Practical Imaging Interpretation in Patients Suspected of Having Idiopathic Pulmonary Fibrosis

[Audio] Imaging serves a key role in the diagnosis of patients suspected of having idiopathic pulmonary fibrosis (IPF). Accurate pattern classification at thin-section chest CT is a key step in multidisciplinary discussions, guiding the need for surgical lung biopsy and determining available pharmacologic therapies. The recent approval of new treatments for fibrosing lung disease has made it more critical than ever for radiologists to facilitate accurate and early diagnosis of IPF. This document was developed by the Radiology Working Group of the Pulmonary Fibrosis Foundation with the goal of providing a practical guide for radiologists. In this review, the critical imaging patterns of IPF, pitfalls in imaging classifications, confounding imaging findings with other fibrotic lung diseases, and reporting standards for cases of lung fibrosis will be discussed..

ILD. Interstitial lung disease (ILD) comprises numerous distinct diseases with overlapping lung injury patterns on CT scans. This article focuses on key imaging findings for evaluating idiopathic pulmonary fibrosis (IPF), a progressive chronic lung disease of unknown cause. PFT : Restrictive and reduced diffusion capacity.

[Audio] The Pulmonary Fibrosis Foundation has created a network of care centers to ensure excellent management of idiopathic pulmonary fibrosis (IPF) and other fibrotic lung conditions. To stay at the forefront of advancements in the field, the foundation has established working groups. These groups offer insights and perspectives on important topics related to the diagnosis and treatment of pulmonary fibrosis, relying on published data and expert opinions. Specifically, the foundation has formed a Radiology Working Group, which aims to provide a practical guide for the radiologic diagnosis of fibrotic lung disease, incorporating recent evidence-based recommendations..

Chest radiograph. initial screening test wide availability and low radiation exposure. normal radiographs were observed in approximately 10%-15% of ILD patients, alone are insufficient for fully characterizing ILD and guiding diagnosis and management. False-positive interpretations can occur in obese or underinflated patients due to the perceived increase in interstitial markings. to assess patients with pulmonary fibrosis for alternative diagnoses like pneumonia or pneumothorax..

CT. Technical factors used for the thin-section CT scanning protocol are important and can help prevent diagnostic errors when properly set. Excessive edge enhancement can lead to image noise that interferes with interpretation. A moderate edge-enhancing reconstruction algorithm is preferred(Siemens B45f, GE Bone, Philips D or YB, and Toshiba Lung Std Section thickness affects partial volume averaging. A thickness of 1.5 mm or less is recommended to maintain definition of small structures Noncontiguous thin-section CT imaging is no longer necessary due to the availability of multidetector CT, which provides contiguous visualization of the entire lung and improves diagnostic yield..

Review and repeat if necessary Respiratory motion: pulsation or star artifact, particularly in the lingula. thin streaks mimicking reticular abnormality or doubling artifacts mimicking bronchiectasis. Proper patient coaching on inspiratory and expiratory effort.

[Audio] Evaluate small airways disease. Air trapping at expiratory thin-section CT -correlate with obstructive deficits at pulmonary function testing-substantially change the differential diagnosis..

Prone imaging. Detect early or mild interstitial lung disease (ILD) Dependent lung atelectasis, commonly present in supine inspiratory scanning. Omitted if supine imaging does not show any potential subpleural abnormality or fibrosis is convincingly evident on supine imaging alone..

Thin-Section CT Search Pattern. Each of the following should be evaluated: (a) the airways (including the trachea ,main bronchi, and smaller bronchioles) (b) lung parenchyma(generally lobe by lobe) (c) pleura (d) mediastinum (e) upper abdomen (e) musculoskeletal system.

Lung parenchyma. Interstitium and secondary pulmonary nodule. Clinical diseases can present with diverse imaging and histologic patterns, and occasionally, multiple patterns can coexist within the same patient. It is essential to consider both the imaging/histologic pattern and the clinical context when diagnosing and categorizing interstitial lung diseases. UIP pattern + rheumatological condition: CTD-ILD instead of IPF.

Thin-Section CT Finding Reticular opacities Common Clinical Disease Idiopathic pulmonary fibrosis Nonspecific interstitial pneumonia Asbestosis Drug-related fibrosis Fibrotic hypersensitivity pneumonitis Connective tissue disease, interstitial lung disease.

Reticular pattern. The reticular pattern, also known as reticulation, is characterized by a fine network or mesh of overlapping linear lines within the secondary pulmonary lobule. The presence of a reticular pattern indicates interstitial injury and is often associated with fibrotic interstitial lung disease (ILD). This pattern is commonly observed alongside other signs of fibrosis, such as architectural distortion and bronchiectasis..

Architectural Distortion. Any distortion of the normal lung parenchymal anatomy In the setting of ILD, this generally refers to an abnormal appearance of the secondary pulmonary lobule shape or size with evidence of volume loss.

Traction Bronchiectasis and Bronchiolectasis. Traction bronchiectasis and bronchiolectasis both refer to irreversible dilatation of an airway related to surrounding or adjacent lung fibrosis. The dilated airway is often irregular and tortuous. Traction bronchiectasis differs from nontraction bronchiectasis, which is not associated with fibrosis and is usually associated with other signs of airways disease.

Honeycomb Cysts. Subpleural clustered cystic air spaces( 3-5mm). Contiguous and must touch pleural surface. Despite honeycombing being seemingly identifiable at first glance, its accurate identification can pose challenges in clinical practice. However, in the categorization of usual interstitial pneumonia (UIP) patterns, the significance of honeycombing as a required feature most times of idiopathic pulmonary fibrosis (IPF) has been reconsidered within the appropriate clinical context. This revision helps address the reliability concerns associated with the consistent identification of honeycombing in routine clinical practice..

Honeycomb Cysts versus Paraseptal Emphysema. 5 mm or less in diameter Thick walls Usually multilayered a/w reticular abnormality and architectural deformity.

Honeycomb Cysts versus Traction Bronchiectasis and Bronchiolectasis.

Traction bronchiectasis is distinguished from bronchiectasis caused by chronic inflammation and intrinsic airways disease by its association with underlying fibrotic lung abnormalities and the absence of significant airway-related changes like wall thickening or mucoid impaction.

[Audio] Comparison of traction bronchiectasis with bronchiectasis from chronic airway inflammation. (a) Axial CT scan demonstrates traction bronchiectasis in a patient with fibrotic nonspecific interstitial pneumonia. Note the substantial reticular abnormality and architectural distortion adjacent to the irregular dilated airways. (b) Axial CT scan demonstrates cylindrical bronchiectasis in the right lower lobe of a patient with underlying immunodeficiency. In contrast to traction bronchiectasis, this postinflammatory bronchiectasis lacks adjacent fibrosis and"tethering" of the airways. There are also associated findings of bronchial wall thickening and mucoid impaction..

Key Definitions Seen in Patients without IPF. The following features may suggest an alternative diagnosis Ground glass opacity Consolidation Micronodules Mosaic attenuation Air trapping Cysts:.

GGO. Homogeneous areas of increased lung attenuation in which the increased opacity does not obscure the underlying bronchial and vascular structures. Not a feature typical of UIP/IPF but can be seen in the setting of overlapping or superimposed disease..

[Audio] Axial inspiratory CT scan demonstrates mosaic attenuation due to small airways disease in a case of constrictive bronchiolitis. (c) Axial expiratory CT imaging (same patient as b) demonstrates accentuation of the areas of hyperlucency from the adjacent lung, confirming small airways disease as the cause of mosaic attenuation. Air trapping in the setting of ILD is most commonly seen associated with HP, constrictive bronchiolitis, and sarcoidosis..

[Audio] Nevertheless, there is a growing acknowledgment that the presentation of UIP may not be typical, and the diagnostic criteria have been broadened to acknowledge characteristics that allow for the identification of IPF in atypical scenarios..

[Audio] classic pattern and has a predictive value of greater than 90% for histologic UIP.

[Audio] This pattern was previously known as possible UIP pattern. Probable UIP pattern is similar to the typical UIP pattern, except that honeycombing is not present. About 80% of patientswith this pattern have UIP.

[Audio] In this pattern, the CT features are not sufficient for a firm diagnosis of UIP. About 50% of cases with this pattern have UIP.

CT Features Most Consistent with a Non-IPF Diagnosis.

Alternative diagnosis. NSIP Fibrotic Hypersensitivity Pneumonitis Sarcoidosis Idiopathic Pleuroparenchymal Fibroelastosis Acute Exacerbation of UIP Combined Pulmonary Fibrosis and Emphysema Interstitial Pneumonia with Autoimmune Features.

NSIP. Overlapping but visually distinct features: Predominant abnormalities in NSIP: GGO with reticulation Honeycombing can be seen with NSIP but is usually mild and should not be the predominant finding. Lower lung predominance with subpleural sparing Patchier and peribronchovascular distribution of traction bronchiectasis. Gradual progression of fibrosis. Importance of prior imaging: Having access to prior imaging is crucial for properly categorizing patients with NSIP, as the progression of fibrosis can lead to misdiagnosis.

[Audio] Nonspecific interstitial pneumonia. (a) Axial CT scan demonstrates fibrotic nonspecific interstitial pneumonia early in the disease course with lower lung fibrosis and ground-glass opacity with some subpleural sparing. (b) Axial CT scan 10 years later demonstrate substantial progression of the pulmonary fibrosis, which now demonstrates increased reticular abnormality, less ground-glass abnormality, and more traction bronchiectasis. Understanding the evolution of the disease by reviewing the prior imaging is critical in these cases..

Fibrotic Hypersensitivity Pneumonitis. Similarity to Usual Interstitial Pneumonia (UIP): Fibrotic HP can mimic UIP on thin-section CT scans in approximately 50% of cases. Lower Lung Predominance: Fibrotic HP can involve the lower lungs , contrary to the classical notion that it primarily affects the upper lungs. Differentiating HP from UIP: The presence of air trapping (especially lobular air trapping) and centrilobular ground-glass nodules on CT scans should raise suspicion of fibrotic HP rather than UIP..

[Audio] CT pattern most consistent with a nonidiopathic pulmonary fibrosis diagnosis. Coronal CT scan demonstrates pulmonary fibrosis but with substantial upper lung reticular opacities and architectural distortion in addition to ground-glass abnormality and mosaic attenuation. This combination points to chronic hypersensitivity pneumonitis as the likely diagnosis rather than idiopathic pulmonary fibrosis.

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Sarcoidosis. All stages of sarcoidosis typically show a greater involvement of the upper lungs. Fibrosis associated with sarcoidosis tends to have a distribution that is more central or around the bronchovascular structures It radiates outward from the superiorly retracted hila Small airways disease, characterized by air trapping commonly seen with sarcoidosis and not just HP.

[Audio] Advanced fibrotic sarcoidosis. (a–c) Axial inspiratory CT and (d) coronal inspiratory CT images demonstrate mid to upper lung–predominant pulmonary fibrosis with marked architectural distortion, associated lung nodularity, and some mosaic attenuation. Note also the calcified mediastinal lymph nodes. This case would be categorized as most consistent with a nonidiopathic pulmonary fibrosis diagnosis based on these features..

Idiopathic Pleuroparenchymal Fibroelastosis. rare condition characterized by fibrosis and elastosis predominantly affecting the upper lungs. upper lung-predominant fibrosis and significant apical pleural thickening. While IPPFE is generally characterized by a distribution that points away from IPF, it can also be seen in conjunction with a concomitant usual interstitial pneumonia (UIP) pattern. This means that in some cases, the features of IPPFE and UIP may coexist..

Combined Pulmonary Fibrosis and Emphysema. upper lobe–predominant emphysema and lower lobe–predominant pulmonary fibrosis. different clinical, physiologic, and radiologic outcome when compared with patients with either pulmonary fibrosis or emphysema alone,.

Interstitial Pneumonia with Autoimmune Features. can be associated with ILD. In some cases, ILD may present as the initial or sole manifestation of a CTD, without fulfilling the diagnostic criteria for a specific autoimmune disease = the term "interstitial pneumonia with autoimmune features“= ERS (European Respiratory Society) and ATS (American Thoracic Society) task force.

Nonspecific interstitial pneumonia (NSIP): NSIP is characterized by a uniform appearance of ground-glass opacities or reticular patterns. Organizing pneumonia, also known as bronchiolitis obliterans organizing pneumonia (BOOP), presents as patchy areas of consolidation and ground-glass opacities. Lymphoid interstitial pneumonia: Lymphoid interstitial pneumonia (LIP) manifests as diffuse infiltrates and nodules The diagnosis requires integration of clinical, serologic, and morphologic findings ..

Acute Exacerbation of UIP. short prodrome of 1 to 2 months with progressive dyspnea or cough. diffuse alveolar damage and/or organizing pneumonia superimposed on UIP.

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Final Diagnosis of IPF for a Given Thin-Section CT Pattern.

[Audio] When contemplating the need for a biopsy, it is essential to bear in mind that open lung biopsy carries potential risks for the patient. While some patients may require a biopsy to establish a definitive diagnosis with certainty, it may not be suitable due to their individual risk factors. Furthermore, a biopsy may not provide significant benefits unless there are specific treatment alterations that would be influenced by confirming the diagnosis..