MRI Assessment of Infarct Depth
On diffusion-weighted (DWI) and FLAIR images, the lateral ventricle wall serves as a boundary that allows for estimating the volume of ischemic damage.
In an infarct within the posterior temporo-occipital territory of the middle cerebral artery (MCA), the hyperintense lesion is located above the lateral sulcus (Sylvian fissure). The pathological process predominantly involves the cortex (angular and supramarginal gyri, Wernicke's center), but may extend deep into the white matter, directly reaching the lateral ventricle wall.
Clinical consequences depend on the structures involved in the lesion:
- Optic radiation: its damage in the deep parts of the parietal lobe causes right-sided hemianopsia (loss of the right half of the visual field).
- Precentral region: even partial involvement of the precentral gyrus leads to hemiparesis.
Hemispheric Disconnection Syndromes
The study of commissural fibers passing above the lateral ventricles was conducted in patients with "split-brain" syndrome. It occurs due to agenesis or surgical transection of the corpus callosum (callosotomy) to treat refractory epilepsy.
Olfactory system: Olfactory pathway fibers do not cross, and the connection between centers occurs via the anterior commissure. If it is damaged, the patient cannot name an odor inhaled through the right nostril. Information enters the right hemisphere, but does not reach the speech centers in the left.
Visual system: Fibers from the nasal halves of the retinas cross, and visual fields are projected to the opposite hemispheres. In disconnection:
- Objects on the left (projecting to the right hemisphere) cannot be named or read by the patient (selective aphasia and alexia develop).
- Complex patterns on the right (projecting to the left hemisphere) cannot be analyzed by the patient, as spatial analysis centers are located in the right hemisphere.
Complex Motor Disorders (Apraxia)
The term was introduced by H. Jackson in 1870, and the classification was proposed by G. Liepmann. Apraxia is the inability to perform complex sequences of goal-directed movements while muscle strength is preserved, motivation is present, and isolated and automatic movements are unaffected.
Types of apraxia:
- Motor apraxia: inability to perform a basic motor act (e.g., intentionally picking up an object).
- Ideomotor apraxia: damage to association areas of the left hemisphere; manifested by omission of movement elements.
- Ideational apraxia: a rare form resulting from a lesion in the left temporoparietal region. The purpose of movement is lost, and the patient cannot plan it, although physically capable of performing it.
- Constructive apraxia: damage to the parietal lobe of the right hemisphere. Characterized by difficulties in drawing geometric shapes (acopia).
Agnosia and Gerstmann Syndrome
Association areas of the posterior parietal lobe integrate somatosensory, visual, and motor information. Their damage leads to agnosia—the loss of the ability to recognize objects despite intact sensory organs.
- Visual agnosia: the patient sees an object, describes it, but cannot name it. Includes prosopagnosia (inability to recognize faces) and alexia.
- Somatosensory agnosia: includes astereognosis (inability to recognize by touch) and asomatognosia (impaired perception of one's own body).
An ischemic lesion of the left parietal lobe may lead to Gerstmann syndrome (described in 1924), which includes a tetrad of symptoms: finger agnosia, dysgraphia (impaired writing), dyscalculia (impaired calculation), and right-left confusion.
Briefly: answers to topical questions
What anatomical parts are distinguished in the structure of the lateral ventricle?
Several main anatomical parts are distinguished in the structure of the lateral ventricle. These include:
- Anterior horn (cornu anterius) — projects into the frontal lobe;
- Central part (body) — the middle part of the ventricle;
- Posterior horn (cornu posterius) — directed into the occipital lobe;
- Inferior horn (cornu inferius) — descends into the temporal lobe;
- Collateral trigone (trigonum collaterale) — an expansion at the transition of the central part into the posterior and inferior horns.
Through which foramina do the lateral ventricles communicate with the third ventricle?
The lateral ventricles communicate with the cavity of the third ventricle via paired interventricular foramina.
- Interventricular foramen (foramen interventriculare), also known as the foramen of Monro, connects each lateral ventricle to the anterosuperior part of the third ventricle.
It is through these foramina that the circulation pathway of cerebrospinal fluid begins from the lateral ventricles.
Which structures form the walls of the anterior horn of the lateral ventricle?
The walls of the anterior horn of the lateral ventricle are formed by structures of the white and gray matter of the brain.
- Corpus callosum (corpus callosum) — forms the roof of the anterior horn;
- Head of the caudate nucleus (caput nuclei caudati) — forms the lateral wall and closely adheres to the anterior horn.
The anterior horn itself projects into the frontal lobe of the hemisphere.
Where exactly in the lateral ventricles is cerebrospinal fluid produced?
The production of cerebrospinal fluid in the lateral ventricles occurs within their choroid plexuses (plexus chorioideus). These plexuses are most prominent in the lateral ventricles and actively secrete cerebrospinal fluid.
What functions do the lateral ventricles of the brain perform?
The primary function of the lateral ventricles is the production and circulation of cerebrospinal fluid (CSF). They represent a system of cavities containing vascular choroid plexuses (plexus chorioideus). These plexuses continuously and actively secrete cerebrospinal fluid. From the lateral ventricles, CSF begins its circulation pathway, passing through the interventricular foramina into the third ventricle and further into the subarachnoid space.
Gerstmann's tetrad: "Fingers, Letters, Numbers, Sides" (finger agnosia, agraphia, acalculia, right/left confusion in left parietal lobe lesions).
Class and exam questions
How deep does the ischemic lesion extend in Wernicke's area infarction?
In severe cases, the ischemic lesion zone extends through the white matter all the way to the lateral ventricle wall.
Why does a patient fail to recognize smells with the right nostril when the anterior commissure fibers are damaged?
Olfactory pathways do not cross. The impulse from the right nostril goes to the right hemisphere and, due to damage to the commissure, cannot be transmitted to the speech centers of the left hemisphere.
What are the key differences between apraxia and paresis?
In apraxia, muscle strength, the ability to perform involuntary (automatic) movements, and isolated muscle contractions are preserved, but the skill of complex goal-directed actions is lost.
What else to study on this topic
- Features of diffusion-weighted (DWI) and FLAIR MRI images
- Topographic diagnosis of optic radiation lesions
- The role of the corpus callosum and consequences of callosotomy
- Ideational and ideomotor apraxia: differential diagnosis
- Types of visual and somatosensory agnosia
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