Symptoms of midbrain lesions

The roof of the midbrain is made up of the tectum lamina, the base is made up of the cerebral peduncles, and the nuclei of the midbrain are located in the middle part.

The dorsal part (roof) of the midbrain is located behind the cerebral aqueduct and is represented by the roof plate. It has two superior and inferior colliculi. The inferior colliculi are more simply constructed and consist of medium-sized neurons. These colliculi provide hearing and complex reflexes in response to auditory stimuli.

The superior colliculi are organized in a more complex way. They perform automatic reactions associated with the visual function, i.e. they participate in the implementation of unconditioned reflexes in response to visual stimuli (squinting, jerking the head, etc.) - starter reflexes. In addition, they coordinate the movements of the trunk, facial reactions, eye movements, head movements, etc. in response to visual stimuli. These reflex reactions are provided by the tectospinal tract, which originates in the superior colliculi.

Below the roof plate is the cerebral aqueduct, which is surrounded by a layer of the reticular formation.

The cerebral peduncles are dense strands of white matter (descending tracts) and can be conditionally divided into three parts: external, middle, and internal. The fibers of the occipital-temporal-pontine and frontal-pontine tracts pass on the outside and then go to the cerebellum. The fibers of the pyramidal system (corticonuclear and corticospinal tracts) pass through the middle part of the cerebral peduncle. The fibers that innervate the muscles of the face and tongue are located medially, the muscles of the lower limbs are laterally, and the muscles of the upper limbs are in the middle. At the border of the peduncles of the bridge with the tegmentum is the nucleus of the substantia nigra, lying in the form of a plate on the conducting tracts. Between the roof of the midbrain and the substantia nigra are the red nucleus, the nuclei of the oculomotor and trochlear nerves, the medial longitudinal fasciculus, and the medial loop. Two fiber bundles of the medial longitudinal fasciculus are located paramedially at the bottom of the cerebral aqueduct. At the same level, more externally, lie the nuclei of the oculomotor (at the level of the superior colliculi) and trochlear nerves (at the level of the inferior colliculi). The red nucleus is located between these nuclei and the medial longitudinal fasciculus, on the one hand, and with the black substance, on the other. In the lateral part of the midbrain pass afferent fibers - the medial loop (consisting of fibers of the bulbothalamic tract). It conducts impulses of deep sensitivity from the thin and cuneate nuclei of the medulla oblongata and the spinothalamic tract - conductors of superficial sensitivity. In the anterior part of the midbrain, at the level of the superior colliculi, are localized the nuclei of the medial longitudinal fasciculus.

When the nuclei or roots of the oculomotor nerve are damaged, external and internal total ophthalmoplegia develops; trochlear nerve - convergent strabismus, diplopia when looking down, vertical nystagmus (spontaneous vertical nystagmus - Bobbing syndrome), incoordination of eye movements, ophthalmoplegia, horizontal nystagmus, Nothnagel syndrome (impaired balance, hearing, paralysis of the oculomotor muscles, choreic hyperkinesis), paresis and paralysis of the limbs, cerebellar disorders, decerebrate rigidity (associated with damage to the centers of the midbrain that regulate muscle tone below the red nucleus).

Porto syndrome: vertical gaze paresis, impaired convergence of the eyeballs, partial bilateral ptosis of the eyelids; horizontal movements of the eyeballs are not limited; the syndrome is observed with damage to the superior colliculi of the roof of the midbrain and with a tumor of the pineal gland.

Red nucleus syndrome: intention hemitremor, hemihyperkinesis; Claude syndrome (inferior red nucleus syndrome): damage to the oculomotor nerve (ptosis, divergent strabismus, mydriasis) on the side of the lesion; intention hemitremor, hemiataxia and muscle hypotonia - on the opposite side.

Foix's syndrome (upper red nucleus syndrome): intention hemitremor, hemihyperkinesis.

Substantia nigra syndrome: plastic muscular hypertonia, akinetic-rigid syndrome on the side opposite the lesion.

Tegmental syndrome: on the side of the lesion - ataxia, Claude Bernard-Horner syndrome, tremor, myoclonus on the side opposite the lesion - hemihypesthesia, disturbances of the quadrigeminal reflexes (rapid orienting movements in response to unexpected visual and auditory stimuli - starter reflexes).

Weber's syndrome: peripheral paralysis of the oculomotor nerve on the side of the lesion and hemiparesis (hemiplegia) on the opposite side; the lesion is located at the base of the cerebral peduncle and disrupts the pyramidal bundle and fibers of the oculomotor nerve.

Benedict's syndrome: paralysis of the oculomotor nerve on the side of the lesion (ptosis, divergent strabismus, mydriasis), intention tremor and athetoid movements in the limbs on the side opposite the lesion; the lesion damages the fibers of the oculomotor nerve, the red nucleus and the cerebellar conductors of the dentate-red tract approaching it.

When one half of the pons is damaged, the following alternating syndromes develop.

Miikr-Gubler-Juble syndrome: peripheral paralysis of the facial muscles on the side of the lesion and hemiplegia on the opposite side; the lesion is located at the base of the lower part of the pons, the nucleus of the n. facialis and the pyramidal fasciculus are affected.

Foville's syndrome: peripheral paralysis of the facial muscles and the external rectus muscle of the eye (convergent strabismus) on the side of the lesion, hemiplegia on the opposite side; this syndrome occurs when the lower part of the base of the pons is affected; the pyramidal fasciculus, the nucleus of the facial nerve, and the axons of the cells of the nucleus of the abducens nerve are affected.

Gasperipe's syndrome: peripheral paralysis of the abducens, facial nerve, hearing loss, hypoesthesia in the trigeminal nerve area on the side of the lesion and conduction hemianesthesia on the opposite side; develops with a unilateral lesion of the pons tegmentum.

Brissot-Sicard syndrome: spasm of the facial muscles on the affected side (hemispasm of the facial muscles from irritation of the facial nerve nucleus) and spastic hemiparesis on the side opposite the lesion (lesions of the pyramidal system).

Raymond-Sestang syndrome: paralysis caused by combined damage to the medial longitudinal fasciculus and pontine gaze center, middle cerebellar peduncle, medial lemniscus and pyramidal tract; gaze paresis toward the lesion, ataxia, choreoathetoid hyperkinesis on the side of the lesion; contralaterally - spastic hemiparesis and hemianesthesia.

Grene's syndrome: on the side of the lesion - loss of superficial sensitivity on the face according to the segmental type; contralaterally - hemianesthesia of superficial sensitivity on the trunk and limbs (lesion of the nucleus of the fifth pair of cranial nerves and the spinothalamic tract).

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