Fourth ventricle(fourth vehicle), shaped like a tent, located atMedulla oblongata、PonsandcerebellumBetween them, the upper part is connected with the midbrain aqueduct, and the lower part is connected with the central canal of the spinal cord.It also communicates with the subarachnoid space through a median hole and two lateral holes.
It is a flat rhomboid cavity, located in front of the cerebellum, at the back of the pons and the upper half of the medulla oblongata. Its cavity is connected with the mesencephalic aqueduct above and the central medullary canal below.The bottom of the fourth ventricle is rhomboid fossa, which is formed by the depression of pons and medulla oblongata.The ventricular roof consists of superior cerebellar peduncle, anterior medullary velum, part of cerebellum, posterior medullary velum and choroid tissue.The lower outer side includes the tubercle of the thin bundle, the tubercle of the cuneiform bundle and the lower cerebellar peduncle, and the upper outer side includes the middle cerebellar peduncle and the upper cerebellar peduncle.The fourth ventricle communicates with the subarachnoid space through a median foramen and bilateral foramen on the choroid tissue.
The highest point at the top of the fourth ventricle divides the top part into upper and lower parts.The upper half is composed of thicker nerve tissue, namely the superior medullary velum, which is attached to the base of the velamen above and reaches the top of the fourth ventricle below;The surface of the cephalic fourth ventricle of the midline in the lower half is vermicular tubercle, and the rest is composed of inferior medullary velum and choroid.The connecting line between the inferior medullary velum and the choroid, namely, the junction of the membranous velum, extends from the tubercle of the vermis to the lateral recess on each side.After bilateral suboccipital craniotomy, the cerebellar surface that forms the surface of the cisterna magna at the top end of the fourth ventricle is exposed.The vermis is located in the midline of the posterior cerebellar notch between the hemispheres, and is composed of vermis lobes, vermis nodules, vermis pyramids and vermis pendulum from top to bottom. The vermis pendulum and tonsils occupy the lower part of the cerebellar valley, and the vermis pendulum is often hidden between bilateral tonsils.The tonsil is connected to the cerebellum through the tonsil footwhite matterThe lower part and midline side are free.The fissure between the tonsil and the medulla oblongata is called the medullary tonsillar gap, which is the main part of the cerebellomedullary fissure.This space extends cephalically to the tip of the top of the fourth ventricle and laterally to the cerebellomedullary cistern.The cerebellomedullary fissure observed from the outside extends to the upper midline side to the space between the vermis and tonsil, which is called vermistonsilAfter the tonsil and the second ventral lobe are removed, the bottom of the fissure can be clearly observed.The bottom of cerebellomedullary fissure is the top of the fourth ventricle, which is composed of choroid membrane and inferior medullary velum.The choroid is attached to the medulla oblongata laterally through the choroid cord in a "V" shape. The choroid cord enters the lateral recess along the fourth ventricle towards the opening side.The lateral recess is a curved pocket structure, which is composed of the top and bottom of the fourth ventricle. The posterior wall is the rhomboid lip, and the top is the lateral extension of the choroid and inferior medullary velum.The wall of the fourth ventricle can only be exposed after the choroid cord has been removed, including the bottom of the fourth ventricle, the lateral wall, the deep paraaqueductal area and the lateral recess. The bottom is rhomboid, called rhomboid recess. Its cranial end is located at the level of the aqueduct, the lower end is connected to the cerebellomedullary cistern through the median hole, and both sides are connected to the cerebellopontine angle through the lateral recess and the lateral hole.The line connecting the openings of the two lateral recesses is at the level of the junction between the pons and the medulla oblongata, where the medullary striae cross, and the pons in the middle of the bulge forms an extended bulge, called the facial colliculus.The lateral wall is composed of three pairs of cerebellar peduncle, the cranial end is only composed of the upper cerebellar peduncle, and the caudal end is composed of the upper cerebellar peduncle, the middle cerebellar peduncle, and the lower cerebellar peduncle.
Introduction
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It is a lacuna in the brain, located between cerebellum, medulla and pons.Its shape is like a tent with the tip upward.The fourth ventricle is connected to the midbrain aqueduct and the spinal cord central canal.There are holes in the lateral and lower corners of the bottom of the ventricle (rhomboid fossa), called the lateral and middle holes of the fourth ventricle, which are connected with the subarachnoid space.The fourth ventricle receives cerebrospinal fluid from the third ventricle through the midbrain aqueduct, and flows to the subarachnoid space through the middle or lateral foramen, and then enters the venous system through the arachnoid granules.The bottom of the fourth ventricle is rhomboid, and the pontine and medulla oblongata are mostly adjacent to it, such as hypoglossal nucleus, dorsal nucleus of vagus nerve, cochlear and vestibular nucleus of medulla oblongata;Facial nucleus, trigeminal motor nucleus and trigeminal sensory nucleus of pons.
Principle of disease
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When a tumor occurs in the fourth ventricle, the cerebrospinal fluid circulation is blocked first. When the tumor expands and invades around the ventricle or compresses the surrounding tissues, the corresponding clinical symptoms will occur, mainly cranial nerve damage.
Cause of disease
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When tumors at the bottom of the fourth ventricle and from the choroid plexus and vermis of the fourth ventricle invade the fourth ventricle, they can affect the vestibular nucleus and autonomic nerve structures, and early symptoms of the fourth ventricle such as high intracranial pressure appear.
Symptoms
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The fourth ventricle is located between the medulla oblongata, pons and cerebellum. It is shaped like a rhomboid pyramid with a bottom. It is connected to the central canal of the spinal cord at the bottom and the mesencephalic aqueduct at the top, containing cerebrospinal fluid.The symptoms of the fourth ventricle are often caused by tumor compression.
clinical manifestation
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High intracranial pressure
When the tumor of the fourth ventricle occurs, the symptoms of high intracranial pressure may occur, headache, vomiting and obvious papilledema may occur earlier.
Muscular tension
The compression lesions of the fourth ventricle often have muscle tension changes.For example, the tension of neck and back muscles increases.
Imbalance
When the vestibular nucleus is compressed or the cerebellar vermis is affected, imbalance may occur.Some cases suffer from persistent imbalance, difficulty in walking, and incline forward or backward.
Neurosis
Due to the spread and development of the tumor, the seventh, ninth, tenth and seventh cranial nerve symptoms appeared in the late cases.In some cases, the fifth and sixth pairs of cranial nerves are paralyzed.Autonomic nerve symptoms include arrhythmia, respiratory rhythm disorder, unstable blood pressure, polyuria, and diabetes.
differential diagnosis
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Ventricular tumor
（tumor of fouth ventricle）
When the tumor of the fourth ventricle occurs, the symptoms of intracranial hypertension appear in the early stage, which are mostly intermittent and sometimes related to head position.Rapid neck rotation may cause headache and vomiting.In the late stage, the headache is obvious, mostly in the occipital part, and spreads to the neck and back and shoulders. In the early stage, there is obvious papilloedema, which can lead to blindness for a little longer time.
Brain stem tumor
（brain stem tumor）
It tends to happen to children and young people.Most of the patients had slow onset, progressive exacerbation, long course of disease, and a few cases had remission and recurrence.Except for midbrain tumors, intracranial hypertension is not very significant, or it may occur in late stage.Slow progressive cross paralysis is the prominent feature of the disease, accompanied by multiple cranial nerve damage, which may lead to forced head position and eyeball masking.
Angular tumor
（cerebellopontine ）
The disease progresses slowly, and the symptoms often develop in a certain order. Cranial nerve dysfunction is the main symptom, which is mostly seen on the diseased side. Hearing impairment is the most common, followed by trigeminal sensory impairment.About half of the patients have facial paralysis, and about 30% of the patients have posterior cranial nerve disorders.Intracranial hypertension and ataxia are rare and occur late.Half of the patients had papilledema.
Cerebellar tumor
（cerebelar hemisphere ）
Most patients with this disease have increased intracranial pressure, and headache is often the first symptom. The pain is often located in the posterior occipital region. Headache attacks are increasingly frequent, accompanied by nausea, vomiting, papilledema and vision decline, and some have diplopia.When the occipital foramen hernia is caused by high intracranial pressure, the patient shows forced head position.Common symptoms of trigeminal nerve, facial nerve, auditory nerve and glossopharyngeal nerve damage, upper and lower limb ataxia, nystagmus, dizziness.
Intracranial tumor
（intracranial tumor ）
The onset of the disease is usually suddenly aggravated on the basis of the original headache, accompanied by high skull symptoms such as vomiting and papilledema, and with varying degrees of nerve damage.
Pathogenic site
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Part I
It is located in the cavity between the medulla oblongata, pons, and cerebellum.The bottom is rhomboid fossa, and the top extends into cerebellum.
Part II
It communicates with the central canal of the spinal cord and the midbrain aqueduct, and communicates with the subarachnoid space through the median foramen and lateral foramen of the fourth ventricle.
Fourth Ventricular Orifice Occlusion Syndrome
Non communicating encephaloma, also known as Dandy Walker malformation, Dandy Walker syndrome.
