Glioma, also known as glioblastoma or glioma for short, is a tumor that occurs in the neuroectoderm and is therefore also called neuroectodermal tumor or neuroepithelial tumor. Tumors originate from neurointerstitial cells, i.e., glial, ventricular canal, choroid plexus epithelium and neuroparenchymal cells, i.e., neurons. Most tumors originate from different types of glia, but based on the similar histogenetic origin and biological characteristics, all kinds of tumors that occur in the neuroectoderm are generally referred to as gliomas. As tumors gradually increase in size, they form intracranial occupying lesions and are often accompanied by peripheral cerebral edema, which produces increased intracranial pressure when the compensatory limit is exceeded.
When the tumor obstructs the cerebrospinal fluid circulation or compresses the vein, which leads to the obstruction of venous return, the intracranial pressure increases even more. If hemorrhage, necrosis and cyst formation occur in the tumor, the process can be accelerated. When the increase of intracranial pressure reaches the critical point, the intracranial volume continues to have a small increase and the intracranial pressure will increase rapidly. If intracranial pressure monitoring is performed, when the pressure reaches 6.67-13.3 kPa Hg, plateau wave appears, and plateau wave appears repeatedly and lasts for a long time, which is the clinical sign. When the intracranial pressure is equal to the arterial pressure, cerebrovascular paralysis occurs, cerebral blood flow stops, blood pressure drops, and the patient will die soon.
I. Clinical manifestations of glioma.
The course of glioma varies according to its pathological type and location. The time from the appearance of symptoms to the consultation is usually weeks to months, and a few may reach several years. The history is shorter for highly malignant and posterior cranial fossa tumors and longer for more benign tumors or tumors located in the so-called quiet zone. If the tumor has hemorrhage or cyst formation, the progression of symptoms may be accelerated, and some may even resemble the progression of cerebrovascular disease. The symptoms are mainly manifested in two aspects. One is the increase of intracranial pressure and other general symptoms, such as headache, vomiting, loss of vision, diplopia, seizures and psychiatric symptoms. The other is the local symptoms produced by the compression, infiltration and destruction of brain tissue by tumor, resulting in neurological deficits.
Headache is mostly caused by the increase of intracranial pressure. The growth of tumor gradually increases the intracranial pressure, which compresses and involves pain-sensitive structures in the skull such as blood vessels, dura mater and certain cranial nerves and produces headache. Most of the headaches are throbbing and swelling pains, mostly in the frontotemporal or occipital area. For tumors in the superficial hemisphere of one side of the brain, the headache may be mainly on the affected side.
Vomiting is caused by stimulation of the medullary vomiting center or vagus nerve, and may be jet-like without nausea. In children, the headache is not significant due to the separation of cranial suture, and vomiting is more prominent because tumor in posterior cranial fossa is common.
Increased intracranial pressure may produce optic papillar edema and cause secondary optic nerve atrophy and vision loss. If the tumor compresses the optic nerve, primary optic nerve atrophy will occur, which also leads to vision loss. The adductor nerve is easily squeezed and pulled, which often leads to paralysis and diplopia.
Some patients with tumors have seizure symptoms, which can be early. Epilepsy begins in adulthood the latter is usually symptomatic and mostly due to brain tumors. The presence of a brain tumor should be considered in all cases where the seizures are not easily controlled by medication or have a change in nature. Tumors adjacent to the cortex are prone to epilepsy, while those deeper in are less common. Focal epilepsy has localization implications. Some tumors, especially those located in the frontal lobe, may gradually develop psychiatric symptoms, such as personality changes, apathy, decreased speech and activity, inattention, memory loss, lack of concern for things, and lack of awareness of neatness.
The local symptoms will be aggravated progressively depending on the location of the tumor. In particular, malignant glioma grows faster, infiltrates and destroys brain tissues, and the surrounding brain edema is also significant, so the local symptoms are more obvious and develop faster. Tumors in the intracerebroventricular region or tumors located in the quiet zone may have no local symptoms in the early stage. In contrast, tumors in the brainstem and other important functional areas show local symptoms at early stage, and it takes a long time before the symptoms of increased intracranial pressure appear. For some tumors with slow development, due to the compensatory effect, the symptoms of increased intracranial pressure often appear only in late stage.
Diagnosis of glioma.
Diagnosis is based on age, gender, site of occurrence and clinical course, and estimation of its pathological type. In addition to the medical history and neurological examination, some auxiliary examinations are also needed to help diagnose localization and characterization.
(1) Cerebrospinal fluid examination: the pressure of lumbar puncture is mostly increased, and the amount of cerebrospinal fluid protein may be increased if the tumor is located on the surface of the brain or in the ventricles, and the number of white blood cells may also be increased, and some tumor cells may be detected. However, if the intracranial pressure is significantly increased, lumbar puncture may promote the risk of brain herniation. Therefore, it is usually done only when necessary and when it is necessary to differentiate from inflammation or hemorrhage. In cases of significant pressure increase, the operation should be performed with caution and not to release more cerebrospinal fluid. Give mannitol drip after the operation and pay attention to observation.
(2) Ultrasound examination: It can help to fix the side and observe the presence or absence of hydrocephalus. For infants, B-type ultrasound scan can be performed through fontanel, which can show tumor images and other pathological changes.
(3) EEG examination: The EEG changes of glioma are on the one hand the changes of brain waves confined to the tumor site. On the other hand, there are general widely distributed frequency and wave amplitude changes. These are influenced by tumor size, infiltration, degree of cerebral edema, and increased intracranial pressure, with superficially located tumors prone to limited abnormalities and deeper tumors less likely to have limited changes. In the more benign astrocytomas and oligodendrogliomas, they mainly present as restricted delta waves, with some visible epileptic waveforms such as spikes or sharp waves. Large glioblastoma multiforme may show extensive δ waves, sometimes only fixed laterally.
(4) Radioisotope scan (Y-ray encephalography): Tumors with faster growth and rich blood flow have high blood-brain barrier permeability and high isotope uptake. For example, glioblastoma multiforme shows isotopically concentrated images, and there may be low-density areas formed due to necrosis and cysts in the middle, which need to be differentiated from metastases according to their shape and multiplicity. Astrocytomas and other benign gliomas are less concentrated, often slightly higher than the surrounding brain tissue, and the images are less clear, and some of them may be negative.
(5) Radiological examination: including cranial plain film, ventriculography and computed tomography scan. Cranial plain film can show intracranial pressure increase, tumor calcification and pineal gland calcification displacement, etc. Ventriculography can show cerebral vascular displacement and tumor vascular condition. These abnormal changes, which vary in different types of tumors in different locations, can help localize and sometimes even characterize the tumor. Especially, CT scan has the greatest diagnostic value. Intravenous contrast-enhanced scan has almost 100% accuracy of localization and more than 90% correct rate of qualitative diagnosis. It can show the site, scope, shape, brain tissue reaction and ventricular compression displacement of the tumor. However, it still needs to be considered together with the clinical aspects in order to make a clear diagnosis.
(6) MRI: The diagnosis of brain tumor is more accurate than CT, and the image is clearer, and it can find tiny tumors that cannot be shown by CT. Positron emission tomography can obtain images similar to CT, and can observe the growth and metabolism of tumors and identify benign malignant tumors.
Treatment methods of glioma
However, due to the infiltrative growth of the tumor, there is no obvious boundary between the tumor and brain tissue, except for the small tumor in the early stage and the appropriate location, it is difficult to remove all of them. We should strive for early diagnosis and timely treatment to improve the treatment effect. Late stage is not only difficult to operate, but also dangerous and often has neurological deficits. Especially for tumors with high malignancy, they often recur within a short period of time.
(1) Surgery: The principle is to remove the tumor as much as possible while preserving the neurological function. In early stage, all tumors should be removed if they are small. For shallow tumors, the cortex can be cut around the tumor, and for white matter tumors, the important functional areas should be avoided for cortical incision. When separating the tumor, it should be done at a certain distance from the tumor and within the normal brain tissue, not close to the tumor. Especially for more benign tumors such as astrocytoma and oligodendroglioma in the frontal or anterior temporal lobes or cerebellar hemispheres, better results can be obtained.
For larger tumors located in the frontal or anterior temporal lobes, lobectomy can be performed to remove them together with the tumor. In the frontal lobe, the posterior margin of the incision should be at least 2 cm in front of the anterior central gyrus, in the dominant hemisphere and should avoid the motor speech center. In the temporal lobe, the posterior margin should be before the inferior anastomotic vein and avoid damage to the lateral fissure. If the frontal or temporal lobe tumors are too extensive to be removed, the frontal pole or frontal pole can be removed as much as possible for internal decompression, which can also prolong the recurrence time.
If the tumor involves more than two lobes of the cerebral hemisphere, but does not invade the basal ganglia, thalamus or the contralateral side, hemispherectomy can be performed. If the tumor is located in motor and speech area without obvious hemiparesis and aphasia, attention should be paid to maintain the neurological function to remove the tumor appropriately to avoid serious sequelae. Sub-temporal muscle or debridement decompression can be performed at the same time. Or, decompression can be performed after biopsy only. If the thalamus tumor compresses and obstructs the third ventricle, shunt can be performed, otherwise decompression can also be performed.
Ventricular tumor can be removed from the non-important functional area to enter the ventricle according to the location of the tumor, so as to remove the tumor and relieve the ventricular obstruction. Care should be taken to avoid damaging the hypothalamus or brainstem adjacent to the tumor to prevent danger. Except for small nodular or cystic tumors, brain stem tumors can be resected, and those with increased intracranial pressure can be shunted. If the tumor is difficult to be resected, shunt can also be performed.
For those who are in critical condition, dehydration medication should be given to the supratentorial tumor first, and the diagnosis should be confirmed by examination as soon as possible, and then surgery should be performed immediately. Posterior cranial fossa tumor can be treated by ventricular drainage first, and then surgery after 2-3 days when the condition improves and stabilizes.
(2) Radiation therapy: The radiation sources used for external irradiation are high-voltage x-ray therapy machine, 60Co therapy machine, electronic gas pedal and so on. The latter two are high-energy rays with strong penetrating power, low skin dose, small bone absorption and little bypass scattering. Gas pedals, on the other hand, concentrate the dose at the expected depth, beyond which the dose drops sharply, and can protect the normal brain tissue behind the lesion. Radiation therapy should be administered as soon as possible after the general condition has recovered from surgery.
The irradiation dose is usually given to 5000-6000 cGy for glioma and is completed within 5-6 weeks. The sensitivity of various types of gliomas to radiation therapy varies. It is generally believed that poorly differentiated tumors are more sensitive than well differentiated ones. Medulloblastoma is the most sensitive to radiotherapy, followed by ventriculoblastoma. Glioblastoma multiforme is only moderately sensitive, and astrocytoma, oligodendroglioma, and pineal cell tumor are even worse. For medulloblastoma and ventricular meningioma, whole spinal canal irradiation should be included because they are easily disseminated with cerebrospinal fluid.
(3) Chemotherapy: chemotherapeutic drugs with high lipolytic properties that cross the blood-brain barrier are suitable for cerebral gliomas. In astrocytoma grade III-IV, the blood-brain barrier is destroyed due to edema, allowing water-soluble macromolecules to pass, so some people think that the selection of drugs can be expanded to many water-soluble molecules. However, in fact, the blood-brain barrier is not severely damaged in the peritumor area where proliferating cells are dense. Therefore, it is still appropriate to choose drugs mainly with fat-soluble molecules.