**Core Concept**
Endoscopic sinus surgery (ESS) is a minimally invasive procedure to treat chronic rhinosinusitis and other sinus disorders. It requires thorough preoperative evaluation to assess the sinus anatomy and identify potential challenges.

**Why the Correct Answer is Right**
The correct prerequisite for ESS is a thorough **preoperative computed tomography (CT) scan** of the paranasal sinuses. This imaging study helps to identify the sinus anatomy, including any anatomical variations, such as a concha bullosa or a Haller cell, which may impact the surgical approach. The CT scan also helps to identify any underlying conditions, such as a deviated septum or nasal polyps, that may need to be addressed during surgery.

**Why Each Wrong Option is Incorrect**
**Option A:** A thorough medical history and physical examination are essential in evaluating patients for ESS, but they are not the primary prerequisite for the procedure.
**Option B:** A nasal endoscopy may be performed to evaluate the nasal cavity and sinuses, but it is not a prerequisite for ESS.
**Option C:** A blood test may be ordered to evaluate for underlying conditions, such as anemia or bleeding disorders, but it is not a prerequisite for ESS.

**Clinical Pearl / High-Yield Fact**
A thorough preoperative CT scan of the paranasal sinuses is essential in planning and executing ESS, as it helps to identify potential challenges and allows for a more effective and safe surgical approach.

**Correct Answer: B. A nasal endoscopy may be performed to evaluate the nasal cavity and sinuses, but it is not a prerequisite for ESS.**