Making a confident diagnosis is a complex task for a specific form of interstitial lung disease and providing appropriate management in an attempt to achieve normalization of the disease can put up an alarming process for the clinicians. A set of diffuse and restrictive lung diseases incorporate with idiopathic interstitial pneumonias, showing inflammation and fibrosis of the interstitium due to parenchymal damage. High-resolution computed tomography (HRCT) has magnified the diagnostic standpoint in stepwise identification and classified various patterns in the evaluation of interstitial lung disease. The aim of our review is to elaborate clinical, radiographic and typical and atypical HRCT findings of idiopathic interstitial pneumonias by correlating with its differential diagnosis. Idiopathic pulmonary fibrosis is the most predominant idiopathic interstitial pneumonias and its diagnosis needs to omit all other well-known causes of interstitial lung diseases. According to the 2011 evidence-based guidelines, usual interstitial pneumonia can be diagnosed by HRCT when all criteria are fulfilled. Non-specific interstitial pneumonia is distinguished by bilateral patchy ground-glass opacities and irregular linear/reticular opacities. Respiratory bronchiolitis associated-interstitial lung disease and desquamative interstitial pneumonia show centrolobular nodules and ground-glass opacities as imaging patterns. Cryptogenic organizing pneumonia consists of patchy peripheral or peribronchial consolidations, while ground-glass opacities with tendency for migration, which is evolving to fibrosis, in acute interstitial pneumonia. Lymphoid interstitial pneumonia and idiopathic pleuro-parenchymal fibroelastosis are classified under rare idiopathic interstitial pneumonias. HRCT images help radiologists in diagnosis and mapping specific patterns of idiopathic interstitial pneumonias. This article reviews the stages of evolution in HRCT features for idiopathic interstitial pneumonias.
According to The American Thoracic Society (ATS) and European Respiratory Society (ERS), ILD is a heterogeneous group of non-neoplastic disorders incidental from damage to the lung parenchyma by inflammation and fibrosis that vanishes the lungs capacity for alveolar gas diffusion [
The ATS/ERS in 2002 publicized classifications of idiopathic interstitial pneumonias (IIPs) [
As for the physicians due to limited symptoms it becomes a nightmare in diagnosing patient with or without ILD. In many diseases, commonly occurring breathlessness and cough are seen in mildly aged and elder patients, mainly taken as COPD or heart failure. As soon as ruling out non-respiratory causes for breathlessness is done, the physicians should see the potential of IDL in mildly aged or elderly patients which shows unexplained chronic dyspnoea on exertion, particularly those who are more breathless than would be expected based on their lung function and other contributory factors such as obesity, or the once with the long duration of cough [
Significant contribution of HRCT in finding and diagnosing of diseases has made the radiologist play an important role in the diagnosis of IIP. According to 2011, ATS/ERS have revised HRCT features for IDL (
According to international guidelines idiopathic pulmonary fibrosis (IPF) is defined asa specific form of chronic, progressive, fibrosing interstitial pneumonia of unfamiliar influence, which limits to the lungs of elderly adults, with the histopathological and/or radiological pattern of UIP [
On a chest X-Ray the image findings can be misdiagnosed in the early stages, lower lobes and costophrenic angles with reticular pattern and bronchiectasis are engaged preponderantly. Honeycombing is the most important picturing feature on HRCT for IPF [
UIP pattern (all) | Possible UIP (all) | Inconsistent with UIP (any) |
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1. Basal and subpleural predomination 2. Reticular patterns with traction bronchiectasis association 3. Honey combing appearance 4. Deficits of features listed as inconsistent with UIP pattern | 1. Reticular pattern with presence or absence 2. Typical gradients (lower lobes & subpleural) 3. Deficits of features listed as inconsistent with UIP pattern | 1. Upper and middle lung predomination 2. Peribronchiovascular predomination 3. Extensive ground glass abnormality 4. Profuse micronodules (bilateral, upper lobes predominance) 5. Separate cysts( multiple, bilateral, off honeycombing areas) 6. Diffuse air trapping(bilateral 3 or more lobes) 7. Parenchymal consolidations |
Criteria for usual interstitial pneumonia on high-resolution computed tomography. UIP: Usual interstitial pneumonia. UIP pattern and Possible UIP: all criteria ought to be fulfilled. Inconsistent with UIP: among 7 any 1 of the criteria ought to be fulfilled.
Idiopathic interstitial pneumonias | High-resolution computed tomography features |
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UIP | Reticular pattern with presence or absence of transaction bronchiectasis, honeycombing appearance, basal and subpleural predomination, in UIP pattern deficits of features listed as inconsistent with UIP. |
NSIP | Bilateral ground glass regions, reticular opacities. |
RB-ILD | Badly defined centrilobular nodules, bronchial wall thickening or centrilobular emphysema. |
DIP | Diffuse ground glass opacities, irregular linear opacities, Microcysts. |
COP | Distinctive peripheral or peribronchial patchy consolidations, Ground-glass opacities with migrating tendency, rarely a mass or nodule that may cavitate the typical appearance of an “atoll sign”. |
AIP | Ground glass attenuation regions with mosaic pattern, independent area with air space consolidation. |
LIP | Perivascular cysts and ground glass opacities, centrilobular and subpleural nodules. |
PPFE | Apical regions with subpleural thickening, small subpleural consolidations. |
Features of idiopathic interstitial pneumonias on high-resolution computed tomography. UIP: Usual interstitial pneumonia; NSIP: Non-specific interstitial pneumonia; RB-ILD: Respiratory bronchiolitis with associated interstitial lung disease; DIP: Desquamative interstitial pneumonia; COP: Cryptogenic organizing pneumonia; AIP: Acute interstitial Pneumonia; LIP: Lymphoid interstitial pneumonia; PPFE: Pleuroparenchymal fibroelastosis.
it should be correlated with histological appearances of IPF. The guidelines for matching histological results are, 1) Histology procedures should not be done for the confirmation of UIP pattern. After exclusion of identifiable causes of ILD, HRCT should be done in diagnosing of IPF, even if surgical lung biopsy is possible, probable or non-classifiable [
NSIP is one of the most common interstitial pneumonias after UIP. Respective studies based on histological features have shown some fact that some cases of interstitial pneumonia do not show resemblance with UIP, DIP or AIP [
With infiltrates preponderantly in lower lobes, showing reticular patterns and bronchiectasis, making image findings of chest X-Ray (CXR) not precise. Some important HRCT features shows [
RB-ILD is known as pathological lesion of RB related with clinical manifestation of interstitial lung disease [
Radiographic findings are comparatively not obvious [
Reference [
Chest X-Ray may show bilateral hazy opacities like interstitial infiltrates, but for detection of DIP this pattern is non-specific. HRCT scans for spotting pathognomonic radiological features of DIP include, 1) Diffuse ground glass opacities 2) Irregular linear opacities. 3) Microcysts (seen in half majority of patients) [
Reference [
Three main patterns are observed in the imaging findings of COP, 1) Typical form (occurrence of multiple alveolar opacities) 2) Focal consolidation associated form (focal COP) 3) Infiltrative form (occurrence of infiltrative opacities). COP is characterized radiographically by multiple bilateral areas of consolidation [
AIP is a form of interstitial pneumonia which is severe and sudden onset with rapid progression. Reference [
Chest X-Ray shows bilateral airspace opacifications with air bronchograms in which costophrenic angles are spared [
Reference [
Diffuse or predominantly lower bilateral abnormalities usually show in HRCT images. In patients with LIP, presence of lymphatic nodes is often seen [
According to recent ATS/ERS revised guidelines, Idiopathic PPFE has been categorized under IIPs classification as rare IIP [
Chest radiographs shows lesser subpleural pulmonary consolidations with apical regions showing aspecific pleural thickening. Such imaging pattern shows similarity with many chronic pulmonary infections such as tuberculosis. Reference [
Knowledge of imaging features of IIP on HRCT images brings help for radiologists in its diagnosis. Furthermore, multidisciplinary approach is needed due to overlapping of imaging features. Particularized IIPs shows specific pattern on HRCT, hence making radiologist more capable in diagnosing ILDs on HRCT. Chronic respiratory conditions presents with similar symptoms in ILD, leading to regular misdiagnosis in their primary care, mostly COPD and heart failure. Among all IIPs, most prevalling is IPF and by excluding all other well-known causes of interstitial lung diseases helps in its diagnosis with presence of reticulations, bronchiectasis and honeycombing. According to 2011 revised guidelines [
Zoheb Gulab Shaikh,Cheng Li,Yiming Li, (2016) Idiopathic Interstitial Pneumonias (IIPs): Review of Clinical, Radiographic and High-Resolution Computed Tomography (HRCT). Advances in Computed Tomography,05,19-29. doi: 10.4236/act.2016.52002