Interstitial Lung Disease

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Brandon Fainstad, MD – author
Diana Zhong, MD – edits
Cameron Baston, MD – expert review (pulmonologist, University of Pennsylvania)

OBJECTIVES
1. Describe the typical radiographic features (distribution, extent, and characteristics) in common interstitial lung diseases.
2. Utilize a four-step approach to differentiate the common interstitial lung diseases.

** This talk takes ~60 minutes.  Consider breaking it up into two sections: 1. Case stem + terminology and 2. Differentiation of ILDs + case resolution. **

This talk was designed to provide learners with a framework for describing and interpreting imaging findings of ILD within a basic clinical context.  It is by no means a comprehensive approach to ILD, but should be a good place to start.  It  is intended to be delivered directly from the computer monitor or projector.  Due to the reliance on clinical images it is difficult to reproduce on a whiteboard.  Have a learner read the case and describe the chest imaging.  A formal interpretation is given below the images.  Next, review the proposed three-step process for describing lung findings and go through the images and explanations of the key characteristics detailed below.  After the learners are familiar with the terminology outline the four-step approach to narrowing the differential for ILD.  This approach focuses on what is most common, testable and treatable before attempting to tackle the idiopathic interstitial diseases and more rare ILDs. 

CASE
A 77 yo M presents with two months of nonproductive cough and exertional dyspnea. He denies any chest pain, orthopnea or lower extremity edema. He denies URI symptoms, fevers/chills or recent sick contacts. At baseline, he is able to walk several miles without difficulty and now is limited to < 1 city block. His PMH is notable for paroxysmal atrial fibrillation for which he has been on warfarin and amiodarone for several years. He also has an AICD for his history of non-ischemic cardiomyopathy (most recent EF of 40%).

There is diffuse basilar predominant fibrosis and ground glass opacities without honeycombing along with traction bronchectasis seen best on the coronal image in the left base. 

TERMINOLOGY - Follow this three-step approach to describing lung disease

1. Distribution

Apical vs. Basilar predominance
Central vs. Peripheral

2. Extent

Focal vs. Diffuse vs. Isolated
Dense vs. Patchy

3. Characteristics

Gray and hazy area with intact airway and vessel structures 
Non-specific finding that could represent:
1. Atalectasis, including normal exhalation
2. Alveolar filling
3. Interstitial thickening

e.g. Amioderone toxicity
   Case courtesy of A.Prof Frank Gaillard, Radiopaedia.org. From the case rID: 6539

Clustering or stacking of well defined cysts, usually at the bases and periphery
Usually represents irreversible interstitial scaring/fibrosis

e.g. UIP / IPFCase courtesy of Dr Ahmed Abdrabou, Radiopaedia.org. From the case rID: 25270

Abnormal dilation of the airways.
Defined as an airway being larger than it’s accompanying vessel (signet ring) and will have linear and parallel airways (tram tracking) rather than taper towards the periphery.Usually a result of chronic airway inflammation from:
1. Recurrent infection (e.g. necrotizing pneumonia, chronic aspiration, TB, ABPA, immune deficiency, etc.)
2. Poor airway clearance (e.g. cystic fibrosis or ciliary dysfunction)
3. Obstruction from malignancy or foreign body

e.g. “Signet Ring”Case courtesy of A.Prof Frank Gaillard, Radiopaedia.org. From the case rID: 2587

e.g. “Tram Tracking”Case courtesy of Dr Ian Bickle, Radiopaedia.org. From the case rID: 40909

 

e.g. traction bronchiectasis 
Occurs when parenchymal scaring causes loss of lung volumes and “pulls” the airways apartCourtesy of Dr. Brandon Fainstad

Consolidation
An irregularly bordered opacity – either dense or patchy

e.g. Pulmonary infarct – dense pleural-based consolidation with surrounding ground glass opacityCourtesy of Lauren Brown, MD

Nodules
Well-circumscribed density (opposed to consolidation, ill-defined) that is less than 3cm (opposed to a mass, >3cm).

e.g. Pulmonary metastasesCourtesy of Lauren Brown, MD

Hilar Lymphadenopathy
Hilar “fullness” is often due to enlarged pulmonary arteries or lymphadenopathy.  This case is distinctly lymphadenopathy based on the bulbous appearance that does not taper peripherally as a vessel would.


e.g. SarcoidosisCourtesy of Lauren Brown, MD

Perilymphatic
Lymphatic and hematogenous spread of disease.  Small opacities located in the subpleura, fissues, intralobular Septa and often coalesce into a faint gray that can be mistaken as ground glass opacities.

e.g. lymphagitis carcinomatosis

Case courtesy of A.Prof Frank Gaillard, Radiopaedia.org. From the case rID: 8530

Centrilobular
Small opacities along airways that spare the periphery

e.g. pneumoconioses – silicosisCase courtesy of A.Prof Frank Gaillard, Radiopaedia.org. From the case rID: 12515

Extending from the pleura inward
Either a direct extension of the pleura (e.g. mesothelioma) or a hematogenous process that terminated with greatest effect in the periphery (e.g. pulmonary infarct).

e.g. Pulmonary infarct – dense pleural based consolidation with surrounding ground glass opacityCourtesy of Lauren Brown, MD

Margin of unaffected lung along the pleura

In direct contrast to pleural-based opacities, sub-pleural sparing describes an thin area of unaffected parenchyma along the periphery of the involved lobe.  This is a relatively specific, but not sensitive, finding for Non-Specific Interstitial Pneumonia (NSIP) and can help differentiate it from IPF.  

e.g. NSIPCourtesy of Brandon Fainstad, MD

DIFFERENTIATING INTERSTITIAL LUNG DISEASES

Start by ruling out the most common, easily testable and easily treatable conditions.  After that, you are left with idiopathic interstitial pneumonias (IPP) and the very rare conditions.  

1. Is it sarcoidosis?

2. Obtain a good exposure history.

3. Rule out collagen vascular related disease with serologies.

4. If none of the above, it is likely an IPP.  Obtain a biopsy.  If it is acute, consider urgent immunosuppression. 

Approach to Interstitial Lung Diseases

The history of sub-acute and progressive respiratory symptoms in the setting of ongoing amiodarone use and basilar predominant fibrosis without honeycombing is most consistent with amiodarone-associated NSIP.  This was confirmed by biopsy which lacked histology typical of UIP.  The patient stopped taking amiodarone and was treated with a prolonged taper of steroids.  He recovered to his prior baseline with minimal to no residual disease on imaging:

REFERENCES

Weissleder R, Wittenberg J, Harisinghani MG et-al. Primer of diagnostic imaging. Mosby Inc. (2007) ISBN:0323040683.

Schwaiblmair, Martin. “Drug Induced Interstitial Lung Disease.” The Open Respiratory Medicine Journal, vol. 6, no. 1, 2012, pp. 63–74., 

Crystal, RG. Interstitial lung disease. In: Wyngaarden, JB, Smith, LH, Jr, Bennett, JC, (Eds), Cecil Textbook of Medicine, 19th ed, WB Saunders Co, Philadelphia, 1992