**Core Concept**
Acute alveolar abscess is a localized collection of pus within the periodontal ligament space of a tooth, often resulting from bacterial infection. Early diagnosis is crucial for effective treatment and prevention of further complications. In the initial stages, radiographic findings can provide valuable clues for its identification.

**Why the Correct Answer is Right**
PDL (Periodontal Ligament) widening is a characteristic radiographic feature of acute alveolar abscess. This occurs due to inflammation and edema of the periodontal ligament, which leads to increased space between the tooth and the surrounding bone. The widening of the periodontal ligament space is a direct result of the body's response to infection, making it a reliable indicator of acute alveolar abscess on radiographs. This is often observed in the early stages of the condition, before significant bone loss or other complications arise.

**Why Each Wrong Option is Incorrect**
**Option A:** No change is incorrect because radiographic evidence of acute alveolar abscess is usually present, and the periodontal ligament space will typically be affected.
**Option B:** A diffuse radiolucency is not a specific indicator of acute alveolar abscess, as it can be seen in various other conditions affecting the jaw.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that early diagnosis of acute alveolar abscess relies heavily on radiographic findings, including PDL widening. A thorough clinical examination and history also play a crucial role in identifying this condition.

**✓ Correct Answer: C. PDL widening.**