. In every case, the key feature is the centrilobular location of these opacities, at a distance of at least 3 mm from the pleura.

Technical parameters that need to be selected for any scan include: collimation thickness, tube current [milliamperage (mA)], and kilovoltage (kV). 5 mm. 75 mm) increases the radiation dose by approximately 30% with our in-house reduced protocol and is applied only in selected cases of vascular abnormalities, visualization of small structures, and cardiac CT (Table 2). The axial images are reconstructed at 5-mm thickness and archived to the picture archiving and communication system (PACS) system within our hospital.