Study of different high resolution computed tomography patterns in patients with diffuse interstitial lung diseases

 

 

Abstract              Background: Interstitial lung diseases (ILDs) are a diverse group of diseases which affect the lung interstitium and share similar clinical and radiological manifestations. HRCT is the non-invasive, high spatial resolution cross sectional imaging modality for evaluation of lung parenchyma. It assesses the presence of disease in lung, type of disease, changes of active lung disease, biopsy site localization, change in disease activity following treatment. Present study aimed to study basic HRCT patterns associated with Interstitial Lung Disease and correlation of HRCT patterns with clinical data in differential diagnosis of Interstitial Lung Disease. Material and Methods: Present study was a Cross sectional study, conducted in patients above 20 years, clinically diagnosed as Interstitial Lung Disease, confirmed by HRCT. Results: The present cross-sectional study included 51 patients, 21 (41.17%) were in the age group of 41-50 years followed by 18 (35.29%) patients in the age group of 51-60 years. 33 (64.7%) were males and 18 (35.29%) were females. 11 (21.56%) were smokers, all were males. The overall patterns documented on HRCT (n = 51) were ground glass opacities 45 (88.23%), reticular opacities 37 (72.54%), honey-combing 32 (62.74%), nodular opacities 23 (45.09), hilar adenopathy 21 (41.17%), cyst-like 17 (33.33%) and linear opacities 11 (21.56%). In the present study, distribution of cases according to ATS/ERS 2003 Guidelines were studied. IPF was the most common pattern seen in 17 (33.33%) cases, whereas, NSIP, COP, RB-ILD, DIP and AIP patterns were revealed in 12 (23.52%), 8 (15.68%), 6 (11.76%), 3 (5.88%) and 2 (3.92%) cases respectively. Conclusion: Rigorous application of an ordered, pattern approach to HRCT abnormalities allows for reproducible and accurate interpretation. The advent of HRCT as an imaging modality has obviated the need for a lung biopsy in many patients. Characteristic findings on HRCT scans are often sufficient to diagnose ILDs.

Keywords: ILD, HRCT patterns, Interstitial Lung Disease, pulmonary fibrosis.

 

INTRODUCTION

Interstitial lung diseases (ILDs) are a diverse group of diseases which affect the lung interstitium and share similar clinical and radiological manifestations. These are a heterogeneous group of disorders that predominantly affect the lung parenchyma and vary widely in etiology, clinic-radiologic presentation, histopathologic features, and clinical course.¹ ILDs are characterized by infiltration of cellular or non-cellular material into the lung parenchyma. Anatomic distribution of these processes may affect not only the interstitial compartment but also alveolar airspaces, blood vessels, and distal airways.² Known causes of ILDs include inhaled organic and inorganic substances, cigarette smoking, drugs, radiation, and systemic disorders like connective tissue diseases. However, for some ILDs the cause is unknown.^3,4HRCT is the non-invasive, high spatial resolution cross sectional imaging modality for evaluation of lung parenchyma. It assesses the presence of disease in lung, type of disease, changes of active lung disease, biopsy site localization, change in disease activity following treatment. The advent of HRCT has revolutionized the ability to detect and characterize interstitial lung diseases in vivo.⁵ The components of the HRCT findings that are helpful in the diagnosis of ILD include the pattern of parenchymal abnormality (e.g., consolidation, reticular pattern), the anatomic distribution (upper vs lower, central vs peripheral), and associated findings (e.g., mediastinal lymphadenopathy).⁶ Present study aimed to study basic HRCT patterns associated with Interstitial Lung Disease and correlation of HRCT patterns with clinical data in differential diagnosis of Interstitial Lung Disease

 

MATERIAL AND METHODS

Present study was a Cross sectional study, conducted in department of radiodiagnosis, Sri Siddhartha Medical College, Tumkur. The study was conducted from November 2014 to November 2016 in patients clinically diagnosed as Interstitial Lung Disease referred for HRCT Chest.

Inclusion criteria

Patients above 20 years, clinically diagnosed as Interstitial Lung Disease, confirmed by HRCT.

 

Exclusion Criteria

Patients with acute dyspnoea. Post traumatic patients with dyspnoea. Acute first episode of lung infections.

HRCT examinations will be conducted to all patients using CT scanners TOSHIBA Aquilion 16. The HRCT scan was conducted in supine position for the axial scanning, prone or supine position with hyper extended neck for coronal scanning. Various patterns of Interstitial lung diseases were studied and ILDs were classified according to the “ Revised ATS/ERS classification of Idiopathic Interstitial Pneumonias: multidisciplinary diagnoses 2013 update”. The data collected was entered in MS Excel sheet and analysed.

 

RESULTS

The present cross-sectional study included 51 patients diagnosed with interstitial lung disease on the basis of clinical and radiological characteristics to study the different HRCT patterns of diffuse ILDs. Majority of the patients 21 (41.17%) were in the age group of 41-50 years followed by 18 (35.29%) patients in the age group of 51-60 years. 33 (64.7%) were males and 18 (35.29%) were females. 11 (21.56%) were smokers, all were males.

A total of 16 (31.37%) patients were known cases of ILD diagnosed few years back, whereas, 35 (68.62%) cases were newly diagnosed depending on clinical, radiological and pathological findings. The symptoms were present for than 6 months in 35 (68.62%) cases. Dry cough and breathlessness on exertion were the symptoms present for more than 6 months with mean duration of 3 years.

DISCUSSION

The principal causes of diffuse interstitial lung disease are fibrosing alveolitis, inhalation disorders (asbestos, silica), drug induced lung disorders, interstitial pneumonias, hypersensitivity pneumonitis and connective tissue disorders/ collagen vascular diseases. These abnormalities can lead to impaired V/Q (ventilation/perfusion) mismatching, decreased diffusion and decreased lung compliance.⁷ A basic understanding of the anatomy of the interstitium and the secondary pulmonary lobule is essential for understanding the pathologic processes that take place in interstitial lung diseases and their subsequent radiologic manifestations.⁸ILD is commonly seen in the middle-aged patients, and the incidence advances with increasing age. In present study peak incidence was found between 41- 60 years age group. Other studies also correlate with this study with peak incidence between 40 to 59 years.^9,10 Male predominance was noted in present study, raises possibility of occupational factor in etiology.21.56% were smokers. It has been appreciated that cigarette smoking is related to the development of several ILDs including desquamative interstitial pneumonia (DIP), respiratory bronchiolitis-associated interstitial lung disease (RBILD), pulmonary Langerhans cell histiocytosis (PLCH) and IPF.^11,12Idiopathic pulmonary fibrosis (IPF) was the most common entity of the ILDs (33.33%). Patients with IPF present with progressively worsening dyspnea and nonproductive cough. A history of cigarette smoking seems to be a risk factor for the development of IPF. Ground-glass opacities are present in the majority of patients with IPF.¹³In the present study, ground-glass opacity on HRCT was seen in 88.23% ILD patients. Majority (68.62%) of the patients included in this study were newly diagnosed with active infection. Ground-glass opacity is a nonspecific finding that may reflect volume averaging of abnormalities that cannot be completely resolved with HRCT technique, a purely interstitial abnormality, a purely alveolar abnormality, or a disease process that involves both the pulmonary interstitium and the air spaces. The significance of ground-glass opacity depends on the patients symptoms (acute versus chronic, and the actual presenting symptoms); the distribution of the ground- glass opacity on HRCT; and the presence or absence of other findings on the HRCT study. Remy-Jardin et al.¹⁴ showed that ground-glass opacity on HRCT corresponded to active, reversible pulmonary inflammation in 65% of patients undergoing biopsy. In the study by Leung et al.82% of patients with ground-glass opacity on HRCT had reversible disease shown on lung biopsy.¹⁵ Reticular opacities pattern was observed in 37 (72.54%) cases. The most important form of reticular opacity encountered on HRCT imaging is intralobular interstitial thickening. Intralobular interstitial thickening is a common finding in patients with usual interstitial pneumonia– idiopathic pulmonary fibrosis, and may be the pre- dominant finding before honeycombing is evident. Non-specific interstitial pneumonia (NSIP) was found to be less than IPF (33.33% Vs 23.52%). NSIP is less common than IPF.¹⁶ 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.¹⁷ Patients present with gradually worsening dyspnea over several months, and they often experience fatigue and weight loss. On high-resolution CT, common manifestation consists of patchy ground-glass opacities combined with irregular linear or reticular opacities and scattered micronodules. The end stage of interstitial lung disease is characterized by honeycombing. It reflects extensive lung fibrosis with alveolar destruction, thereby resulting in a characteristic reticular appearance.¹⁸ On HRCT, it is associated with gross distortion of lung architecture, where individual lobules are no longer visible. In our study, such honey-combing was seen in 32 (62.74%) of the cases. On HRCT, honeycombing was much more accurately diagnosed by the presence of thick walled, air filled cysts, usually measuring 3mm to 1cm in diameter, typically occurring in several layers at the pleural surface. Nodular opacities are another common manifestation of interstitial lung diseases. In our study 23 (45.09) had nodular opacities on HRCT. The appearance of the nodules themselves can be an indicator as to whether they are interstitial or air space nodules. Interstitial nodules tend to be sharply marginated while air space nodules poorly defined.¹⁸ Nodules were classified as peri lymphatic, random and centrilobular based on their distribution on HRCT. This distinction of nodules was much better appreciated on HRCT scans. The scenario in which there is a high clinical suspicion of lung disease but with normal chest radiograph is a common reason for requesting HRCT. HRCT allows earlier diagnosis of IPF, helps to narrow the differential diagnosis based on the CT patterns. HRCT of the chest can be performed as stand-alone study or as an adjunct to conventional CT,¹⁹ there are two key differences between HRCT and conventional CT images. First beam collimation is narrower (1-3 mm). By reducing slice thickness to improves the spatial resolution and hence reduces partial volume averaging effect.²⁰ Secondly specialized algorithm is used to reconstruct the data (high frequency) and take advantage of the intrinsically high contrast milieu of the lungs.²¹ The scans are performed during breath holding at the end inspiration and image slices will be inter-spaced (usually a gap of 10mm). Expiratory HRCT scan may be performed to identify air trapping.²²In suspected interstitial fibrosis, where CT abnormalities are subtle, limited number of images with patient prone may be performed to distinguish established disease rather than gravitational induced atelectasis. Compared to conventional (10 mm collimation) sections HRCT improves the detection of subtle parenchymal abnormalities, ground-glass opacification, small cystic air spaces.²³

 

CONCLUSION

Rigorous application of an ordered, pattern approach to HRCT abnormalities allows for reproducible and accurate interpretation. The advent of HRCT as an imaging modality has obviated the need for a lung biopsy in many patients. Characteristic findings on HRCT scans are often sufficient to diagnose ILDs.

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