Secondary Lobule Research Articles

Pulmonary nodule distribution modeling as a diagnostic tool for HRCT image analysis

In an attempt to improve pulmonary CT scan reading, a computerized model of lung has first been elaborated. The secondary lobule was used as structuring lung element. The entire organ was composed of several lobule layers and of broncho-vascular trees. As pulmonary nodule distribution modes may turn the diagnostic onto specific pathology type, it is very important to define them as precisely as possible. Seven nodule distributions have been modeled: homogenous, peripheral, centrolobular, pleural, lymphatic, and broncho-vascular. A software tool was developed which allows the radiologist to spread nodules either in the whole lung or in anatomical lung areas, using one or more defined distribution modes until the simulated images mimic the CT scans under analysis. First results show a good agreement between scans and synthesized slices. The software tool described here help the physician to determine the true underlying nodule distribution involved in the pulmonary CT under analysis and lead then to a more precise diagnosis. Moreover, it can be used for radiologist education and training.

Miliary lung disease revisited

This article reviews the high-resolution computed tomography imaging features of miliary pattern, a characteristic radiologic manifestation of diffuse micronodular lung disease. The most common entities with this pattern are miliary tuberculosis, pneumoconiosis, sarcoidosis, metastases, and hypersensitivity pneumonia. According to the distribution of the nodules in relation to the secondary lobule, high-resolution computed tomography findings divide miliary patterns into 3 groups: centrilobular, perilymphatic, and random presentation. The radiologic features that help in the differential diagnosis are discussed.

Miliary lung disease revisited

This article reviews the high-resolution computed tomography imaging features of miliary pattern, a characteristic radiologic manifestation of diffuse micronodular lung disease. The most common entities with this pattern are miliary tuberculosis, pneumoconiosis, sarcoidosis, metastases, and hypersensitivity pneumonia. According to the distribution of the nodules in relation to the secondary lobule, high-resolution computed tomography findings divide miliary patterns into 3 groups: centrilobular, perilymphatic, and random presentation. The radiologic features that help in the differential diagnosis are discussed.

HRCT evaluation of secondary lobules and acini of the lung.

We evaluated normal lung parenchyma with high-resolution computed tomography (HRCT) to assess the visibility of lobular and sublobular structures. Series of HRCT slices were obtained using the usual parameters for HRCT examinations. We used a limited reconstruction field (4-10 cm) with a narrow window to increase visibility of small structures. The boundaries of normal secondary lobules are difficult to identify because the septa are very thin; interstitial disease may increase septal thickness so that more lobules become visible. Position and approximate morphology of lobules can be identified, however, by observing the centrolobular bundles. Normally, many acini are usually visible; their mean diameter (6 mm) and thickness of periacinar capillary net (approximately 0.3 mm) make them identifiable with modern CT scanners. In conclusion, a good knowledge of HRCT lung anatomy is essential to correctly evaluate early interstitial disease.

Hydrostatic Versus Oleic Acid-Induced Pulmonary Edema: High-Resolution Computed Tomography Findings in the Pig Lung

We evaluated the differences between combined hydrostatic and hypervolemic edema and oleic acid-induced edema on high-resolution computed tomography (HRCT) scans. Twelve anesthetized and ventilated pigs were studied. Hydrostatic edema was induced by ligation of the abdominal aorta and infusion of normal saline (n = 4); permeability edema was induced by intravenous injection of oleic acid (n = 4). Four pigs were studied as normal controls. Serial scans were obtained before and after induction of edema at a constant position in the caudal lobe of the lung. The distribution of edema was assessed visually. Cross-sectional areas (CSAs) of the pulmonary artery and vein were measured both at the lobar and segmental levels. Gravity-dependent opacity, peribronchovascular fluid collection, prominent centrilobular core, thickening of the interlobular septa, and air-space consolidation at the dependent site were the sequential HRCT findings of hydrostatic edema. Randomly distributed, diffuse patchy high attenuation areas with a tendency for predilection in the subpleural and peripheral areas of the secondary lobule were the findings of oleic acid-induced edema. Hydrostatic edema increased the mean CSAs of the lobular vein by 137.8% +/- 78.7, but oleic acid edema decreased the mean CSAs by 33.2% +/- 22.7. Changes in the mean CSAs of the pulmonary arteries were not significant. The mean vein-to-artery ratio increased significantly in hydrostatic edema but decreased in oleic acid edema. HRCT findings for hydrostatic and oleic acid-induced pulmonary edema differed both in distribution of edema and in pulmonary vascular response.

High-resolution CT appearance of miliary tuberculosis.

The purpose of this study was to define the range of abnormalities and to assess the contribution of high-resolution CT (HRCT) in the evaluation of miliary tuberculosis involving the lung parenchyma. The authors retrospectively reviewed HRCT scans of 11 patients with microbiologically or clinically proved miliary tuberculosis. In 10 patients, the most characteristic HRCT finding of miliary tuberculosis was the presence of small nodules uniformly distributed throughout both lungs. The profusion of nodules was numerous in all 10 patients. High-resolution CT scans showed both sharply and poorly defined, small nodules varying in sizes from 1 to 2 mm (n = 6), 1 to 3 mm (n = 2), and 1 to 4 mm (n = 2) in diameter. These nodules had a diffuse random distribution in the secondary lobule in all 10 patients. In 1 of the 10 patients with small nodules on HRCT, chest radiography had shown no evidence of miliary nodules in the lung. In addition to nodules, HRCT showed diffuse or localized reticular opacities superimposed on nodules in five patients, especially in the lower lung zones. In 1 of all 11 patients, ground-glass attenuation was the predominant abnormality seen on HRCT. We believe that in the appropriate clinical situation, miliary tuberculosis may be suggested on HRCT. Moreover, in cases with no evidence of miliary nodules on the chest radiograph, HRCT scan may depict miliary nodules in the lung parenchyma.

HRCT studies of lung anatomy

An accurate definition of lung anatomy is the first, necessary step to obtain an accurate and early diagnosis of diffuse and focal lung disease with HRCT. Secondary lobules are visible with conventional CT and HRCT as polygonal portions of lung parenchyma, surrounded by thin and incomplete septa and centred by a dense dot; acini are sometimes visible as rounded structures with a central dot. Morphological definition of these structures in normal subjects will greatly help in characterizing early signs of parenchymal disease.

Bronchiolitis obliterans on high-resolution CT: a pattern of mosaic oligemia.

Bronchiolitis obliterans, when not associated with organizing intraalveolar pneumonia or extensive peribronchiolar fibrosis, is often difficult to distinguish clinically and radiographically from other forms of chronic obstructive pulmonary disease. The aim of this study was to demonstrate a pattern on high-resolution CT (HRCT) that could suggest this diagnosis. Two patients with a clinical diagnosis of bronchiolitis obliterans, moderate-to-severe obstruction on pulmonary function tests, and normal chest radiography were studied with HRCT. High-resolution CT of the patients with chronic bronchiolitis demonstrated a mosaic pattern of low attenuation probably corresponding to secondary lobules. We conclude that the low attenuation areas represent either air trapping or hypoxic vasoconstriction in secondary pulmonary lobules from obstruction of small airways. This pattern of mosaic oligemia was, until recently, only recognized with occlusive vascular disease and may suggest obstructive disease in the small airways.

High-resolution computed tomography and diffuse lung disease

Diffuse lung diseases are often difficult to characterize on chest radiographs. It has been a challenge for the radiologist to obtain useful diagnostic information from these studies and then communicate that information to the clinician. Robert Heitzman recognized the utility of understanding lung diseases in terms of their effect on the structures of the secondary lobule. Unfortunately, he needed inflated lung specimens to reliably visualize the small structures within the secondary lobule. Such specimens are no longer needed. High-resolution computed tomography (HRCT) scans of the lung provide an excellent representation of the secondary lobule. In this monograph, we have attempted to explain the normal anatomy of the secondary lobule, the patterns of abnormality, the technique for performing HRCT, and an approach to diffuse lung disease. In the second half of the article we have classified the more common diffuse lung diseases according to the dominant pathologic change: high versus low attenuation.

HR-Computertomographie interstitieller Lungenerkrankungen

In 50 patients with pulmonary disease of varying aetiology and involvement of the pulmonary interstitium, high resolution CT with 1 mm sections have been performed. Various morphological changes within the secondary lobule could be demonstrated which helped in reducing the differential diagnosis. Compared with conventional CT with 10 mm cuts it was also possible to improve the demonstration of pleural lesions by changing window levels.

The secondary pulmonary lobule: normal and abnormal CT appearances.

The secondary pulmonary lobule is a unit of lung supplied by three to five terminal bronchioles and contained by fibrous septa. High-resolution CT is able to show features of the secondary lobule, including interlobular septa, terminal bronchioles, and pulmonary arteries within a bronchiolovascular bundle. Because interstitial diseases have been shown to affect different components of the secondary lobule, high-resolution CT was used to compare the appearance of the normal secondary lobule with the abnormal secondary lobule in three patients with interstitial diseases primarily affecting lymphatic channels: lymphangitic carcinomatosis, sarcoidosis, and lymphangioleiomyomatosis. In lymphangitic carcinomatosis, the bronchiolovascular bundles and interlobular septa were thicker than those seen in a normal subject. In sarcoidosis, the interlobular septa and bronchiolovascular bundles were also thicker than normal. However, fibrosis caused distortion of the normal polygonal shape of the secondary lobule, not seen in either the normal subject or the patient with lymphangitic carcinomatosis. Lymphangioleiomyomatosis was characterized by multiple cysts within secondary lobules, often obliterating the normal polygonal appearance.

Exercise-induced pulmonary haemorrhage in the horse: results of a detailed clinical, post mortem and imaging study. VIII. Conclusions and implications.

This paper reviews a series of clinical, post mortem and imaging studies on exercise-induced pulmonary haemorrhage (EIPH) performed on 26 Thoroughbred racehorses. Post mortem techniques included routine gross, subgross and histological examination; coloured latex perfusions of pulmonary and bronchial circulations; and microradiography and computerised tomography scans of lungs with contrast injected vasculature. The major lesions were multiple, separate and coalescing foci of moderately proliferative small airway disease accompanied by intense neovascularisation of the bronchial circulation. As a result of bronchial artery angiogenesis, the systemic circulation dominated the vascular supply of the air exchange structures in affected areas, producing an apparent left to right shunt. Extensive areas of sequestered haemosiderophages indicated previous haemorrhage from vessels apparently supplied by the bronchial arteries. Diffuse and focal parenchymal destruction and connective tissue reactions in affected areas were considered to be secondary to localised haemorrhage and macrophage-induced damage. The aetiology of EIPH was not determined, but the multifocal, small airway-centred lesions indicated that low grade bronchiolitis, possibly of viral origin, was a factor. Gravitational effects also appear to contribute to dorsal distribution of the lesions. The mild focal and subclinical lesions confined to secondary lobules are thought to evolve into the serious lung pathology observed in EIPH cases through the effects of localised hypoxia induced by maximal exercise and partial airway obstruction. Once initiated, a vicious cycle of increasing inflammatory damage and further local bleeding is set in motion.

Morphology of Oleic Acid-Induced Lung Injury Observations from Computed Tomography, Specimen Radiography, and Histology

Previously, we reported that oleic acid infusion in dogs produced a patchy and predominantly peripheral increase in lung density. The present study examines in more detail the morphology of the early stages of development of the oleic acid lesion using computed tomography (CT), specimen radiography, and conventional histology. Dogs were sacrificed 10, 30, 60, and 240 minutes after infusion of oleic acid (.05 ml/kg). After freezing in dry-ice, the thorax was scanned and cut into 1-cm thick sections. Frozen sections were then contact radiographed and sampled for histology. Within 10 minutes of infusion, subtle increases in peripheral lung density were visible on the contact radiographs. Patchy areas of peripheral density, resembling secondary lobules, were especially prominent 60 and 240 minutes after infusion. These lesions were often clearly associated with the distal bronchovascular structures. Histologic signs of edema were present in all animals sacrificed 30 or more minutes after receiving oleic acid. These correlative studies provide additional insight into the early subgross development of oleic acid-induced injury by showing the relationship between the developing edema and the bronchovascular structure of the lung.

Postnatal growth and size of the pulmonary acinus and secondary lobule in man.

The acinus and the secondary lobule are important anatomic, functional, and pathologic units in the human lung; there are, however, few studies that specifically describe their postnatal growth and size. Normal lungs from 15 children and adults dying without evidence of pulmonary disease were fixed and dried using a standardized technique and were radiographed after tantalum or silver nitrate bronchoacinography. The acini and secondary lobules were identified and the diameters of these terminal respiratory units determined. The mean diameter of the pulmonary acinus at 1 month was 1 mm; 1 year, 2.5 mm; and at 2 years, 3 mm. The mean acinar diameter had increased to 6 mm at 12 years and reached a normal adult range of 6-10 mm during late adolescence. Acinar size seemed to be related to both height and age. The mean diameter of the secondary lobule at birth measured 3 mm, increased to 5 mm by the end of the first year of life, and by the fourth year measured 9 mm; at 12 years it measured 15 mm, and in late adolescence and adult life it ranged between 13 and 20 mm. A knowledge of the size of the acinus and secondary lobule has a practical application in radiologic practice and will be important in regional structural analysis of the pulmonary parenchyma with computed tomography.

Interacinar pathways in the human lung.

Normal lung specimens from patients 18 to 86 years of age were inflated, fixed, and cleared. After micropuncture of the distal airspaces and injection of silicone rubber, the dissemination pattern was studied by cinematography. Free interacinar flow was commonly observed. The major pathways of spread among adjacent acini were the interacinar ducts. These were short, tubular structures 200 mum in diameter that were continuous with respiratory bronchioles and alveolar ducts. The flow of silicone rubber was impeded only by the septa of the secondary lobule of Miller. Our finding support the view that the smallest morphologic unit of airspace disease is more likely to be the secondary lobule than the acinus.

Functional Morphology of the Distal Lung

Publisher Summary This chapter reviews the information concerning the form and function of the distal lung, defined as terminal bronchioles, respiratory bronchioles, and alveolar ducts, from the viewpoint of cell biology. The chapter summarizes the data produced by microscopy, electron microscopy, biochemistry, and cell and tissue culture. The concept of a continuous epithelium in the lung implies continuity proximally and relationships between the cuboidal (type-II) alveolar cells and the squamous epithelial (type-I) alveolar cells. To discuss the epithelium without considering the interstitial space, the alveolar space and the endothelium ignores the intimate relationships among these zones and the cell membranes that define them. Therefore, it produces a modern version of the functional morphology of the secondary lobule, emphasizing particularly its conduits of ingress and egress for both gases and liquids.

Analysis of relative contributions to the alveolar-arterial oxygen gradient.

A fundamental analysis has been undertaken of O2 transmission across a static inert gas with simultaneous diffusion of CO2 in the reverse direction. The overall alveolar-arterial, (A-a) DO2, gradient has then been derived as the simple sum of four terms representing shunt, ventilation/perfusion inequalities, membrane diffusion and airway diffusion with due allowance for any variation of each process throughout the lung. The expression provides a mathematical framework from which to isolate the net contribution of each process to the overall gradient—each value being a mean weighted according to the ventilation distribution of the gas exchange units. Airway diffusion resistance can be isolated with change of pressure and, from such data, has been estimated as about 6–7% of total (A-a) DO2 in a healthy man breathing air at normal pressure. The same O2 data has enabled the effective diameter of the functional gas exchange unit to be estimated as 14.2 mm.—well within the morphological limits for the secondary lobule.

The secondary pulmonary lobule: a practical concept for interpretation of chest radiographs. II. Application of the anatomic concept to an understanding of roentgen pattern in disease states.

The secondary pulmonary lobule forms the basic unit of lung structure and function (7). The normal roentgen anatomy of the secondary pulmonary lobule has been discussed previously (3). That report indicated that the elements forming the secondary pulmonary lobule could be divided into “core structures” and “septal structures.” The “core structures” of radiologic significance are the pulmonary arteriole and terminal bronchiole, while the “septal structures” of radiologic significance are the connective tissue, the pulmonary lymphatics, and the pulmonary veins. In order to emphasize the practical importance of considering the secondary pulmonary lobule when evaluating abnormal chest radiographs, examples of pathology involving each of these 5 structures will be illustrated and discussed. The usefulness of the concept, however, extends well beyond these examples into almost every aspect of pulmonary pathology. Pathology of the “Core Structures” Pulmonary Arteriole Since the lung can be considered an aggregate of secondary pulmonary lobules, a pulmonary infarct must represent a combination of infarcted secondary pulmonary lobules. Formalin fume-fixed lung specimens often show well established infarcts to be composed of secondary pulmonary lobules sharply demarcated from adjacent normal lobules by the interlobular septum (Fig. 1). Failure of infarcts to be truly cone-shaped is usually ascribed to the presence of an anastomotic circulation which keeps the apex viable. Such an anastomotic circulation cannot be between the pulmonary arteries because these vessels have been clearly shown to be true end arteries (6, 7). Anastomoses between bronchial arteries and pulmonary veins are, however, well documented (1). The role of the bronchial arterial circulation in pulmonary infarction is unclear, but it would appear that any communication between bronchial arteries and pulmonary veins, even if effective in supplying blood to a portion of lung distal to the pulmonary embolus, would still not afford a satisfactory anatomic explanation for the location of the viable lung-infarct interface seen on radiographs and gross specimens. It seems more reasonable to assume that the shape of infarcts is due to the anatomic configuration, in irregular layers, of the infarcted secondary lobules. Further confirmation that devitalized secondary pulmonary lobules represent the building blocks of which infarcts are constructed is afforded by Figure 2, which shows a secondary pulmonary lobule in an area of pulmonary infarction and yet still viable despite the fact that the surrounding lobules are devitalized. It is possible that this segment of viable lung within the infarct represents a portion of a secondary pulmonary lobule supplied by another pulmonary arteriole. A second theoretic possibility is that such a viable lobule was protected because it was not being perfused during the period of the embolic shower.

Stratified pulmonary blood flow: some consequences in emphysema and pulmonary embolism.

Both ventilation and blood flow in the secondary lobule of the lung are stratified; each unit of lung tissue in the proximal portion of the lobule receives up to four times the blood flow of units in the peripheral portion. Questions of the limiting role of gas diffusion within the small airways become virtually irrelevant in the face of this stratification of function.The central portion of the lobule, with its high ventilation, blood flow, and gas exchange, is very vulnerable; small lesions at this site will produce disproportionately large disturbances of gas exchange and of pulmonary vascular resistance. This may well account for some of the phenomena of conditions such as centrilobular emphysema and pulmonary microembolism.

Stratified distribution of blood flow in secondary lobule of the rat lung.

Stratified distribution of blood flow in secondary lobule of the rat lung.