Thin-section CT of the secondary pulmonary lobule: anatomy and the image--the 2004 Fleischner lecture

Distinct quantitative computed tomography emphysema patterns are associated with physiology and function in smokers

RATIONALE

Emphysema occurs in distinct pathologic patterns, but little is known about the epidemiologic associations of these patterns. Standard quantitative measures of emphysema from computed tomography (CT) do not distinguish between distinct patterns of parenchymal destruction.

OBJECTIVES

To study the epidemiologic associations of distinct emphysema patterns with measures of lung-related physiology, function, and health care use in smokers.

METHODS

Using a local histogram-based assessment of lung density, we quantified distinct patterns of low attenuation in 9,313 smokers in the COPDGene Study. To determine if such patterns provide novel insights into chronic obstructive pulmonary disease epidemiology, we tested for their association with measures of physiology, function, and health care use.

MEASUREMENTS AND MAIN RESULTS

Compared with percentage of low-attenuation area less than -950 Hounsfield units (%LAA-950), local histogram-based measures of distinct CT low-attenuation patterns are more predictive of measures of lung function, dyspnea, quality of life, and health care use. These patterns are strongly associated with a wide array of measures of respiratory physiology and function, and most of these associations remain highly significant (P < 0.005) after adjusting for %LAA-950. In smokers without evidence of chronic obstructive pulmonary disease, the mild centrilobular disease pattern is associated with lower FEV1 and worse functional status (P < 0.005).

CONCLUSIONS

Measures of distinct CT emphysema patterns provide novel information about the relationship between emphysema and key measures of physiology, physical function, and health care use. Measures of mild emphysema in smokers with preserved lung function can be extracted from CT scans and are significantly associated with functional measures.

Multiple lung parenchymal abnormalities: Don't panic, let's be pragmatic! The 6 question rule - a checklist strategy

Analysis of multiple lung parenchymal abnormalities on HRCT is a real diagnostic challenge. These abnormalities may be due to a disease of the pulmonary interstitial tissue, the bronchial tree, the cardiovascular system or to abnormal alveolar filling with fluid, blood, cells or tumor, several of these etiologies possibly being concomitant. Systematic pathophysiological reasoning, in the form of a logical checklist, guides reflection and covers many of the most frequent diagnoses and potentially treatable emergencies that can be identified by the non-specialist radiologist. This approach also provides a basis for deepening knowledge of each area. The use of the mnemonic FIBROVAKIM (fibrosis-bronchi-vascular-cancer-infection-medication) is easy to apply and summarizes this strategy.

Association of bronchoalveolar lavage yield with chest computed tomography findings and symptoms in immunocompromised patients

INTRODUCTION:

Fiber-optic bronchoscopy (FOB) with bronchoalveolar lavage (BAL) is a common procedure performed in immunocompromised patients with undiagnosed pulmonary pathology. Identifying patients with the highest potential diagnostic yield may help to avoid morbidity in patients unlikely to benefit from the procedure. We sought to determine which patient factors, specifically chest computed tomography (CT) findings, affected diagnostic yield of BAL.

METHODS:

Retrospective chart review of immunocompromised patients who underwent FOB with BAL from 01/01/2010 to 12/31/2011 at an academic medical center was performed. The lung lobe lavaged, characteristics of pulmonary infiltrate on radiograph, patient symptoms, and diagnostic yield were collected. A positive diagnostic yield was defined as a positive microbiological culture, finding on cytopathologic staining, diffuse alveolar hemorrhage, alveolar eosinophilia or a positive immunologic or nucleic acid assay.

RESULTS:

The overall diagnostic yield was 52.6%. Infiltrates that were predominantly reticular or nodular by CT had a lower diagnostic yield than predominantly consolidated, ground-glass, or tree-in-bud infiltrates (36.5% vs. 61.2%, P = 0.0058). The diagnostic yield was significantly improved in patients with both fever and chest symptoms compared to patients without symptoms (61.3% vs. 29.6%, P = 0.0066).

CONCLUSION:

CT findings of reticular and nodular infiltrates portend a worse diagnostic yield from BAL than those that are alveolar in nature. Symptomatic patients are more likely to have diagnostic FOB with BAL than asymptomatic patients.

A practical approach to high-resolution CT of diffuse lung disease

Diffuse lung disease presents a variety of high-resolution CT findings reflecting its complex pathology, and provides diagnostic challenge to radiologists. Frequent modification of detailed pathological classification makes it difficult to keep up with the latest understanding. In this review, we describe a practical approach to high-resolution CT diagnosis of diffuse lung disease, emphasizing (1) analysis of "distribution" of the abnormalities, (2) interpretation of "pattern" in relation to distribution, (3) utilization of associated imaging findings and clinical information, and (4) chronicity of the findings. This practical approach will help radiologists establish a way to interpret high-resolution CT, leading to pin-point diagnosis or narrower differential diagnoses of diffuse lung diseases.

Lung sonography

Lung sonography represents an emerging and useful technique in the management of some pulmonary diseases. For many years, sonography of the thorax was limited to the study of pleural effusion and thoracic superficial masses because alveolar air and bones of the thoracic cage limit the propagation of the ultrasound beam. Only recently has it been highlighted that lung sonography is highly sensitive to variations of the pulmonary content and balance between air and fluids, like a real lung densitometer. Dynamic and static analysis of a combination of sonographic artifacts and real images makes accurate diagnosis of many lung disorders possible, particularly when lung sonography is applied in the emergency and critical care settings. Sonography is useful in the diagnosis of lung diseases in which the alveolar air content is impaired and interstitial and alveolar fluids are increased and also when air or fluids are collected in the pleural space. This article analyzes the basic principles of lung ultrasonography and all of the supposed limitations to its diagnostic usefulness. Moreover, the article reviews the three main fields of lung sonography application: interstitial, alveolar, and pleural syndromes.

Chronic obstructive pulmonary disease: lobe-based visual assessment of volumetric CT by Using standard images--comparison with quantitative CT and pulmonary function test in the COPDGene study

PURPOSE

To provide a new detailed visual assessment scheme of computed tomography (CT) for chronic obstructive pulmonary disease (COPD) by using standard reference images and to compare this visual assessment method with quantitative CT and several physiologic parameters.

MATERIALS AND METHODS

This research was approved by the institutional review board of each institution. CT images of 200 participants in the COPDGene study were evaluated. Four thoracic radiologists performed independent, lobar analysis of volumetric CT images for type (centrilobular, panlobular, and mixed) and extent (on a six-point scale) of emphysema, the presence of bronchiectasis, airway wall thickening, and tracheal abnormalities. Standard images for each finding, generated by two radiologists, were used for reference. The extent of emphysema, airway wall thickening, and luminal area were quantified at the lobar level by using commercial software. Spearman rank test and simple and multiple regression analyses were performed to compare the results of visual assessment with physiologic and quantitative parameters.

RESULTS

The type of emphysema, determined by four readers, showed good agreement (κ = 0.63). The extent of the emphysema in each lobe showed good agreement (mean weighted κ = 0.70) and correlated with findings at quantitative CT (r = 0.75), forced expiratory volume in 1 second (FEV(1)) (r = -0.68), FEV(1)/forced vital capacity (FVC) ratio (r = -0.74) (P < .001). Agreement for airway wall thickening was fair (mean κ = 0.41), and the number of lobes with thickened bronchial walls correlated with FEV(1) (r = -0.60) and FEV(1)/FVC ratio (r = -0.60) (P < .001).

CONCLUSION

Visual assessment of emphysema and airways disease in individuals with COPD can provide reproducible, physiologically substantial information that may complement that provided by quantitative CT assessment.

The role and potential of imaging in COPD

Chronic obstructive pulmonary disease is a heterogeneous condition of the lungs and body. Techniques in chest imaging and quantitative image analysis provide novel in vivo insight into the disease and potentially examine divergent responses to therapy. This article reviews the strengths and limitations of the leading imaging techniques: computed tomography, magnetic resonance imaging, positron emission tomography, and optical coherence tomography. Following an explanation of the technique, each section details some of the useful information obtained with these examinations. Future clinical care and investigation will likely include some combination of these imaging modalities and more standard assessments of disease severity.

Association of human leukocyte antigen with interstitial lung disease in rheumatoid arthritis: a protective role for shared epitope

Introduction

Interstitial Lung Disease (ILD) is frequently associated with Rheumatoid Arthritis (RA) as one of extra-articular manifestations. Many studies for Human Leukocyte Antigen (HLA) allelic association with RA have been reported, but few have been validated in an RA subpopulation with ILD. In this study, we investigated the association of HLA class II alleles with ILD in RA.

Methods

An association study was conducted on HLA-DRB1, DQB1, and DPB1 in 450 Japanese RA patients that were or were not diagnosed with ILD, based on the findings of computed tomography images of the chest.

Results

Unexpectedly, HLA-DRB1*04 (corrected P [Pc] = 0.0054, odds ratio [OR] 0.57), shared epitope (SE) (P = 0.0055, OR 0.66) and DQB1*04 (Pc = 0.0036, OR 0.57) were associated with significantly decreased risk of ILD. In contrast, DRB1*16 (Pc = 0.0372, OR 15.21), DR2 serological group (DRB1*15 and *16 alleles) (P = 0.0020, OR 1.75) and DQB1*06 (Pc = 0.0333, OR 1.57, respectively) were significantly associated with risk of ILD.

Conclusion

HLA-DRB1 SE was associated with reduced, while DR2 serological group (DRB1*15 and *16) with increased, risk for ILD in Japanese patients with RA.

Computed tomographic imaging of the airways in COPD and asthma

Computed tomography (CT) is the modality of choice for imaging the airways. Volumetric data sets with isotropic spatial resolution based on multidetector thin-section CT with overlapping reconstruction should be used. Chronic obstructive pulmonary disease and asthma are the 2 most common disease entities that are defined by airflow obstruction. The morphologic correlates of airway changes are dilation of the lumen, thickening of the wall, visibility of small airways due to mucus or edema, air trapping, hypoxic vasoconstriction, and collapsibility. To assess air trapping, additional expiratory low-dose scans are recommended. In clinical routine, these findings are visually assessed and should be routinely reported. However, the interobserver variability is high, and there is a clear need for objective software-based measurements. The development of such tools is challenging, and they are just becoming available on a broader scale. Novel techniques based on dual-energy CT aim to measure iodine distribution maps to assess pulmonary perfusion as well as the distribution of inhaled xenon gas to assess the distribution and time course of pulmonary ventilation. However, these techniques are still being investigated in clinical studies. This review will provide an overview of CT for the diagnosis of chronic obstructive pulmonary disease and asthma, its role in phenotyping these diseases, and the measurement of disease severity and functional compromise.

EMPHYSEMA QUANTIFICATION IN A MULTI-SCANNER HRCT COHORT USING LOCAL INTENSITY DISTRIBUTIONS

This article investigates the suitability of local intensity distributions to analyze six emphysema classes in 342 CT scans obtained from 16 sites hosting scanners by 3 vendors and a total of 9 specific models in subjects with Chronic Obstructive Pulmonary Disease (COPD). We propose using kernel density estimation to deal with the inherent sparsity of local intensity histograms obtained from scarcely populated regions of interest. We validate our approach by leave-one-subject-out classification experiments and full-lung analyses. We compare our results with recently published LBP texture-based methodology. We demonstrate the efficacy of using intensity information alone in multi-scanner cohorts, which is a simpler, more intuitive approach.

[CT imaging of chronic interstitial lung diseases: from diagnosis to automated quantification]

Computed tomography is important for the diagnosis and follow-up of chronic diffuse interstitial lung diseases. Image quality has improved from each generation of scanner to the next and this continues to allow a better characterization of extent of pathology, or even the nature of the pathological process (potentially reversible inflammatory lesions compared to fibrotic lesions). The diagnostic imaging approach has evolved at the same time as technological developments. We initially thought in terms of the predominant lesions (nodular, alveolar consolidation, ground-glass opacity), and then moved to reasoning based on patterns, which are a combination of several elementary lesions (typically for the diagnosis of idiopathic pulmonary fibrosis). Nowadays, studies are focused on building models characterizing a specific disease and which combine several distinct patterns (typically for ground-glass opacity analysis). CT also allows a quantification of the extent of lung disease, which is linked to the prognosis of the disease and helps to monitor its progression. This quantification is usually based on visual criteria, the principles of which are summarized here. The development of automated quantification software could in the near future, be a support for the radiologist.

Lung volumes and emphysema in smokers with interstitial lung abnormalities

BACKGROUND

Cigarette smoking is associated with emphysema and radiographic interstitial lung abnormalities. The degree to which interstitial lung abnormalities are associated with reduced total lung capacity and the extent of emphysema is not known.

METHODS

We looked for interstitial lung abnormalities in 2416 (96%) of 2508 high-resolution computed tomographic (HRCT) scans of the lung obtained from a cohort of smokers. We used linear and logistic regression to evaluate the associations between interstitial lung abnormalities and HRCT measurements of total lung capacity and emphysema.

RESULTS

Interstitial lung abnormalities were present in 194 (8%) of the 2416 HRCT scans evaluated. In statistical models adjusting for relevant covariates, interstitial lung abnormalities were associated with reduced total lung capacity (-0.444 liters; 95% confidence interval [CI], -0.596 to -0.292; P<0.001) and a lower percentage of emphysema defined by lung-attenuation thresholds of -950 Hounsfield units (-3%; 95% CI, -4 to -2; P<0.001) and -910 Hounsfield units (-10%; 95% CI, -12 to -8; P<0.001). As compared with participants without interstitial lung abnormalities, those with abnormalities were more likely to have a restrictive lung deficit (total lung capacity <80% of the predicted value; odds ratio, 2.3; 95% CI, 1.4 to 3.7; P<0.001) and were less likely to meet the diagnostic criteria for chronic obstructive pulmonary disease (COPD) (odds ratio, 0.53; 95% CI, 0.37 to 0.76; P<0.001). The effect of interstitial lung abnormalities on total lung capacity and emphysema was dependent on COPD status (P<0.02 for the interactions). Interstitial lung abnormalities were positively associated with both greater exposure to tobacco smoke and current smoking.

CONCLUSIONS

In smokers, interstitial lung abnormalities--which were present on about 1 of every 12 HRCT scans--were associated with reduced total lung capacity and a lesser amount of emphysema. (Funded by the National Institutes of Health and the Parker B. Francis Foundation; ClinicalTrials.gov number, NCT00608764.).

Probabilistic elastography: estimating lung elasticity

We formulate registration-based elastography in a probabilistic framework and apply it to study lung elasticity in the presence of emphysematous and fibrotic tissue. The elasticity calculations are based on a Finite Element discretization of a linear elastic biomechanical model. We marginalize over the boundary conditions (deformation) of the biomechanical model to determine the posterior distribution over elasticity parameters. Image similarity is included in the likelihood, an elastic prior is included to constrain the boundary conditions, while a Markov model is used to spatially smooth the inhomogeneous elasticity. We use a Markov Chain Monte Carlo (MCMC) technique to characterize the posterior distribution over elasticity from which we extract the most probable elasticity as well as the uncertainty of this estimate. Even though registration-based lung elastography with inhomogeneous elasticity is challenging due the problem's highly underdetermined nature and the sparse image information available in lung CT, we show promising preliminary results on estimating lung elasticity contrast in the presence of emphysematous and fibrotic tissue.

Prospective evaluation of drug-induced lung toxicity with high-resolution CT and transbronchial biopsy

PURPOSE

This study compared the results of high-resolution computed tomography (HRCT) and cytohistology after transbronchial biopsy in the evaluation of drug-related interstitial lung disease (DR-ILD).

MATERIALS AND METHODS

Patients with a clinical and imaging diagnosis of DR-ILD were prospectively included in a study protocol lasting 5 years. All patients were evaluated by bronchoscopy with transbronchial biopsy or bronchoalveolar lavage (BAL) following an HRCT examination that raised a suspicion of DR-ILD. Two radiologists (one senior and one junior), unaware of the diagnosis, reported the single HRCT findings, their distribution and predominant pattern. In the event of disagreement, the diagnosis was subsequently reached by consensus. Cytohistological examination was considered the gold standard in the diagnosis of DR-ILD. Patients who were unable to undergo the endoscopic procedure were excluded from the study.

RESULTS

The study included 42 patients (25 men, 17 women; age range 20-84 years). Transbronchial biopsy was performed in all but four patients (one case of alveolar haemorrhage and three cases of lipoid pneumonia) in whom the diagnosis was established with BAL. Assessment of the HRCT images revealed the following patterns: noncardiogenic pulmonary oedema (n=13); organising pneumonia (OP) (n=9); hypersensitivity pneumonitis (HP) (n=2); alveolar haemorrhage (AH) (n=2); nonspecific interstitial pneumonia (NSIP) (n=5); lipoid pneumonia (LP) (n=1); sarcoid-like pattern (n=1). Cytohistological diagnosis revealed diffuse alveolar damage (DAD) in 11 patients, OP in seven, HP in three, AH in three, chronic interstitial pneumonia (CIP) in eight, LP in three and pseudosarcoidosis in one. Subdivision of the drugs into antineoplastic and nonantineoplastic agents showed that the most common patterns were CIP (n=6), DAD (n=2) and OP (n=2) in the antineoplastic group and DAD (n=9) and OP (n=5) in the nonantineoplastic group. Sensitivity and specificity of the radiological analysis was excellent, especially for patterns such as OP and DAD (sensitivity 0.86 and specificity 0.88 for OP; sensitivity 1 and specificity 0.93 for DAD).

CONCLUSIONS

HRCT demonstrated excellent sensitivity and specificity. In cases in which its specificity was low, HRCT was nonetheless useful for biopsy planning and clinical-radiological monitoring after discontinuation of the drug treatment.

Illustrated Brazilian consensus of terms and fundamental patterns in chest CT scans

The objective of this new Brazilian consensus is to update and to continue the standardization of the principal terms and fundamental patterns in chest CT scans in Portuguese. There is a succinct definition of the principal terms used to describe chest CT findings, as well as illustrations of classic examples. The group of authors comprised radiologists specializing in chest radiology and holding membership in the Brazilian College of Radiology and Diagnostic Imaging, as well as pulmonologists having a special interest in diagnostic imaging and holding membership in the Brazilian Thoracic Association.

Multidetector high-resolution computed tomography of the lungs: protocols and applications

Advances in computed tomography (CT) scanner technology have made isotropic volumetric, multiplanar high-resolution lung imaging possible in a single breath-hold, a significant advance over the incremental high-resolution CT (HRCT) technique in which noncontiguous images sampled the lung, but lacked anatomic continuity. HRCT of the lungs is an established imaging technique for the diagnosis and management of interstitial lung disease, emphysema, and small airway disease, providing a noninvasive detailed evaluation of the lung parenchyma, and providing information about the lungs as a whole and focally. In addition to having a high degree of specificity for diagnosing conditions such as emphysema, sarcoidosis, usual interstitial pneumonitis, Langerhans cell histiocytosis, and small airway disease, there is a growing body of medical evidence to support the use of HRCT findings or diagnosis to predict patient prognosis. In this article, we review the technique, advantages, and clinical applications of the current HRCT technique.

Diagnostic imaging in COPD

Chronic obstructive pulmonary disease (COPD) is a pathological pulmonary condition characterized by expiratory airflow obstruction due to emphysematous destruction of the lung parenchyma and small airways remodeling. Although spirometry is a very useful diagnostic tool for screening large groups of smokers, it cannot readily differentiate the etiologies of COPD and thus has limited utility in characterizing subjects for clinical and investigational purposes. There has been a longstanding interest in thoracic imaging and its role in the in vivo characterization of smoking-related lung disease. Research in this area has spanned readily available modalities such as chest -ray and computed tomography to more advanced imaging techniques such as optical coherence tomography (OCT) and magnetic resonance imaging (MRI). Although the chest x-ray is almost universally available, it lacks sensitivity in detecting both airway disease and mild emphysema and is not generally amenable to objective analysis. Computed tomography has become the standard modality to objectively visualize lung disease. It can provide useful measures of the presence and extent of emphysema, airway disease, and, more recently, pulmonary vascular disease for clinical correlation. It does, however, face limitations in standardization across brands and generations of scanners, and the ionizing radiation associated with image acquisition is of concern to both patients and health care providers. Newer techniques such as OCT and MRI offer exciting in vivo insights into lung structure and function that were previously available only in necropsy specimens and physiology laboratories. Given the more limited availability of these techniques, they will be viewed here as adjuncts to computed tomographic imaging.

Bronchiolar disorders: a clinical-radiological diagnostic algorithm

Bronchiolar disorders are generally difficult to diagnose because most patients present with nonspecific respiratory symptoms of variable duration and severity. A detailed clinical history may point toward a specific diagnosis. Pertinent clinical questions include history of smoking, collagen vascular disease, inhalational injury, medication usage, and organ transplant. It is important also to evaluate possible systemic and pulmonary signs of infection, evidence of air trapping, and high-pitched expiratory wheezing, which may suggest small airways involvement. In this context, pulmonary function tests and plain chest radiographs may demonstrate abnormalities; however, they rarely prove sufficiently specific to obviate bronchoscopic or surgical biopsy. Given these limitations, in our experience, high-resolution CT (HRCT) scanning of the chest often proves to be the most important diagnostic tool to guide diagnosis in these difficult cases, because different subtypes of bronchiolar disorders may present with characteristic image findings. Three distinct HRCT patterns in particular are of value in assisting differential diagnosis. A tree-in-bud pattern of well-defined nodules is seen primarily as a result of infectious processes. Ill-defined centrilobular ground-glass nodules point toward respiratory bronchiolitis when localized in upper lobes in smokers or subacute hypersensitivity pneumonitis when more diffuse. Finally, a pattern of mosaic attenuation, especially when seen on expiratory images, is consistent with air-trapping characteristic of bronchiolitis obliterans or constrictive bronchiolitis. Based on an appreciation of the critical role played by HRCT scanning, this article provides clinicians with a practical algorithmic approach to the diagnosis of bronchiolar disorders.

[HRCT of the lung: nodular pattern: anatomy and differential diagnosis]

Since the spectrum of differential diagnoses is wide, the interpretation of a nodular pattern in lung lesions detected on CT is a frequent problem. Number, size, localization, and morphology (shape, density, margins) contribute to evaluating the most probable differential diagnosis. "Classical" high resolution CT or high resolution image reconstructions from multiple row detector CT helical acquisitions achieve a detail resolution that makes it possible to distinguish findings by their typical predominance in certain anatomical compartments of the lung. The position of bronchial, vascular and lymphatic structures can be determined down to the secondary pulmonary lobule, the smallest subunit of the lung to be separated by septa of connective tissue. Based on this, a centrilobular predominance of nodules, i.e. with a tree-in-bud pattern, is a frequent sign of bronchiolitis. Perilymphatic predominance in the periphery of the lobules is associated with sarcoidosis or lymphangitic spread of cancer. Random distribution of nodules is interpreted as a sign of hematogenic spread of disease. Hence the subtle interpretation of specific findings on HRCT can contribute substantially to clinical decision making, although these signs may not always replace biopsy and histologic workup.

[Pathophysiological approach to infiltrative lung diseases on CT]

The analysis of HRCT findings of interstitial lung diseases frequently allows to predict the reversible nature of abnormalities, to recognize the involved components of the lung and to suggest the underlying pathophysiological mechanisms. Pathologic alterations in the anatomy of secondary pulmonary lobules include interlobular septal thickening or/and diseases with peripheral lobular distribution, centrilobular abnormalities, and panlobular abnormalities. Consolidations and ground glass opacities are better analyzed by taking into account the way lung responds to injury rather than anatomic distribution of lesions. The recognition of the topographic distribution of lesions and associated abnormalities, including airway diseases, pulmonary hypertension and embolus, diaphragmatic and pharyngeal dysfunctions, provides a better understanding of underlying disease mechanisms and allows a limited differential diagnosis.

High resolution computed tomography in idiopathic interstitial pneumonias

In June 2001, using an "international multidisciplinary consensus," the American Thoracic Society and European Respiratory Society classified the idiopathic interstitial pneumonias (Am J Respir Crit Care Med 2002;165:277-304). The American Thoracic Society and European Respiratory Society coined the term idiopathic interstitial pneumonias because the diseases in question have both unknown etiologies and various combinations of inflammation and fibrosis within the lung parenchyma. The consensus included the development of a classification standard of the interstitial pneumonias and discussed the role of surgical lung biopsy and bronchoalveolar lavage evaluation. The classification of idiopathic interstitial pneumonias is based on histologic criteria, which correlate to imaging patterns on high-resolution computed tomography. The group of lung diseases under the umbrella of idiopathic interstitial pneumonias includes the following: usual interstitial pneumonia, nonspecific interstitial pneumonia, desquamative interstitial pneumonia, respiratory bronchiolitis interstitial lung disease, acute interstitial pneumonia, cryptogenic organizing pneumonia, and lymphoid interstitial pneumonia.

Sonographic interstitial syndrome: the sound of lung water

OBJECTIVE

Ultrasound lung comets (ULCs) now have an acknowledged correlation with extravascular lung water, but they present in different orders and numbers in different pathologic pulmonary entities. How these artifacts are created is not yet known, and the literature gives discordant hypotheses. Understanding their formation is the first step in understanding lung disease. The purpose of this study was to show the morphologic and genetic variability of interstitial lung disease studied with echography and thus to propose a unitary mechanism for the formation of ULCs.

METHODS

This study included 3 parts: (1) a retrospective analysis of echographic lung images of patients with interstitial syndrome; (2) an analysis of the literature for definitions of the size of the pulmonary lobule; and (3) an experimental model of different air-water interfaces scanned with varying ultrasonic frequencies.

RESULTS

The retrospective analysis of echographic lung images included 176 patients with diffuse ULCs: 118 patients had acute pulmonary edema; 18 had acute lung injury/acute respiratory distress syndrome; and 40 were premature neonates with respiratory distress syndrome. Experimental models permitted us to discover that ring-down artifacts are produced only by single and double layers of bubbles in specific structural settings.

CONCLUSIONS

Reverberation between bubbles with a critical radius seems to be at the origin of ring-down artifacts. Echographic manifestations of interstitial lung disease, whose genesis lies in the partial air loss of lobes and segments, are acoustic phenomena originating from variations in the tissue-fluid relationship of the lung. A correlation between anatomopathologic characteristics and structures of sonographic artifacts could allow more rapid and noninvasive diagnoses.

[Identification of lung architecture using HRCT]

The pulmonary interstitium is divided into different compartments, with the secondary pulmonary lobule representing the smallest subunit surrounded by connective tissue. Identification of the lobular architecture is a prerequisite for categorizing the broad spectrum of pulmonary interstitial diseases into distinct patterns. High-resolution computed tomography (HRCT) patterns comprise reticular and nodular opacities, ground-glass opacities, and consolidation. Air trapping and emphysema are associated with decreased pulmonary attenuation. The features of these patterns are derived from the anatomic basis and are linked with typical differential diagnoses, although the nonspecificity of the different patterns should be kept in mind. A main objective is to focus on mixed patterns.

From the archives of the AFIP: pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis (PAP) may develop in a primary (idiopathic) form, chiefly during middle age, or less commonly in the setting of inhalational exposure, hematologic malignancy, or immunodeficiency. Current research supports the theory that PAP is the result of pathophysiologic mechanisms that impair pulmonary surfactant homeostasis and lung immune function. Clinical symptomatology is variable, ranging from mild progressive dyspnea to respiratory failure. There is a strong association with tobacco use. The predominant computed tomographic feature of PAP is a "crazy-paving" pattern (smoothly thickened septal lines on a background of widespread ground-glass opacity), often with lobular or geographic sparing. The radiologic differential diagnosis of crazy-paving includes pulmonary edema, pneumonia, alveolar hemorrhage, diffuse alveolar damage, and lymphangitic carcinomatosis. Definitive diagnosis is made with lung biopsy or bronchoalveolar lavage specimens that reveal intraalveolar deposits of proteinaceous material, dissolved cholesterol, and eosinophilic globules. Symptomatic treatment includes whole-lung lavage, and multiple procedures may be required. New therapies directed toward the identified defect in immune defense have met with moderate clinical success.