AUTHOR AND EDITOR INFORMATION

Section 1 of 7  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 7  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• Intervention
• Multimedia
• References

Background

Croup is a generic term that encompasses a heterogeneous group of relatively acute conditions (mostly infectious) that are characterized by a syndrome of distinctive brassy coughs. These conditions may be accompanied by inspiratory stridor, hoarseness, and signs of respiratory distress as a result of laryngeal obstruction. The word croup derives from an old Scottish term roup, which means "to cry out in a shrill voice."

The most common form of croup is acute laryngotracheobronchitis or viral croup, an infection of both the upper and lower respiratory tracts. A reactive inflammatory response causes subglottic edema. Narrowing of the airway can be life threatening in infants and young children because of their small airway.

Pathophysiology

The cells of the respiratory epithelium are infected following viral inhalation. The inflammation is diffuse in the involved airway, but airway narrowing is most marked in the lateral walls of the subglottic larynx because of the surrounding fixed cricoid cartilage. The subglottic larynx and tracheal lumens are normally quite narrow in infants and young children; thus, a small incremental decrease in lumen diameter in infants and small children can be critical, resulting in a large increase in both airway resistance and the work of breathing. Older children have milder symptoms because the airway lumen diameter is beyond the critical size; however, croup can occasionally create severe illness in older children who have congenital or acquired subglottic stenosis.

Of all cases of croup, 75% are caused by parainfluenza virus types 1 and 3.¹ Influenza and respiratory syncytial viruses cause most of the remaining cases. Viral croup may be complicated by bacterial tracheitis that is caused by Staphylococcus aureus, Haemophilus influenzae, Streptococcus pneumoniae, or Moraxella catarrhalis. The supraglottic tissues in bacterial tracheitis are normal, but the subglottic mucosa may be ulcerated, may be partly necrotic, and is frequently covered by a thick, purulent exudate (see Image 5).

Frequency

United States

The frequency of croup varies with geography and season. Most cases of viral croup occur in the autumn because of the prevalence of the parainfluenza virus. In the winter, respiratory syncytial virus is more common, and in the spring, influenza virus type B is more common. Viral agents tend not to cause simultaneous epidemics in the same community. The incidence rate of croup varies with climate.

Two studies, summarized in the table below, demonstrate that the frequency of croup peaks during the first 2 years of life.^{1, 2}

Table. Frequency of Croup in Children in North Carolina and Seattle

Mortality/Morbidity

Morbidity: Croup is responsible for 250,000 emergency department visits per year, at an aggregate cost of $50 million. Parainfluenza virus types 1 and 3 are responsible for 70,000 hospitalizations per year, at a total cost of $140 million.

Mortality: The overall mortality rate for croup is unknown. A higher mortality rate is associated with males (male-to-female incidence rate is 1.7:1) and young age (86% in children aged <3 y). Superinfection can complicate croup; superinfection with bronchopneumonia and measles is associated with higher mortality rates in children who have croup.

Race

Croup is more common in white children than in black children, with a relative risk of 1.85 in white children.

Sex

In children younger than age 6 months, males are affected more commonly than females, with a male-to-female incidence rate of 1.43:1. In older children, boys and girls are equally affected.

Age

Viral croup is most common in patients aged 6 months to 5 years, with a peak incidence in the second year of life. Croup is rare in the first 6 months of life; stridor that presents in the first 6 months of life should instigate a search for other causes of the stridor. Congenital anomalies and subglottic hemangiomas should be considered in the differential diagnosis; these conditions narrow the airway and cause stridor in infants. The youngest reported child with croup was aged 3 months.

Croup is less common in school-aged children, but this condition is occasionally seen in older children who have preexisting subglottic stenosis.

Anatomy

Anatomic differences in the larynx of infants and young children render them more susceptible to respiratory compromise than adults. The larynx of a neonate is located higher in the neck than in older children, and the epiglottis is narrow, omega shaped, and vertically positioned. The submucosa in the subglottic area, the narrowest segment of the larynx, is nonfibrous, resulting in a looser attachment of the mucous membrane than occurs in adults, thus facilitating the accumulation of edema. Additionally, the cartilaginous support of the airways in infants is soft, easily allowing dynamic collapse of the airways during inspiration.

The airway of a neonate measures 5-6 mm in diameter at its narrowest point, which is at the cricoid ring. Therefore, infants are at higher risk for respiratory failure when any compromise to the patency of the airway occurs. In addition, infants are easily fatigued by the work of breathing that is necessary to generate the pressures needed to maintain airflow. The work of breathing increases exponentially with narrowing of the cross-sectional area. Obstruction of the glottis and the subglottic area results in airflow of increased turbulence and velocity. As high-velocity airflow passes across the vocal cords and aryepiglottic folds, these structures vibrate, resulting in stridor.

Clinical Details

Croup typically begins with symptoms of an upper respiratory infection, rhinorrhea, sore throat, and mild fever for several days. Later, the child develops a characteristic barking cough, hoarseness, and inspiratory stridor. Inspiratory stridor is often the symptom that causes parents to seek medical attention for their affected child.

Physical examination

On physical examination, signs of respiratory distress include increased respiratory and cardiac rates, nasal alar flaring, and retractions. The retractions can be suprasternal, intercostal, and sternal. Increasing chest-wall retraction occurs as the pleural pressure becomes increasingly negative and correlates with the severity of the upper airway obstruction. Rib cage and abdominal asynchrony occur as the respiratory compromise increases. If hypoxemia develops, the anxious or restless child may develop depressed consciousness or cyanosis. On auscultation, the breath sounds are normal, without added sounds except transmission of the stridor. Occasionally, wheezing may be heard, indicating severe airway narrowing, bronchitis, or possibly coexistent asthma.

Most children with croup have a mild illness and require no specific treatment. Symptoms may last 7-14 days. By the time medical attention is sought, the airway obstruction often does not progress but usually lasts for 4 more days; however, in a minority of children, the airway obstruction progresses to become severe.

Hospitalization

Among children who are hospitalized for viral croup, fewer than 1% require intubation. The duration of hospitalization is related inversely to the child's age. Children who are admitted with sternal and chest-wall retractions experience longer hospitalizations; frequently receive medical intervention, such as aqueous mist therapy or racemic epinephrine; and are at increased risk of requiring artificial airway support. Rarely, negative-pressure pulmonary edema occurs in cases of severe airway obstruction. Approximately 50% of patients with croup progress to recurrent croup. Asthma and atopy in children are associated with previous severe or recurrent episodes of croup.

Complications

Croup increases bronchial hyperreactivity and doubles the incidence of developing asthma. Viral croup may be complicated by bacterial tracheitis. The supraglottic tissues in bacterial tracheitis are normal, but the subglottic mucosa may become ulcerated, may become partly necrotic, and is frequently covered by a thick, purulent exudate. A child with bacterial tracheitis may present initially with signs and symptoms that are similar to those of viral croup, but he/she will progress to high fever, toxicity, and progressive respiratory distress.

Epiglottitis

In some children, the viral prodrome of croup is absent, and the clinical features may be confused with epiglottitis. In contrast to croup, epiglottitis is characterized by bacterial cellulitis, primarily of the supraglottic tissues.

Vaccination has reduced the number of cases of epiglottitis caused by H influenzae type b; streptococci are the most common cause of bacterial epiglottitis in the immunized population. Children with epiglottitis are usually aged 2-4 years and were previously healthy; the symptoms of sore throat with painful swallowing, fever, and toxicity develop within hours. Drooling is frequent, and the neck is hyperextended in an attempt to maintain airway patency. Airway edema can progress rapidly to occlusion. Signs and symptoms of epiglottitis usually provide clinical distinction from croup; however, the distinction is not always possible.

Note: Epiglottitis is a life-threatening medical emergency. In children who have symptoms that are suggestive of epiglottitis, direct visualization of the epiglottis must be performed in a controlled setting by a physician who is experienced in airway management.

Preferred Examination

• Most children with clinical croup require no testing beyond a thorough history and physical examination. Observation and frequent physical examination remain the best ways to monitor affected children. Pulse oximetry is useful if the patient also has bronchiolitis or pneumonia. The oral cavity and oropharynx are examined in the emergency department to exclude other causes of stridor or respiratory distress such as peritonsillar or retropharyngeal abscess or uvulitis.
• Laryngoscopy and airway support in a well-controlled environment is required if complete airway obstruction is imminent. Flexible nasopharyngoscopy can be used safely during the acute episode to evaluate the glottic and supraglottic areas. The subglottic area can frequently be visualized by looking through the vocal cords—take care not to pass the scope below the glottis.
• Endoscopy has a role in atypical, severe, or recurrent cases of laryngotracheobronchitis. In addition, endoscopy may be used to evaluate children in whom extubation has failed and in whom evidence is seen of severe subglottic trauma, in which case reintubation may not be advisable.
• Neck radiographs may be helpful to evaluate the various causes of stridor.

Limitations of Techniques

• Pulse oximetry: Most children with croup have normal pulse oximetry findings unless they have severe bronchospasm. Hypoxia that results in low oxygen saturation is detected in severe croup. Frequent decreases in oxygen saturation are caused by movement artifacts.
• Direct endoscopy: The indications for endoscopy in patients who have laryngotracheitis are not well defined. Instrumentation of the already edematous subglottic area may precipitate the need for intubation and should be reserved for children with historic evidence that suggests a diagnosis other than viral croup. Noisy breathing or an abnormal cry between episodes of croup, progressively more severe or frequent episodes of croup, intubation in the neonatal period, and choking or gagging before the onset of symptoms are possible indications for endoscopy.
• Radiographic studies: The diagnosis of croup is primarily clinical and requires no further testing. Anteroposterior (AP) and lateral soft-tissue technique radiographs of the neck can help the clinician to differentiate croup from other causes of stridor and respiratory distress, such as foreign body, epiglottitis, and retropharyngeal abscess. Lateral neck radiographs detect croup with up to 93% sensitivity and 92% specificity. The steeple sign on AP radiographs is not specific for croup and may be seen in some children with epiglottitis. The steeple sign can also be absent in some children with croup. A pseudo-steeple sign, which is a normal variant, may be seen at times during the respiratory cycle in some children without croup.

Patient Education:

For excellent patient education resources, visit eMedicine's Lung and Airway Center. Also, see eMedicine's patient education articles Croup and Coughs.

DIFFERENTIALS

Section 3 of 7  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• Intervention
• Multimedia
• References

Other Problems to Be Considered

Conditions that cause obstruction in the region of the larynx include the following:

Laryngeal foreign body aspiration
Acute angioedema (presents with other evidence of swelling of face and neck)
Retropharyngeal abscess
Parapharyngeal abscess
Bacterial tracheitis
Infectious mononucleosis
Laryngeal diphtheria
Paraquat poisoning
Burns or thermal injuries
Smoke inhalation
Neoplasm or hemangioma
Acute laryngeal fracture
Chiari I Malformation
Chiari II Malformation
Dandy-Walker Malformation
Laryngomalacia
Laryngeal papillomatosis
Extrinsic obstruction by a vascular ring

RADIOGRAPH

Section 4 of 7  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• Intervention
• Multimedia
• References

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.

INTERVENTION

Section 5 of 7  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• Intervention
• Multimedia
• References

Medical/Legal Pitfalls

• Failure to correctly differentiate croup from epiglottitis
• Epiglottitis is a life-threatening medical emergency. In children with suspected epiglottis, direct visualization of the epiglottis must be performed in a controlled setting by a physician who is experienced in airway management.

MULTIMEDIA

Section 6 of 7  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• Intervention
• Multimedia
• References

Media file 1:  Normal lateral neck radiographs. During inspiration, the undersurface of the vocal cords is wide apart and not visualized. During phonation (saying "e"), the undersurface of the vocal cords are well visualized.
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Media file 2:  Normal anteroposterior radiograph of the neck. The normal convex borders (shoulders) of the vocal cords are outlined in the larynx.
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Media file 3:  Lateral radiograph in a patient with croup. This image shows the presence of subglottic haziness and narrowing, as well as distention of the hypopharynx. The epiglottis and prevertebral soft tissues are normal.
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Media file 4:  Anteroposterior radiograph in a patient with croup. This image shows the steeple sign, with loss of the normal shoulders of the subglottic larynx.
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Media type:  X-RAY

Media file 5:  Lateral radiograph in a patient with membranous croup (bacterial tracheitis). This image shows haziness in the subglottic region of the trachea. Soft-tissue defects are identified within the airway. The hypopharynx is overdistended.
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Media type:  X-RAY

Media file 6:  Lateral radiograph in a 2-year-old child with stridor and fever. This image shows a swollen epiglottis and aryepiglottic folds that are typical of epiglottitis. The epiglottis contour resembles a thumb.
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Media type:  X-RAY

REFERENCES

Section 7 of 7

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• Intervention
• Multimedia
• References

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Article Last Updated: Sep 12, 2007