**Core Concept**
Postoperative parotitis is an inflammatory condition of the parotid gland, often occurring after head and neck surgery, particularly after procedures involving the facial nerve. It is characterized by pain, swelling, and tenderness of the parotid gland. The condition is usually self-limiting but can be associated with significant morbidity if left untreated.

**Why the Correct Answer is Right**
Postoperative parotitis is primarily caused by the manipulation of the facial nerve during surgery, leading to its temporary paralysis or damage. This results in the accumulation of saliva in the parotid gland, causing inflammation and infection. The facial nerve is responsible for the innervation of the stylohyoid and digastric muscles, which in turn regulate the opening and closing of the parotid gland's orifice. Damage to the facial nerve disrupts this mechanism, leading to the stasis of saliva and subsequent inflammation.

**Why Each Wrong Option is Incorrect**
**Option A:** Prolonged anesthesia can lead to various complications, but it is not a direct cause of postoperative parotitis.
**Option B:** While dehydration can exacerbate postoperative parotitis, it is not a primary cause of the condition.
**Option C:** Infection is a possible complication of postoperative parotitis, but it is not the primary cause of the condition.

**Clinical Pearl / High-Yield Fact**
It is essential for surgeons to be aware of the risk of postoperative parotitis, particularly after procedures involving the facial nerve. Prompt recognition and treatment of the condition can prevent significant morbidity and improve patient outcomes.

**Correct Answer: C. Infection**