<unk>  seen on CT scan. Honeycomb fibrosis is seen at the bases of both lungs.<unk>  may be diagnosed by a radiologist using computed tomography (CT) scan of the chest, or by a pathologist using tissue obtained by a lung biopsy. Radiology Radiologically, the main feature required for a confident diagnosis of<unk>  is honeycomb change in the periphery and the lower portions (bases) of the lungs. On high-resolution computed tomography (HRCT), the following categories, depending on imaging findings, have been recommended by a collaborative effort by the American Thoracic Society, European Respiratory Society, Japanese Respiratory Society, and the Latin American Thoracic Society: *UIP pattern: :*Honeycombing, with or without peripheral traction bronchiectasis; or bronchiolectasis (dilatation of the terminal bronchioles) :*Predominantly subpleural and basal :*Often heterogenous distribution, being occasionally diffuse, and may be asymmetrical There may be superimposed CT features such as mild ground-glass opacity, reticular pattern and pulmonary ossification. *Probable<unk>  pattern: :*Predominantly subpleural and basal :*Often heterogenous distribution :*Reticular pattern with peripheral traction bronchiectasis or bronchiolectasis :*There may be mild ground-glass opacity *Indeterminate for<unk> : :*Predominantly subpleural and basal :*Subtle reticular pattern :*May have mild ground-glass opacity or distortion (“early<unk>  pattern”) *Findings suggestive of another diagnosis, including: :*Other predominant distribution: ::*Peribronchovascular ::*Perilymphatic ::*Upper or mid-lung :*Cysts :*Marked mosaic pattern :*Predominant ground-glass opacity :*Profuse lung micronodules :*Lung nodules, especially centrilobular :*Consolidation :*Pleural plaques (indicating asbestosis) :*Dilated esophagus (indicating connective tissue disease) :*Distal clavicular erosions (indicating rheumatoid arthritis) :*Extensive lymph node enlargement :*Pleural effusion :*Pleural thickening (indicating connective tissue disease/drugs) Histology The histologic hallmarks of<unk> , as seen in lung tissue under a microscope by a pathologist, are interstitial fibrosis in a "patchwork pattern", honeycomb change and fibroblast foci (see images below). Image:UIPlungbiopsy.Appearance of<unk>  <unk>  in a surgical lung biopsy at low magnification. The tissue is stained with hematoxylin (purple dye) and eosin (pink dye) to make it visible. The pink areas in this picture represent lung fibrosis (collagen stains pink). Note the "patchwork" (quilt-like) pattern of the fibrosis. Image:Honeycomb change.Appearance of honeycomb change in a surgical lung biopsy at low magnification. The dilated spaces seen here are filled with mucin. Hematoxylin-eosin stain, low magnification. Image:Fibroblast focus.A fibroblast focus in a surgical lung biopsy of<unk> . Hematoxylin-eosin stain, high magnification. The white space to the left is an airspace. The pale area to the right is a fibroblast focus. It is an area of active fibroblast proliferation within the interstitium of the lung. Differential diagnosis The differential diagnosis includes other types of lung disease that cause similar symptoms and show similar abnormalities on chest radiographs. Some of these diseases cause fibrosis, scarring or honeycomb change. The most common considerations include: *chronic hypersensitivity pneumonitis *non-specific interstitial pneumonia *sarcoidosis *pulmonary Langerhans cell histiocytosis *asbestosis
Usual interstitial pneumonia
Desquamative interstitial pneumonia
Lymphocytic interstitial pneumonia
Granulomatous–lymphocytic interstitial lung disease
Diffuse panbronchiolitis
Non-specific interstitial pneumonia
Cryptogenic organizing pneumonia
Pulmonary hyalinizing granuloma