**Core Concept**
Antrochoanal polyps are benign nasal polyps that originate from the mucous membranes of the maxillary sinus and extend into the nasopharynx through the choana. The treatment of choice aims to remove the polyp and address the underlying cause of nasal obstruction and sinusitis.

**Why the Correct Answer is Right**
The treatment of choice for antrochoanal polyps is endoscopic sinus surgery (ESS). ESS involves the use of nasal endoscopes to visualize the nasal passages and sinuses, allowing for precise removal of the polyp and any underlying diseased tissue. This approach is preferred over traditional open surgery due to its minimally invasive nature and lower risk of complications. The success of ESS in treating antrochoanal polyps is attributed to its ability to address the polyp's origin in the maxillary sinus, reducing the likelihood of recurrence.

**Why Each Wrong Option is Incorrect**
**Option A:** Antrostomy alone may not be sufficient to treat antrochoanal polyps, as it may not address the polyp's origin in the maxillary sinus.
**Option B:** Functional endoscopic nasal surgery (FENS) is a broader term that encompasses ESS, but it is not the specific treatment of choice for antrochoanal polyps.
**Option C:** Caldwell-Luc procedure is a traditional open surgery approach that is generally reserved for more complex sinus cases and is not the preferred treatment for antrochoanal polyps.

**Clinical Pearl / High-Yield Fact**
ESS is a highly effective treatment for antrochoanal polyps, with a high success rate and low recurrence rate when performed by an experienced surgeon.

**Correct Answer: D. Endoscopic sinus surgery (ESS)**