**Core Concept**
Anastomotic leakage is a serious complication of colorectal surgery, occurring when there is a breach in the integrity of the anastomosis, leading to leakage of fecal material into the peritoneal cavity. The clinical presentation of anastomotic leakage can vary depending on the location and severity of the leak.

**Why the Correct Answer is Right**
The appearance of anastomotic leakage following a low colonic anastomosis most often manifests as peritonitis, a clinical syndrome characterized by inflammation of the peritoneum. This occurs due to the leakage of fecal material into the peritoneal cavity, which triggers a systemic inflammatory response. The peritoneal cavity's rich lymphatic drainage and presence of resident macrophages facilitate the rapid onset of peritonitis. **Option C: Peritonitis** is the correct answer because it is the most common and clinically relevant manifestation of anastomotic leakage in this context.

**Why Each Wrong Option is Incorrect**
**Option A:** Fecaluria is a possible manifestation of anastomotic leakage, but it is less common and typically occurs in the setting of a higher colonic anastomosis.
**Option B:** Abdominal pain is a non-specific symptom that can occur in various conditions, including anastomotic leakage. However, it is not the most specific or sensitive indicator of this complication.

**Clinical Pearl / High-Yield Fact**
In the post-operative period, a high index of suspicion for anastomotic leakage is essential, particularly in patients with symptoms such as abdominal pain, fever, and leukocytosis. A prompt diagnosis and management plan can significantly improve patient outcomes.

**Correct Answer:** C. Peritonitis.