Posterior limb of the internal capsule là gì bao trong năm 2024

Maingard J, Luong D, Bell D, et al. Internal capsule. Reference article, Radiopaedia.org (Accessed on 29 Mar 2024) https://doi.org/10.53347/rID-29687

The internal capsule (TA: capsula interna) is a deep subcortical structure that contains a concentration of afferent and efferent white matter projection fibers. Anatomically, this is an important area because of the high concentration of both motor and sensory projection fibers 1,2. Afferent fibers pass from cell bodies of the thalamus to the cortex, and efferent fibers pass from cell bodies of the cortex to the cerebral peduncle of the midbrain 2. Fibers from the internal capsule contribute to the corona radiata.

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The internal capsule is made up of five parts. These are the anterior limb, genu, posterior limb, retrolentiform and sublentiform parts of the internal capsule 1,2:

• anterior limb (anterior crus)
  • lies between the head of the caudate nucleus medially and the lentiform nucleus laterally
  • contains the anterior thalamic radiation and frontopontine fibers
• genu
  • lies medial to the apex of the lentiform nucleus
  • contains corticonuclear fibers (previously called corticobulbar fibers)
• posterior limb (posterior crus)
  • lies between the thalamus medially and the lentiform nucleus laterally
  • contains
    • corticospinal fibers lying in the anterior two-thirds of the posterior limb
      • fibers from anterior to posterior: arm, hand, trunk, leg, perineum 2
    • the middle thalamic radiation which contains somatosensory fibers from the ventral posterior thalamic nucleus
• retrolentiform part
  • lies posterior to the lentiform nucleus
  • contains the
    • geniculocalcarine or optic radiation (from the lateral geniculate nucleus)
    • corticopontine fibers (parietopontine and occiptopontine fibers) 2
• sublentiform part
  • lies inferior to the lentiform nucleus
  • contains the
    • auditory radiations (from the medial geniculate nucleus)
    • temporopontine fibers

The blood supply of the internal capsule is variable but is commonly from small perforating branches of the middle cerebral artery and anterior cerebral artery. These include the lateral lenticulostriate arteries and the recurrent artery of Heubner respectively 3. In addition, the anterior choroidal artery from the internal carotid artery supplies the posterior limb and retrolentiform part of the internal capsule 3,4.

CT

• best appreciated on axial images at the level of the insular cortex
• appears relatively hypodense to surrounding basal ganglia structures

MRI

in term neonates, internal capsule appears as higher T1-weighted and lower T2-weighted intensity when compared to basal ganglia and thalamus 6

The internal capsule, a white matter structure, is a unique location where a large number of motor and sensory fibers travel to and from the cortex. Damage of any kind in this location will cause some relatively unique findings that can allow you to localize the lesions to the internal capule by exam alone.

Location

The internal capsule is one of the subcortical structures of the brain.

Subcortical structures: internal capsule, caudate, putamen, globus pallidus, thalamus, brainstem

The anterior limb of the internal capsule separates the caudate nucleus and lenticular nucleus

The posterior limb separates the thalamus and lenticular nucleus

Types of fibers

• Anterior limb: frontopontine fibers (frontal cortex to pons), thalamocortical fibers (thalamus to frontal lobe)
• Genu (angle): corticobulbar fibers (cortex to brainstem)
• Posterior limb: corticospinal fibers (cortex to spine), sensory fibers

Blood Supply

• Anterior limb: mainly fed by the lenticulostriate branches of middle cerebral artery(MCA), less often branches of anterior cerebral artery (ACA)
  • The lenticulostriate arteries are small penetrating blood vessels that supply blood flow to most of the subcortical structures.
• Genu: lenticulostriate branches of MCA
• Posterior limb: lenticulostriate branches of MCA & anterior choroidal artery (AChA) of internal carotid artery

Symptoms and Signs

Weakness of the face, arm, and/or leg (pure motor stroke)

Known as one of the classic types of lacunar infarcts, a pure motor stroke is the result of an infarct in the internal capsule.

Pure motor stroke caused by an infarct in the internal capsule is the most common lacunar syndrome.

Upper motor neuron signs

hyperreflexia, Babinski sign, Hoffman present, clonus, spasticity

Mixed sensorimotor stroke

Since both motor and sensory fibers are carried in the internal capsule, a stroke to the posterior limb of the internal capsule (where motor fibers for the arm, trunk and legs and sensory fibers are located) can lead to contralateral weakness and contralateral sensory loss

If a patient has weakness +/- sensory deficits, how can you tell whether the stroke is subcortical or cortical? What other symptoms or signs can help you localize the stroke to the internal capsule as opposed to the cortex?

A patient who presents with arm and leg weakness may have either a small internal capsule stroke or a large ACA + MCA cortical stroke. Looking at the homunculus in the figure above, the cortical leg area is supplied by the ACA and the arm area is supplied by the MCA. However, the injury to the cortices produces other symptoms and signs that not commonly produced by injury to the subcortical areas.

The presence of these cortical signs may exclude an internal capsule stroke:

gaze preference or gaze deviation

expressive or receptive aphasia

visual field deficits

visual or spatial neglect

If any of these signs are present, the patient may have a cortical stroke, not an internal capsule stroke.