Croup

Croup (acute laryngotracheobronchitis) is the most common cause of acute upper airway obstruction in young children. The peak incidence occurs between 6 months and 3 years of age. The mean age at presentation of croup is 1 year of age. In children older than 3 years, other causes of airway obstruction should be suspected. Croup is viral in cause and is usually a benign, self-limited disease. Redundant mucosa in the subglottic region becomes inflamed, swells, and encroaches upon the airway. The children present with a barky (“croupy”) cough and intermittent inspiratory stridor. It usually occurs following or during other symptoms of lower respiratory tract infection. Most children with croup are managed supportively as outpatients, and the parents are managed by reassurance. Inhaled corticosteroids are becoming a popular therapy in children with croup. They have been shown to reduce the length and severity of illness.

The purpose of obtaining radiographs in a patient with suspected croup is not so much to confirm the diagnosis but rather to exclude other, more serious causes of upper airway obstruction that require intervention. However, characteristic radiographic findings that indicate croup are best seen on frontal radiographs. With croup, there is loss of the normal shoulders (lateral convexities) of the subglottic trachea secondary to symmetric subglottic edema ( Fig. 2-1 ). Normally, the subglottic trachea appears rounded, with “shoulders” that are convex outward ( Fig. 2-2 ). In croup, the subglottic trachea becomes long and thin, with the narrow portion extending more inferiorly than the level of the pyriform sinuses. The appearance has been likened to an inverted V or a church steeple (see Fig. 2-1 ). The term church steeple can be confusing because some steeples look like croup and some are shaped like the normal subglottic airway ( Fig. 2-3 ). Lateral radiographs may demonstrate a narrowing or loss of definition of the lumen of the subglottic trachea (see Fig. 2-1 ) or hypopharyngeal overdistention. With croup, the epiglottis and aryepiglottic folds appear normal.

Croup.

A, Frontal radiograph showing symmetric subglottic narrowing (arrows) with loss of normal shouldering. The narrowing extends more inferiorly than the piriform sinuses. B, Lateral radiograph showing subglottic narrowing (arrow) . Note normal-appearing epiglottis (arrowhead) and thin aryepiglottic folds. Also note mildly enlarged adenoid (A) and palatine (P) tonsils.

Normal frontal radiograph of the airway.

The subglottic airway demonstrates rounded shoulders (arrows) that are convex outward.

Steeple sign.

The term steeple sign can be confusing. It is meant to denote the pointed configuration of the subglottic trachea on a frontal radiograph of the airway when subglottic edema has effaced the normally convex lateral shoulders in this region. However, some steeples look like croup (white arrows) , and some look like a normal subglottic airway (black arrow) .

Epiglottitis

In contrast to croup, epiglottitis is a life-threatening disease that can potentially require emergent intubation. The possibility that a child with epiglottitis might arrive in a deserted radiology department was once a constant source of anxiety for on-call radiology residents. However, most cases of epiglottitis are caused by Haemophilus influenzae and are now preventable by immunization (HiB vaccine), so the incidence of epiglottitis has dramatically decreased. The causes of epiglottitis are now also more heterogeneous. Related to this, care of children with epiglottitis is now more of a challenge because health care workers are less used to recognizing and treating patients with this disorder. Children with epiglottitis are usually toxic appearing and present with an abrupt onset of stridor, dysphagia, fever, restlessness, and an increase in respiratory distress when recumbent. In the pre-HiB vaccine era, the classically described peak age of incidence was 3.5 years. However, since the introduction of the HiB vaccine, there has been a marked increase in the mean age of presentation to 14.6 years. Because of the risk for complete airway obstruction and respiratory failure, no maneuvers should be performed that make the patient uncomfortable. If the diagnosis is not made on physical examination, a single lateral radiograph of the neck should be obtained, usually with the patient erect or in whatever position that allows the patient to breathe comfortably. Children with epiglottitis should never be made to lie supine against their will to obtain a radiograph because it can result in acute airway obstruction and, potentially, death.

With epiglottitis, on the lateral radiograph, there is marked enlargement of the epiglottis. A normal epiglottis typically has a thin appearance with the superior aspect being sharply pointed. The swollen epiglottis has been likened to the appearance of a thumb. With epiglottitis, there is also thickening of the aryepiglottic folds ( Figs. 2-4 and 2-5 ). The aryepiglottic folds are the soft tissues that extend from the epiglottis anterosuperiorly to the arytenoid cartilage posteroinferiorly and normally are convex downward. When the aryepiglottic folds become abnormally thickened, they appear convex superiorly. Symmetric subglottic narrowing, similar to croup, may be seen on frontal radiography (if obtained); do not let that be confusing.

Epiglottitis.

Lateral radiograph showing marked thickening of the epiglottis (arrow) . The aryepiglottic folds are also narrowed.

Epiglottitis.

Sagittal CT image showing low-attenuation swelling of the epiglottis (arrowhead) . Also note marked thickening and low-attenuation edema of the aryepiglottic folds (arrows) .

An obliquely imaged, or so-called omega-shaped, epiglottis may artifactually appear wide because both the left and right sides of the epiglottis are being imaged adjacent to each other. This should not be confused with a truly enlarged epiglottis. The absence of thickening of the aryepiglottic folds can be helpful in making this differentiation. With an omega-shaped epiglottis (normal variant), often both the left and right walls of the epiglottis are visible.

In current times, related to both the uncommon occurrence of epiglottitis and the frequent reliance on computed tomography (CT) to evaluate more common inflammatory neck conditions (such as retropharyngeal abscess), it is increasingly more common to see and diagnose epiglottitis on CT rather than on radiography. Although not classically advocated as a diagnostic tool for epiglottitis (given the risks of laying such patients supine and giving them intravenous [IV] contrast), the findings of epiglottitis are easily identified on CT (see Fig. 2-5 ). Findings include swelling and low-attenuation edema of the epiglottis and aryepiglottic folds associated with inflammatory stranding in adjacent fat.

Exudative Tracheitis

Exudative tracheitis (also known as bacterial tracheitis, membranous croup, or membranous laryngotracheobronchitis) is another uncommon but potentially life-threatening cause of acute upper airway obstruction. The disorder is characterized by a purulent infection of the trachea in which exudative plaques form along the tracheal walls (much like those seen in diphtheria). Affected children are usually older and more ill than those with standard croup; typically their ages range from 6 to 10 years. Although initial reports described most cases to be secondary to infection by Staphylococcus aureus , other reports have noted multimicrobial infections. It is unclear whether the disease is a primary bacterial infection or a secondary bacterial infection that occurs following damage to the respiratory mucosa by a viral infection. A linear soft tissue filling defect (a membrane) seen within the airway on radiography is the most characteristic finding. A plaquelike irregularity of the tracheal wall is also highly suspicious ( Fig. 2-6 ). Nonadherent mucus may mimic a membrane radiographically. In cooperative patients, having them cough and then repeating the film may help to differentiate mucus from a membrane. Other findings include symmetric or asymmetric subglottic narrowing in a child too old typically to have croup and irregularity or loss of definition of the tracheal wall. Membranes and tracheal wall irregularities may be seen on frontal or lateral radiographs and often seen on one but not the other; therefore it is important to get both views.

Exudative tracheitis.

Lateral radiograph showing irregular plaquelike filling defects (arrows) and airway wall irregularities within trachea. Again, note the normal appearance of the nonthickened epiglottis in this patient.

If one of these exudative “membranes” is sloughed into the lumen, it can lead to airway occlusion and respiratory arrest. Therefore children who are suspected to have exudative tracheitis are often evaluated endoscopically, the exudative membranes are stripped, and elective endotracheal intubation is performed.

A number of controversies regarding exudative tracheitis exist. First, it is seen with great frequency at some institutions and not at all at others. Second, although it is considered a life-threatening condition, to my knowledge, no patient has ever died at home of this disease—which seems odd. Both of these points raise the question of the validity of this diagnosis. My take is that there are definitive cases of this disease, but it is probably overdiagnosed and overtreated at some institutions.

Retropharyngeal Cellulitis and Abscess

Retropharyngeal cellulitis is a pyogenic infection of the retropharyngeal space that usually follows a recent pharyngitis or upper respiratory tract infection. Children present with sudden onset of fever, stiff neck, dysphagia, and occasionally stridor. Most affected children are young, with more than half of the cases occurring between 6 and 12 months of age. On lateral radiography, there is thickening of the retropharyngeal soft tissues ( Fig. 2-7 ). In a normal infant or young child, the soft tissues between the posterior aspect of the aerated pharynx and anterior aspect of the vertebral column should not exceed the anterior-to-posterior diameter of the cervical vertebral bodies. If these soft tissues are thicker, an abnormality should be suspected. Apex anterior convexity of the retropharyngeal soft tissues provides supportive evidence that there is true widening of the retropharyngeal soft tissues (see Fig. 2-7 ).

Retropharyngeal abscess.

A, Lateral radiograph showing marked thickening of the retropharyngeal soft tissues (A) , which are wider than the adjacent vertebral bodies. Note the anterior convexity of soft tissues. B and C, Contrast-enhanced CT in sagittal and axial planes shows a low-attenuation region with enhancing rim (A) , suggestive of a drainable abscess.

However, in infants, who have short necks, it is common to see pseudothickening of the retropharyngeal soft tissues when the lateral radiograph is obtained without the neck being well extended ( Fig. 2-8 ). If it is unclear on the initial lateral radiograph whether the soft tissues are truly rather than artifactually widened, it is best to repeat the lateral radiograph with the neck placed in full extension (see Fig. 2-8 ). Fluoroscopy can also be used to evaluate whether the pseudothickening is persistent. The only radiographic feature that can differentiate abscess from cellulitis is the identification of gas within the retropharyngeal soft tissues.

Pseudoretropharyngeal soft tissue thickening secondary to lack of extended neck positioning.

A, Initial lateral radiograph showing apparent thickening of retropharyngeal soft tissues mimicking potential retropharyngeal abscess (A). Note mildly enlarged palatine tonsils (P). B, Repeat lateral radiograph with neck extended, shows normal thickness of retropharyngeal soft tissues (arrows) , much narrower in thickness than adjacent vertebral bodies. Note palatine (P) and adenoid (A) tonsils.

CT is commonly performed to define the extent of disease and to help to predict cases in which a drainable fluid collection is present (see Fig. 2-7 ). On CT, a low-attenuation, well-defined area with an enhancing rim is suspicious for a drainable fluid collection (see Fig. 2-7 ). Cellulitis without abscess is actually more common than the presence of a drainable abscess.