Stridor (Latin for "creaking or grating noise") is a high-pitched extra-thoracic breath sound resulting from turbulent air flow in the larynx or lower in the bronchial tree. It is different from a stertor which is a noise originating in the pharynx. Stridor is a physical sign which is caused by a narrowed or obstructed airway. It can be inspiratory, expiratory or biphasic, although it is usually heard during inspiration. Inspiratory stridor often occurs in children with croup. It may be indicative of serious airway obstruction from severe conditions such as epiglottitis, a foreign body lodged in the airway, or a laryngeal tumor. Stridor should always command attention to establish its cause. Visualization of the airway by medical experts equipped to control the airway may be needed. Causes Stridor may occur as a result of: foreign bodies (e.g., aspirated foreign body, aspirated food bolus); infections (e.g., epiglottitis, retropharyngeal abscess, croup); subglottic stenosis (e.g., following prolonged intubation or congenital); airway edema (e.g., following instrumentation of the airway, tracheal intubation, drug side effect, allergic reaction); laryngospasm (from aspiration, GERD, or complication of anesthesia) subglottic hemangioma (rare); vascular rings compressing the trachea; thyroiditis such as Riedel's thyroiditis; vocal cord palsy; tracheomalacia or tracheobronchomalacia (e.g., collapsed trachea). congenital anomalies of the airway are present in 87% of all cases of stridor in infants and children. vasculitis. infectious mononucleosis peritonsillar abscess Laryngeal edema is a common cause of stridor post extubation (occurring from pressure of the endotracheal tube on the mucosa as a result of endotracheal tube that is too large (e.g. pediatrics), cuff over inflation, and prolonged intubation times.); tumor (e.g., laryngeal papillomatosis, squamous cell carcinoma of larynx, trachea or esophagus); ALL (T-cell ALL can present with mediastinal mass that compresses the trachea and causes inspiratory stridor) Diagnosis Stridor is mainly diagnosed on the basis of history and physical examination, with a view to revealing the underlying problem or condition. Chest and neck x-rays, bronchoscopy, CT-scans, and/or MRIs may reveal structural pathology. Flexible fiberoptic bronchoscopy can also be very helpful, especially in assessing vocal cord function or in looking for signs of compression or infection. Treatments The first issue of clinical concern in the setting of stridor is whether or not tracheal intubation or tracheostomy is immediately necessary. A reduction in oxygen saturation is considered a late sign of airway obstruction, particularly in a child with healthy lungs and normal gas exchange. Some patients will