Anatomy Atlas

Internal capsule

Capsula interna
Also: Posterior limb of internal capsule · Lacunar infarct · Lacunar stroke
OrganHigh-yielddraftNeuro

Compact band of white matter carrying motor and sensory fibers between the cortex and the brainstem. A small (lacunar) infarct here can cause a pure motor hemiparesis of the face, arm and leg.

Core anatomy

Location

Deep in each hemisphere, V-shaped in horizontal section, between the caudate and thalamus (medially) and the lentiform nucleus (laterally) — see basal ganglia, thalamus.

Parts
  • Anterior limb (between caudate and lentiform): frontopontine and thalamocortical (anterior/mediodorsal) fibers
  • Genu: corticobulbar fibers (face, head)
  • Posterior limb (between thalamus and lentiform): corticospinal fibers (arm anterior, leg posterior) and thalamocortical sensory radiations (from VPL/VPM)
  • Retrolenticular and sublenticular parts: optic radiations and auditory radiations
  • Continues below as the cerebral peduncle of the midbrain and above as the corona radiata
Relations

Because motor fibers for the whole half-body are packed tightly together, a small lesion causes a large deficit — contralateral face, arm and leg equally.

Arterial supply

Lenticulostriate arteries (from the MCA) — most of the capsule; anterior choroidal artery (from the ICA) — lower posterior limb; recurrent artery of Heubner (from the ACA) — anterior limb and genu. See cerebral arteries (ACA, MCA, PCA).

Notes

Contains the corticospinal tract and the sensory projections from the thalamus.

Mentioned in

Generated automatically from links in other entries.

Horizontal section of the hemisphere showing the internal capsule with the motor (red) fibers at the genu and posterior limb and the thalamocortical sensory fibers (blue), and the optic radiation
Tracts in the internal capsule: motor (red) and sensory (blue) fibers and the optic radiation.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 746. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))
Coronal section showing the caudate nucleus, internal capsule, putamen, globus pallidus, claustrum, insula, lateral and third ventricles and optic chiasm
Coronal section showing the internal capsule between the caudate and lentiform nuclei.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 744. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Lacunar infarcts PANCE

Mechanism / lesion

Occlusion of a single deep penetrating artery (lipohyalinosis) from chronic hypertension and diabetes; infarcts under 1.5 cm.

Classic presentation

Classic syndromes, without cortical signs (no aphasia, neglect or visual field loss): pure motor hemiparesis (posterior limb or basis pontis — contralateral face, arm and leg equally); pure sensory stroke (thalamus); sensorimotor stroke (thalamus + capsule); ataxic hemiparesis and dysarthria–clumsy hand syndrome (capsule or pons).

Hypertensive intracerebral hemorrhage PANCE

Mechanism / lesion

Rupture of lenticulostriate vessels in the putamen or thalamus extending into the capsule.

Classic presentation

Sudden contralateral hemiplegia and sensory loss, headache, vomiting, declining consciousness; very high blood pressure. Noncontrast CT; lower BP, reverse anticoagulation.

High-yield PANCE pearls

  • Pure motor hemiparesis of face, arm and leg equally, no cortical signs → lacunar infarct of the posterior limb.
  • Lacunes → hypertension and diabetes (small vessel disease).
  • Cortical signs (aphasia, neglect, field cut, gaze deviation) → cortical (large vessel) stroke, not lacunar.

Imaging anatomy

CT

Noncontrast CT excludes hemorrhage; small acute lacunes are often invisible early.

MRI

DWI MRI shows acute lacunar infarcts; T2/FLAIR shows chronic small vessel disease (white matter hyperintensities, old lacunes).

Physical exam

Strength / function testing

Compare face, arm and leg strength (equal involvement suggests capsular lesion; face/arm > leg suggests MCA cortex); check for cortical signs — language, neglect, visual fields, cortical sensation; upper motor neuron signs (hyperreflexia, Babinski).

Self-quiz

Q1.

A 66-year-old with long-standing hypertension develops weakness of the left face, arm and leg to the same degree. Sensation, language, visual fields and attention are normal. Where is the most likely lesion?

Show answer

B

Pure motor hemiparesis of the face, arm and leg equally, with no cortical signs, is a lacunar infarct of the posterior limb of the internal capsule (lenticulostriate branch of the MCA).

Q2.

Which fibers pass through the genu of the internal capsule?

Show answer

B

The genu carries corticobulbar fibers to cranial nerve motor nuclei. Corticospinal fibers and sensory radiations are in the posterior limb; optic radiations are retrolenticular.

Q3.

Which risk factors are most associated with lacunar infarcts of the internal capsule?

Show answer

B

Lacunes are small-vessel infarcts from lipohyalinosis of deep penetrating arteries, caused mainly by chronic hypertension and diabetes. Atrial fibrillation causes embolic cortical strokes.

Q4.

Which finding argues against a lacunar infarct?

Show answer

E

Lacunar syndromes lack cortical signs: aphasia, neglect, visual field loss and gaze deviation point to a cortical (large-vessel) stroke.

Q5.

Which vessels supply most of the internal capsule?

Show answer

A

Most of the internal capsule is supplied by the lenticulostriate arteries of the MCA, with contributions from the anterior choroidal artery (posterior limb) and the recurrent artery of Heubner (anterior limb and genu).

Flashcards

See also