Medial sphenoid wing meningioma of the anterior clinoid process are uncommon tumors, acknowledged by most experienced surgeons to be among the most challenging meningiomas to completely remove due to their propensity to encase the internal carotid artery (ICA) and its branches, and invade the cavernous sinus and the optic canal 1) 2) 3) 4).
Meningiomas of the anterior clinoid process may infiltrate the bone over which they arise, therefore requiring an anterior clinoidectomy to achieve a Simpson Grading System 1 resection. A clinoidectomy, however, is not without risks.
Anterior clinoidal meningiomas are frequently grouped with suprasellar meningioma or sphenoid ridge meningiomas, masking their notorious association with a high mortality and morbidity rate, failure of total removal, and recurrence. To avoid injury to encased cerebral vessels, most surgeons are content with subtotal removal. Without total removal, however, recurrence is expected. Recent advances in cranial-base exposure and cavernous sinus surgery have facilitated radical total removal. The author reports 24 cases operated on with vigorous attempts at total removal of the tumor with involved dura and bone. This experience has distinguished three groups (I, II, and III) which influence surgical difficulties, the success of total removal, and outcome. These subgroups relate to the presence of interfacing arachnoid membranes between the tumor and cerebral vessels. The presence or absence of arachnoid membranes depends on the origin of the tumor and its relation to the naked segment of carotid artery lying outside the carotid cistern. Total removal was impossible in the three patients in Group I, with postoperative death occurring in one patient and hemiplegia in another. Total removal was achieved in 18 of the 19 patients in Group II, with one death from pulmonary embolism. In the two patients in Group III, total removal without complications was easily achieved 9).
A cavernous hemangioma presenting as a clinoid meningioma is extremely rare.
A 36-year-old male with an asymptomatic intracranial mass found incidentally after an ATV accident. Preoperative MRI revealed a well-defined dural-based lesion arising from the right anterior clinoid process which was nearly homogenously enhancing, with a radiological diagnosis of meningioma. The mass was resected via right pterional craniotomy with microsurgical technique. Complete resection of the mass was performed with no complications and, notably, no significant bleeding. Contrasting with the radiologic and gross tumor appearance, histopathologic examination revealed dilated vascular spaces, sclerotic vessels without intervening neural tissue, and intravascular thrombi suggesting slow blood flow - all consistent with cavernous hemangioma.
Anterior clinoid dural-based cavernous hemangioma are extremely rare. Though preoperative diagnosis is difficult using imaging, this etiology should be considered for any dural-based middle fossa lesion due to the tendency for these lesions to bleed heavily during resection in some instances 10).
It is hard to argue that any group of skull base meningiomas represent a unified group of uniform pathologic anatomy. While some skull base meningiomas present as a localized mass, others present as a diffuse mass, infiltrating the cavernous sinus, encasing vessels, and invading cranial nerve foramina. Most skull base surgeons are well aware that not all clinoid meningiomas are the same. However, due to the rarity of these lesions, it has been difficult to sub-stratify and sub-analyze these lesions differently based on differing radiographic features. Thus, the literature to date has generally not analyzed outcomes for clinoidal meningiomas in the same way that skull base surgeons think of them when they are planning an operation 11).
The medical records of 36 consecutive patients underwent surgery from 1995 to 2015 with clinoidal meningiomas were retrospectively reviewed. Using selected clinical features and tumor characteristics, a grading scale was devised and utilized to assess a degree of tumor resectability. The factors included: preoperative visual status(no visual loss=0, visual loss=1), tumor volume: small (<13.5cm3=1), moderate (13.5-30cm3=2), and large (>30cm3=3),relationship with the internal carotid artery (no displacement=0, displacement=1, encasement=2, stenosis=3 and bilateral involvement=4) tumor extension into the cavernous sinus (yes=1, no=0) and invasion into the optic canal (yes=1, no=0), (defined as tumor beyond the falciform ligament). A grading system was designed using the total scores (10) in this classification and separating patients into two groups: group 1 with scores of 5 or less, group 2 with scores more than 5.
The patients mean age at the time of intervention was 61 years. The tumor involved the cavernous sinus in 38.9% of patients and invaded the optic canal in 36% of cases. The patient presented with visual impairment in 89% of cases. Vision improved in 28% and remained stable in 63% of cases. The mean volume of a tumor was 16.99cm3. The most common approach involved pterional with or without anterior clinoidectomy. After stratification, group 1 consisting of 22 patients and in group 2, 14 patients. Gross total resection (Simpson Grade I or II) was achieved in 75% of surgeries and subtotal and partial resections were achieved in 25% of cases. Group 1 patients had higher gross total resection rate than group 2 (p=0.009). Only optic canal involvement was significantly associated with the extent of resectabilty in a univariate analysis (p=0.03). Four patients developed tumor recurrence with median recurrence duration of 89 months (53-204 months). Three patients underwent GKRS and one patient underwent repeat surgery at the time of recurrence.
A grading system can be employed in patients who present with clinoidal meningiomas and serve as an aid in planning an appropriate treatment strategy and establishing the prognosis. Radical resection can be planned in patients with favorable tumor criteria (groups 1) while a less aggressive surgical approach followed by stereotactic radiosurgery may be better suited for patients with less favorable tumor characteristics (group 2) 12).
Patients having undergone resection of a clinoid region meningioma between 2001 and 2011 were identified. Included in further analysis were those patients in whom a clinoidectomy was performed with subsequent pathologically confirmed presence or absence of tumor in the clinoid process on decalcified specimens. Two neuroradiologists, blinded to pathology results, independently reviewed available preoperative imaging and stated whether or not they anticipated the clinoid to be involved by tumor. Interobserver agreement and the ability to accurately predict tumor involvement of the clinoid were then analyzed.
Sixty-two patients were included in the final analysis. Interobserver agreement was 100%. Sensitivity and specificity of preoperative imaging to predict tumor involvement was 89% and 52%, respectively, with positive and negative likelihood ratios of 1.85 and 0.20. Positive and negative predictive values were 73% and 76%, respectively.
Preoperative imaging of clinoid region meningiomas can accurately predict the presence or absence of tumor involvement of the clinoid in only approximately 75% of cases. In light of the fact that a quarter of patients with radiographically negative clinoids will have tumor present on pathological analysis, Copeland et al. recommend a clinoidectomy for all anterior clinoid region meningiomas 13).
29 patients with anterior clinoid meningiomas who underwent surgical resection between 1991 and 2007. The median length of follow-up was 7.5 years (range: 2.0 to 18.6 years). Similar to others, gross total resection was seldom safely achievable in these patients. Despite this, only 1/20 of patients undergoing subtotal resection without immediate postoperative radiosurgery experienced tumor progression. The optic canal was unroofed in 18/29 patients in this series, while in 11/29 patients it was not. Notably, all five patients experiencing visual improvement underwent optic canal unroofing, while three of four patients experiencing visual worsening did not.
These data provide some evidence suggesting that unroofing the optic canal in anterior clinoid meningiomas might improve visual outcomes in these patients 14).