Clinical Differentiation of Cortical and Subcortical Strokes

Strokes can be divided into those affecting the cerebral cortex (cortical), and those affecting structures below the cortex (sub-cortical), such as the internal capsule, thalamus, basal ganglia, brainstem, and cerebellum.  The differentiation is important clinically as the etiology of cortical and subcortical strokes are often different.  For instance, middle cerebral artery occlusions result in cortical strokes and have a different differential diagnosis than a small perforating artery resulting in a lacunar (subcortical) stroke in the internal capsule.

Cortical strokes often affect higher and synthetic mental functions.  Depending on the side of the brain and the lobe involved, different mental functions are affected.  Left frontal parietal strokes may result in aphasia (disturbance of language), alexia (disturbance of reading), agraphia (disturbance of writing), and acalculia (disturbance of calculating).  Right frontal parietal strokes may result in neglect and difficulty in spatial organization (drawing, copying or interpreting pictures).  In addition, it is important to remember that the motor and sensory control of specific regions of the body are “mapped” to specific regions of surface area of the cortex, producing a representation known as the homunculus.  On the homunculus, more area is devoted to the lower face, lips and tongue, as well as the hand and fingers.  The pattern of a hemiparesis affecting the distal extremities more than the proximal, and the arm and lower face more than the leg are characteristic of cortical strokes.  In addition, cortical sensory loss can be seen with parietal strokes.  As opposed to loss of primary sensory functions, more complex sensory functions are disturbed, including impaired double simultaneous stimulation, astereognosia (unable to tell shapes); and agraphesthesia (unable to tell what number or letter is written on a limb).

Lesions of the occipital lobes result in disturbances in vision.  Similar deficits occur with cortical strokes affecting the temporal and parietal lobes where the optic radiations travel.  Most often, lesions of the occipital cortex or optic radiations result in a contra lateral field abnormalities, especially hemianopsia or quadrantanopsia.  Other cortical visual abnormalities may also be seen, including visual agnosias, asimultagnosia (unable to see several objects at once), and cortical blindness.

Lesions of the medial temporal and frontal lobes often result in disturbances of  behavior and memory, especially recent memory and the ability to make new memories.

Subcortical strokes affect areas of the brain that chiefly consist of tracts of nerve axons leading to and from the cortex. Higher functions are typically spared, and motor or sensory involvement typically manifests as complete involvement of one-side of the body (e.g., pure motor hemiparesis, or pure sensory stroke affecting one side of the body), rather than the more discrete lesions characteristic of the homunculus. If the tracts to or from the brainstem and cerebellum are affected, cranial nerve findings may be seen (e.g., ptosis, double vision, facial numbness, ataxia, nystagmus, dysmetria, and dysdiadokinesis, etc).

TABLE Clinical Distinction of Cortical and Subcortical Strokes*

* Please know that all of the above are general guidelines.  Some exceptions may occur.  For instance, involvement of lateral geniculate nucleus (subcortical) may result in a disturbance of visual function mimicking a disorder of the optic radiations or occipital cortex.  Also, higher mental functions can be involved by large subcortical strokes that undercut the white matter tracts to large areas of cortex. 

Revised 12/14/01.
Copyright 2001 Case Western Reserve University School of Medicine.