**Core Concept**
The left paracentral lobule is part of the precentral gyrus in the cerebral cortex and is responsible for motor control of the contralateral lower limb and perineal region via the descending motor pathways. Injury here disrupts the corticospinal tract, leading to contralateral motor deficits.

**Why the Correct Answer is Right**
The left paracentral lobule lies in the precentral gyrus and is the primary motor area for the contralateral leg and perineum. Damage to this region results in **contralateral lower limb paresis** (right leg) and **perineal dysfunction** due to disruption of the corticospinal tract and its projection to spinal cord levels. The perineal innervation arises from the ventral primary motor cortex via the corticospinal tract, which decussates in the medulla and continues to the lower spinal segments.

**Why Each Wrong Option is Incorrect**
Option B: Left face – The face is controlled by the **contralateral** facial nucleus (via the corticobulbar tract), and injury to the left paracentral lobule does not affect the left face.
Option C: Right face – The right face is innervated by the **left** corticobulbar tract, which originates in the **right** precentral gyrus, not the left paracentral lobule.
Option D: Right shoulder & trunk – These areas are controlled by the **upper motor cortex** and **postcentral gyrus**, not the paracentral lobule; the paracentral lobule primarily controls the lower limb, not trunk or shoulder.

**Clinical Pearl / High-Yield Fact**
Remember: **"Paracentral = contralateral leg and perineum"**. Always associate paracentral lesions with **contralateral lower limb weakness** and **perineal paresis**, not facial or upper limb deficits.

✓ Correct Answer: A. Rt. Leg and perineus