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An 18 month old female presented to the Emergency Department with a history of fever, noisy breathing, a harsh cough, and drooling. The fever and coughing began yesterday, but tonight the fever is higher and the cough sounds very harsh. The sound of this cough was alarming to the parents. The highest temperature measured was 39.5 degrees rectally. She was noted to be drooling more than usual, but this was attributed to teething. Her cry was more raspy than her normal cry. She was not taking in solids well, but she was taking liquids well. Exam: VS T39.1 degrees rectally, P170, R28, BP 100/66. She appeared alert, awake, not toxic, in no acute distress. She did not appear to prefer an upright or a forward leaning position. Skin was warm & moist, without rash. No head or sinus tenderness were noted. Tympanic membranes were normal. The oral pharynx was clear and the mucosa was moist. Excessive drooling was not noticed by the examiner. The neck was supple with small lymph nodes bilaterally. Heart regular without murmurs. Lungs clear when resting. However, when she was crying, mild inspiratory stridor was noted. An occasional croupy cough was noted. The abdominal exam was unremarkable. Color and perfusion were good. A soft tissue lateral neck radiograph was ordered. View lateral neck radiograph. Is this radiograph consistent with croup? The epiglottis is normal in shape. The pre-epiglottic (vallecular) space is preserved. The airway is patent. There is pre-vertebral soft tissue swelling noted. This radiograph is consistent with a retropharygeal abscess, not croup. Discussion and teaching points: The retropharyngeal space is a pocket of connective tissue that extends from the base of the skull approximately to the tracheal carina. It harbors two chains of lymphoid tissue that drain the nasopharynx, adenoids, and posterior paranasal sinuses. Bacterial infections of the areas drained may result in suppuration of the nodes and abscess formation. These lymphatic chains begin to atrophy about the third or fourth year of life. Thus, 50% of the cases of retropharyngeal abscess occur between 6 and 12 months of age, and 96% of cases occur in children under 6 years of age (prior to lymphatic atrophy). Staph aureus and group A beta-hemolytic streptococci are the most common pathogens; however, Hemophilus influenza and anaerobes have also been recovered. There is usually a prodromal nasopharyngitis or pharyngitis with dysphagia, refusal of feeding, severe throat pain, hyperextension of the head, and noisy respirations. Previous trauma or evidence of associated infectious conditions should be sought. Respirations may be labored. There may be drooling, stridor, a raspy voice (cry), and a croupy cough. A bulge in the retropharynx may be visible. Meningismus may result from irritation of the paravertebral ligaments. Pain in the back of the neck or shoulder may be precipitated by swallowing. However, in many cases, a retropharyngeal abscess may be difficult to clinicially distinguish from croup. A lateral view of the soft tissues of the neck is frequently helpful in making the diagnosis, demonstrating the retropharyngeal mass in the stable patient. Normal prevertebral spaces are as follows: Anterior to C2: Less than or equal to 7mm in children and adults. Anterior to C3 and C4: less than 5mm in children or adults or less than 40% of the AP diameter of the C3 and C4 vertebral bodies. To simplify things, others suggest that the upper pre-vertebral soft tissue should be no wider than one vertebral body width. Adequate hyperextension of the head and neck is necessary in order to properly interpret the film if there is no history of trauma. If the head and neck are not properly positioned, the pre-vertebral space will appear to be widened because the neck is not extended enough. Repeating the radiograph with proper positioning may resolve this problem. If proper positioning is not possible or if the clinician is unsure if plain films are definitive, CT of this area can more accurately define any abnormalities of this region. Most patients presenting with symptoms of croup have viral croup. While epiglottitis is usually not difficult to distinguish clinically from croup, an early retropharyngeal abscess may be difficult to distinguish from croup. A lateral neck radiograph may reveal this occult diagnosis in selected cases, such as those with high fever, unexpected lymphadenopathy, or those wit h a suspicious bulge in the pharynx. Other causes of partial upper airway obstruction include epiglottitis, croup, peritonsillar abscess, severe tonsillitis, infectious mononucleosis, cystic hygroma, hemangioma, or neoplasms. Retained upper esophageal foreign bodies, trauma to the retropharynx from foreign body ingestion, instrumentation, and C-spine injury can also cause localized swelling or obstruction. View another cause of stridor. This radiograph shows evidence of epiglottitis (also called supraglottitis). The epiglottis is thumb-like in appearance (instead of triangular or flat in shape) and the aryepiglottic folds are thickened. The pre-epiglottic space is preserved to some degree, but it is not as large as it should be. In many cases of epiglottitis, the pre-epiglottic space is obliterated (replaced by edematous tissue). The retropharyngeal space (pre-vertebral tissue) is not widened. View another cause of stridor. This radiograph looks normal except for a mild degree of subglottic airway narrowing. This type of pattern correlates best with patients presenting with viral croup. References Fleisher GR. Infectious Disease Emergencies. In: Fleisher GR, Ludwig S (eds). Textbook of Pediatric Emergency Medicine, third edition. Baltimore, Williams & Wilkins, 1993, pp. 613-621. Santamaria J, Abrunzo TJ. Ear, Nose, and Throat. In: Barkin R (ed). Pediatric Emergency Medicine Concepts and Clinical Practice. Chicago, Mosby Year Book, 1992, pp. 680-682.