OVERVIEW
Ventricular meningiomas occur in the ventricles of the brain and are more prevalent in children than in adults. They occur in the posterior cranial fossa, and the incidence of ventricular meningiomas and ventriculoblastomas ranks third after medulloblastomas and cerebellar astrocytomas among the tumors of the posterior cranial recess in children, with an annual incidence of 2.19-3.5 per 1 million children, accounting for 6.3%-12% of pediatric intracranial tumors, and 5%-10% of the primary tumors of the central nervous system in children. It accounts for 18.8% of posterior cranial recess tumors in children. The peak age of onset is 4 to 12 years (75.1%), and about 60% are more common in children under 5 years of age. Most scholars report more males than females. The tumors are mostly located in the ventricles of the fourth ventricle, and a few in the paraventricular tissues, with slow, infiltrative growth. Tumor cells may also be shed in the subarachnoid space to produce disseminated implants.
Etiology
There are two types of neuroepithelial tumors. One type is formed by the mesenchymal cells of the nervous system (i.e., glial cells) and the other type is formed by the parenchymal cells of the nervous system (i.e., neurons). Since it is not now possible to distinguish these two classes of tumors completely from each other pathogenetically and morphologically, and since gliomas are common, neuronal tumors are included in gliomas. Tumors of neuroepithelial origin are the most common intracranial tumors, accounting for approximately 44% of all intracranial tumors.
Symptoms.
Since the tumor is located in the fourth ventricle, it is very easy to block the cerebrospinal fluid circulation pathway, and symptoms of increased intracranial pressure often appear early. When the tumor compresses the nuclei of the cerebral nerves at the base of the fourth ventricle or presses the cerebellar peduncle laterally, it may cause cerebral nerve damage and cerebellar symptoms.
1. Symptoms of increased intracranial pressure
It is characterized by early appearance, intermittent, and related to the change of head position. In the late stage, the head is often in a forced head position, and the head is mostly flexed anteriorly or anterolaterally. The change of body position may stimulate the nerve nuclei at the base of the fourth ventricle, especially the nucleus of vagus nerve and vestibular nerve, which manifests as severe headache, dizziness, vomiting, change of pulse and respiration, sudden loss of consciousness and diplopia and nystagmus due to the influence of the nucleus of the spreading nerve, which is called Brun’s sign. Due to the activity of the tumor, the median foramen or aqueduct can be suddenly blocked, causing cerebrospinal fluid circulation obstruction, and thus episodic intracranial pressure increase can occur, which mostly occurs due to the sudden change of body position. Severe intracranial pressure increase can occur cerebellar crisis.
2. Symptoms of brainstem and cerebral nerve damage
Brain stem symptoms are rare, but when the tumor compresses or infiltrates into the base of the fourth ventricle, symptoms of pontine and medullary nerve nuclei involvement may occur, mostly after the increase of intracranial pressure, and in a few cases, cerebral nerve symptoms may be the first symptom. The appearance of cerebral nerve symptoms, the process and scope of involvement are closely related to the location and extension direction of the tumor.
3. Cerebellar symptoms
Cerebellar symptoms are generally mild, which are caused by the tumor growing along the lateral or dorsal side and affecting the cerebellar peduncle or cerebellum ventrally, and are manifested as unsteady walking, nystagmus, ataxia, and hypomuscularity in some patients.
Examination
1. Cranial X-ray film
Signs of increased intracranial pressure are common, and calcified spots in the posterior cranial recess can be seen in some patients (2.8%).
2.CT examination
The fourth ventricle is occupied by equal or slightly high density, and some low density cystic changes and calcification are more common. The boundary of the tumor is still clear and easy to strengthen, but it is mostly inhomogeneous.
3.MRI examination
It is mostly long T1 and long T2 lesions with heterogeneous signal, nodular, uneven enhancement, and clear boundary. Sagittal position is helpful for distinguishing the position of the tumor from the base of the fourth ventricle and the cerebellar earth part, and the length of extension into the spinal canal.
Diagnosis
When the symptoms of cranial hypertension appear early in the course of the disease, and when the symptoms of irritation of the nucleus pulposus at the base of the fourth ventricle, signs of pressure on the pyramidal tract, and cerebellar damage appear gradually, the possibility of ventricular meningioma should be thought of, and the combination of the findings of the imaging examination will help to make the diagnosis. It should be differentiated from pediatric cerebellar astrocytoma and medulloblastoma.
Treatment
Surgical total excision of the tumor is the preferred treatment option for ventricular meningiomas. The surgical mortality rate for supratentorial ventricular meningiomas has been reduced to 0% to 2%, while the surgical mortality rate for infratentorial tumors is 0% to 13%. Because the tumor mostly adheres to the brainstem and posterior group of cerebral nerves, which reduces the rate of total surgical resection, intraoperative strengthening of neurophysiological monitoring will be conducive to a more complete resection of the tumor, and reduce postoperative complications and mortality. For the tumor growing from the base of the fourth ventricle, it is not necessary to force total resection, and a thin layer of tumor tissue can be left in the base of the fourth ventricle, so as to avoid damage to the facial thalamus and the brainstem, but the surgery must make the cerebrospinal fluid obstruction to restore the patency. For patients who fail to undergo total tumor resection, postoperative radiation therapy should be performed. Although there is no uniform understanding of postoperative radiotherapy for ventricular meningiomas, most authors recommend a dose of 50-55 Gy. Prophylactic irradiation of the cerebrospinal cord is not necessary for ventricular meningiomas because the vast majority are in situ recurrences in the tumor bed. Postoperative chemotherapy is not effective in adult patients, but it is still an important adjuvant treatment for patients with recurrence or young children who are not suitable for radiotherapy. Commonly used chemotherapeutic agents include carmustine, lomustine, etoposide (etoposide), cyclophosphamide and cisplatin, etc. Chemotherapy for infants and young children under the age of 3 years can be started at 2-4 weeks after surgery, and the next course of treatment can be started after 4 weeks of rest, which can prolong the survival of the patients, and then the patients can be treated with radiotherapy after the age of 3 years. Surgery for mesenchymal ventricular meningioma is still the main therapeutic measure, and postoperative radiotherapy is necessary, which should be given early and at a higher dose of 55-60 Gy. Prophylactic cerebro-spinal radiotherapy should also be added. Chemotherapy is one of the means of adjuvant treatment to control tumor growth in the short term.
The recurrence rate of ventricular meningiomas is high, and the prognosis of posterior cranial recess tumors in children is poor, with almost all cases recurring at various times after surgery. Ventricular meningiomas are prone to intravertebral dissemination of implantation. In one study, 436 cases of ventricular meningiomas were counted in all age groups, and those with intravertebral implantation accounted for 11%. Intravertebral implantation of subepithelial ventricular meningiomas was more common than that of supratentorial ones. The incidence of ventriculoblastoma metastasis was significantly higher than that of ventricular meningioma. Extracranial metastases of intracranial ventricular meningiomas are rare and have been reported only in isolated cases. Clinical reports of disseminated implantation often underestimate the true rate at which this occurs because spinal cord imaging is not routinely done in the vast majority of cases. Analysis of clinical data on patients with spinal cord implantation metastases from ventricular meningiomas in the posterior cranial fossa showed a 6% incidence of disseminated implantation, whereas 21 series reported a combined incidence of 15%.
Prognosis.
The prognosis of the disease is poor, especially in children. The main factors affecting the prognosis include the patient’s age, the location of the tumor, the degree of surgical resection, the pathological type of the tumor, and postoperative radiotherapy, of which the degree of surgical resection is more important.