Internal Capsule (IC)
The internal capsule is a dense white matter pathway located between the thalamus/caudate (medially) and the lentiform nucleus (laterally). It is a highly frequent site for lacunar infarcts.
1. Anatomy of the Limb Divisions
- Anterior Limb: Contains frontopontine fibers and thalamocortical fibers (connects mediodorsal thalamus to frontal lobe).
- Genu (The “Knee”): Contains corticobulbar fibers (motor pathways for CNs).
- Posterior Limb: Contains the corticospinal tract (anterior 2/3) and sensory fibers (posterior 1/3) carrying thalamocortical radiations.
2. Clinical Correlation: Lacunar Strokes
| Lesion Site | Classic Presentation |
|---|---|
| Posterior Limb | Pure motor stroke or pure sensory stroke (due to dense packing of fibers). |
| Genu | Contralateral facial weakness or dysarthria (corticobulbar involvement). |
NEET PG Hint: The blood supply is high-yield: the IC is supplied by the lenticulostriate arteries (branches of the MCA). Hypertension is the primary risk factor for rupture or thrombosis of these small vessels, leading to classic lacunar infarcts. A “pure motor” stroke without cortical signs (like aphasia or neglect) strongly points to an internal capsule lesion.