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E1620. Imaging of Large Airways Disorders: A Pictorial Review
Authors
  1. Yashmin Nisha; The Ottawa Hospital, University of Ottawa
  2. Anuj Dixit ; The Ottawa Hospital, University of Ottawa
Background
The trachea as well as the main, lobar and segmental bronchi are considered to be the “large airways”. Although non-neoplastic diseases of these airways are uncommon, it is important that radiologists be familiar with the appearances on computed tomography (CT) in order to provide an accurate and useful differential diagnosis. This is paramount as the clinical symptoms such as cough, dyspnea, wheezing, or stridor are often nonspecific which can cause a delay in diagnosis. Chest radiography is often the initial test performed in patients with suspected large airways disease, however it is insensitive and abnormalities of the large airways can be easily overlooked. The detection and characterization of large airways diseases is significantly improved with computed tomography (CT). CT allows for rapid non-invasive evaluation of the tracheobronchial tree with the added benefit of 3D reconstructions as well as dynamic expiratory imaging.

Educational Goals / Teaching Points
Familiarity with large airway anatomy is a fundamental building block in order to build a concise and accurate differential diagnoses. The trachea consists of 4 layers: an inner mucosal layer, a submucosal layer, cartilage and muscle, and an outer adventitial layer. The anterior trachea is composed of C-shaped cartilaginous rings, however, the posterior tracheal wall lacks cartilaginous support and is only supported by the trachealis muscle. The posterior aspect is also known as the membranous portion of the trachea. It is for this reason that CT imaging of the trachea will demonstrate anterior bowing of the posterior membranous portion during expiration whereas the anterolateral trachea has little change in contour.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
We will use this approach to illustrate the CT imaging features of common as well as rare non-neoplastic tracheal diseases by using examples from our tertiary care center with bronchoscopy correlation when possible. Special emphasis will be given on teaching points to differentiate the various pathologies which can have similar CT appearances. This exhibit will include cases such as tracheomalacia, saber sheath trachea, relapsing polychondritis (RPC), tracheobronchopathia osteochondroplastica (TBO), amyloidosis, granulomatosis with polyangiitis (GPA, formerly known as Wegener granulomatosis), Mounier-Kuhn syndrome, mucous membrane phemphigoid, sarcoidosis and tracheal papillomatosis.

Conclusion
A systematic approach aids in narrowing the differential diagnosis of large airways diseases on CT. Important points along the decision-making tree include determining which airways are involved as lesions that predominately affect the trachea differ from those that are cantered within the bronchi. The next discriminator is whether the lesion is diffuse or focal. Finally, paying careful attention to whether there is involvement of the posterior wall will also help to fine tune the differential diagnoses.