## Why Retropharyngeal abscess is right Widening of the prevertebral soft tissue space (marked **A**) beyond the normal limits of < 7 mm at C2 and < 22 mm at C7 in adults is a classic radiographic sign of retropharyngeal abscess. In this case, the measurement of 18 mm at C2 far exceeds the normal 7 mm threshold, indicating significant soft tissue swelling in the retropharyngeal space. Combined with the clinical presentation of severe pharyngitis, dysphagia, fever, and trismus, this finding is pathognomonic for deep space neck infection. The patient requires urgent imaging (CT neck with contrast) for confirmation and drainage planning. (Maheshwari Orthopedics 10e; Harrison 21e Ch 461) ## Why each distractor is wrong - **Epiglottitis with thumbprint sign**: While epiglottitis does cause prevertebral soft tissue widening, the classic radiographic finding is the "thumbprint sign" (swollen epiglottis on lateral neck X-ray), not simply widened prevertebral space. The clinical presentation (trismus, muffled voice) is more consistent with retropharyngeal abscess than acute epiglottitis, which typically presents with drooling, stridor, and respiratory distress. - **C-spine trauma with hematoma**: Although cervical trauma can cause prevertebral soft tissue widening from hematoma, there is no history of trauma in this patient. The acute infectious presentation (fever, sore throat, dysphagia) rules out traumatic etiology. - **Acute pharyngitis without deep space involvement**: Uncomplicated pharyngitis does not cause significant prevertebral soft tissue widening. The markedly elevated measurement (18 mm at C2) indicates deep space involvement, not simple mucosal inflammation. **High-Yield:** Prevertebral soft tissue > 7 mm at C2 or > 22 mm at C7 in adults = retropharyngeal pathology (abscess, hematoma, or foreign body) until proven otherwise. [cite: Maheshwari Orthopedics 10e; Harrison 21e Ch 461]
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