Today’s USMLE® Step 2 CK Question of the Day involves a child who’s evaluated on inpatient rounds for a retropharyngeal abscess, and the physician tells his parents that urgent treatment is needed. Do you know why? Let’s find out!
A 5-year-old boy is evaluated on inpatient rounds for a retropharyngeal abscess. Temperature is 102 °F, pulse is 122/min, respiratory rate is 20/min. The patient is awake and oriented and appears tired. He is not struggling to breathe and is otherwise resting comfortably. An area of erythematous inflammation is seen in the posterior oropharynx, and the patient has mild submandibular lymphadenopathy. Parenteral antibiotic therapy is initiated with clindamycin and metronidazole. The physician explains to the parents at the bedside that urgent treatment is required due to the potential spread of infection into a region called the “danger space.” Which of the following best describes the boundaries of this space?
A. Buccopharyngeal fascia anteriorly and alar fascia posteriorly
B. Buccopharyngeal fascia anteriorly and prevertebral fascia posteriorly
C. Pretracheal fascia anteriorly and alar fascia posteriorly
D. Alar fascia anteriorly and prevertebral fascia posteriorly
The correct answer to today’s USMLE® Step 2 CK Question is…
D. Alar fascia anteriorly and prevertebral fascia posteriorly
Before we get to the Main Explanation, let’s see why the answer wasn’t A, B, C, or E. Skip to the bottom if you want to see the correct answer right away!
Incorrect Answer Explanations
A. Buccopharyngeal fascia anteriorly and alar fascia posteriorly
Incorrect: These are the boundaries of the retropharyngeal space. The ‘danger space’ is posterior to the retropharyngeal space and bounded anteriorly by the alar fascia and posteriorly by the prevertebral fascia.
B. Buccopharyngeal fascia anteriorly and prevertebral fascia posteriorly
Incorrect: The ‘danger space’ is posterior to the retropharyngeal space and bounded anteriorly by the alar fascia and posteriorly by the prevertebral fascia.
C. Pretracheal fascia anteriorly and alar fascia posteriorly
Incorrect: The ‘danger space’ is posterior to the retropharyngeal space and bounded anteriorly by the alar fascia and posteriorly by the prevertebral fascia.
Main Explanation
Posterior to the pharynx, there is a potential space called the retropharyngeal space. This space is bounded anteriorly by the buccopharyngeal fascia, the superior continuation of the pretracheal fascia, and posteriorly by the alar fascia. Infection in the retropharyngeal space can also lead to a retropharyngeal abscess, resulting in difficulty swallowing and speaking.
Another important space is the ‘danger space,’ which is posterior to the retropharyngeal space and bounded anteriorly by the alar fascia and posteriorly by the prevertebral layer of the deep cervical fascia. This space extends from the base of the skull into the posterior mediastinum and down to the level of the diaphragm, making it the most important route for the spread of infection between the neck and thorax.
Major Takeaway
The “danger” space lies posterior to the retropharyngeal space. It is bounded by the alar fascia anteriorly and the prevertebral fascia posteriorly. It is a potential space that provides a path for retropharyngeal infections to extend from the neck into the mediastinum in the thorax.
References
Mnatsakanian A, Minutello K, Bordoni B. Anatomy, Head and Neck, Retropharyngeal Space. [Updated 2021 Jul 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537044/
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