Imaging of Non-tuberculous (Atypical) Mycobacterial Pulmonary Infection

Pulmonary infections due to mycobacterial organisms are increasing in incidence. Non-tuberculous (atypical) mycobacteria (NTM) represent a significant proportion of mycobacterial infections and may prove difficult to diagnose due to their non-specific clinical and radiographic presentations. An increasing volume of radiological data is now available for the more common non-tuberculous mycobacterial infections, and we have summarized the imaging features found in such cases, identifying radiographic features that would favour the diagnosis of a non-tuberculous mycobacterium and that, in some cases, suggest a specific organism.

Computed tomography of diffuse lung disease: functional correlates

An appreciation of functional and morphological characteristics is fundamental to the understanding of diffuse lung disease. The detailed information available from high-resolution computed tomography (HRCT) and the facility to subjectively or objectively quantify disease has elucidated the sometimes complex pulmonary function profiles of several diffuse lung diseases. The many reasons why correlations between the extent of HRCT abnormalities and physiological measures of disease may be less strong than expected and are considered in this review.

Nonspecific interstitial pneumonia and usual interstitial pneumonia: comparative appearances at and diagnostic accuracy of thin-section CT

PURPOSE

To compare the morphologic abnormalities on thin-section computed tomographic (CT) images in a group of patients with histopathologically confirmed nonspecific interstitial pneumonia (NSIP) or usual interstitial pneumonia (UIP) and a clinical presentation of idiopathic pulmonary fibrosis.

MATERIALS AND METHODS

Thin-section CT imaging patterns and distribution of disease in 53 patients with histologic diagnoses of NSIP (n = 21) or UIP (n = 32) were quantified retrospectively and independently by four observers. The appearances of NSIP and UIP at CT were compared with univariate and multivariate techniques.

RESULTS

The use of thin-section CT proved to have moderate sensitivity (70%), specificity (63%), and accuracy (66%) in the diagnosis of NSIP. An increased proportion of ground-glass attenuation was the cardinal feature of NSIP at CT (odds ratio: 1.04 for each 1% increase in the proportion of ground-glass attenuation). A histologic diagnosis of NSIP was most frequent (in 24 of 35 observations [69%]) when ground-glass attenuation predominated, and was more frequent with mixed (35 of 79 observations [44%]) than with predominantly reticular disease (25 of 98 [26%] observations, P < .005). Logistic regression analysis of the data indicated that misdiagnosis of UIP in patients with NSIP was associated with less ground-glass attenuation (P < .005) at CT and a subpleural disease distribution (P = .02), with the converse being true for UIP cases misdiagnosed as NSIP.

CONCLUSION

In patients with a clinical presentation of idiopathic pulmonary fibrosis, the accuracy of thin-section CT in identifying NSIP is considerably higher than previously reported. At CT, NSIP is characterized by more ground-glass attenuation and a finer reticular pattern than is UIP. Nevertheless, considerable overlap in thin-section CT patterns exists between NSIP and UIP.

High-resolution CT of diffuse lung disease: value and limitations

The relative speed with which HRCT has become the imaging technique of choice for evaluating patients with suspected lung disease can be regarded as a testament to its effectiveness. It is as well, however, to remember some of the caveats that apply to the interpretation of the numerous studies that have championed the clinical application of HRCT. It seems unlikely that CT will be supplanted in the near future by other cross-sectional or volumetric imaging techniques for the evaluation of diffuse lung disease. The scope for further technical refinement of the hardware aspects of HRCT is probably limited but improvements in postprocessing of image data, with the potential to advance understanding of the pathophysiology of diffuse lung disease, can be anticipated.

ERS transform for the automated detection of bronchial abnormalities on CT of the lungs

The identification of bronchi on Computed Tomography (CT) images of the lungs provides valuable clinical information in patients with suspected airways diseases including bronchiectasis, emphysema, or constrictive obliterative bronchiolitis. The automated recognition of the airways is, therefore, an important part of a diagnosis aid system for resolving potential ambiguities associated with intensity-based feature extractors. On CT images, near-perpendicular cross sections of bronchi normally appear as elliptical rings and this paper presents a novel technique for their recognition. The proposed method, the edge-radius-symmetry (ERS) transform, is based on the analysis of the distribution of edges in local polar coordinates. Pixels are ranked according to local edge (E) strength, radial (R), uniformity and local symmetry (S). A discrete implementation of the technique is provided which reduces the computational cost of the ERS transform by using a geometric approximation of the intensity patterns. The identification of the adjacent pulmonary vessels with template matching then allows for the automated measurement of bronchial dilatation and bronchial wall thickening. Computationally, the method compares favorably with other methods such as the Hough transform. Noise-sensitivity of the technique was evaluated on a set of synthetic images and nine patients under investigation for suspected airways disease. Agreement for the automated scoring of the presence and severity of bronchial abnormalities was demonstrated to be comparable to that of an experienced radiologist (kappa statistics kappa > 0.5 ).

Computed tomography screening for lung cancer: back to basics

After some years in the doldrums, interest in screening for lung cancer is resurging. Conflicting evidence from previous lung cancer screening trials, based on plain chest radiography, has been the subject of much debate: the failure to demonstrate a reduction in mortality has led to the widely held conclusion that screening for lung cancer is ineffective. The validity of this assumption has been questioned sporadically and a large study currently under way in the U.S.A. should help settle the issue. Recently, there has been interest in the use of computed tomography to screen for lung cancer; radiation doses have been reduced to 'acceptable' levels and the superiority of computed tomography (CT) over chest radiography for the identification of pulmonary nodules is unquestioned. However, whether improved nodule detection will result in a reduction in mortality has not yet been demonstrated. The present review provides a historical background to the current interest in low-dose CT screening, explains the arguments that previous studies have provoked, and discusses the recent and evolving status of lung cancer screening with CT. Ellis, S. M. et al. (2001).

Functional consequences of pleural disease evaluated with chest radiography and CT

PURPOSE

To identify a system for the quantification of pleural thickening with an acceptable level of interobserver variation and good functional correlation in individuals with pleural disease.

MATERIALS AND METHODS

The extent of pleural thickening and plaques was assessed in 50 patients by using the following: (a) a radiographic score based on the International Labour Office system, (b) a subjective simple computed tomographic (CT) score, (c) a subjective comprehensive CT score, (d) an objective nonautomated method, and (e) an objective computer-aided semiautomated method.

RESULTS

Similar correlations between the extent of diffuse pleural thickening and forced vital capacity were seen for each system (objective CT, r = -0.72, P <.001; simple CT, r = -0.69, P <.001; radiographic, r = -0.67, P <.001; comprehensive CT, r = -0.66, P <.001). Comparable correlations were observed for total lung capacity. After controlling for extent of diffuse pleural thickening, pleural plaque scores were functionally irrelevant.

CONCLUSION

Comparable functional-morphologic correlations were achieved by using different CT and radiographic scoring systems for pleural disease. A subjective simple CT system had the advantages of ease of application and potential to aid in the accurate assessment of the lung parenchyma, which may be important in individuals exposed to asbestos.

Small airways diseases: detection and insights with computed tomography

Diseases affecting the small airways are difficult to detect by traditional diagnostic tests. Widespread involvement is needed before symptoms and abnormalities on pulmonary function testing or chest radiography become apparent. Obstruction of the bronchioles may be detected indirectly by computed tomography (CT) because regional under-ventilation results in reduced perfusion which in turn is shown as a mosaic attenuation pattern of the lung parenchyma. When there is inflammation of the bronchioles with accompanying exudate, the airways may become directly visible on CT, for example in cases of diffuse panbronchiolitis. Quantification of the various morphological features of small airways disease is possible from CT images and this increased precision has aided investigations of structure/function relationships. An understanding of the pathology and microscopic distribution of disease in relation to the airways allows some prediction of the likely computed tomography appearances in this wide spectrum of conditions, and thus helps to refine the differential diagnosis.

Pulmonary perfusion in supine and prone positions: an electron-beam computed tomography study

Acute respiratory distress syndrome is characterized by alterations in the ventilation-perfusion ratio. Present techniques for studying regional pulmonary perfusion are difficult to apply in the critically ill. Electron-beam computed tomography was used to study the effects of prone positioning on regional pulmonary perfusion in six healthy subjects. Contrast-enhanced sections were obtained sequentially in the supine, prone, and (original) supine positions at full inspiration. Regions of interest were placed along the nondependent to dependent axis and relative perfusion calculated. When corrected for the redistribution of lung parenchyma, a gravitational gradient of pulmonary perfusion existed in both supine and prone positions. The distribution of perfusion between the supine or prone positions did not differ, but data analysis using smaller regions of interest demonstrated marked heterogeneity of perfusion between anatomically adjacent regions of lung. The distribution of lung parenchyma was more uniform in the prone position. Gravity was estimated to be responsible for 22-34% of perfusion heterogeneity in the supine and 27-41% in the prone positions. These data support the hypothesis that factors other than gravity may be at least as important in determining the distribution of pulmonary perfusion in humans. The influence of nongravitational factors may not be detectable if techniques that sample large tissue volumes are employed.

Pulmonary perfusion in supine and prone positions: an electron-beam computed tomography study

Acute respiratory distress syndrome is characterized by alterations in the ventilation-perfusion ratio. Present techniques for studying regional pulmonary perfusion are difficult to apply in the critically ill. Electron-beam computed tomography was used to study the effects of prone positioning on regional pulmonary perfusion in six healthy subjects. Contrast-enhanced sections were obtained sequentially in the supine, prone, and (original) supine positions at full inspiration. Regions of interest were placed along the nondependent to dependent axis and relative perfusion calculated. When corrected for the redistribution of lung parenchyma, a gravitational gradient of pulmonary perfusion existed in both supine and prone positions. The distribution of perfusion between the supine or prone positions did not differ, but data analysis using smaller regions of interest demonstrated marked heterogeneity of perfusion between anatomically adjacent regions of lung. The distribution of lung parenchyma was more uniform in the prone position. Gravity was estimated to be responsible for 22-34% of perfusion heterogeneity in the supine and 27-41% in the prone positions. These data support the hypothesis that factors other than gravity may be at least as important in determining the distribution of pulmonary perfusion in humans. The influence of nongravitational factors may not be detectable if techniques that sample large tissue volumes are employed.

Acute respiratory distress syndrome caused by pulmonary and extrapulmonary injury: a comparative CT study

PURPOSE

To determine computed tomographic (CT) differences between acute respiratory distress syndrome (ARDS) due to pulmonary injury (ARDS(p)) and extrapulmonary injury (ARDS(ex)).

MATERIALS AND METHODS

CT appearances in 41 patients (27 male, 14 female; mean age, 47.1 years +/- 17.1 [SD]; age range, 17-79 years; those with ARDS(p), n = 16; those with ARDS(ex), n = 25) were categorized as typical or atypical of ARDS by two observers. The extent of individual CT patterns was also quantified.

RESULTS

Typical CT appearances were more frequent in ARDS(ex) than ARDS(p) (18 [72%] of 25 vs five [31%] of 16 patients, respectively; P <.01). Sensitivity, specificity, and accuracy of a typical CT pattern for the diagnosis of ARDS(ex) were 72%, 69%, and 71%, respectively. Atypical appearances were characterized by more extensive nondependent intense parenchymal opacification (IPO) (P =.03) and cysts (P =.05), whereas typical CT appearances had more extensive dependent IPO (P =.01). Typical appearances at CT were independently related to the cause of ARDS (odds ratio, 8.9; 95% CI: 1.8, 44.2; P <.01) but were independent of the time from intubation. Foci of nondependent IPO were more extensive in ARDS(p) (P =.05) than ARDS(ex), but this finding was ascribable to differences in time to CT (after intubation) between ARDS(p) and ARDS(ex).

CONCLUSION

The differentiation between ARDS(p) and ARDS(ex) can, with some caveats, be based on whether the CT appearances are typical or atypical of ARDS but not on any individual CT pattern in isolation.

The prognostic significance of the histologic pattern of interstitial pneumonia in patients presenting with the clinical entity of cryptogenic fibrosing alveolitis

Lone cryptogenic fibrosing alveolitis (CFA) is a progressive interstitial lung disease, with a median survival of 3 to 6 yr from the onset of dyspnea. CFA can be subdivided into prognostically significant histopathologic patterns, including nonspecific interstitial pneumonia (NSIP). We reviewed 78 patients with a clinicopathologic diagnosis of CFA, biopsied between 1978 and 1989, to evaluate the prevalence and prognostic significance of these histopathologic patterns, in particular NSIP. Biopsy appearances were reclassified by two pulmonary histopathologists as usual interstitial pneumonia (UIP) (47%), NSIP (36%), or desquamative interstitial pneumonia (DIP)/respiratory bronchiolitis-associated interstitial lung disease (RBILD) (17%). The kappa coefficient of agreement between pathologists was 0.49. In 67 cases, follow-up was complete to death or 10 yr after biopsy, with 50 deaths during a median follow-up of 42 mo (UIP, 89%; NSIP, 61%, DIP/RBILD, 0%). Survival was highest in DIP/RBILD and higher in NSIP than UIP, p < 0.0005. When analysis was confined to patients with UIP or NSIP, the mortality of UIP remained higher, p < 0.01, but the 5-yr survival in patients with fibrotic NSIP was only 45%, indicating that this histologic appearance is often associated with a poor outcome. A response to treatment was more frequent in DIP/RBILD than in NSIP (p < 0.01) or UIP (p < 0.0005). This study confirms the prognostic value of subclassifying patients with CFA according to histopathologic pattern. However, in patients with clinically typical CFA, a histologic diagnosis of fibrotic NSIP needs to be interpreted with caution and does not necessarily denote a good outcome.

Nonspecific interstitial pneumonia: variable appearance at high-resolution chest CT

PURPOSE

To describe the computed tomographic (CT) findings in patients with nonspecific interstitial pneumonia (NSIP) and to compare these with the CT findings of other chronic infiltrative lung diseases.

MATERIALS AND METHODS

Findings in 50 patients with biopsy-proved NSIP and a CT scan were reviewed by two thoracic radiologists in consensus. After the findings were described, the observers judged whether the findings were compatible with previously published descriptions of NSIP or whether the findings would support the diagnosis of a different chronic infiltrative lung disease.

RESULTS

Eleven (22%) of the 50 patients had CT findings that were compatible with previous descriptions of NSIP. Sixteen (32%) patients had CT findings that were more compatible with usual interstitial pneumonia. The other 23 (46%) patients had findings that were nondiagnostic or most compatible with the diagnosis of another chronic infiltrative lung disease.

CONCLUSION

Contrary to previously published articles, there are a wide variety of CT findings in cases of NSIP.

Computed tomography of diffuse interstitial lung disease in children

Unlike diseases of the airways, interstitial lung diseases in childhood are exceedingly rare and are usually associated with significant morbidity and mortality. Interstitial lung disease in the paediatric age group is a particular diagnostic challenge because the clinical presentation and radiographic features are so non-specific. High resolution computed tomography (HRCT) has proved its worth in adults with interstitial lung disease and has a role, albeit more limited, in the non-invasive evaluation of paediatric interstitial lung disease.

Asbestos-related benign pleural disease

Benign pleural disease is the commonest manifestation of asbestos exposure encountered by radiologists. Benign pleural thickening can appear as circumscribed parietal pleural plaques or as more diffuse thickening of the visceral pleura. Benign-asbestos induced pleural effusions are a significant and under-recognized manifestation of asbestos exposure with important sequelae, such as diffuse pleural thickening which may be associated with functional impairment and for which compensation may be sought. This review concentrates on the strengths and weaknesses of chest radiography and computed tomography for the detection and characterization of benign asbestos-related pleural disease and the relevance of imaging abnormalities to compensation and functional impairment.Peacock, C. (2000). Clinical Radiology55, 422-432.

Gradient correction and classification of CT lung images for the automated quantification of mosaic attenuation pattern

PURPOSE

The detection of density differences, or "mosaic attenuation pattern," on CT images may be difficult when the regional inhomogeneity of the density of the lung parenchyma is subtle. The purpose of this work was to develop a fully automated method for the reproducible quantification of the underattenuated areas of the lung parenchyma. This technique may be useful in increasing the precision of investigation of structure/function relationships.

METHOD

Anatomical segmentation was achieved by a structure-filtering operator based on mathematical morphology. To compensate for the density gradient visible on lung CT scans, a model-based iterative deconvolution filter and an adaptive clustering algorithm were developed. Validation was performed with CT images from a lung phantom, 15 patients with constrictive obliterative bronchiolitis, and 8 normal subjects.

RESULTS

The accuracy of the estimate of the density gradient on phantom studies was 93.3%. The automated quantification of the areas of decreased attenuation on scans of constrictive obliterative bronchiolitis was within 8.2% from the average scoring of two experienced observers.

CONCLUSION

The proposed technique is fully automated and can accurately correct for density gradient and classify areas of decreased attenuation on lung CT images.

Pulmonary sequelae of bronchopulmonary dysplasia survivors: high-resolution CT findings

OBJECTIVE. We examined the high-resolution CT findings of adult survivors of bronchopulmonary dysplasia. CONCLUSION. The cardinal CT features of bronchopulmonary dysplasia survivors include multifocal areas of reduced lung attenuation and perfusion, bronchial wall thickening, and decreased bronchus-to-pulmonary artery diameter ratios.

Lateral cavity wall thickening as an early radiographic sign of mycetoma formation

The sensitivity of chest radiography for the early detection of mycetoma formation within fibrotic cavities is poor. The purpose of this study was to determine the predictive value of the secondary sign of lateral cavity wall thickening for the detection of a radiographically occult mycetoma. The chest radiographs and CT scans of 70 patients who had a total of 109 fibrotic cavities on CT were reviewed by two observers. Dimensions of the cavity, mycetoma, and cavity wall thickness on chest radiography and CT scans were recorded. Mycetomas were visible in 41 of 99 cavities on chest radiographs and in 61 of 109 cavities on CT. Using CT as the gold standard for detecting the presence of mycetomas, the sensitivity of chest radiography for the presence of a mycetoma was 62 % and the specificity 94 %, and the positive and negative predictive values were 93 and 66 %, respectively. On logistic regression analysis, lateral wall thickness on chest radiography was predictive of the presence of a mycetoma (p < 0.0005) independent of other radiographic features. In patients with chronic fibrocavitary disease on chest radiography, the presence of lateral wall thickening is highly suggestive of an underlying mycetoma.

Airflow obstruction in bronchiectasis: correlation between computed tomography features and pulmonary function tests

BACKGROUND

An obstructive defect is usual in bronchiectasis, but the pathophysiological basis of airflow obstruction remains uncertain. High resolution computed tomographic (CT) scanning now allows quantitation of static morphological abnormalities, as well as dynamic changes shown on expiratory CT scans. The aim of this study was to determine which static and dynamic structural abnormalities on the CT scan are associated with airflow obstruction in bronchiectasis.

METHODS

The inspiratory and expiratory features on the CT scan of 100 patients with bronchiectasis undergoing concurrent lung function tests were scored semi-quantitatively by three observers.

RESULTS

On univariate analysis the extent and severity of bronchiectasis, the severity of bronchial wall thickening, and the extent of decreased attenuation on the expiratory CT scan correlated strongly with the severity of airflow obstruction; the closest relationship was seen between decreased forced expiratory volume in one second (FEV(1)) and the extent of decreased attenuation on the expiratory CT scan (R(s) = -0.55, p<0. 00005). On multivariate analysis bronchial wall thickness and decreased attenuation were consistently the strongest independent determinants of airflow obstruction. The extent of decreased attenuation was positively associated with the severity of bronchial wall thickness, but was not independently linked to gas transfer levels. Endobronchial secretions seen on CT scanning had no functional significance; the severity of bronchial dilatation was negatively associated with airflow obstruction after adjustment for other morphological features.

CONCLUSIONS

These findings indicate that airflow obstruction in bronchiectasis is primarily linked to evidence of intrinsic disease of small and medium airways on CT scanning and not to bronchiectatic abnormalities in large airways, emphysema, or retained endobronchial secretions.

Nitrofurantoin-induced lung disease: two cases demonstrating resolution of apparently irreversible CT abnormalities

A reticular pattern on high resolution CT (HRCT) invariably represents significant lung pathology and is the dominant feature of irreversible fibrosis. We present two cases of nitrofurantoin-induced pulmonary toxicity in which the initial HRCT showed a widespread reticular pattern and associated distortion of the lung parenchyma, thought to represent established fibrosis. Follow-up HRCT scans after withdrawal of the drug showed resolution of this supposedly irreversible pattern.

Diagnostic accuracy of thin-section CT and chest radiography of pediatric interstitial lung disease

OBJECTIVE

We assessed the accuracy of thin-section CT and chest radiography to diagnose pediatric interstitial lung disease.

MATERIALS AND METHODS

We identified 20 infants, boys, and girls (age range, 1 month to 14 years) with histopathologic confirmation of interstitial lung disease. Six boys and girls without interstitial lung disease were also included. Two observers independently assessed chest radiograph and CT images. The observers stated the most likely diagnosis and a differential diagnosis. We evaluated individual CT features and their distribution.

RESULTS

Observers' diagnoses on CT images were correct (first choice or differential) in 66% of observations versus 45% on chest radiographs (p < 0.025). Correct diagnoses were made on first choice in 61% of CT observations versus 34% on chest radiographs (p < 0.005). Observers were confident (versus uncertain) in 42% of the CT observations versus 18% on chest radiographs; of the confident diagnoses made on CT, 91% were correct. CT interpretations were most accurate in the diagnosis of pulmonary alveolar proteinosis, congenital lymphangiectasia, and idiopathic pulmonary hemosiderosis. All healthy patients examined with CT were correctly identified as such. We noted a distinctive CT pattern in three patients with nonspecific interstitial pneumonitis and one patient with desquamative interstitial pneumonitis; the CT pattern consisted of upper zone predominant honeycombing on a background of ground-glass attenuation.

CONCLUSION

A higher proportion of pediatric interstitial lung diseases can be diagnosed on thin-section CT than on chest radiographs. In our study, confident and correct diagnoses were made more frequently with CT than with chest radiographs.