Diagnoses Croup (demo)



  • Also referred to as laryngotracheobronchitis or laryngotracheitis
  • Variants include spasmodic croup, infectious laryngitis or epiglottitis
  • Generally only seen in children from 3 months to 6 years
  • In most cases a parainfluenza virus infection causes swelling and mucus production in the upper airway (larynx, trachea and bronchi)
  • Annual incidence in children younger than 6 years ranges from 1.5% to 6%

Before the era of immunizations and antibiotics, croup was a dreaded and deadly disease, usually caused by the diphtheria bacteria. Today, most cases of croup are mild. Nevertheless, it can still be dangerous.

Croup is an infection that often comes after a child experiences an acute viral infection of the upper respiratory tract. The infection may extend from the vocal cords (larynx) to the trachea and bronchi. This infection results in inflammation and increased mucus production. Although croup usually goes away on its own, between 5-10% of children with croup will require admission to the hospital.

The Parainfluenza virus


The pharynx is a funnel shaped tube extending from the internal nares to the inferior border of the cricoid cartilage as shown in the diagram. Its walls are composed of skeletal muscle. It allows passage of air and food and produces speech. Its three sections are the nasopharynx which is situated above the soft palate, the oropharynx and the laryngopharynx. The sections are shown on the diagram.

The larynx or laryngopharynx, also known as the voice box, is made up of a strong cartilaginous skeleton linked by a number of membranes. As well as letting air into and out of the lungs, it is vital for speech production. It also protects the lungs from aspiration during swallowing. During swallowing the vocal cords close and the epiglottis folds backwards covering the opening of the larynx and the larynx is pulled upwards and forwards beneath the tongue.


  • 48% Parainfluenza virus type 1
  • 9% Parainfluenza virus type 2
  • 17% Parainfluenza virus type 3
  • 10% Respiratory syncytial virus
  • 4% Influenza A
  • 3% Influenza B
  • 9% Others

There are different aetiologies encompassed in the diagnosis of croup, but the most common cause is viral. The entity known as spasmodic croup is not easily distinguished from viral croup except that spasmodic croup has a greater tendency to recur. The treatment and evaluation are similar.

Aetiology of Croup


HES figures for 2004/2005 include 8,127 admissions for croup (acute obstructive layngitis):

  • 5.41% Acute laryngitis
  • 2.36% Acute tracheitis
  • 0.94% Acute laryngotracheitis
  • 85.33% Acute obstructive laryngitis
  • 5.47% Acute epiglottitis
  • 0.48% Acutre laryngopharyngitis
Incidence of croup

Croup incidence peaks during the second year of life, with a mean age of 18 months, and is more common in boys than girls.

In North America croup has an average annual incidence of 3% and accounts for 5% of emergent admissions to hospital in children under 6 years of age. Fewer than 2% of hospitalized children require intubation. Although exact mortality is unknown, one 10-year study found a mortality rate of less than 0.5% in intubated patients.

Signs and symptoms

Children with croup usually have cold-like symptoms for one to two days before developing a harsh, barking croup-like cough that is frequently associated with a hoarse voice. There is a narrowing of the subglottic area due to inflammation and inspiratory stridor often develops. In mild cases the stridor is present only when the child is upset. As the narrowing gets worse, however, the stridor gets more severe and can occur during both inspiration and expiration and even when the child is at rest.

Differential Diagnosis

Epiglottitis is a rare type of croup that is very serious that can sometimes prove fatal. It is caused by the Haemophilus influenza type b (Hib) bacterium. Unlike the other types of croup that involve the swelling of the windpipe and trachea, epiglottitis involves the sudden swelling and inflammation of the epiglottis (the flap of cartilage at the back of the tongue that closes off the windpipe during swallowing). The swollen epiglottis obstructs breathing and if left untreated could lead to death by suffocation (lack of oxygen).

Epiglottis is still an important differential diagnosis of croup, but thankfully due to the recent HIB vaccination campaign is rarely seen.

Table comparing Croup and Epiglottitis


Croup increases bronchial hyper-reactivity 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, partly necrotic and frequently covered by a thick purulent exudate. A child with bacterial tracheitis may present initially with signs and symptoms similar to viral croup, but will progress to high fever, toxicity, and progressive respiratory distress.

Include following text underneath image: Soft tissue lateral neck (edge enhanced) shows a slightly dilated hypopharynx (red arrow), dilatation of the laryngeal ventricle (white arrow) and narrowing of the sub-glottic trachea (blue arrow). Image courtesy of Learning Radiology.com

Clinical cases

In this case you will see the video of an alert 8-month old boy who has had no previous respiratory illness. You can hear a very noticable stridor when he is at rest, and you can hear a marked croup-like cough. His stridor is significant and he has quite marked sternal recession.

This 20-month old child has had a stormy neonatal course, but had been well for the last 12 months. On this occasion he presented with a runny nose for two days and stridor. You can see that he has a pectus carinatum and Harrison’s Sulki and is quite upset. He has marked subcostal recession and in-drawing is also seen of his lower ribcage at the insertion of his diaphragm. An audible stridor is heard and a barking croup-like cough. On ausculation biphasic stridor is heard.


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