October 2023
Congenital cardiovascular abnormality and dynamic airways collapse
October 2023
Dr Liam Peng, Dr Xinyi Qiu, Dr Emily Hughes, Dr Ryan Grech, Dr Gruschen Veldtman, Dr John Dreisbach
Case History:
A 65-year-old female with a history of asthma and chronic rhinosinusitis presented with wheezy cough and persistent exertional dyspnoea, having previously been reasonably fit and active during her childhood and earlier adult life. Spirometry showed an obstructive pattern, with partial improvement in FEV1 following bronchodilator therapy. Peak flow was, however, persistently low with a truncated expiratory flow volume loop. An initial HRCT with inspiratory and expiratory scans demonstrated a right aortic arch with narrowing of the trachea and right main bronchus. The patient was further investigated with a CT angiogram and 4D dynamic airways CT.
CT Angiogram:
A CT angiogram demonstrated a mirror-image right arch with a vascular ring completed by a left ligamentum arteriosum extending from a left-sided retroesophageal ductal diverticulum from the right-sided proximal descending aorta to the left pulmonary artery. Additionally, there was moderate dilation of the proximal descending aorta partly related to the ductal diverticulum.
CT angiogram. Mirror-image right arch with a left ligamentum arteriosum completing a vascular ring, as well as moderate dilation of the proximal descending aorta related to the ductal diverticulum.
4D Dynamic Airways CT:
A 16 cm volume CT covering the trachea and central bronchi was performed while the patient instructed to gently breath in and out during a continuous 4-second long acquisition with multiple phase reconstructions throughout the respiratory cycle (DLP 185.70 mGy.cm; effective dose 2.6 mSv).
The vascular ring, formed by the proximal descending aorta, right arch, brachiocephalic trunk, and left ligamentum arteriosum, resulted in mild resting narrowing of the mid trachea but only mild dynamic collapse (~40% decrease in cross-sectional area).
There was, however, also moderate resting narrowing of the right main bronchus, compressed between the dilated proximal descending aorta and right pulmonary artery, with severe dynamic collapse (~80% decrease in cross-sectional area).
4D dynamic airways CT of the mid trachea at the level of the vascular ring demonstrating mild dynamic collapse.
4D dynamic airways CT of the right main bronchus demonstrating compression between the descending aorta and right pulmonary artery with severe dynamic collapse.
Management:
In addition to the medical therapy for concurrent asthma and rhinosinusitis, potential surgical strategies which are sometimes required in the paediatric population but very rarely in adults are being discussed in the regional tertiary referral centre. Options include posterior descending aortopexy to relieve the severe right main bronchus compression with division of the ligamentum arteriosum to relieve the modest tracheal compression.
Discussion:
This case represents a very rare variant of a right aortic arch with mirror-image branching and a left ligamentum arteriosum forming a complete vascular ring. In stark contrast to the vast majority of cases of mirror-image right aortic arches which have a right ligamentum arteriosum, it is not typically associated with congenital heart disease. Complete vascular rings often present with symptoms related to tracheal and/or oesophageal compression.
Despite the presence of a complete vascular ring, however, there was only mild tracheal compression and mild dynamic collapse, with instead more significant compression and severe dynamic collapse of the right main bronchus compressed between the dilated proximal descending aorta and right pulmonary artery.
The patient presented with a wheezy cough and exertional dyspnoea, as well as obstructive but otherwise poorly specific pulmonary function tests. The findings on the initial HRCT inspiratory and expiratory scans were confirmed and complemented by the CT angiogram and 4D dynamic airways CT. The latter provided comprehensive isotropic anatomic coverage assessment of the central tracheobronchial tree with isophasic dynamic assessment of large airway dynamics at a modest radiation dose, obviating the need for traditional ‘gold standard’ of bronchoscopy.
The typical surgical approach to a complete vascular ring in a mirror right aortic arch with a left ligamentum arteriosum would involve division of the ligament and possibly resection of the ductal diverticulum. In this case, however, the complete vascular ring is remote from the severe right main bronchus compression, which could potentially be treated with a posterior descending aortopexy, in which the aorta would be surgically displaced to the paravertebral gutter creating more space between the right pulmonary artery and descending aorta.
References:
1. Hanneman K et al. Congenital variants and anomalies of the aortic arch. RadioGraphics, 37(1), (2017), pp. 32–51.
2. Wagnetz U et al. Dynamic airway evaluation with volume CT: initial experience. Can Assoc Radiol J, 61(2) (2010), pp. 90-97.
3. Shieh HF et al. Descending Aortopexy and Posterior Tracheopexy for Severe Tracheomalacia and Left Mainstem Bronchomalacia. Seminars in Thoracic and Cardiovascular Surgery. 31(3), (2019), pp. 479 – 485.
4. Mitropoulos A. et al. Detection and diagnosis of large airways collapse: a systematic review. ERJ Open Research, 7(3), (2021), 00055-2021.
5. Han J.J et al. A vascular ring: Right aortic arch and descending aorta with left ductus arteriosus. The Annals of Thoracic Surgery, 71(2), (2001), pp. 729–731.