**Core Concept**
Antoni A and Antoni B patterns are histopathological features seen in schwannomas, representing areas of dense, well-differentiated Schwann cells (Antoni A) and loose, fibrous, hypocellular areas (Antoni B). These patterns reflect the tumor's growth dynamics and are key in differentiating schwannomas from other nerve sheath tumors.

**Why the Correct Answer is Right**
In schwannomas, Antoni A regions show tightly packed, palisaded Schwann cells with uniform nuclei, forming a "spindle cell" pattern, while Antoni B regions are loose, fibrous, and hypocellular. This biphasic structure is a hallmark of schwannomas, especially in peripheral nerve sheath tumors. The pattern arises due to alternating zones of active proliferation and quiescence in the tumor.

**Why Each Wrong Option is Incorrect**
Option B: Neurofibroma does not show Antoni A/B patterns. It presents with a loose, fibrous stroma and spindle cells, lacking the distinct biphasic structure.
Option C: Meningioma shows a typical "meningothelial" pattern with pseudorosettes and nested arrangements, not Antoni A/B.
Option D: Teratoma displays a mixture of mature tissues (e.g., hair, teeth, bone), not spindle cell or biphasic patterns.

**Clinical Pearl / High-Yield Fact**
Remember: **"Antoni A = dense, well-differentiated; Antoni B = loose, fibrous"** — this is specific to schwannomas. Never confuse with meningioma or neurofibroma. Always check for the presence of these patterns when evaluating nerve sheath tumors.

✓ Correct Answer: A. Schwannoma