bubble_chart Overview

The fourth ventricle is located in the posterior cranial fossa below the tentorium and has a tent-like shape with its apex pointing upward. Its roof is formed by the anterior and posterior medullary vela, with the cerebellum on its dorsal side and the pons and medulla oblongata on its ventral side. The fourth ventricle connects superiorly to the cerebral aqueduct of the midbrain and inferiorly communicates with the subarachnoid space via the lateral apertures, situated at the cerebellopontine angle, and with the cisterna magna via the median aperture. It receives cerebrospinal fluid from the third ventricle through the cerebral aqueduct and directs it into the subarachnoid space via the median or lateral apertures, eventually entering the venous system through arachnoid granulations. The floor of the fourth ventricle has a rhomboid shape, and many nerve nuclei of the pons and medulla oblongata are adjacent to it, including the hypoglossal nucleus, dorsal vagal nucleus, cochlear and vestibular nuclei in the medulla, as well as the facial nucleus, motor trigeminal nucleus, and sensory trigeminal nucleus in the pons. Therefore, when a tumor arises in the fourth ventricle, it first obstructs cerebrospinal fluid circulation. As the tumor expands into surrounding tissues or compresses adjacent structures, corresponding clinical symptoms emerge, primarily involving cranial nerve deficits. Primary tumors of the fourth ventricle are often choroid plexus papillomas. Tumors originating from the ventricular wall not only grow into the fourth ventricle but also frequently invade the brainstem or cerebellum, such as ependymomas and hemangioblastomas. Tumors at the roof of the ventricle usually arise from the cerebellar vermis, with medulloblastomas being the most common. Fourth ventricle tumors predominantly occur in children and young adults.

bubble_chart Clinical Manifestations

1. Increased intracranial pressure The course of fourth ventricle tumors is generally short, and symptoms of increased intracranial pressure can appear early due to obstruction of cerebrospinal fluid circulation caused by the tumor. Almost all patients initially present with headaches caused by increased intracranial pressure, accompanied by nausea and vomiting, and some may also experience dizziness. The headache is often localized to the occipital region. Headaches, vomiting, and dizziness caused by fourth ventricle tumors are often fluctuating, manifesting as intermittent episodes that can be triggered by changes in head or body position. Consequently, patients often maintain a specific posture, known as a forced head position, where they tilt their head forward, backward, or sideways to reduce symptoms. In rare cases, changes in head or body position may stimulate the nerve nuclei at the base of the fourth ventricle, leading to corresponding clinical symptoms such as vertigo, headache, vomiting, diplopia, ocular tremor, changes in vital signs, or even unconsciousness. Some intraventricular tumors are highly mobile. When they do not obstruct the cerebral aqueduct, median aperture, or lateral apertures, patients may not experience symptoms of increased intracranial pressure like headaches or vomiting. However, when head or body position changes, the tumor may shift within the ventricle, suddenly blocking the cerebrospinal fluid pathway, leading to episodic increases in intracranial pressure. Severe intracranial hypertension can result in cerebellar crisis and brain herniation.

2. Chronic occipital bone foramen magnum herniation Due to tumor compression and continuous growth, the pressure on brain tissue increases. Prolonged intracranial hypertension causes the cerebellar tonsils to herniate into the foramen magnum, leading to corresponding clinical symptoms. However, patients generally remain in relatively good condition. The herniated cerebellar tonsils may become congested and edematous, compressing the medulla oblongata and upper cervical spinal cord, but symptoms are usually mild or absent. The herniation of the cerebellar tonsils can obstruct the median aperture of the fourth ventricle, further increasing intracranial pressure, which in turn exacerbates the herniation. Chronic occipital bone foramen magnum herniation often results in adhesions, making reduction difficult.

(1) Occipital pain: The herniated mass irritates the meninges, blood vessels, and upper cervical nerve roots at the foramen magnum, causing occipital pain, which radiates from the upper neck to the occiput. Patients often exhibit tenderness in the suboccipital region.

(2) Neck stiffness and forced head position: Compression of the medulla oblongata and upper cervical spinal cord by the herniated brain tissue triggers a protective reflex in the neck muscles, leading to spasm and fixation of the head in a specific position to avoid worsening symptoms. Neck stiffness is usually more pronounced on the affected or more severely herniated side, though in most cases, the degree of cerebellar tonsillar herniation is nearly equal on both sides, so neck muscle rigidity is generally symmetrical.

(3) In occipital bone foramen magnum herniation, traction on the lower cranial nerves may cause corresponding clinical manifestations, such as dysphagia and hearing impairment.

(4) Acute episodes may occur on the basis of chronic occipital bone foramen magnum herniation, leading to a sudden rise in intracranial pressure, compression of the medulla oblongata, changes in vital signs, and even death due to respiratory or circulatory failure.

3. Cerebellar symptoms When the tumor grows posteriorly, compressing or invading the cerebellar peduncles or cerebellum, cerebellar symptoms appear. Since the cerebellum coordinates muscle movements, patients exhibit ataxia, manifested as unsteady gait, staggering, and a tendency to fall toward the affected side or backward. Muscle tone is reduced, and abnormal limb postures may occur. The affected limbs may display coarse, irregular tremors, known as intention tremors. In addition to these symptoms, cerebellar damage is often accompanied by horizontal, vertical, or rotational ocular tremors.

4. Brainstem Symptoms Brainstem symptoms refer to cranial nerve symptoms caused by tumors invading the floor of the fourth ventricle, stimulating or damaging the cranial nerve nuclei of the medulla oblongata and pons. It is relatively rare for fourth ventricle tumors to present with brainstem symptoms as the initial manifestation. When the upper part of the fourth ventricle is affected, patients exhibit early signs of increased intracranial pressure, primarily including vertigo, eye tremor, and forced head position. Some patients may also experience hearing loss, deviation of the mouth, facial sensory disturbances, chewing weakness, and abducens nerve palsy. Damage to the lower part of the fourth ventricle floor affects the nuclei of the Ⅸ, Ⅹ, Ⅺ, and Ⅻ cranial nerves, leading to symptoms such as vomiting, hiccups, difficulty swallowing, hoarseness, and possible cardiovascular and respiratory disturbances. Tumors in the lower part of the fourth ventricle floor typically present with early symptoms of increased intracranial pressure. Additionally, due to compression of the brainstem by occipital bone foramen magnum herniation, long tract signs may appear. Patients may experience sensory and motor impairments, such as weakness in the legs leading to easy falls, diminished tendon reflexes, and occasionally pathological reflexes.

5. Changes in the optic nerve head  Due to the tumor's tendency to obstruct the cerebrospinal fluid circulation pathway, increased intracranial pressure occurs, leading to optic nerve head edema. This manifests as blurred borders and disappearance of the physiological depression. Over time, secondary atrophy of the optic nerve develops, resulting in decreased vision or even blindness in patients.

bubble_chart Auxiliary Examination

1. Electroencephalography (EEG) The EEG shows generalized abnormalities, with paroxysmal synchronous slow waves in both cerebral hemispheres, predominantly diffuse delta and theta waves in the occipital region. Some statistics indicate that among patients with increased intracranial pressure accompanied by papilledema, 28% exhibit abnormal EEG findings.

2. Cerebral Angiography Due to obstruction of cerebrospinal fluid circulation, hydrocephalus develops, leading to uniform enlargement of the ventricles. Carotid artery angiography reveals signs of hydrocephalus, showing upward displacement of the anterior cerebral artery and outward shift of the sylvian artery. The lateral view demonstrates upward straightening of the pericallosal artery and disappearance of the genu, as well as elevation of the middle cerebral artery’s sylvian segment. Since fourth ventricle tumors often cause tonsillar herniation into the foramen magnum, vertebral artery angiography may show displacement of the cerebellar tonsillar branches, which may shift into or below the foramen magnum.

3. Ventriculography Ventriculography is highly valuable for diagnosing fourth ventricle tumors. The ventricles dilate due to obstructed cerebrospinal fluid circulation, and the imaging reveals uniform ventricular enlargement, with nodular or mass-like tumor shadows visible in the fourth ventricle. If the tumor invades the cerebellomedullary cistern or extends into the spinal canal, the imaging shows irregular tumor shadows within the cerebellomedullary cistern.

4. Skull X-ray Plain skull X-rays indicate increased intracranial pressure, manifested as increased convolutional markings, absorption or destruction of the posterior clinoid process, and sellar changes.

5. Others Isotope scanning can aid in the diagnosis of fourth ventricle tumors. Brain CT scans may reveal tumor shadows within the fourth ventricle.

bubble_chart Differentiation

(1) Fourth Ventricular Cysticercosis Fourth ventricular cysticercosis presents with increased intracranial pressure due to cyst obstruction of the median aperture or the lower opening of the cerebral aqueduct. Cerebral cysticercosis is generally multifocal, with cysts not only located in the ventricles but also more commonly found in the cerebral cortex or subcortical structures, often accompanied by epileptic seizures. Patients typically have a history of consuming infected pork or traveling to endemic areas. Multiple subcutaneous nodules are often visible, and excision of these nodules frequently reveals cysticerci. Both cerebrospinal fluid and blood complement fixation tests are positive. Ventriculography shows uniform ventricular enlargement, with soft tissue shadows or filling defects in the fourth ventricle.

(2) Posterior Fossa Arachnoiditis Patients often have infections in adjacent brain regions, brain tissue, or systemic infections. During the acute phase, patients exhibit fever and grade I increased intracranial pressure. There is usually a prolonged remission stage, with symptom exacerbation triggered by common colds or fatigue. Arachnoiditis can lead to stenosis or occlusion of the cerebral aqueduct, along with adhesions at the median aperture of the fourth ventricle and the cisterna magna, disrupting cerebrospinal fluid circulation and causing increased intracranial pressure. Clinically, this manifests as headache, nausea, vomiting, and papilledema. If the brainstem is involved, symptoms of posterior cranial nerve dysfunction may occur, but focal brain lesions are generally absent. Most cases progress rapidly and severely, with a high mortality rate. Lumbar puncture reveals elevated cerebrospinal fluid cell counts and significantly increased intracranial pressure. Skull radiographs show signs of intracranial hypertension, while pneumoencephalography may demonstrate non-filling of the subarachnoid space and cisterna magna. Ventriculography reveals uniform enlargement of the ventricular system above the cerebral aqueduct.

(3) Cerebellar Tuberculoma Tuberculomas may be solitary or multiple, commonly seen in children and young adults. In multiple cases, aside from tuberculomas in the posterior fossa, active tuberculous lesions are also present elsewhere in the body. Patients generally exhibit poor health, with systemic tuberculous toxicity symptoms such as low-grade fever, night sweats, flushed complexion, and weight loss. Some patients may also present with tuberculous meningitis symptoms, showing meningeal irritation signs. In solitary tuberculomas, cerebellar symptoms are prominent, including ataxia, nystagmus, and, in severe cases, cerebellar rigidity. A minority of patients exhibit tuberculous toxicity symptoms, though most remain in relatively good condition. Lumbar puncture shows elevated cerebrospinal fluid pressure and protein levels, with normal cell counts and glucose content.

(4) Cerebellar Abscess Cerebellar abscesses are often caused by otitis media or mastoiditis, with inflammation spreading upward from the posterior wall of the tympanic cavity. Hematogenous spread is less common. Patients typically present with symptoms of the primary infection and systemic infection, such as fever, chills, leukocytosis, and elevated erythrocyte sedimentation rate. Concurrently, patients exhibit increased intracranial pressure, with headache, nausea, and vomiting. Cerebellar signs are prominent, including ataxia, unsteady gait, hypotonia, and forced head posture. Occasionally, symptoms of posterior cranial nerve dysfunction may appear. Ventriculography, showing deformation and displacement of the fourth ventricle, is diagnostically significant.

(5) Cerebellar Hemisphere Tumor Most patients with cerebellar hemisphere tumors present with increased intracranial pressure, often initially manifesting as headache, typically localized to the occipital region and accompanied by nausea and vomiting. Headache episodes become increasingly frequent, with papilledema and visual decline; some may experience diplopia. Damage to the cerebellar hemisphere leads to ataxia (ipsilateral limbs), nystagmus, and dizziness. Tumor extension laterally may injure cranial nerves, commonly the trigeminal, facial, auditory, and glossopharyngeal nerves, resulting in symptoms such as facial sensory impairment, hearing loss, and choking. Brainstem involvement causes long tract signs. Prolonged intracranial hypertension and tumor growth may lead to tonsillar herniation, presenting as forced head posture. Ventriculography reveals deformation, displacement, and filling defects of the fourth ventricle.

(VI) Vermis Tumor Tumors in the cerebellar vermis are prone to obstruct the cerebrospinal fluid circulation pathway, leading to increased intracranial pressure. Patients may experience headache, nausea, vomiting, and optic disc edema, which are also the main symptoms of cerebellar vermis tumors. Due to the small volume of the cerebellar vermis, tumors often push the cerebellar hemispheres to both sides, injuring the cranial nerves (IV, VI, VII, VIII). Damage to the cerebellar vermis results in truncal ataxia, and nystagmus may sometimes occur. Cerebellar vermis tumors are highly likely to cause occipital bone foramen magnum herniation, where the bilateral cerebellar tonsils symmetrically herniate into the foramen magnum of the occipital bone. Patients may exhibit a forced head position, often with the head tilted forward, and some may assume a knee-chest posture. Ventriculography can confirm the diagnosis.

(7) Brainstem Tumors Brainstem tumors are more common in children, with gliomas being the most prevalent. Clinically, they present with increased intracranial pressure, consciousness and mental disorders, and focal deficits. Increased intracranial pressure usually appears in the advanced stage, but tumors in the midbrain, especially those located in the tegmentum, can cause increased intracranial pressure early due to compression of the cerebral aqueduct. Damage to the brainstem reticular formation can lead to drowsiness, apathy, and even unconsciousness. The most prominent focal symptom after brainstem damage is crossed paralysis, followed by cranial nerve, pyramidal tract, and cerebellar damage symptoms, such as hearing loss, dysphagia, paralysis, ataxia, and nystagmus. Cerebrospinal fluid examination shows increased pressure and elevated protein content. Skull X-rays may occasionally reveal bone destruction in areas like the internal auditory canal. Ventriculography shows uniform enlargement of the ventricles, often with filling defects in the posterior third ventricle. Vertebral angiography reveals displacement of the posterior cerebral artery and superior cerebellar artery.

(8) Cerebellopontine Angle Tumors Cerebellopontine angle tumors are mostly acoustic neuromas, followed by epidermoid cysts and meningiomas. Clinically, they manifest as cerebellopontine angle syndrome, involving dysfunction of the trigeminal, acoustic, facial, abducens, glossopharyngeal, vagus, hypoglossal nerves, and cerebellar damage. Additionally, brainstem compression and displacement, along with increased intracranial pressure in the advanced stage, lead to persistent tinnitus, progressive deafness, facial numbness, decreased corneal sensation, dysphagia, hoarseness, etc. Patients may also exhibit mild facial nerve palsy, slurred speech, ataxia, and inward eye deviation. A few patients may develop grade I hemiplegia and hemisensory deficits.

1. Acoustic Neuroma Acoustic neuromas are more common in middle-aged and elderly individuals, particularly women. The initial symptoms are stimulation and damage to the acoustic nerve, presenting as high-pitched tinnitus, followed by hearing loss, vertigo, nausea, vomiting, and nystagmus. Due to tumor compression and invasion, dysfunction of cranial nerves V, VII, IX, and X may occur, manifesting as decreased corneal sensation, facial numbness, weak chewing, dysphagia, and hoarseness. A few patients experience pain in the trigeminal nerve distribution area. Cerebellar damage may cause ataxia. Skull X-rays show enlargement or bone destruction of the internal auditory canal.

2. Epidermoid Cyst of the Cerebellopontine Angle The incidence of epidermoid cysts in the cerebellopontine angle is second only to acoustic neuromas, commonly affecting young and middle-aged adults. Clinically, they present with cranial nerve damage symptoms, with trigeminal neuralgia being the most frequent, characterized by burning or electric shock-like severe pain in the second and third branches of the trigeminal nerve, with trigger points. Other symptoms include tinnitus, deafness, and unsteady gait. A few patients may exhibit glossopharyngeal and vagus nerve damage symptoms such as dysphagia and hoarseness.

(9) Foramen Magnum Tumors Meningiomas and neurofibromas are the most common foramen magnum tumors, originating from the periphery of the foramen magnum or the upper spinal canal. Most patients are adults, experiencing early-stage pain in the posterior occipital and upper cervical regions, radiating to the vertex, worsening with exertion or coughing, leading to neck stiffness and forced head positioning. Limb movement disorders may also occur, often starting in one limb and spreading to others, or beginning in both upper or lower limbs. Some may exhibit spinal hemisection syndrome, presenting as ipsilateral hemiplegia of varying degrees, contralateral limb sensory deficits, and shoulder muscle atrophy. In the advanced stage, increased intracranial pressure and cranial nerve damage (comm involving cranial nerves XI, IX, and X, followed by trigeminal and facial nerve damage) may occur, along with hiccups, nystagmus, ataxia, vertigo, and cervical sympathetic nerve palsy. Cerebrospinal fluid examination showing elevated protein levels aids diagnosis. Skull X-rays may reveal bone hyperplasia or destruction around the foramen magnum, with possible destruction of the upper cervical lamina and vertebral arch. Brain CT scans are highly diagnostic.