Croup (Laryngotracheobronchitis) By Rajeev Bhatia, MD, Phoenix Children's Hospital Reviewed / Revised Jan 2022 | Modified Sep 2022 View Patient Education Etiology Pathophysiology Symptoms and Signs Diagnosis Treatment Key Points Topic Resources Stridor Crackles X-Ray of a Child With Croup.. X-Ray of a Child With Croup.. Subglottic Narrowing Caused.. Croup is acute inflammation of the upper and lower respiratory tracts most commonly caused by parainfluenza virus type 1 infection.