Meningioma]
It is a common intracranial tumor that can occur in any area containing dura mater, arachnoid membrane components or arachnoid granules. The incidence rate of meningioma is 2/100,000; in the skull cap, the convex surface of the brain, parsagittal, pars falciform, cerebellar curtain, lateral ventricle and skull base, the olfactory groove, suprasellar, pterygoid crest, pontocerebellar angle, middle and posterior cranial fossa are the common sites. Surgery is the main treatment for meningioma.
Principles of meningioma surgery
1. Try to protect the brain tissue around the tumor and important blood vessels and nerves.
2. Control the blood supply of the tumor and sever the adhesions between the tumor and the meninges.
3. If conditions permit, the tumor should be completely removed.
The surgical approach and flap design should take into account the factors of tumor exposure, flap blood flow and patient aesthetics. When opening the bone flap, attention should be paid to hemostasis, the involved dura mater and skull should be removed, and the dura mater of the defective bone window should be repaired by self or artificial materials. Among meningiomas convex meningiomas have the best resection results. Sagittal sinus and pars falciformis meningioma: if the tumor is located on one side, the surgery is relatively simple. If it develops to the contralateral side, the chance of complete resection is significantly reduced. During surgery, care should be taken to protect the brain tissue, especially the brain tissue in the central region, and protect the blood vessels including the central vein to prevent severe postoperative cerebral edema and hemorrhage; protecting the sagittal sinus is the key to prevent hemorrhage. The blood supply of the tumor comes from the superficial temporal artery, middle meningeal artery and anterior cerebral artery branches.
Meningioma lock-hole surgery concept]
According to each patient’s CT MRI and other imaging examinations, individualized design is performed to remove the tumor according to the characteristics of the lesion site, nature and important local structures, minimizing the trauma of conventional craniotomy. It is not the simple pursuit of small incision, but the intraoperative brain relaxation techniques such as reasonable surgical position and cerebrospinal fluid release to minimize and avoid unnecessary exposure and traction, and with the increase of surgical depth, the surgical field is further expanded to effectively remove the tumor and reduce postoperative reactions and complications. Lockhole surgery or surgery using the lockhole concept is never just a formal small incision or bone window. If the lesion is not completely removed or if it causes greater damage it can never be called lockhole surgery, and the indications for surgery should be mastered. Conditions for performing lockhole surgery: fine surgical operation techniques, microsurgical skills, good microscope and other equipment, constantly improved microscopic instruments and automatic pulling hooks to gradually separate and remove the tumor.
[Meningioma recurrence].
Most meningiomas are benign tumors and surgical resection is the preferred method. Most of them will be cured without recurrence after total resection, but some of them still have recurrence. The recurrence rate of benign meningioma is 5-15% within 10 years after total resection. Atypical meningiomas have a 5-year recurrence rate of 38%. Malignant meningioma is 78%. The higher the malignancy, the higher the postoperative recurrence rate.
The main factors affecting the recurrence of meningioma are
1. Tumor shape Round << span="">foliated << span="">mushroom-shaped
2. Tumor size Tumor diameter >4 cm has high recurrence rate
3. Tumor site: High recurrence rate after surgery in the skull base near the large vein
4. Peritumor edema Peritumor edema is obvious, and the recurrence rate is high when the interface between tumor and brain is unclear.
5.Histological type Benign 9-15% recurrence in 5 years, atypical 38%, malignant 78%, increasing with pathological level
6.The extent of surgical resection The extent of surgical resection is closely related to postoperative recurrence.
7.CT-enhanced morphology shows high recurrence rate of inhomogeneous contrast enhancement
8.Bone changes Osteolytic changes > osteomalacia
9. With or without calcification No calcification〉calcification
Meningioma invasive behavior imaging shows peritumoral edema, irregular or mushroom-shaped edges, bony changes, inhomogeneous contrast enhancement and tumor protrusion into brain parenchyma.
Meningioma of the pontocerebellar horn (retrobulbar meningioma)
Meningioma originates from the dura behind the rock bone and forms an occupancy in the pontocerebellar horn area, which has many clinical and imaging similarities with auditory neuroma. The main symptoms are hearing, cerebellar ataxia and trigeminal nerve. The order of symptoms varies depending on the site of origin. Depending on the relationship between the meningioma and the internal auditory tract, it is divided into several types so that the relationship between the tumor and the important neurovascular vessels in the area can be evaluated intraoperatively. In turn, their important neurological functions are protected. It can be divided into anterior and posterior upper and lower and peri-internal auditory tract meningiomas, and also into internal and external and posterior types, with the medial type involving the cavernous sinus and slope, and the posterior type involving the facial and auditory nerves. The surgical difficulty is significantly greater than that of the lateral type. In order to separate the tumor wall, the supply vessels from the rock cone should be cut off first (the main supply arteries are external pharyngeal artery, occipital artery, vertebral artery and anterior inferior cerebellar artery, etc.). If the tumor is soft, it is easy to be removed, but if it is hard and the wall is tightly adhered to the brainstem, it should be carefully separated. After removing the tumor, the attached dura mater should be removed. The abnormal part of bone should be removed. After the tumor is removed from the internal auditory tract, the tumor should be closed with tissue adhesive to prevent cerebrospinal fluid leakage, and the tumor should be completely removed as much as possible on the basis of ensuring the neurological integrity. If the tumor and the brainstem cranial nerve are not easily separated, it is not necessary to remove it.
Meningioma of the cerebellar curtain
Meningioma of the cerebellar curtain is divided into supratentorial and infratentorial. The tumor may come from the incisive edge of the cerebellar curtain or invade the transverse sinus, straight sinus and sinus sink. The choice of surgical approach depends on the tumor site, growth direction, and relationship with surrounding tissues.
1. Supratentorial type
In parieto-occipital and temporo-occipital approach, the tumor should be separated from the basal adhesions first, and the larger tumor should be excised in pieces, and the tumor should be separated from the venous sinus, so as not to damage the labbe vein.
2.Subcurtain type
Suboccipital approach, due to tumor extrusion, the transverse sinus is moved upward, and the bone window exposes the transverse sinus and sigmoid sinus to protect the brainstem and cerebellum.
3. Inferior and superior curtain type
Combined parieto-occipital-suboccipital approach, the transverse sinus is a dural bridge, the tumor involves the straight sinus, only the tumor is stripped from the straight sinus.
Points to note.
1. Different surgical approaches are used for different parts of tumor. The size of the bone window should meet the tumor exposure and try to expose to the edge of the venous sinus.
2. Reduce cranial pressure and brain relaxation.
3. If the tumor is large and the attachment surface is wide, intraperitoneal resection is recommended and the blood supply should be blocked as early as possible.
4. Close adhesion with sinus sink or transverse sinus or the tumor has invaded the sinus should not be forcibly resected, or the transverse sinus should be cut off. If the tumor has been confirmed to invade the transverse sinus and completely occluded, the transverse sinus can be cut off.
The surgery should be performed between the surface of the brainstem and the two layers of arachnoid membrane between the tumor, so as not to damage the normal structure, and not only to strive for total resection, but also to ensure the quality of survival.
Lateral ventricular meningioma]
In early stage, there is often no clinical symptom because the tumor grows in the ventricular cavity. When the tumor grows large and blocks the cerebrospinal fluid circulation pathway or the tumor compresses the surrounding brain tissue, the corresponding clinical manifestation appears. The imaging shows that the tumor is clearly defined and there is no cerebrospinal fluid between the tumor and the lateral ventricular wall. It usually enters the lateral ventricle through the lateral ventricular triangle. If the tumor is small, the anterior choroidal artery can be found in front of the tumor, and the tumor can be removed completely after electrocautery cutting; if the tumor is large, the tumor can be removed in pieces first, and then separated around after the tumor is reduced. The lateral ventricles and interventricular foramen should be protected during surgery to avoid blood flow into other ventricles.
Contemporary skull base surgery techniques]
1. Brain relaxation technique: fully release cerebrospinal fluid through brain pool, lumbar puncture or ventricular drainage to fully relax the brain parenchyma, and use no or less brain pressure plate for brain traction during surgery.
2.Technology of interrupting tumor blood supply: large tumor is rich in blood supply, reach the base of brain tumor at an early stage, block the blood supply as early as possible to reduce intraoperative bleeding, electrocoagulation dissection and intracapsular resection are performed crosswise until the base is completely disconnected and the tumor is fully reduced, and finally the tumor is removed.
3.Separation of arteries and cranial nerves through arachnoid membrane technique: leaving a layer of arachnoid membrane to cover important nerves and blood vessels, most tumors can be safely resected completely. Separating the arteries encircled by the tumor and the cranial nerves adhering to the brain tumor is the key to total resection of brain tumor.
The goal of surgical treatment for skull base meningioma is to maximize neurological function, reduce the disability rate, and maintain and improve the quality of patient’s survival, without simply pursuing total brain tumor resection.
Meningioma of olfactory groove and tumor blood supply
The blood supply of the tumor is mainly the sieve plate artery, sometimes the middle meningeal artery and branches of the anterior and middle cerebral arteries also participate in the blood supply. The bone window is low enough to separate the tumor wall from the brain tissue from the anterior part of the tumor by electrocoagulation of the blood supply artery from the sieve foramen.
Principle of surgical access selection for oblique meningioma].
If the preoperative impactology shows that the brainstem is edematous and the blood vessels are completely surrounded by the tumor with basilar artery blood supply, suggesting a high risk of permanent neurological deficit, when the tumor is huge or the arachnoid interface disappears, total resection cannot be considered. At this time, the surgical approach can be a simple inferior temporal cerebellar curtain, or a posterior occipital mastoid approach. Sub-total resection r-knife treatment is beneficial to protect patients’ neurological function and reduce the surgical disability rate. Recently, there has been a trend toward individualized treatment plans with the core of maintaining the patient’s quality of survival. The invasive surgical protocol with the aim of simple tumor removal is gradually discarded. Surgical technique: In the past, total resection was not considered difficult for those with a subarachnoid space between the tumor and the brain. For those who have lost the subarachnoid space, separation is often difficult. With patience and gentle separation, total resection is still possible. In the case of soft meningeal invasion, separation is very difficult and even total resection is not possible.
Between brain tumor and brainstem tissue
There is always arachnoid or soft meninges between tumor and brainstem tissue, but some interfaces are more difficult to identify. In some cases, there are multiple nodules embedded in the surface of the tumor compressing the brainstem and closely adhering to the soft meningeal vessels. The tumor should be carefully peeled off along this interface and the integrity of the envelope should be maintained. When separating the tumor, we should never tear the interface between the two with violence or cauterize the soft meningeal vessels. If the nerve attached to the brain tumor is encountered, firstly, intra-tumor resection should be performed to reduce the tension of the nerve, and then the arachnoid membrane between the nerve and the tumor can be separated by cutting. The artery supplying the brainstem often adheres to the tumor and sends out small branches, which are drilled into the tumor in a “Y” shape. When separating the tumor, we must not cauterize the brainstem supplying vessels, nor tear the small tumor supplying artery, otherwise the severed end will retract and it will be difficult to stop bleeding. Otherwise, it will be very difficult to stop the bleeding. And it is easy to damage the brainstem supply vessels.