Teaching Case

A 64-year-old female presented to the outpatient department with a history of breathlessness and cough for the last 1 week. No history of fever, haemoptysis, or weight loss. She is a known case of bronchial asthma on medication for the past 28 years. Her vitals were stable and had bilateral wheeze on auscultation. 

Frontal Radiograph chest: shows non-homogenous radio opacities involving bilateral upper zones in the paratracheal location with a V-shaped configuration. The right hilum appears enlarged with similar radio opacities seen in the right para hilar location involving predominantly right mid-zone showing typical finger-in-glove appearance. 

Computed tomography(non-contrast) Thorax: Dilatation of central segmental bronchi (cylindrical bronchiectasis) with uniformly hyperdense areas/collection seen within the dilated bronchi possibly representing hyperattenuating mucus (HAM) of average HU ~ 112 with surrounding areas of resorptive /obstructive atelectasis are seen involving bilateral upper lobes and right middle lobe. 

Narrowing of the proximal aspect of central segmental bronchi in the perihilar region (possibly secondary due to mucus plugging) is noted with few areas of small centrilobular nodules of varying sizes seen in bilateral upper lobes.

Background

Allergic bronchopulmonary aspergillosis (ABPA) is a pulmonary disorder characterised by a hypersensitivity reaction to Aspergillus sp, involving type I (IgE-mediated) and type III (IgG-mediated) immunologic responses ^[1,2,3]     

Clinical perspective

This entity is most commonly encountered in adults before the age of 40 years, with longstanding asthma, which is the most important contributing factor (occurs in 0.25-11% of asthmatic patients). It is seen occasionally associated with cystic fibrosis and other underlying bronchiectatic diseases ^[2]. Patients generally experience symptoms of recurrent asthma exacerbations (wheezing, cough and dyspnoea). Occasionally, chest pain, fever, expectoration of dark mucous plug and haemoptysis may be associated ^[3,4].

Imaging Perspective

On chest radiograph, ABPA shows tubular branching radio opacities extending from the

hilum with the appearance of a “finger in glove”, which may be associated with air-fluid levels in dilated bronchi. 

On HRCT Thorax, Central bronchiectasis (cystic or varicose) and mucoid impaction of underlying bronchiectatic airway, forming large bronchoceles, typically with involvement of the upper lobes. Hyperattenuating mucus on CT scans has been reported as a diagnostic criterion for ABPA, corresponding to an attenuation superior to 70 Hounsfield Unit (denser than the para-spinal muscles). The presence of hyperdense mucous plugging impaction has been shown as a 100% specific criterion of ABPA and thus may be considered pathognomonic ^[2,6,7]. 

Pulmonary collapse may be seen as a consequence of endobronchial mucoid impaction ^[1,2,5].

Other CT findings in acute exacerbation of ABPA include bronchial wall-thickening, centrilobular nodules (as a tree-in-bud pattern), consolidation and mosaic pattern with air trapping ^[1,2,5,6].

According to Patterson et al. ABPA was classified based on HRCT chest findings as ABPA-CB and ABPA-S, depending on the presence or absence of bronchiectasis ^[8].

The classification scheme was revised by studies done by Ritesh et al. based on HAM was the most consistent, with the progressive increase in immunological severity from ABPA-S (mild) through ABPA-CB (moderate) at diagnosis not only representing immunologically severe disease but also identifies the patient at risk for recurrent relapses. 

Outcome

The established major criteria for the diagnosis of ABPA include history of asthma, immediate skin reactivity to Aspergillus, elevated total serum IgE (>1000 ng/ml), elevated IgE or IgG to Aspergillus and central bronchiectasis ^[2,4]. Treatment of ABPA aims to control inflammation and prevent further injury to the lungs, based on the combination of oral corticosteroids and anti-fungal medications. Moreover, the presence of HAM at diagnosis not only represents immunologically severe disease but also identifies the patient at risk for recurrent relapses ^[9].

Take home message

ABPA can present with a variety of clinico-radiologic manifestations, among which patients with a history of bronchial asthma and HRCT thorax findings of central bronchiectasis with high attenuating mucus (HAM) have high diagnostic accuracy. Patients with a strong suspicion of ABPA should be confirmed with bronchoalveolar lavage, serological and immunological tests for clinical confirmation.