IMAGING BEYOND THE MAIN AIR PIPE: HRCT SIGNS OF SMALL AIRWAY DISEASES AND BRONCHIOLITIS

Abstract

Purpose:
Primary objectives were:

1)To recognize specific signs of small airway diseases on high resolution computed tomography scan (HRCT) and their prevalence among our local patients presenting with cough and dyspnea.
3) To assess the role of paired inspiratory-expiratory CT scans and multiplanar reconstructions with maximum intensity projection (MIP) and minimum intensity projection (MinIP) in diagnosing small airway diseases.

Materials and Methods: We retrospectively identified 100 patients referred to radiology department for HRCT chest with a principal diagnosis of small airway disease. A random sample of the entire HRCT chest patients from January 2013 to December 2015 was selected. To be eligible, patients had to present to the hospital with cough and shortness of breath (dyspnoea) and with clinical suspicion of airway disease. HRCT scans were done using 128-slice Multidetector Computed tomography (MDCT) scanner in the Radiology department of Rehman Medical Institute Peshawar. Complimentary expiratory scans were performed when indicated. 0.5mm reconstructed images in lung window and 3mm images in mediastinal window were viewed on 5.1 vitrea workstation in axial, coronal and sagittal planes. All data was entered and analyzed using Microsoft excel 2007. Retrospective review of HRCT scans on vitrea workstation was done by at least two qualified radiologists with minimum three years of experience in HRCT chest reporting. Scans were assessed for presence or absence of signs of small airway diseases, extent and zonal distribution of HRCT findings, severity of architectural distortion or ancillary findings such as lymphadenopathy and associated pleural or cardiac changes.

Results:
Four radiological patterns of small airway disease were identified on HRCT; bronchiolitis in 40% (n=40), bronchiolitis with specific signs of airtrapping in 35% (n=35), extensive chronic small airway disease pattern in 15% (n= 15) and 10 % (n=10) had only centrilobular ground glass nodules. Bronchiolitis was seen mostly in infectious bronchiolitis, bronchiolitis with air trapping in allergic alveolitis and bronchiolectasis with plugs and consolidations in patients with organizing pneumonia.
Direct signs were seen in 68% of cases and indirect signs in 32% .The most Common finding was Tree in bud nodules. The presence of signs of small airway diseases like bronchiolitis, bronchiolectasis and air trapping in each lobe were documented. Consensus reporting diagnosed bronchiolar wall thickening in 13, isolated centrilobular nodules in 11, bronchiolectasis in 4, mosaic pattern in 22, air trapping in 10, mucus plugs in 11, tree in bud nodules in 36 and chronic small airway pattern in 3 patients. The diagnostic accuracy for each observer with and without MIP/MinIP was compared. Improvement in diagnosing mosaic pattern and centrilobular nodules was noted by use of MinIP and MIP respectively. The improvement did not reach statistical significance. However, our results suggest that MinIP and MIP seems to improve the confidence in diagnosing small airway diseases. There was agreement between observers in the diagnosis of air trapping when the images were used in conjunction with expiratory images.

Conclusion:

We conclude from our results that HRCT images can accurately identify thickened airway walls, plugged small airways and air trapping.  The most common HRCT finding of small airway disease in our study was bronchiolitis, which is recognized as bronchiolar wall thickening. The most common HRCT sign was tree in bud nodules and the most common diseases affecting small bronchioles were infective bronchiolitis and allergic alveolitis.
Our results show that there is improvement in diagnosing mosaic pattern and centrilobular nodules by use of MinIP and MIP respectively .The diagnosis of air trapping was more confidently made when the images were used in conjunction with expiratory images.

Keywords:

Multidetector Computed Tomography (MDCT), High Resolution Computed Tomography (HRCT), Bronchiolitis, Small airway diseases.