Meningioma is a common benign intracranial tumor in adults, accounting for 14.3% to 19% of primary intracranial tumors, and is second only to glioma in incidence. The peak age of onset is around 45 years, with a male to female incidence of 1s1.8. 19% to 24% of juvenile meningiomas occur in neurofibromatosis type I (von Recklinghausen’s).
Meningiomas are associated with the arachnoid membrane and can occur at any site where arachnoid cells are present (between the brain and skull, within the brain ventricles, along the spinal cord), especially coinciding with areas of concentrated distribution of arachnoid granules. Meningiomas are most often associated with the dura mater, but they can also occur without association with the dura mater, as in meningiomas occurring in the ventricles.
Meningiomas are usually slow-growing, well-defined (non-invasive), benign lesions. They may be malignant and/or rapidly growing in a small number of cases. 8% of patients have multiple tumors, especially in patients with neurofibromatosis. Occasionally, the tumor grows in a large prostrate pattern (plaque meningioma).
Diagnosis
(I) Prevalent sites
Common sites include: parsagittal sinus, hemispheric convexity, saddle node, pterygoid crest, olfactory groove, fossa cerebri, lateral ventricles, cerebellar curtain, middle cranial fossa, orbit, pontocerebellar angle, slope and foramen occipitalis. Approximately 60% to 70% grow along the falx (including parsagittal sinus), pterygoid (including saddle node) or convex surface of the brain. Meningiomas are rare in children, with 28% occurring in the ventricles.
(II) Clinical manifestations
Meningioma is a benign tumor with slow growth and long course. Because the tumor grows expansively, patients often have headache and epilepsy as the first symptoms.
2.Symptoms of increased intracranial pressure may not be obvious. Many patients only have mild headache, or even meningioma is found by chance through CT scan. Because of the slow growth of the tumor, the tumor often grows very large, while the clinical symptoms are not yet serious. Sometimes, the patient’s fundus optic papillary edema is quite obvious and even secondary optic nerve atrophy occurs, while the headache is not severe and there is no vomiting. It is worth noting that when the tumor in the “dumb area” grows so large that it cannot be compensated and the intracranial pressure increases, the condition will suddenly deteriorate and even brain herniation will occur within a short period of time.
3.Local neurological dysfunction According to the different parts of tumor growth and adjacent neurovascular structure, there may be different local neurological dysfunction. For example, the lateral type of pterygoid pterygoid meningioma (or pterygoid point type) is similar to the convex meningioma; the medial type (bed protrusion type) has corresponding cerebral ischemia and cranial nerve dysfunction because it encircles the cranial nerve and optic nerve of ICA, MCA, supraorbital fissure. Olfactory groove meningioma mostly grows to a large size before symptoms appear, including: Foster-Kennedy syndrome (ipsilateral optic nerve atrophy, contralateral optic papilla edema), mental changes, such as compression of the optic pathway leading to visual field defects, etc.
4. Cranial changes Meningioma can often cause changes in the bone quality of the adjacent skull, manifested as thinning and destruction of the bone plate, or even erosion through the bone plate to the subcapsular tendon membrane, and local elevation of the scalp. Sometimes, the tumor can also thicken the inner plate of the skull, and the thickened skull can contain tumor tissue.
5.Epilepsy Meningioma located in frontal or parietal area is prone to produce irritation symptoms and cause restricted epilepsy or generalized seizures.
(C) Pathology
There are various pathological classifications, and there are transitional types between the major types, and more than one pathological feature is seen in the same tumor. The main types include
1. Three main types of “typical meningioma”
(1) Endothelial type: Also known as syncytial cellular, it is the most common and has a large number of polygonal cells. Some people refer to endothelial meningiomas with dense blood vessels as angiomatous meningiomas.
(2) Fibrous or fibroblast type: The cells are separated by connective tissue and have a tougher texture than endothelial and transitional meningiomas.
(3) Transitional type: between endothelial type and fibrous type, cells are spindle-shaped, typical meningioma cells can be seen in some areas, swirling arrangement, some have calcification (sand-like tumor vesicles).
2. Angioblastoma type: Different authors have different names for it. Some call it “extravascular meningioma”, while others call it “hemangioblastoma” because it resembles angiogenic cells in terms of pathology.
Atypical meningiomas: These include any of the above meningiomas with more than one of the following features: increased mitotic activity (1 to 2 schizophrenic images/high magnification view), increased cell density, focal necrosis, and giant cells. Cellular pleomorphism is not uncommon, but is not significant in itself. With elevated atypia, the aggressiveness of the tumor is enhanced.
4. Malignant meningioma: Also known as mesenchymal, papillary or sarcomatoid meningioma, characteristic changes are common mitosis, invasion of the cortex, and rapid recurrence even in the case of total resection. Very rarely, metastases occur. The large number of mitotic images or the presence of papillary changes strongly suggests malignancy. It may be more common in younger patients. Compared to other types, angioblastoma meningioma exhibits more malignant clinical features.
Extra-central nervous system metastases from meningiomas are extremely rare and are mostly hemangioblast type or malignant, with common metastatic sites being the lung, liver, lymph nodes and heart.
(IV) Ancillary tests
1.Electroencephalogram (EEG) Because meningioma develops slowly and has restricted expansion growth, there are usually no obvious slow waves during EEG. However, when the tumor grows quite large, compressing the brain tissue and causing cerebral edema, the EEG may show slow waves, mostly limited abnormal Q waves and lazy waves, and the changes of background EEG are mild. The richer the vascularity of meningioma, the more obvious the waves are. Patients with cerebral hemispheric convexity or parsagittal sinus meningioma may have a history of epilepsy, and EEG can assist in the diagnosis.
Because of the close relationship between meningioma and skull and the common blood supply pathway, it is easy to cause changes in the skull, and the localization sign of cranial plain film can be 30% to 60%, and the intracranial pressure elevation can be more than 70%. The main manifestations are.
(1) Restricted bone changes There may be thickening of the inner plate, diffuse hyperplasia of the bone plate, and pin-like radial hyperplasia of the outer plate bone. It is generally believed that the tumor cells reach the dura mater and enter the skull through the vascular pathway, causing a proliferative response in the surrounding or bone cells. Regardless of the presence or absence of tumor cell invasion, the site of tumor hyperplasia is suggestive of the central location of the tumor. The incidence of meningioma causing local bone plate thinning and destruction is about 10%. Intra-tumor calcification accounts for about 10%.
(2) Increased vascular indentation of the cranial plate Thickening and distortion of the meningeal arterial sulcus can be seen, most commonly in the middle meningeal arterial sulcus. Abnormal increase of local cranial plate barrier vein.
3.Cranial CT and MRI
(1) CT shows uniform density of the lesion with obvious enhancement and basal width attached to the dura mater. 60-70 CT non-enhanced scans are often accompanied by calcification of sandy tumor. There is usually no significant cerebral edema, but a few may have significant peritumoral edema, sometimes extending to the entire cerebral hemisphere. The advantage of CT is that it can clearly show the calcification and bony changes (hyperplasia or destruction) of the tumor.
(2) MRI generally shows equal or slightly longer T1 and T2 signals. 60% of the tumors are isosignal to the gray matter on T1 images and 30% are hyposignal below the gray matter. On T2 image, 50% are isosignal or high signal, 40% are moderate high signal, and may be mixed signal. The tumor is well-defined, round or round-like, and most of the edges have a low-signal band in an arc or ring shape, which is the residual subarachnoid space (cerebrospinal fluid). The parenchymal part of the tumor shows homogeneous and obvious enhancement by venous enhancement. MRI has the advantage of clearly showing the relationship between the tumor and the surrounding soft tissue. The disappearance of the subarachnoid interface between the meningioma and the brain indicates that the tumor is growing aggressively, making total surgical resection more difficult.
(3) Enhancement of the dura mater at the base of the tumor may form a “meningeal tail sign”, which is a characteristic sign of meningioma, but is not unique to meningioma. Other lesions in the adjacent dura mater, such as metastatic carcinoma and glioma, may also have similar imaging features.
(4) Simultaneous CT and MRI enhancement scans and comparative analysis can lead to a more correct localization and qualitative diagnosis.
4.Cerebral angiography can understand the blood supply of tumor. The relationship between tumor and important blood vessels, as well as the condition of dural venous sinuses (to decide whether they can be ligated during surgery). Also, cerebral angiography provides the conditions for embolization before surgery.
In about half of meningiomas, cerebral angiography may show tumor shadowing. Usually, meningiomas characteristically appear on cerebral angiography images as follows.
(1) The meningeal vessels appear as a network of small arteries of uniform thickness and neat arrangement, with a clear outline in an encircling shape.
The tumor receives dual blood supply from the external and internal carotid arteries or vertebral artery system at the same time. Meningioma located at the base of anterior cranial fossa can receive blood supply from ophthalmic artery, sieve artery and anterior cerebral artery branches; meningioma located at the base of middle cranial fossa can receive blood supply from middle meningeal artery and ascending pharyngeal artery; meningioma at the base of posterior cranial fossa can receive blood supply from occipital artery, anterior branch of vertebral artery and posterior meningeal artery.
(iii) Angiography may also reveal obstruction of the dural sinuses, particularly in sagittal sinus/parsagittal meningiomas. The degree of superior sagittal sinus patency is more reliably assessed based on oblique films.
④ The circulation velocity of the tumor is slower than the cerebral blood flow, and the contrast agent is often retained in the tumor. In the venous phase of cerebral angiography, even in the sinus phase, tumor staining can still be seen, i.e. delayed blush. The distinct and uniform delayed filling of tumor vessels helps to confirm the diagnosis.
(5) The cerebral vessels around the meningioma are wrapped and displaced.
The above features may be seen in the cerebral angiogram of meningioma, or may be partially seen.
Principles of treatment
(I) Surgical treatment
Surgical removal of meningioma is the most effective treatment. With the development of microsurgery technology, the surgical effect of meningioma has been improved and most patients can be cured, but the possibility of recurrence cannot be excluded.
2.Pre-surgery preparation
(1) If cerebral edema is severe, hormone therapy is given 3 days before surgery. Methylprednisolone tablets 8mg, or prednisone 5mg twice daily.
(2) Anti-epileptic treatment should be given to those with seizures before surgery. For those who do not have seizures in their medical history but the tumor is located in a site prone to seizures, oral antiepileptic drugs should be given 1 week before surgery and intravenously on the day of surgery, such as sodium valproate, to prevent seizures.
(3) Tumor blood supply artery embolization For blood-rich tumor with external carotid artery involved in blood supply, blood supply artery embolization is feasible before surgery.
3.Surgical principles
(1) Position Depending on the location of tumor, lateral, supine and prone positions are commonly used.
A. The head position should be slightly higher than the horizontal line of the body, which can reduce bleeding during surgery.
B. The center of the tumor should be positioned at the highest point of the operative field as possible.
C. When rotating the head and neck, do not overdo it to avoid obstruction of the jugular vein and/or airway, resulting in increased intracranial pressure.
(2) Incision design
A. The surgical incision should be designed according to the location of the tumor provided by the imaging data, combined with the body projection of structures such as the pterygoid point, coronal suture, lateral fissure and central sulcus.
B. The surgical approach should try to choose the path that reaches the closest distance to the tumor, while important nerves and blood vessels should be avoided; the approach for skull base tumors should also take into account the minimal strain on brain tissue.
C. For superficial lesions, such as convex meningioma, the key to design the incision is to place the tumor exactly in the center of the bone window. For deep lesions consideration should also be given to the possibility of early treatment of the tumor base.
D. The base of the flap should be wide enough to guarantee proper blood supply.
E. The incision should be designed within the hairline as much as possible to guarantee a good cosmetic result.
F. The size of the bone flap should ensure that the tumor can be fully exposed and the involved dura mater can be removed.
G. If a micro-osseous approach is used, the site of the surgical incision can be determined with the help of surgical navigation techniques. A Marker is placed near the scalp projection of the tumor as a reference point one day before surgery, and a cranial CT or MRI scan is performed to locate the site, and the incision is designed according to the CT or MRI results.
(3) To reduce the strain on the brain tissue during surgery, lumbar puncture is feasible after the patient is anesthetized, and a drainage tube is placed in the subarachnoid space. Before cutting the dura, slowly release 30-40 ml of cerebrospinal fluid. for those with significant cerebral edema, mannitol can be given intravenously at a dose of 1 g to 2 g/kg body weight when the scalp is incised. To prevent postoperative seizures, Depakene (800 mg into the pot) is given intravenously 30 minutes before the end of surgery.
(4) Application of surgical microscope Separation of tumor under surgical microscope makes the operation more meticulous and can protect the brain tissue and important neurovascular to the maximum.
(5) The dura mater and cranial bone eroded by the tumor should be removed together if possible to prevent postoperative recurrence. For the invaded dura mater that cannot be removed, electrocautery and other methods are feasible. Venous sinuses that have been occluded by imaging and confirmed intraoperatively can also be resected. The defective dura and skull can be repaired with autologous fascia or other dural repair materials, titanium plates, etc.
4.Post-operative treatment
(1) After surgery, the patient should be sent to ICU for 24-48 hours.
(2) If the postoperative cerebral edema is severe, dehydrating drugs and glucocorticoids should be given intravenously after surgery.
(3) Immediately after the patient wakes up from anesthesia, perform neurological function assessment and make records. If neurological deficits occur, the cause must be further analyzed. If intracranial hematoma formation is suspected, CT examination or direct craniotomy to the operating room is required immediately to remove the hematoma.
(4) Anti-epileptic treatment
If the tumor involves motor or sensory cortex, or if the patient has a history of seizure before surgery, intravenous antiepileptic drugs should be applied during surgery and on the day of surgery to prevent seizure. The patient may resume the pre-surgical (oral) antiepileptic treatment regimen after eating on the first day after surgery. Post-surgical antiepileptic therapy is given for at least three months, and the dosage can be gradually reduced until the medication is discontinued in seizure-free patients. In patients with a history of epilepsy prior to surgery, the duration of antiepileptic therapy should be appropriately extended, with 1 to 2 years generally recommended.
(5) Prevention of lower extremity thrombosis and pulmonary embolism
If the patient has postoperative limb movement disorders or elderly patients who cannot get out of bed for a short period of time, medication (e.g., rapid avoidance of coagulation, 0.3 ml, subcutaneous injection next to the umbilicus) and elastic stockings should be given if necessary.
(6) Cerebrospinal fluid leakage If there is a possibility of cerebrospinal fluid leakage after surgery, head high position and continuous drainage by lumbar puncture should be taken for 2 to 3 days; in case of cerebrospinal fluid leakage, it can last for 5 to 7 days, and it can usually heal spontaneously. If the cerebrospinal fluid leak is still not relieved, a second surgery should be considered to repair the leak.
5.Grading of meningioma resection
At present, the internationally used grading method for meningioma resection is Simpson’s grading method. This classification is an important reference value for unifying resection standards and evaluating the surgical results of meningioma. However, some people believe that this classification is more applicable to convex meningioma, but not necessarily to intracerebroventricular and skull base meningioma, such as meningioma in the lateral ventricular triangle, where there is no dura and skull attachment, and it is difficult to remove the involved skull and even dura in skull base meningioma surgery. Therefore, some authors have proposed a grading of meningioma resection for skull base meningioma, which has not been widely accepted yet, so we will not introduce it in detail here.
Simpson’s grading of meningioma resection
Grade
Extent of resection
Grade I
Total resection of the dura mater and cranial bone under the operating microscope (including the invaded dural sinus)
Grade II
Microscopic total resection of the dura mater with electrocoagulation or laser treatment
Grade III
Total surgical microscopic excision of the involved dura and extra-dural extensions (e.g., hyperplastic cranial bone) without treatment
Grade IV
Partial resection of tumor
Grade V
Tumor decompression alone (and/or biopsy)
(II) Non-surgical treatment
Radiation therapy For meningioma and malignant meningioma that cannot be completely resected, radiation therapy is required after surgery. Radiation therapy is effective for malignant meningioma and vascular ependymal meningioma. However, care should be taken to avoid side effects such as radiation damage.
(C) Recurrence of meningioma and its management
As with any tumor, recurrence of tumor regrowth is likely to occur if there is a little residual in the primary site after the first surgery for meningioma. The 5-year recurrence rates of malignant and atypical meningiomas are 38% and 78%, respectively. There are two reasons for benign meningioma recurrence, one is that the tumor is not completely removed when it invades or encases important nerve and vascular tissues, such as cavernous sinus meningioma; the other is that some tumor cells are more or less residual around the primary site due to local invasive growth. Recurrence of meningioma after surgery is mostly seen in the dura mater invaded by the tumor.
Recurrent meningioma treatment methods
1. Radiation therapy Radiation therapy may be effective with prolonged mean time to recurrence. Considering the possible side effects of radiation therapy such as radiation damage and necrosis, patients with possible recurrence of meningioma can also be followed up by CT or MRI, and radiation therapy can be performed when clear signs of recurrence are found.
2.Surgical resection According to the patient’s age, physical condition, symptoms and signs, as well as imaging data, we will decide whether to operate again. The outcome of reoperation depends not only on the patient’s age and general condition, but also on the location of the tumor. For example, if the meningioma of the pterygoid crest has grown into the cavernous sinus at the time of recurrence, it will be more difficult to operate again; however, if the recurrent paraganglioma has invaded and obstructed the superior sagittal sinus, the second operation can remove the tumor and the occluded superior sagittal sinus together and obtain a cure.