**Core Concept**
Antrochoanal polyps are benign, unilateral nasal polyps originating from the mucosa of the maxillary antrum and extending into the nasal cavity through the nasal meatus. They are characterized by a stalk-like attachment to the underlying bone and are often associated with chronic nasal obstruction and sinusitis.

**Why the Correct Answer is Right**
Antrochoanal polyps are typically single, unilateral lesions, and their growth is usually slow and asymptomatic. They are often associated with antral mucosal hypertrophy and are usually found in younger patients. The polyp's stalk-like attachment to the underlying bone is a characteristic feature.

**Why Each Wrong Option is Incorrect**
**Option A:** Antrochoanal polyps are indeed typically unilateral, but this is not an exception to the statement.
**Option B:** Antrochoanal polyps are indeed often associated with chronic nasal obstruction and sinusitis, but this is not an exception to the statement.
**Option C:** Antrochoanal polyps are indeed usually single, but this is not an exception to the statement.

**Clinical Pearl / High-Yield Fact**
Antrochoanal polyps are often mistaken for other nasal masses, such as inverted papillomas or nasopharyngeal carcinomas. A thorough endoscopic examination and imaging studies are essential for accurate diagnosis.

**Correct Answer:** D.