Correct Answer: A. Acute laryngotracheobronchitis
Acute laryngotracheobronchitis (croup) is the most common cause of upper airway obstruction in children aged 6 months to 3 years, with peak incidence at 2 years. The classic X-ray finding in croup is the "subglottic narrowing" or "steeple sign" — a characteristic narrowing of the subglottic trachea on anteroposterior (AP) neck radiograph, caused by subglottic edema and inflammation. This radiological sign is pathognomonic for croup. The condition is typically viral (parainfluenza virus most common in India), presenting with barky, seal-like cough, inspiratory stridor, and hoarseness. The steeple sign reflects the anatomical predilection of viral inflammation to the subglottic region in young children, where the cricoid cartilage forms a fixed ring that cannot expand, making even mild edema clinically significant. Management is supportive with dexamethasone and nebulized epinephrine in severe cases. The X-ray finding is diagnostic and distinguishes croup from other causes of upper airway obstruction in this age group.
Why the other options are wrong
B. Parapharyngeal abscess — Parapharyngeal abscess presents with lateral pharyngeal swelling, deviation of soft palate, and dysphagia. X-ray shows lateral neck soft tissue swelling or a mass effect, NOT subglottic narrowing. The clinical presentation includes fever, trismus, and neck stiffness — absent in simple croup. This is a space infection requiring drainage, not a viral inflammatory condition. C. Acute epiglottitis — Epiglottitis causes supraglottic narrowing, not subglottic. The classic X-ray finding is the 'thumb sign' — loss of normal epiglottic outline with a rounded, thumb-like appearance. Epiglottitis is a medical emergency with severe dysphagia, drooling, and tripod posture. It is now rare in India due to Hib vaccination. The steeple sign is NOT seen in epiglottitis. D. Acute pharyngitis — Acute pharyngitis is inflammation of the pharynx without airway obstruction. X-rays are typically normal or show only mild pharyngeal wall thickening — no characteristic narrowing pattern. There is no stridor, and the condition does not produce the steeple sign. Pharyngitis is managed with supportive care and antibiotics if bacterial; it does not require airway-specific imaging findings.
High-Yield Facts
- Steeple sign on AP neck X-ray = subglottic narrowing, pathognomonic for croup (laryngotracheobronchitis)
- Peak age: 6 months to 3 years; most common at 2 years — matches this case
- Parainfluenza virus is the most common causative agent in India; RSV and influenza are also common
- Barky, seal-like cough + inspiratory stridor + hoarseness = clinical triad of croup
- Dexamethasone (0.6 mg/kg) is first-line treatment; nebulized epinephrine for severe cases with respiratory distress
- Supraglottic narrowing (thumb sign) = epiglottitis, NOT croup; this is the key radiological discriminator
Mnemonics
CROUP vs EPIGLOTTITIS — Radiological Distinction CROUP = Cricoid (subglottic) narrowing = Steeple sign | EPIGLOTTITIS = Epiglottic (supraglottic) narrowing = Thumb sign. Use: When you see a neck X-ray in a 2-year-old with stridor, ask 'Where is the narrowing?' — subglottic = croup; supraglottic = epiglottitis. Croup Presentation — 3 B's Barky cough (seal-like) + Bronchitis (lower airway involvement) + Birthday age (6 mo–3 yr). Use: Rapid recall of the classic clinical triad and age group.
NBE Trap
NBE may pair epiglottitis with croup to test whether students confuse the radiological findings — both cause stridor and upper airway obstruction, but the X-ray sign is the discriminator. The steeple sign (subglottic) vs. thumb sign (supraglottic) is the key differentiator that NBE expects students to recognize.
Clinical Pearl
In Indian pediatric practice, croup is the most common cause of stridor in toddlers presenting to emergency departments. The steeple sign on X-ray is diagnostic and helps avoid unnecessary antibiotics and invasive procedures. Most cases resolve with dexamethasone alone; only severe cases with respiratory distress require nebulized epinephrine and admission.
_Reference: OP Ghai (Pediatrics) Ch. 13; Bailey & Love (ENT) Ch. 24; Harrison Ch. 471_