Meningioma resection

  Meningiomas of the posterior cranial recess are classified into meningiomas of the cerebellar vermis (30%), cerebellar hemispheres (10%), retrobulbar meningioma (42%), slope meningioma (11%) and foramen magnum meningioma (4%) according to the attachment site of the tumor on the dura mater. In the literature, meningiomas in the posterior cranial sulcus are more common than meningiomas behind the rock bone. In contrast to the supratentorial cranial cavity, the relatively small posterior cranial recess houses the nerve centers that maintain vital functions. All cranial nerves, except for the Ⅰ and Ⅱ pairs of cranial nerves, travel here.  Compression of the midbrain aqueduct and the four ventricles can affect cerebrospinal fluid circulation. Because of the slow growth of meningioma, early symptoms are insidious, especially in patients with cerebellar curtain and cerebellar hemisphere tumors, only headache and dizziness may occur at the initial stage.  The application of CT and MRI has significantly improved the diagnosis of posterior cranial recess meningioma. The diagnosis can be made based on the morphology, density (in CT), intensity (in MRI), and enhancement characteristics of the tumor, as well as the identification of cranial hypertrophy, tumor calcification, vascular encapsulation or erosion, and blood supply arteries and draining veins. Cerebral angiography is the most visual and clear means of understanding the blood supply of posterior cranial sulcus meningiomas. Meningiomas in the posterior cranial sulcus are usually multivessel in blood supply.  The main blood supply arteries of the posterior cranial sulcus dura are: 1) the posterior meningeal artery, which supplies the posterior cerebellar falx and its adjacent dura; 2) the meningeal branch of the occipital artery, which supplies the lateral dura of the posterior cranial sulcus; 3) the anterior meningeal branch of the vertebral artery, which supplies the dura of the lower slope and the anterior lip of the greater occipital foramen; 4) the arteries of the cerebellum may also participate in the blood supply of the posterior cranial sulcus dura.  Understanding the blood supply to the posterior cranial sulcus dura and carefully analyzing it with the patient’s preoperative imaging data is necessary to reduce intraoperative bleeding and ensure surgical safety. For meningioma behind the rock, the lateral suboccipital approach is usually used, and the patient is usually placed in a semi-sitting or lateral ventral position.  The patient is placed in a semi-prone position with the head slightly tilted to the side of the tumor and the head frame fixed so that the bone window is directly below the operator and the posterior anterior axis of the patient’s rock cone is in line with the operator’s line of sight, which facilitates observation and operation and reduces the operator’s fatigue due to prolonged surgery. Precordial Doppler flow monitor and central venous pressure monitoring were routinely used. Generally, the tumor invades the dura at the neural foramen, and electrocoagulation of this part may incur nerve damage if trying to achieve radical treatment, therefore, it is difficult to deal with the intradural tumor in this part.  In such cases it is better to have a small piece of tumor left than to damage the cranial nerve, and postoperative radiosurgery can be done as appropriate. The common surgical approaches for rock-slope meningioma include frontotemporal approach, occipital trans-cerebellar approach, inferior temporal-trans-cerebellar approach, trans-cochlear approach, inferior occipital approach, combined inferior temporal-trans-vagus approach, combined inferior occipital-trans-vagus approach, trans-temporal approach and trans-oral approach. Each approach has its own advantages and disadvantages. Different approaches are chosen according to the location, extension and size of the tumor. For superior slope tumors, the pterygoid approach is used, and for inferior slope tumors, the distal lateral-parieto-occipital condylar approach is used. After the anterior ethmoid sinus-vagus, the combined upper and lower approach through the rocky bone curtain is ideal for tumors in the apical region and tumors growing laterally in the mid-slope. With this approach, the cerebellum and temporal lobe can be minimally stretched, the distance to the slope can be shortened, the operator can directly see the tumor and the anterior and lateral parts of the brainstem, the cochlea, vagus and facial nerve can be preserved, the transverse sinus, ethmoid sinus, Labbe vein and occipital basilar vein can be preserved, the blood supply to the tumor can be blocked as early as possible, and if the rock bone is eroded, the rock bone can also be removed. The disadvantage is that it is unfavorable to deal with tumors growing contralaterally in the slope. The surgical mortality rate for posterior cranial recess meningiomas in early life is quite high. It is tentatively believed that direct intraoperative injury to the brainstem and cranial nerves as well as blocking the blood supply to the brainstem are important causes of prognosis and result in patient death.