Medial sphenoid wing meningiomas can invade the cavernous sinus, encircle the vessels, affect nerves and even invade the bone. These nearby critical anatomic structures can limit the extent of resection, which may result in higher recurrence rates[16, 5, 13, 4]. Therefore, surgical management of mSWM is challenging. In this study, our scoring system, based on preoperative 3D multimodality fusion imaging data of tumor volume, artery encasement, CS involvement, and bone invasion, was able to assess the feature of every tumor intuitively and may provide a preoperative evaluation to predict the extent of resection and help to maximize the safe removal of the tumors and minimize dysfunction.
Classification of Medial Sphenoid Wing Meningiomas
In 1938, Cushing et al. first divided the sphenoid wing meningiomas in detail as “globoid” and “en plaque” tumors. Globoid tumors were further categorized into 3 groups based on their location of origin along the sphenoid wing: 1) deep inner or medial; 2) middle; and 3) lateral. Al-Mefty based his classification of anterior clinoidal meningiomas on the origin of the tumor and whether arachnoid membrane is present [2]. However, the presence of arachnoid membrane cannot be clearly observed preoperatively, thereby limiting its application to our scoring system. Hirsh et al. categorized meningiomas involving CS into three groups based on their relationship to the cavernous carotid to predict the difficulty of resection [10]. Nakamura et al. divided mSWM into 2 groups based on the presence or absence of CS invasion to provide clinical data concerning the visual outcome and recurrence rate[16]. Behari et al. proposed a scoring system for predicting the extent of surgical resection in giant mSWM [3]. However, their study only included 20 patients with giant mSWM (≥ 5 cm in maximum dimension), which may lead to biased results. Moreover, they did not show any statistical analyses of their scoring system. McCracken et al developed a scoring system for evaluating the degree of encasement of arteries surrounded by the SWM on MRI to predict postoperative ischemic complications[14]. Grade of tumor encasement was determined by the circumferential involvement in details. Recently, Guduk et al. proposed a new scoring system, which including the largest tumor diameter, proximal arterial encasement, distal arterial encasement and bone invasion pattern, to predict the extent of resection based on preoperative MRI or CT findings[9]. The study included all groups of SWM such as spheno-orbital, medial, middle, and lateral meningiomas. However, they did not perform any evaluation of their scoring system.
None of the studies to date could provide a reliable and overall prediction of surgical resection grade of mSWM based on the preoperative radiology images. The evolution of 3D multimodality fusion imaging has made more accurate guidance for neurosurgery possible. It can clearly reveal the anatomic relationship of the tumor and its surrounding structures, and assist in the selection of operative approach and tumor resection. Most of the feeding arteries, perforating arteries, and veins were encased or displaced by the deep-seated meningiomas, which may affect interpretation in 2D images[21]. Our scoring system, based on preoperative 3D multimodality fusion imaging, may provide a more feasible method to predict the resection grade of mSWM and avoid some of the surgical complications. It is also the first study to evaluate mSWM with 3D multimodality fusion imaging.
Parameters of Our Scoring System
Tumor volume is significantly associated with the extent of resection in our study. Here we took the meningiomas’ volume calculated by Mimics software rather than the maximum dimension into consideration because most of the meningiomas we analyzed had irregular shapes. Furthermore, there was no significant relationship between the maximum dimension and Simpson excision grade in our cases (P = .36). Larger meningiomas often had the propensity to invade critical regions and increase the difficulty and risk of surgery[3, 8, 13]. So, it is more accurate to analyze the meningiomas’ volume to assess the difficulty encountered during surgery. Cavernous sinus involvement is one of the main factors that increases the difficulty of total resection of medially located tumors. As its location is very close to the cranial nerves, the rate of postoperative cranial nerve palsies is consequently higher[24]. The surgical management of tumors involving the CS remains controversial[1, 4, 12, 26, 6]. A more aggressive approach will increase surgical morbidity. But the extent of removal of cavernous sinus meningiomas is inversely related to the rate of recurrence on the other side[16, 4]. In our 23 cases with meningiomas invading into the CS, only 35% of them achieved Simpson II resection, with 88% of the Simpson II resection cases came out with worse or unchanged symptoms. Arterial involvement has a significant effect on the resectability of mSWM. As vessel encasement by tumor increases, the risk of vascular injury will also increase, which may cause higher morbidity and even mortality[14]. When these meningiomas lack the arachnoid plane between the tumor and cerebral vessels, resection becomes more difficult because they can invade the arterial wall, thereby increasing the risk of vascular injury and the difficulty of total removal[2, 20]. In our study, a new classification was developed to include all the possibility of arterial involvement. Bone Invasion has been found to have an impact on the extent of resection in many studies[3, 9, 22]. The tumor invasion of bone structures such as the superior orbital fissure, optic canal, and orbit is associated with higher risk of morbidity[9] and recurrence[3, 18, 15, 19]. We also found significant difference between bone invasion and resection grade.
All the factors mentioned above had significant association with resection according to our statistical analyses and the surgical experience of our neurosurgeons, especially the arterial encasement and CS involvement. Our scoring system has been proved to be effective and convenient to predict the resection grade before surgery. It is the first scoring system for mSWM based on the preoperative 3D multimodality fusion imaging. We believe that our scoring system can not only show the advantages to predict the resection grade preoperatively, but also be useful for neurological function protection and reducing postoperative complications.