SYNDROMES OF LESIONS IN THE BRAIN STEM AND CRANIAL NERVES

Brief anatomy of the brain stem

Brain stem consists of the medulla oblongata, pons and midbrain. From below, brain stem is limited by Xia spinal roots, coming from the segment C1, from top is optic tract on their way to the intersection of the visual lateral geniculate body (Fig. 6).

Medulla oblongata (Продолговатый мозг) represents lower (caudal) part of the brain stem and is, between the spinal cord and the pons. On its ventral part but both sides of the median fissure is elevated the pyramid, of which there are pyramidal (cortico-spinal-cerebral) tract. On dorsal part of the medulla oblongata but both sides of the median fissure are visible elevation of Burdach's nucleus and soft nucleus, which is the second neuron of deep sensory tract and Rhomboid fossa. Most caudal part of medulla oblongata exit accessory nerve, part of the roots of which originates from the cervical segments, and then departs hypoglossal, vagus and glossopharyngeal nerves. At the border of the connection of medulla oblongata and the pons in cerebellopontine angle in the brain stem enter vestibulocochlear and facial nerves. in the ventral part goes abducens nerve.

Pons (варолиев мост) includes fibers connecting the hemispheres of the cerebellum, which served as its name. Pons is situated between medulla oblongata and midbrain. Its ventral part is cushion and include twisted fibers going from pons to cerebellum (2nd part of cortico-cerebellopontine tract), as well as the cortico-spinal (pyramidal) tract. On lateral side, transverse fibers form the base of the pons middle crus (pedunculus) cerebri of the cerebellum, above which there is a place where trigeminal nerve exit. The main part of the dorsal part of the pons is Rhomboid fossa.

Mesencephalon (Средний мозг) represents the upper (oral) part of the brain stem. Ventral part of the midbrain is the brain stem, which includes the cortico-spinal and cortico-pons tract. The roof of the midbrain is formed by two symmetrical upper and lower colliculus, which contain the nucleus, respectively perceive visual and auditory impulses. Between the roof of the midbrain and the crus (pedunculus) cerebri of the brain are the nucleus of the oculomotor and trochlear nerves, nucleus ruber and substansia nigra. From the interval between the crus (pedunculus) cerebri of the brain, go oculomotor nerves. From the dorsal surface of the midbrain go troclear nerves.

In the brainstem are nuclei of cranial nerves, other clusters of neurons, and are ascending and descending pathways. In brain stem is the reticular formation, neurons which have bilateral relations with the cortex and basal ganglia of the cerebral hemispheres, nuclei of cranial nerves, cerebellum and spinal cord. Part of the nuclei of the reticular formation, mainly localized in the midbrain and the pons, has an activating effect on the cortex of cerebral hemispheres and is important in the maintenance of consciousness, the regulation of the rhythm of sleep and wakefulness. Another group of nuclei of the reticular formation of the pons and the medulla affect autonomic-visceral functions (respiratory center, vasomotor center) and the motor activity of the spinal cord.

Defect of the brain stem appears dysfunction of cranial nerves (CNs), or other clusters of neurons (red nucleus, substantia nigra or other), as well as symptoms pathways (motor and sensory). Extensive damage to the brain stem causes disorder of consciousness and death due to disrupted vital functions (respiratory and circulatory). Damage even in small parts of the midbrain reticular formation of nuclei can cause disorder of consciousness. Any damage to half of the trunk of spinal appears as alternating syndrome: disturbance of function of CNs on the affected side and the central hemiparesis and hemihypoesthesia on the opposite side of the trunk to the extremities (due to destruction of motor and sensory pathways). Description of the major syndromes is given in alternating syndromes of disturbance of CNs.

I pair of cranial nerves, olfactory nerve, n. olfactorius , olfactory systems

Brief anatomy. Olfactory irritation is perceived by sensitive cells (olfactory receptors), mucous membrane of the upper part of the nasal cavity, which form the olfactory fibers passing through openings in the ethmoid bone and goes along to the olfactory bulb. These fibers per se form olfactory nerves. Axons of olfactory second neurons, form the olfactory bulb form the olfactory tract, which the excitation reaches the amygdala of temporal lobe (third neurons) and from them goes to the anterior parahippocampal gyrus (projection and association areas of the field of smell).

Investigations of olfactory function are carried out with aromatic substances (tincture of valerian, camphor oil, etc.) separately in each of the nose entrance.

Reduced sense of smell (hypo-osmia/sphresia) or loss (anosmia) occurs in 1% of the population aged until 60 years and more than 50% of people aged over 60 years. Patients are often unaware of the loss of smell, and complained of breach of taste, in which the perception of odors plays large role. In 2/3 cases of hyposphresia or anosmia are caused rhinogenous diseases, sinusitis, head trauma, degenerative-dystrophic changes in olfactory neurons in older people. Less likely, bilateral anosmia caused by degenerative diseases of the nervous system (Alzheimer's, Parkinson's), epilepsy, somatic (hypothyroidism, kidney disease, diabetes) and mental illness. Unilateral hypo- and anosmia could be the first and only symptom of tumors and other pathological processes on the basis of the frontal lobe (shown in detecting computer or MRI of the head). Transiet distortion of smell is possible during pregnancy, poisoning by chemicals and schizophrenia. Olfactory hallucinations (feeling of absence of odor) may occur in pathological processes (most tumors) in of the temporal lobe, they may be a manifestation of an epileptic seizure.

II pair of cranial nerves, optic nerve, n. opticus and visual system

Brief anatomical data. The visual impulses are perceived by retina as an ordered cluster of specialized cells. Retina has three layers of neurons: the first - rods and cones, the second - the bipolar cells, the third - ganglionic cells. Diagram of the visual system is shown in Fig. 7. 7. In rods and cones, light information through photochemical reactions is converted into pulses that propagate successively to other sections of the neurons. Axons of ganglion cells form optic nerve, which penetrates into the cavity of the skull. At the level of the optic chiasma or chiasmata opticus, fibers from the inner (nasal) part of the retina pass to the opposite side, the fibers from the outer (temporal) half of the retina remain on their side. As a consequence, in the optic tract (tractus opticus), forms after the intersection, in which is located fibers from the temporalpart of the retina of his eye and nasal part of retina of the other eye. - Therefore, right optic tract conduct impulses from the left visual fields, in the left visual tract - from the right visual fields. Optic tract terminates in the lateral geniculate body, where the excitation is transferred to the next (fourth) neurons. Axons of these neurons pass through the posterior part of hind femur internal capsule and in the temporal and occipital lobes form radiatio optica, which ends in sulcus calcarinus of occipital lobe (first projection of visual field). In other divisions (mid-sections and the outer surface) of the occipital lobe is the analysis and recognition of visual images (second visual field).

Investigation of view. Visual acuity was tested with the help of special tables, which have alphabets or simple shapes. The fields of view can be precisely measured using a special device (perimeter). To estimate the field of view, you can use a simpler technique. The patient is asked to close one eye and hand to fix their view on one point, for example on the investigator that is sitting oppositely. The researcher moves the hammer of the perimeter because of the patient's head to the center of his moles from different points of view (right, left, top and bottom) and asks the patient to indicate when he saw the hammer. After examination of one

eye, another eye is examined. The normal boundaries of fields of view (in white) are: external - 90 °, internal - 60 °, lower - 70 °, upper - 60 °. It is important to study the fundus of eye, in which we can see the optic disk and signs of defect (blanching, edema and other changes).

Impairment of view develops as eye and neurological diseases. In case of defect, usually we refer to an ophthalmologist and in those cases where we detect eye diseases, explain by the visual disturbance, are likely due to defect of optic nerves, conducing tract or the cortex of the occipital lobe.

Reduced vision (amblyopia) or its total loss (amaurosis) in one eye in the absence of its pathology shows the defect of the optic nerve. In these cases, in fundus of the eye, there are changes of optic disk in the form of its blanching (atrophy) or edema (often with increased intracranial pressure caused by, for example, brain tumor). With the defect of part of the fibers of optic nerve may causes partial loss of sight (scotoma), in which the patient perceives as a "dark spot" in the eye. Damage to the central part of the visual contralaterally involving intersecting fibers (typical for pituitary tumor) causes a loss of temporal lobe of view, or bitemporal hemianopsia (due to damage of fibers going from the inner part of the retina of both eyes). Less often, damage to the external parts of the visual intersection leads to loss of internal fields of view, or binasal hemianopsia (due to damage of fibers coming from the temporal retina cha STI both eyes).

In case of damage other parts of the visual tract (optic tract, medial geniculate body, optical radiant and calcarine sulcus of occipital lobe), there complete

or partial loss of the either right or left half of the visual field of both eyes, or homonymous hemianopsia (due to damage of fibers going from the inner part of the retina of one eye and the outer part of the retina of another). The loss of sight is marked on the opposite side to the defect, such as damage to the right occipital lobe revealed as left-sided hemianopsia. Loss of view field depends on the amount and localization of damage to the optic path. If the damage is radiatio optica in temporal lobe sometimes causes view loss only in the lower part of the fibers of radiatio optica, and therefore develops a partial hemianopsia, which is limited only the upper quadrants of the visual field (upper-quadrant hemianopsia).

Any damage to the outer cortex of occipital lobe, which is responsible for analysis and recognition of visual graphic, causes psychanopsia (loss of technique to recognize familiar objects). During stimulation of the cortex of occipital lobe, occur possible visual sensations in the form of light flashes (Photopsia) or more complex visual images (visual hallucinations), an increase in items (macropsia) or decrease (micropsia) or distortion of objects (metamorphoopsia).

Fig. 7.7: Visual Analyzer and visual disturbances: A - field of view; B-retina; B - optic nerve; G-optic decussation; D - optic tract; E - lateral geniculate body;F - occipital lobe of the cerebral hemispheres; 1 - amaurosis, 2 - bitemporal hemianopsia, 3 -- binasal hemianopsia, 4-homolateral hemianopsia, 5 – upper quadrate hemianopsia, 6 - homolateral hemianopsia (with preservation of central vision)

The main causes of neurological impairment. Short-term (from minutes to several hours) loss of vision in one eye (amaurosis fungas) usually causes transient ischemic attack in the basin of the orbital artery - branches of the internal carotid artery. In such cases, the patient needs urgent examination and treatment to prevent stroke. Long-term (days, weeks) decrease in visual acuity in one or both eyes may be the result of retrobulbarno optic neuritis, which in most cases is the manifestation of multiple sclerosis. In this case except reduction of view, sometimes is noted pain in the eyeball, which increases when eye moves. Bilateral reduced vision may also result from a toxic optic neuropathy caused by poisoning of alcohol substitute (methanol, ethylene glycol), carbon monoxide, lead, arsenic, thallium, or taking certain medicines (levomixetin, isoniazid, penicillamine, etc.). Progressing reduction of vision in combination with papilledema develop in intracranial hypertension caused by tumor, brain injury or other diseases. In such cases, urgent examination (CT or MRI of the head) and treat it.

The loss of both fields of view (left-handed or right-sided hemianopsia) with acute development is more often caused by stroke or traumatic brain injury, if gradually - a brain tumor. Transient hemianopsia occurs when transient ischemic attack and it’s like aura before migraine attack.. Acute arising of blindness in both eyes is possible in clogging of the main artery, leading to bilateral infarction of occipital lobes. The loss of the outer field of view (bitemporal hemoanopsia) is observed in pituitary tumor, craniopharyngioma, meningioma of turcica sellae, lesion the internal fields of view (binasal hemianopsia) – in aneurysm of the internal carotid artery, a brain tumor.

Major Syndromes Neurological Impairment, And Localization of Lesion The main syndromes of lesions Localization of lesion

Amblyopia, or amaurosis in one eye (in the absence of eyes pathology)

Optic nerve

Bitemporal hemianopsia (loss of temporal field of view) Internal divisions of the visual intersectionBinasal hemianopsia (loss of internal fields of view) The outer sections of the visual intersectionHomonymous (right-or left-sided) hemianopsia From the contralateral side of the optic tract,

medial geniculate body, radiatio optica or calcarine sulcus of the occipital lobe