Radiography
Findings
Perform AP and lateral radiographs using a high-kilovoltage technique, or perform digital fluoroscopy and rapid-sequence imaging to optimize visualization of the airway. Although high-kilovoltage techniques are preferred, conventional techniques may be used. The vocal cords, larynx, and lateral walls of the subglottic larynx and trachea are well depicted on the frontal view. The hypopharynx, epiglottis, aryepiglottic folds, prevertebral soft tissues, larynx, and subglottic airway can be evaluated on the lateral projection (see Image 1).
- Frontal neck radiograph: The lateral walls of the subglottic larynx are normally convex or shouldered (see Image 2). Wall edema in croup narrows this space, with loss of lateral convexity, and creates a steeple shape below the vocal cords (see Image 4). The narrowing may extend for 5-10 mm below the vocal cords.
- Lateral neck radiograph: The hypopharynx is overdistended during inspiration, and the subglottic region is hazy as a result of narrowing of the airway by mucosal edema. The larynx airway is indistinct. The undersurface of the vocal cords that would normally be identified during phonation is not well identified. However, the epiglottis, aryepiglottic folds, and prevertebral spaces appear normal (see Image 3).
Degree of Confidence
Airway radiographs detect croup with up to 93% sensitivity and 92% specificity. Note that subglottic haziness and the steeple sign can also be seen in a small percentage of children who have epiglottitis; however, additional radiographic findings that are specific for epiglottitis are present on the lateral radiograph. Subglottic narrowing from laryngotracheal hemangiomas is typically asymmetric.
False Positives/Negatives
A pseudo-steeple sign may be present in children without symptoms of croup. Other radiographic signs of obstruction are absent. Distention of the hypopharynx can be due to any condition that causes upper airway obstruction. Epiglottitis, foreign body aspiration or ingestion, subglottic hemangioma, or bacterial tracheitis all can create upper airway obstruction.
- Epiglottitis: Epiglottitis is associated with a distended hypopharynx and subglottic narrowing, but this condition also causes thickening of the epiglottis and aryepiglottic folds.
- Foreign body: The most common nonopaque foreign bodies include foods such as peanuts, candy, and hot dogs. Foreign bodies can cause extrinsic airway obstruction if they lodge in the proximal trachea or esophagus. The most common radiopaque foreign bodies are coins, which can lodge in the esophagus at the level of the cricopharyngeus muscle or aortic arch. Airway obstruction is caused by mechanical compression of the posterior trachea or esophagotracheal edema.
- Subglottic hemangioma: Subglottic hemangioma usually presents in the first 3 months of life. If the subglottic hemangioma extends superiorly to involve the true cords, hoarseness may be present in addition to stridor. Subglottic hemangiomas most commonly cause eccentric narrowing of the subglottic airway. Typically, croup causes symmetric subglottic narrowing.
- Membranous croup: In membranous croup, inflammation of the larynx, trachea, and bronchi, with an adherent or semi-adherent mucopurulent membrane in the subglottic space and upper trachea, is present. Radiographs of the airway show marked irregularity and edema of the walls of the trachea. A detached membrane may be seen in the lumen of the trachea and may be mistaken for a tracheal foreign body. If severe obstruction is present, endoscopic removal of the obstructing membrane may improve the clinical condition of the patient.
More on Croup |
| Overview: Croup |
 Imaging: Croup |
| Follow-up: Croup |
| Multimedia: Croup |
| References |
| « Previous Page | Next Page » |
References
Denny FW, Murphy TF, Clyde WA Jr, Collier AM, Henderson FW. Croup: an 11-year study in a pediatric practice. Pediatrics. Jun 1983;71(6):871-6. [Medline].
Foy HM, Cooney MK, Maletzky AJ, Grayston JT. Incidence and etiology of pneumonia, croup and bronchiolitis in preschool children belonging to a prepaid medical care group over a four-year period. Am J Epidemiol. Feb 1973;97(2):80-92. [Medline].
Behrman RE, Kliegman RM, Jenson HB, eds. Nelson Textbook of Pediatrics. 16th ed. Philadelphia, Pa: WB Saunders Co; 2000:990-3; 1275-8.
Chernick V, Boat TF, Fletcher J, eds. Acute infections producing upper airway obstruction. Kendig's Disorders of the Respiratory Tract in Children. 6th ed. Philadelphia, Pa: WB Saunders Co; 1998:152; 452-5.
Coope G, Connett G. Juvenile laryngeal papillomatosis. Prim Care Respir J. Apr 2006;15(2):125-7. [Medline]. [Full Text].
Falagas ME, Mourtzoukou EG, Vardakas KZ. Sex differences in the incidence and severity of respiratory tract infections. Respir Med. Sep 2007;101(9):1845-63. [Medline].
Hopkins A, Lahiri T, Salerno R, Heath B. Changing epidemiology of life-threatening upper airway infections: the reemergence of bacterial tracheitis. Pediatrics. Oct 2006;118(4):1418-21. [Medline].
Johnson DW, Craig W, Brant R, et al. A cluster randomized controlled trial comparing three methods of disseminating practice guidelines for children with croup [ISRCTN73394937]. Implement Sci. 2006;1:10. [Medline]. [Full Text].
Kaditis AG, Wald ER. Viral croup: current diagnosis and treatment. Pediatr Infect Dis J. Sep 1998;17(9):827-34. [Medline].
Lerner DL, Pérez Fontán JJ. Prevention and treatment of upper airway obstruction in infants and children. Curr Opin Pediatr. Jun 1998;10(3):265-70. [Medline].
Loos GD. Pharyngitis, croup, and epiglottitis. Prim Care. Jun 1990;17(2):335-45. [Medline].
Loughlin GM, Eigen H. Acute upper airway obstruction. Pediatric Lung Disease: Diagnosis and Management. Baltimore, Md: Williams & Wilkins; 1994:325-8.
Marx A, Török TJ, Holman RC, Clarke MJ, Anderson LJ. Pediatric hospitalizations for croup (laryngotracheobronchitis): biennial increases associated with human parainfluenza virus 1 epidemics. J Infect Dis. Dec 1997;176(6):1423-7. [Medline].
Mauro RD, Poole SR, Lockhart CH. Differentiation of epiglottitis from laryngotracheitis in the child with stridor. Am J Dis Child. Jun 1988;142(6):679-82. [Medline].
Moore M, Little P. Humidified air inhalation for treating croup: a systematic review and meta-analysis. Fam Pract. Jun 29 2007;epub ahead of print. [Medline].
Quan L. Diagnosis and treatment of croup. Am Fam Physician. Sep 1992;46(3):747-55. [Medline].
Rafei K, Lichenstein R. Airway infectious disease emergencies. Pediatr Clin North Am. Apr 2006;53(2):215-42. [Medline].
Rencken I, Patton WL, Brasch RC. Airway obstruction in pediatric patients. From croup to BOOP. Radiol Clin North Am. Jan 1998;36(1):175-87. [Medline].
Rosekrans JA. Viral croup: current diagnosis and treatment. Mayo Clin Proc. Nov 1998;73(11):1102-6; discussion 1107. [Medline].
Skolnik N. Croup. J Fam Pract. Aug 1993;37(2):165-70. [Medline].
Soler M, Eldadah M. Croup in older children. Case report of 2 school-age children with croup. Clin Pediatr (Phila). Oct 1990;29(10):581-2. [Medline].
Taussig LM, Landau LI. Acute lower respiratory tract infections: general considerations. Textbook of Pediatric Respiratory Medicine. St. Louis, Md: Mosby-Year Book; 1999:556-70.
Walner DL, Ouanounou S, Donnelly LF, Cotton RT. Utility of radiographs in the evaluation of pediatric upper airway obstruction. Ann Otol Rhinol Laryngol. Apr 1999;108(4):378-83. [Medline].
Further Reading
Keywords
acute laryngotracheitis, acute laryngotracheobronchitis, inspiratory stridor
