Brain Internal Capsule – Structure Orientation and Nerve Tracts

Dr Sanjoy Sanyal

Neuroscience Professor Surgeon and Informatician

Preface• The Sub-cortical White Matter of Brain is graphically

represented

• The bulk of this presentation deals with Projection Fibers, more specifically the Internal Capsule

• Formation, Orientation of Internal Capsule and Important Tracts within it are pictorially described

• A brief tabulation of Stroke Syndromes involving the Internal Capsule is also included

• A quick description of Commissural and Association Fibers concludes the presentation

• Every slide is richly graphically illustrated

• Audio commentary accompanying each slide will follow in a separate presentation

SC White Matter

• Axial Section through Cerebral Hemispheres

• Sub-cortical (SC) / Central / Peri-ventricular White Matter

• Commissural (C), Association (A) Projection (P) Fibers

DTI – WMT • Diffusion Tensor Imaging (DTI)

• White Matter Tractography(WMT)

• Coronal View: Commissure (C), Association (A), Projection (P) Fibers

Legend: LF = Longitudinal Fissure; FL = Frontal Lobe; LS = Lateral Sulcus; TL = Temporal Lobe; CC = Crus Cerebri; Py = Pyramid

• Fan-shaped fibers in Cerebral Hemispheres

• Spread like a ‘Radiating Crown’; Oriented in Vertical axisP

roje

ction

Fibe

rs

Projection Fibers • Corona Radiatacontains Descending and Ascending Fibers

• Caudally, fibers are densely packed in region of Basal Ganglia

• Here, Projection Fibers are called Internal Capsule

Projection Fibers • DTI /WMT: Cortico-spinal Tracts (CST) Projection Fibers in Brain and Pyramids (Py) of Medulla

• Some White fibers in either Temporal Lobes are also seen

Internal Capsule – Develop• 5th Week IUL: StriatalEminence (SE) appears on lateral wall of TelencephalicVesicle

• Developing Internal Capsule splits SE into medial and lateral parts

• Internal Capsule descends lateral to developing Thalamus

Internal Capsule – Striatum • Striatum =

Caudate + Putamen

• Gray Matter strands connect the two, giving it Striated appearance

• Internal Capsule fibers pass through Striatum

• Medial part of Striatum is Caudate Nucleus

• Lateral part of Striatum is Putamen

Inte

rnal C

apsu

le• Internal Capsule fibers pass through Striatum

• Fibers pass between Caudate Nucleus medially and LentiformNucleus (Putamen + Globus pallidus) laterally

Axial Sections Through Brain and

Internal Capsule• Next slide shows the Axial

Section findings

Internal Capsule – Axial View• Anterior Limb: Between Caudate and Lentiform Nuclei

• Posterior Limb: Between Thalamus and Lentiform Nucleus

• Genu (‘Knee’): Bent portion connecting 2 Limbs of Internal Capsule

Inte

rnal C

apsu

le –

Tracts

Corticospinal Tract in IC • Diffusion Tensor Imaging (DTI) and White Matter Tracto-graphy(WMT) showing Cortico-spinal Tract (CST) inside Internal Capsule (IC)

• Corpus Callosum(CC) is also visible

Internal Capsule Stroke

Syndromes

CommissureFibers

• Connects corresponding areas of both Cerebral Hemispheres

• Corpus Callosum is largest Commissure

• Connects Neocortex of Cerebral Hemispheres

• 3rd Commissure to develop (12-22 Wk IUL)

• Commissurotomyproduces Sperry’s ‘Split-Brain Syndrome’

Asso

ciation

Fibe

rs• Association Fibers connects 2 areas in same Hemisphere in A-P axis

• Superior Longitudinal Fasciculus (SLF) Lesion causes ‘Conduction Aphasia’