**Core Concept**
Acute retropharyngeal abscess (ARA) is a serious infection that occurs in the retropharyngeal space, which is a potential space located between the buccopharyngeal fascia and the prevertebral fascia in the neck. ARA is often caused by a bacterial infection, typically Staphylococcus aureus or Streptococcus pyogenes, and can be life-threatening if not promptly treated.

**Why the Correct Answer is Right**
Acute retropharyngeal abscess typically presents with symptoms such as neck pain, fever, dysphagia, and respiratory distress. The infection can spread to surrounding structures, including the pharynx, larynx, and mediastinum, leading to severe consequences. The diagnosis of ARA is often made through imaging studies, such as CT or MRI scans, which show a collection of pus in the retropharyngeal space. Treatment typically involves antibiotics, drainage of the abscess, and supportive care.

**Why Each Wrong Option is Incorrect**
**Option A:** ARA is often caused by a viral infection. This is incorrect because ARA is typically caused by a bacterial infection, not a viral one.

**Option B:** ARA is a common complication of pharyngitis. This is incorrect because while pharyngitis can be a precursor to ARA, it is not a direct complication of the condition.

**Option C:** ARA can be treated with oral antibiotics alone. This is incorrect because ARA often requires drainage of the abscess, in addition to antibiotics, to effectively treat the infection.

**Option D:** ARA is a rare condition. This is incorrect because ARA is a relatively rare but serious condition that requires prompt medical attention.

**Clinical Pearl / High-Yield Fact**
ARA can mimic other conditions, such as Ludwig's angina or epiglottitis, so a high index of suspicion is necessary for diagnosis. Imaging studies are essential for accurate diagnosis and treatment planning.

**Correct Answer:** D.