A 58-year-old man from Delhi presents with acute right-sided weakness affecting the face, arm, and leg, along with dysarthria. MRI shows a left internal capsule infarct. All of the following fiber tracts are damaged in this lesion EXCEPT:

## Internal Capsule Stroke — Fiber Tract Localization A left internal capsule infarct produces a classic syndrome of contralateral motor and sensory deficits. Understanding which tracts are damaged and which are spared is essential for clinical correlation. ### Clinical Presentation **Key Point:** Left internal capsule infarct → right-sided hemiplegia (face, arm, leg) + hemisensory loss + dysarthria (not aphasia, because language areas are intact). ### Fiber Tracts Passing Through the Internal Capsule | Tract | Origin | Destination | Lesion Effect | |-------|--------|-------------|---------------| | **Corticospinal** | Motor cortex (M1) | Spinal cord | Contralateral hemiplegia | | **Corticobulbar** | Motor cortex | Brainstem CN nuclei | Facial weakness, dysarthria | | **Thalamocortical (sensory)** | VPL, VPM thalamus | Somatosensory cortex | Contralateral hemisensory loss | | **Frontopontine** | Prefrontal cortex | Pontine nuclei | Cognitive/behavioral change | **High-Yield:** All three of the first three options describe tracts that DO pass through the internal capsule and WOULD be damaged in a left IC infarct. ### Arcuate Fasciculus — The Distractor **Clinical Pearl:** The arcuate fasciculus is an association fiber tract connecting Broca area (inferior frontal, dominant hemisphere) to Wernicke area (superior temporal, dominant hemisphere). It runs *within the superior longitudinal fasciculus* in the white matter of the perisylvian region. **Key Point:** The arcuate fasciculus does NOT pass through the internal capsule. It is a short-range intra-hemispheric association bundle. Damage to it causes conduction aphasia (repetition defect with preserved comprehension), not the motor/sensory syndrome seen with IC infarction. **Warning:** A student might confuse "internal capsule" with "intra-hemispheric white matter" and incorrectly assume all white matter tracts pass through the IC. The IC is a *specific* bundle of projection fibers, not a general conduit for all brain connections. ### Why This Patient Does NOT Have Language Deficits The arcuate fasciculus is spared in an internal capsule lesion because it is anatomically separate. Therefore, this patient has: - ✓ Motor deficits (corticospinal damage) - ✓ Speech articulation deficits (corticobulbar damage → dysarthria) - ✓ Sensory deficits (thalamocortical damage) - ✗ Language comprehension or repetition deficits (arcuate fasciculus intact) **Mnemonic:** **IC-GAP** = Internal Capsule carries Genu (bulbar), Anterior (thalamic), Posterior (spinal). **SLF** (including arcuate) = Separate Lateral Fibers — not in IC.