## **Core Concept**
Peritonitis is inflammation of the peritoneum, typically caused by a bacterial infection. It can be primary (spontaneous) or secondary, with the latter usually resulting from a perforation of the gastrointestinal tract or other abdominal organs. The most common causes vary based on demographic factors, including age and sex.

## **Why the Correct Answer is Right**
The correct answer, **C. Perforated peptic ulcer**, is a leading cause of peritonitis in adult males. This condition arises when a peptic ulcer perforates through the stomach or duodenal wall, releasing acidic gastric contents into the peritoneal cavity. This leads to a severe chemical and bacterial peritonitis. The perforation can be due to long-standing peptic ulcer disease, NSAID use, or stress.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While **Spontaneous bacterial peritonitis (SBP)** is a known cause of peritonitis, it is more commonly associated with cirrhosis and ascites, rather than being the most common cause in adult males without specifying liver disease.
- **Option B:** **Appendicitis** is a common cause of peritonitis, especially in younger individuals, but it is not specified to adult males and can be less common in adults over 50.
- **Option D:** **Diverticulitis** can cause peritonitis, particularly in older adults, but it is less frequently the cause in adult males compared to perforated peptic ulcers.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that the most common cause of peritonitis can vary by age, sex, and underlying health conditions. For adult males, a perforated peptic ulcer is a critical and classic cause that requires immediate surgical intervention. Recognizing the patient's demographics and clinical presentation can guide towards the likely cause.

## **Correct Answer:** . Perforated peptic ulcer