Anatomy of the Posterior Part of the Anterior Limb of the Internal Capsule
The posterior part of the anterior limb of the internal capsule primarily contains corticobulbar fibers that control facial, lingual, and pharyngeal movements.
Anatomical Organization of the Internal Capsule
The internal capsule is a major white matter pathway that can be divided into several parts:
- Anterior limb
- Genu
- Posterior limb
- Retrolentiform part
- Sublentiform part
Fiber Composition of the Posterior Part of Anterior Limb
Based on anatomical studies, the posterior part of the anterior limb of the internal capsule contains:
Corticobulbar fibers: These are the predominant fibers in this region 1
- Control facial movements
- Control lingual (tongue) movements
- Control pharyngeal muscles
- Contribute to speech articulation
Frontal-subcortical connections: These fibers connect frontal cortical regions to subcortical structures 2
- Organized in a posterior-superior to anterior-inferior axis
- Include cognitive and limbic feedback loops
Clinical Significance
The specific location of these fibers explains certain clinical syndromes:
Capsular Genu Syndrome: Although primarily affecting the genu, lesions extending to the posterior part of the anterior limb can cause:
- Contralateral facial and lingual hemiparesis
- Dysarthria
- Unilateral mastication-palatal-pharyngeal weakness
- Vocal cord paresis in some cases 3
Somatotopic Organization: Unlike the posterior limb (which contains corticospinal tracts for limb movement), the anterior limb's posterior portion focuses on bulbar functions 4
Anatomical Relations
The posterior part of the anterior limb of the internal capsule is:
- Situated medial to the lentiform nucleus
- Lateral to the caudate nucleus
- Superior to the genu of the internal capsule
- Continuous with the corona radiata superiorly 1
Imaging Characteristics
On advanced MRI imaging:
- Shows different relaxation properties compared to other parts of the internal capsule
- Has longer T1 and T2 relaxation times compared to adjacent regions
- Demonstrates lower Magnetization Transfer Ratio (MTR)
- These properties reflect the specific fiber composition and possibly lower myelin density in this region 5
Understanding this anatomy is essential for neurosurgeons targeting this region for procedures related to psychiatric disorders, as the organization shows some individual variability but with consistent patterns of connectivity 2.