Corona Virus: Surviving COMES With a Price?

Editor’s Note:

I have to say that when I first started hearing about and thinking about the coronavirus, I pretty much categorized that into what I was most familiar with – which was the swine flu (H1N1). That particular epidemic I have pretty significant familiarity with, probably 250 to 300 hours of ECMO on swine flu patients, none of which survived.

I don’t take losing any patient lightly- ever.  It’s easier to talk about things like this when they are 10 years prior- taking into consideration that time and distance lends it’s own sense of emotional and rational composure.  You don’t ever forget it- you just put it in perspective of your entire body of work- that dampens the shock- but never eliminates your emotional investment at the time you were committed to it.

Please don’t judge or second guess the following comment-

“The fact that they didn’t survive wasn’t really that scary, obviously it was horrible from a human compassion point of view, but I’m pretty sure that you understand how we compartmentalize in order to cope with situations that most people never encounter or have to.”

 I didn’t like what I saw- but I dealt with it from a clinical point of view.  The personal debriefing and coming to terms with it all- is something we each do on different terms- at different levels.

Doing what we do is NOT an emotionless process- on the contrary, it speaks to our expected level of professional composure to rise to the level where we do NOT succumb to that sort of second guessing- or a level of synergy that leads to clouding our natural professional composure and subverting our clinical instincts.  We have hearts obviously- and we DO hearts- clinically- I hope that makes sense?

I’m not exactly sure if in 2011 I was clueless, reckless, or just lucky. I am 100% certain that at some point i was significantly exposed to this virus. I watched it lock on to a 25-year-old, a completely buffed, very muscular young man- and IT totally took him down to the carpet. He died after 10 days.

I think it was dealing with that situation, watching this young man die- a man  who was clearly in his physical prime, that made me realize that there is no way to predict how any individual will react or succumb to a virus of this type. Having been exposed to it and not getting sick didn’t make me feel invulnerable, but it made me realize that it was totally luck of the draw. I’m not sure if it was my immune system- developed over 40+ years working in medicine, or the fact that I had traveled this country and the world so extensively that I was exposed to diseases and viruses, subsequently building up antibodies to a lot of things out there that I didn’t even realize I was exposed to.

So this brings me to the second part of this dialogue, which is in my mind much more disturbing, in that I just listened to an epidemiologist on TV breaking down the 80/20 numbers that we have been given in terms of the 80% that get infected but will barely feel it, versus the 20% that are clearly in the high risk category – that ultimately do or experience a negative impact from the coronavirus.

I was okay with the 80/20 number until it was broken down a little further, and I recalled reading a recent article I had read about an Italian cardiovascular surgeon, that kept frantically repeating the fact that every diagnosis he had seen was ultimately the same: bilateral interstitial pneumonia.  It was panic filled and cryptic- something I DON’T expect from a CV surgeon.

THAT gave me pause, and I researched bilateral interstitial pneumonia, and what I was reading about was kind of scary. So I put that on the back burner for little bit.

But that back burner came back to light when the second part of this reared it’s head- with an epidemiologist on TV.

The second part of this message was that of the 80% that were claimed to be pretty much unaffected, 50% of them (in other words – 40% of infected patients), 50% of these “survivors” would end up suffering some sort of lung scarring with longer-term implications.

This was not the case with H1N1.  Or at least- it presented like that as far as I recall.

So I did a copy and paste of a couple of articles on the topic of bilateral interstitial pneumonia, not necessarily to frighten anybody, or really educate anyone – because no one really knows what we’re dealing with here.  This is primarily a message to all of us…

To not be complacent.

To not take the position that yes, I was exposed and I got over it, and it’s all good.

If you are in the 80 percentile group of being relatively young, and sporting a good immune system, that doesn’t relieve you of the risk that there may be unanticipated long-term pulmonary consequences that none of us realize yet.

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So basically this is a heads up. That’s all it is.

Just be careful out there okay?

Peace 🙂

Frank

Food for Thought: Social Media…

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The Bottom Line

I put this chart on the front end of this article as opposed to the back end of all the information below.  There is a lot of information further down that may be hard to process on the first reading.

BUT what isn’t hard to process are the two columns on the far right of this chart:

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Prognosis & Response to Rx.

What Is Interstitial Lung Disease?

Interstitial lung disease (ILD) is a group of many lung conditions. All interstitial lung diseases affect the interstitium, a part of your lungs. The interstitium is a lace-like network of tissue that goes throughout both lungs. It supports your lungs’ tiny air sacs, called alveoli. Normally, the interstitium is so thin that it doesn’t show up on X-rays or CT scans. Types of Interstitial Lung Disease All forms of interstitial lung disease cause the interstitium to thicken. This can happen from inflammation, scarring, or a buildup of fluid. Some forms of ILD last a short time (acute); others are long-term (chronic) and don’t go away.

Some types of interstitial lung disease include: Interstitial pneumonia . Bacteria, viruses, or fungi can infect the interstitium. A bacteria called Mycoplasma pneumoniae is the most common cause. Idiopathic pulmonary fibrosis . This makes scar tissue grow in the interstitium. Experts don’t know what causes it.

Nonspecific interstitial pneumonitis. This is an interstitial lung disease that often affects people with autoimmune conditions such as rheumatoid arthritis or scleroderma. Hypersensitivity pneumonitis . This happens when dust, mold, or other things that you breathe irritate your lungs over a long time.

Cryptogenic organizing pneumonia (COP). COP is a pneumonia-like interstitial lung disease without an infection. You might hear your doctor call this bronchiolitis obliterans with organizing pneumonia (BOOP).

Acute interstitial pneumonitis. This is a sudden, severe interstitial lung disease. People who have it often need to be connected to a machine called a ventilator that breathes for them. Desquamative interstitial pneumonitis. This is an interstitial lung disease that partly results from smoking.

Sarcoidosis . This causes interstitial lung disease along with swollen lymph nodes. It can also affect your heart, skin, nerves, and eyes. Asbestosis. This is an interstitial lung disease caused by breathing asbestos, a fiber used in building materials. Interstitial Lung Disease Symptoms

The most common symptom of all forms of interstitial lung disease is shortness of breath. Almost everyone with ILD will have breathlessness, which can get worse over time. Other symptoms of interstitial lung disease include: Cough, which is usually dry and doesn’t bring up mucus. Weight loss, most often in people with COP or BOOP. With most forms of ILD, shortness of breath develops slowly (over months). If you have interstitial pneumonia or acute interstitial pneumonitis, your symptoms will come on quickly (in hours or days).

THE Mayo Clinic:

Click on Image Above to View Source Article

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Introduction

The diagnostic approach to idiopathic interstitial pneumonias (IIPs) has long been confusing because these disorders were categorized according to different clinical, radiologic, and histologic classifications (^,1,^,2).

In 2001, the American Thoracic Society (ATS) and European Respiratory Society (ERS) standardized the terminology for IIPs (^,Fig 1) (^,3). This new ATS-ERS classification is the result of a multidisciplinary consensus and includes seven disease entities: idiopathic pulmonary fibrosis (IPF), nonspecific interstitial pneumonia (NSIP), cryptogenic organizing pneumonia (COP), respiratory bronchiolitis–associated interstitial lung disease (RB-ILD), desquamative interstitial pneumonia (DIP), lymphoid interstitial pneumonia (LIP), and acute interstitial pneumonia (AIP).

In their idiopathic form, IIPs are rare diseases. However, more frequent disorders such as sarcoidosis, vasculitis, and connective tissue diseases can display identical morphologic patterns, and the IIPs are considered “prototypes” for these morphologic alterations (^,3). Because imaging plays a crucial role in identifying both the idiopathic and the secondary interstitial pneumonias, radiologists need to be familiar with the morphologic and clinical manifestations and the diagnostic approach to these conditions.

The main clinical symptoms of IIPs are non-specific and consist of cough and dyspnea; however, other factors such as age, gender, risk factors, and course of disease can be helpful in distinguishing between the various entities (^,Table 1).

The classification of IIPs is based on histologic criteria, but each histologic pattern is associated with a characteristic computed tomography (CT) pattern that, provided an adequate CT technique is used, correlates well with histologic findings (^,Table 2) (^,3).

The key role that radiologists play in the work-up of IIPs necessitates a thorough knowledge of the patterns as described in the international classification and an increased awareness of the multidisciplinary challenges involved in their interpretation.

In this article, we illustrate the morphologic characteristics of the patterns included in the ATS-ERS classification of IIPs and present an encyclopedic review of the clinical and radiologic hallmarks associated with these patterns.

Idiopathic Pulmonary Fibrosis

IPF is the most common entity of the IIPs. By definition, IPF is the term for the clinical syndrome associated with the morphologic pattern of UIP (^,3). With a median survival time ranging from 2 to 4 years, IPF has a substantially poorer prognosis than NSIP, COP, RB-ILD, DIP, and LIP (^,3,^,4).

Clinical Features

The typical patient with IPF is 50 years old or older. Patients present with progressively worsening dyspnea and nonproductive cough (^,3). Many patients also report that the subtle onset of their symptoms months or even years earlier was mistaken for a less serious respiratory disease, which delayed referral to a specialized center (^,5). Although there are slightly more cases in men than in women, there is no obvious gender predilection (^,3). A history of cigarette smoking seems to be a risk factor for the development of IPF; however, it does not appear to affect the course of the disease (^,4,^,6,^,7). Usually, patients do not respond to high-dose corticosteroid therapy; data suggest that, due to the considerable side effects of corticosteroids, this therapy might even be contraindicated (^,8). However, a combination therapy of cyclosporin A and corticosteroids seems to be efficacious for acute exacerbations of IPF (^,9). In addition, patients should be considered candidates for lung transplantation early after diagnosis (^,10).

Histologic Features

The histologic hallmark of UIP is the presence of scattered fibroblastic foci (^,Fig 2^,). Typically, the lung involvement is heterogeneous and areas of normal lung alternate with interstitial inflammation and honeycombing (^,1). Owing to the patchy lung involvement, histologic evaluation of multiple biopsy specimens from one patient may reveal discordant histologic patterns. Evidence of the UIP pattern in one biopsy specimen is associated with a worse prognosis, independently of other coexisting patterns (^,11,^,12). Therefore, biopsy samples from more than one lobe should be obtained in any patient with suspected IIP, and high-resolution CT should serve as a guiding tool for determining the appropriate anatomic location of the biopsy site (^,12,^,13).

Imaging Features

The chest radiograph is normal in most patients with early disease. In advanced disease, the chest radiograph shows decreased lung volumes and subpleural reticular opacities that increase from the apex to the bases of the lungs (^,14).

This apicobasal gradient is even better seen on high-resolution CT images. Together with subpleural reticular opacities and macrocystic honeycombing combined with traction bronchiectasis, the apicobasal gradient represents a trio of signs that is highly suggestive of UIP (^,Fig 3^,,) (^,15,^,16). Therefore, UIP should be considered in patients who present with low lung volumes, subpleural reticular opacities, macrocystic honeycombing, and traction bronchiectasis, the extent of which increases from the apex to the bases of the lungs (^,Fig 4^,). In the typical patient with UIP, the disease is most extensive on the most basal section of the high-resolution CT examination. Ground-glass opacities are present in the majority of patients with UIP but are usually limited in extent (^,17). Typically, imaging findings are heterogeneous, with areas of fibrosis alternating with areas of normal lung (^,Fig 5^,).

In patients who show the characteristic distribution and high-resolution CT pattern of UIP and the appropriate clinical features, the diagnosis can be reliably made without biopsy (^,18,^,19). The ATS-ERS has defined eight major and minor criteria for the diagnosis of IPF in the absence of a surgical lung biopsy, which are summarized in ^,Table 3. However, histologic confirmation should be obtained in all patients with atypical imaging findings, such as extensive ground-glass opacities, nodules, consolidation, or a predominantly peribronchovascular distribution (^,3,^,20).

Nonspecific Interstitial Pneumonia

NSIP is less common than UIP but is still one of the most common histologic findings in patients with IIPs (^,21). NSIP is associated with a variety of imaging and histologic findings, and the diagnostic approach is highly challenging. However, the distinction of NSIP from UIP is more than academic, given the better response to corticosteroids seen in a subgroup of patients with NSIP (^,22,^,23).

Owing to the clinical, radiologic, and pathologic variability of NSIP, the term should be considered a provisional diagnosis until further characterization of this entity has been established (^,3).

Clinical Features

The typical patient with NSIP is between 40 and 50 years old and is usually about a decade younger than the patient with IPF. Symptoms of NSIP are similar to those of IPF but usually milder (^,24). Patients present with gradually worsening dyspnea over several months, and they often experience fatigue and weight loss. There is no gender predilection, and cigarette smoking is not an obvious risk factor in the development of NSIP. Treatment of patients with NSIP is based on the use of systemic corticosteroids in combination with cytotoxic drugs, such as cyclophosphamide and cyclosporin, and the majority of patients stabilize or improve with this therapy (^,25).

Although it is primarily defined as an idiopathic disease, the morphologic pattern of NSIP is encountered in association with frequent disorders, such as connective tissue diseases, hypersensitivity pneumonitis, or drug exposure (^,26,^,27). Once the morphologic pattern of NSIP has been determined in a patient, these secondary forms of NSIP must be ruled out by the clinician.

Histologic Features

The histologic pattern of NSIP is characterized by temporally and spatially homogeneous lung involvement (^,28). This homogeneity is a key feature in differentiating the NSIP pattern from the UIP pattern. On the basis of the varying proportions of inflammation and fibrosis, NSIP is divided into cellular and fibrosing subtypes (^,Fig 6^,) (^,1). In cellular NSIP, the thickening of alveolar septa is primarily caused by inflammatory cells; in fibrosing NSIP, interstitial fibrosis is seen in addition to mild inflammation. Cellular NSIP is less common than fibrosing NSIP but shows a better response to corticosteroids and carries a substantially better prognosis (^,21). Histologic distinction between fibrotic NSIP and UIP is difficult and is subject to substantial interobserver variation (^,20). In borderline cases, CT correlation may help by showing features more typical of either UIP or NSIP.

Imaging Features

In patients with early NSIP, the chest radiograph is normal. In advanced disease, bilateral pulmonary infiltrates are the most salient abnormality. The lower lung lobes are more frequently involved, but an obvious apicobasal gradient, as seen in UIP, is usually missing (^,3).

High-resolution CT typically reveals a subpleural and rather symmetric distribution of lung abnormalities (^,Fig 7^,,). The most common manifestation consists of patchy ground-glass opacities combined with irregular linear or reticular opacities and scattered micronodules (^,Fig 8^,) (^,29–^,31). In advanced disease, traction bronchiectasis and consolidation can be seen; however, ground-glass opacities remain the most obvious high-resolution CT feature in the typical patient with NSIP and are related to the histologic finding of homogeneous interstitial inflammation (^,29,^,30).

Other findings in advanced NSIP include subpleural cysts, but compared to those of UIP, these cysts are smaller and limited in extent (^,Fig 9^,) (^,29). The term “microcystic honeycombing” is used for these cystic changes in NSIP, as opposed to the macrocystic honeycombing seen in UIP (^,32,^,33). Although the CT features of cellular and fibrotic NSIP overlap considerably, it has been shown that honeycombing is seen almost exclusively in patients with fibrotic NSIP (^,17,^,29). Other CT findings that have been correlated with increased likelihood of fibrosis in NSIP are the extent of traction bronchiectasis and intralobular reticular opacities (^,29).

Owing to the substantial overlap of high-resolution CT patterns, the major CT differential diagnosis for NSIP is UIP. The key CT features that favor the diagnosis of NSIP over UIP are homogeneous lung involvement without an obvious apicobasal gradient, extensive ground-glass abnormalities, a finer reticular pattern, and micronodules (^,Figs 10, ^,11^,) (^,17,^,20,^,34). Follow-up CT also demonstrates differences between patients with NSIP and those with UIP. In patients with NSIP, ground-glass opacities usually do not progress to areas of honeycombing, even if there is associated bronchiectasis (^,30). However, in patients with UIP, progression of ground-glass attenuation to honeycombing is common and indicates irreversible fibrosis (^,35).

Despite differences in distribution and CT pattern, the differential diagnosis between UIP and NSIP remains challenging, and surgical lung biopsy is required in all patients who do not present with the typical clinical and CT features of UIP.

Cryptogenic Organizing Pneumonia

COP is an IIP with characteristic clinical and radiologic features. The histologic pattern of COP is organizing pneumonia, formerly referred to as bronchiolitis obliterans organizing pneumonia (BOOP). The term BOOP has been omitted to avoid confusion with airway diseases such as constrictive bronchiolitis (^,3).

Clinical Features

The typical patient with COP has a mean age of 55 years. Women and men are equally affected and present with mild dyspnea, cough, and fever that have been developing over a few weeks (^,36). Patients typically report a respiratory tract infection preceding their symptoms, and antibiotics were commonly prescribed at a previous consultation (^,37). There is no association with cigarette smoking; in fact, most patients are nonsmokers or ex-smokers (^,3). The majority of patients recover completely after administration of corticosteroids, but relapses occur frequently within 3 months after corticosteroid therapy is reduced or stopped (^,38). As with the other interstitial pneumonias, the pattern of organizing pneumonia may occur in a wide variety of entities, notably in collagen vascular diseases and in infectious and drug-induced lung diseases (^,26,^,27). Therefore, the final diagnosis of COP should be rendered only after exclusion of any other possible cause of organizing pneumonia.

Histologic Features

The histologic hallmark of organizing pneumonia is the presence of granulation tissue polyps in the alveolar ducts and alveoli (^,Fig 12) (^,39). These fibroblast proliferations result from organization of inflammatory intraalveolar exudates (^,36). Typically, there is patchy lung involvement with preservation of lung architecture. The granulation tissue is all the same age and contains few inflammatory cells.

Imaging Features

The chest radiograph in patients with COP usually shows unilateral or bilateral patchy consolidations that resemble pneumonic infiltrates (^,40). However, the consolidations in COP do not represent an active pneumonia but result from intraalveolar fibroblast proliferations, which may be associated with prior respiratory infection. Some patients present with nodular opacities on the chest radiograph. Lung volumes are preserved in most patients.

Frequently, the CT findings are far more extensive than expected from a review of the plain chest radiograph. The lung abnormalities show a characteristic peripheral or peribronchial distribution, and the lower lung lobes are more frequently involved (^,Figs 13^,,, ^,14^,) (^,41). In some cases, the outermost subpleural area is spared (^,Fig 15) (^,42). Typically, the appearance of the lung opacities varies from ground glass to consolidation; in the latter, air bronchograms and mild cylindrical bronchial dilatation are a common finding (^,41). These opacities have a tendency to migrate, changing location and size, even without treatment (^,42). They are of variable size, ranging from a few centimeters to an entire lobe.

In the appropriate clinical context, that is, consolidation that increases over several weeks despite antibiotics, the CT features of COP are often suggestive. However, apart from the typical imaging pattern of COP, other less specific imaging patterns can be encountered. These atypical imaging findings include irregular linear opacities, solitary focal lesions that resemble lung cancer, or multiple nodules that may cavitate (^,Fig 16^,) (^,43–^,45). In either case, the diagnosis should be confirmed with surgical lung biopsy. The role of transbronchial lung biopsy for diagnosis of COP is currently under evaluation (^,3).

Respiratory Bronchiolitis–associated Interstitial Lung Disease

RB-ILD is a smoking-related interstitial lung disease and is thought to represent an exaggerated and symptomatic form of the histologically common and incidental finding of respiratory bronchiolitis. Because of the significant overlap in clinical, imaging, and histologic features between RB-ILD and DIP, these entities are considered a pathomorphologic continuum, representing different degrees of severity of the same disease process (^,46,^,47).

Clinical Features

Patients with RB-ILD are usually 30–40 years old and have an average smoking history of 30 pack-years (^,47). Men are affected nearly twice as often as women and present with mild dyspnea and cough. Smoking cessation is the most important component in the therapeutic management of RB-ILD. However, the majority of patients also receive corticosteroid therapy (^,48).

Histologic Features

The histopathologic hallmark of RB-ILD is the intraluminal accumulation of pigmented macrophages centered around the respiratory bronchioles (^,Fig 17) (^,49). Mild peribronchiolar inflammation and fibrosis are usually present. Findings in patients with RB-ILD cannot be differentiated histologically from those seen in asymptomatic patients with respiratory bronchiolitis.

Imaging Features

The chest radiograph is insensitive for detection of RB-ILD and is often normal. Sometimes, bronchial wall thickening or reticular opacities can be seen (^,3,^,50).

The distribution at high-resolution CT is mostly diffuse (^,Fig 18^,,) (^,46). The key high-resolution CT features of RB-ILD are centrilobular nodules in combination with ground-glass opacities and bronchial wall thickening (^,Fig 19) (^,47). The ground-glass opacities have been shown to correlate with macrophage accumulation in alveolar ducts and alveolar spaces (^,51). The centrilobular nodules are presumably caused by the peribronchial distribution of the intraluminal infiltrates (^,52). Coexisting moderate centrilobular emphysema is common, given that most patients have a smoking history.

Desquamative Interstitial Pneumonia

DIP is strongly associated with cigarette smoking and is considered to represent the end of a spectrum of RB-ILD. However, DIP also occurs in nonsmokers and has been related to a variety of conditions, including lung infections and exposure to organic dust (^,53,^,54).

Clinical Features

For the majority of patients with DIP, the onset of symptoms is between 30 and 40 years of age. Men are affected about twice as often as women, and most patients are current or past smokers (average smoking history of 18 pack-years) (^,47).

With smoking cessation and corticosteroid therapy, the prognosis is good. Nevertheless, progressive disease with eventual death can occur, notably in patients with continued cigarette smoking (^,48).

Histologic Features

The major histopathologic feature of DIP is the accumulation of pigmented macrophages and a few desquamated alveolar epithelial cells in the alveoli (^,Fig 20). As opposed to the bronchiolocentric distribution in RB-ILD, lung involvement in DIP is more diffuse and uniform (^,55). Usually, there is mild fibrosis in the interstitium. The more common DIP-like lung alterations seen in patients secondary to exposure to organic dust or in association with other IIPs, such as UIP, cannot be differentiated histologically from idiopathic DIP (^,56).

Imaging Features

Chest radiographs of DIP are nonspecific and may reveal hazy opacities (^,57).

At high-resolution CT, DIP is characterized by diffuse ground-glass opacities, which correlate histologically with the spatially homogeneous intraalveolar accumulation of macrophages and thickening of alveolar septa (^,Fig 21^,,) (^,58). Usually, there is a peripheral and lower lung lobe predominance (^,Fig 22) (^,59). Other frequent CT findings include spatially limited irregular linear opacities and small cystic spaces, which are indicative of fibrotic changes (^,Fig 23) (^,3).

Despite differences in the CT appearance of RB-ILD and DIP, imaging findings may overlap and may be indistinguishable from each other. To improve diagnostic accuracy, lung biopsy is required in all cases of suspected RB-ILD or DIP (^,3).

Lymphoid Interstitial Pneumonia

As an idiopathic disease, LIP is exceedingly rare. It is far more common as a secondary disease in association with systemic disorders, most notably Sjögren syndrome, human immunodeficiency virus infection, and variable immunodeficiency syndromes (^,60).

Clinical Features

LIP is more common in women than in men, and patients are usually in their fifth decade of life at presentation. They present with slowly progressive dyspnea and cough over a period of 3 or more years (^,3). Occasionally, patients report systemic symptoms, such as fever, night sweats, and weight loss. In the past, LIP was considered a pulmonary lymphoproliferative disorder, with subsequent progression to malignant lymphoma (^,61). However, many of these cases were reclassified as lymphoma from the outset, and only a small number of definite LIP cases seem to actually undergo malignant transformation (^,62). Corticosteroids are used in the therapy of LIP, but response is unpredictable and no controlled randomized treatment trials have been reported to date (^,60).

Histologic Features

The LIP pattern is characterized by diffuse infiltration of the interstitium by lymphocytes, plasma cells, and histiocytes (^,Fig 24) (^,3). Reactive lymphoid follicles are often present and distributed along the peribronchiolar regions, which are highly inflamed. Although the predominant changes are interstitial, the airspaces display secondary changes, which range from compression by the interstitial infiltrates to proteinaceous fluid and macrophage collections (^,60).

Imaging Features

The chest radiograph in patients with LIP reveals nonspecific findings, such as bilateral reticular, reticulonodular, or alveolar opacities.

High-resolution CT is the radiologic procedure of choice and shows bilateral abnormalities that are diffuse or have a lower lung predominance. The dominant high-resolution CT feature in patients with LIP is ground-glass attenuation, which is related to the histologic evidence of diffuse interstitial inflammation (^,Fig 25^,,) (^,63). Another frequent finding is thin-walled perivascular cysts (^,Fig 26^,) (^,64). In contrast to the subpleural, lower lung cystic changes in UIP, the cysts of LIP are usually within the lung parenchyma throughout the mid lung zones and presumably result from air trapping due to peribronchiolar cellular infiltration (^,64). In combination with ground-glass opacities, these cysts are highly suggestive of LIP. Occasionally, centrilobular nodules and septal thickening are seen (^,63).

Acute Interstitial Pneumonia

AIP is the only entity among the IIPs with acute onset of symptoms. In most cases of AIP, the clinical and imaging criteria for acute respiratory distress syndrome are fulfilled.

Clinical Features

Patients who present with AIP have a mean age of 50 years (^,3). Most patients develop severe dyspnea with a need for mechanical ventilation within less than 3 weeks (^,3). Typically, a history of viral-like illness exists. Men and women are equally affected, and cigarette smoking does not seem to increase the risk for development of AIP. Treatment is largely supportive and consists of oxygen supplementation. Corticosteroids seem to be effective in the early phase of disease (^,65). Nevertheless, the prognosis remains poor, with a mortality rate of 50% or more (^,3). Although recurrences of AIP have been described, most patients who survive the acute phase of the disease later progress to lung fibrosis (^,66,^,67).

Histologic Features

The histologic pattern of AIP includes diffuse alveolar damage, which can be categorized into an early exudative phase and a chronic organizing phase, depending on the timing of the biopsy in relation to the lung insult (^,68). The exudative phase is characterized by interstitial and intraalveolar edema, formation of hyaline membranes, and diffuse alveolar infiltration by inflammatory cells (^,Fig 27). The organizing phase usually begins at the end of the first week after lung injury and is characterized by formation of granulation tissue, which results in alveolar wall thickening. As opposed to the heterogeneous appearance of UIP, fibrotic changes in AIP are uniform and characterized by numerous fibroblasts but relatively little collagen deposition (^,69).

Histopathologic investigation is necessary for a definitive diagnosis of AIP. However, considering the fact that patients with AIP are often too ill to tolerate surgical lung biopsy, transbronchial biopsy seems to be sufficient (^,65).

Imaging Features

The radiographic and high-resolution CT features of AIP are similar to those of acute respiratory distress syndrome; however, patients with AIP are more likely to have a symmetric, bilateral distribution with a lower lobe predominance (^,Fig 28^,,) (^,70). The costophrenic angles are often spared. In the early phase of AIP, ground-glass opacities are the dominant CT pattern and reflect the presence of alveolar septal edema and hyaline membranes (^,Fig 29) (^,69). Areas of consolidation are also present but are usually less extensive and limited to the dependent area of the lung (^,71). In the early phase, airspace consolidation results from intraalveolar edema and hemorrhage.

However, consolidations are also present in the fibrotic phase and then result from intraalveolar fibrosis (^,72). In the late phase of AIP, architectural distortion, traction bronchiectasis, and honeycombing are the most striking CT features and are more severe in the nondependent areas of the lung (^,Fig 30) (^,72,^,73). This can be explained by the “protective” effect of atelectasis and consolidation on the dependent areas of the lung during the acute phase of disease, which attenuate the potential damage associated with mechanical ventilation (^,73).

Conclusions

The ATS-ERS consensus statement of 2002 details the diagnostic approach to the IIPs. ^,Table 4 summarizes 10 teaching points from this consensus statement that radiologists should be aware of when dealing with these conditions. IIPs are associated with typical morphologic patterns. The CT appearances of UIP and COP may be diagnostic in the appropriate clinical context. However, there is substantial overlap in the CT appearances of the other IIPs. Therefore, accurate diagnosis of these disorders requires a dynamic interdisciplinary approach that correlates clinical, radiologic, and pathologic features.