Sphenoid Wing Meningiomas Keywords: meningioma, sphenoid wing, skull base, surgery Abstract Sphenoid wing meningiomas (SWMs) are the most common tumors in the anterior skull base, accounting for approximately 20% of supratentorial meningiomas and represent a great surgical challenge due to their invasion of the bone and, especially, to their close relationship to main arteries and cranial nerves. Lateral or pterional meningiomas usually grow into the sylvian fissure, are fed by middle meningeal artery and its branches, and reach clear relationship with middle cerebral artery (MCA), distal carotid artery, and carotid bifurcation. Medial SWMs grow compressing the proximal internal carotid artery (ICA) and its branches, are fed by dural branches of the ICA, and compress the optic nerve, the third cranial nerve; in some cases, they can invade the cavernous sinus and the optical canal. Surgical excision remains the preferred treatment. Stereotactic radiosurgery and external-beam radiotherapy are being used increasingly for surgically inaccessible, recurrent, or subtotally excised tumors, particularly if they are atypical or anaplastic. We present our experience in the surgical management of SWMs. Meningiomas are the most common benign intracranial tumors, accounting for 13 to 26% of all primary intracranial tumors. 1, 2 Meningiomas are generally slow-growing tumors composed of neoplastic arachnoidal (meningothelial) cells. Occasional tumors, particularly those lying next to the sphenoid ridge, grow in a more diffuse pattern over the dura; in these cases, they are termed meningiomas en plaque. They can be classified according to their dural site of origin, the involvement of adjacent tissues (e.g., venous sinuses, bone, brain, and neurovascular structures), and their histological grading. Histological grading of meningiomas is based on the current WHO classification. Most of them (about 90%) are WHO grade I, reflecting their benign nature. However, atypical meningiomas (WHO grade II), which make up 5 to 7%, and anaplastic variants (WHO grade III), 1 to 3%, are recognized by several histological characteristics. Typical genetic features of meningiomas are monosomy 22 and inactivating mutations of neurofibromatosis type 2 (NF2). More recently, mutations in TRAF7, AKT1, KLF4, SMO, and PIK3CA were identified. More than 80% of meningiomas harbored at least one of the above genetic alterations. NF2 alterations and mutations of the other genes were mutually exclusive with a few exceptions. Clinicopathologically, tumors with mutations in TRAF7/AKT1 and SMO shared specific features; they were located in the anterior fossa, median middle fossa, or anterior calvarium, and most of them were meningothelial or transitional meningiomas. TRAF7/KLF4 type meningiomas occurred in the lateral middle fossa and median posterior fossa as well as anterior fossa and median middle fossa, and contained a secretory meningioma component. 3 Meningiomas present clinically with focal or generalized seizure disorders, focal neurologic deficits, or neuropsychological decline. However, an estimated 2 to 3% of the population has an incidental asymptomatic meningioma. 4 Asymptomatic meningiomas can be treated conservatively because they usually show minimal growth. Nevertheless, close clinical and radiological follow-up is necessary in order to exclude a rapidly growing tumor, particularly in young patients because of the higher growth potential. 5 Serial volumetric measurements are useful for determining the natural history of meningioma. Furthermore, meningiomas with the evidence of calcification on CT scans and low signal intensity on T2-weighted MRI have been associated with slower growth rate. Nevertheless, even if growth has been confirmed, the decision to operate depends on patient’s age, symptomatology, and comorbidities. Furthermore, in series with surgically treated asymptomatic meningiomas the morbidity rate was not negligible especially for patients older than 70 years of age. For symptomatic patients, resection is usually necessary to relieve neurologic symptoms. Complete resection is often curative even if recurrences may develop after many years. Thus, the length of follow-up is the main aspect dealing with recurrence rate in meningioma series. In elderly patients, although complications are more frequent, after detailed preoperative evaluation and appropriate postoperative care, an operation is justified. Recently, a grading system has been proposed to standardize the surgical indication of intracranial meningiomas in the elderly. 6 For the majority of incompletely resected or recurrent tumors, a “wait and see” strategy or for those not previously irradiated, radiotherapy, conventional or stereotactic, is a viable alternative. Furthermore, when the meningioma is considered unresectable or all other treatments (surgery and radiotherapy) have failed, hormonal therapy or chemotherapy may be considered. Surgical excision remains the preferred treatment. Stereotactic radiosurgery and external-beam radiotherapy are being used increasingly for surgically inaccessible, recurrent, or subtotally excised tumors, particularly if they are atypical or anaplastic. Recent advances in clarification of the genetics, molecular biology, and neuropathology of meningiomas, are becoming useful in prediction of prognosis after various treatments. 3 SWMs are the most common tumors in the anterior skull base, accounting for approximately 20% of supratentorial meningiomas and represent a great surgical challenge due to their invasion of the bone and, especially, to their close relationship to main arteries and cranial nerves. 7 Anatomically, the sphenoid wing extends from the anterior clinoid process to the pterion with the greater wing constituting the outer third and the lesser wing the inner two-thirds. The greater wing and the lateral half of the lesser wing represent the lateral and middle portions of the sphenoid wing. The lateral/pterional sphenoid wing meningiomas are usually accompanied by epilepsy, focal weakness, and trouble with language function when present on the dominant side. The tumors of the medial (inner) sphenoid ridge usually present with early unilateral visual impairment due to compression of the optic nerve. Those tumors may also involve the cavernous sinus and oculomotor nerves and cause double vision and numbness of the face. SWMs were first described in detail by Drs. Cushing and Eisenhardt, who distinguished between globoid SWMs and en plaque SWMs. 7, 8 Globoid meningiomas were subdivided into three groups, namely, deep, inner/medial, or clinoidal, middle or alar, and outer or pterional. 7 In this classification scheme, the lesser sphenoid wing is divided into thirds: a medial third, which represents the segment most adjacent to the anterior clinoid process; a middle third, which runs medial to lateral; and a lateral third, which runs anterior to posterior, eventually joining with the temporal squama. Later on, Bonnal and Brotchi divided SWMs in into five groups that raised specific surgical problems: (A) deep or clinoidal or sphenocavernous; (B) invading en plaque the sphenoid wings; (C) invading en mass the sphenoid wings; (D) middle ridge meningiomas; and (E) pterional or sylvian point meningiomas. 9 According to Yasargil, we prefer to distinguish medial and lateral sphenoid wing meningiomas. 10 Middle or alar meningiomas have clinical, radiological, and surgical characteristics similar to lateral or pterional meningiomas. Moreover, even during surgical excision, the exact site of attachment of these two groups cannot be distinguished and thus, they could be considered in a unique group. Lateral or pterional meningiomas usually grow into the sylvian fissure, are fed by middle meningeal artery and its branches, and reach clear relationship with MCA, distal carotid artery, and carotid bifurcation. These arteries may be compressed, engulfed, and rarely invaded by the tumor. On the other hand, medial sphenoid wing meningiomas grow compressing the proximal ICA and its branches, are fed by dural branches of the ICA and compress the optic nerve, the third cranial nerve; in some cases, they can invade the cavernous sinus and the optical canal. More frequently, these tumors may compress, engulf, or invade the arterial wall. Medial sphenoid wing meningiomas may be classified according to their origin around the anterior clinoid process and the lateral wall of the cavernous sinus. Accordingly, Al-Mefty made a subdivision of clinoidal meningiomas into three groups. Group 1 included all tumors that have an attachment on the lower part of the clinoid and that develop in the carotid cistern and encase the artery, adhering directly to the adventitia in the absence of an arachnoidal membrane; group II lesions originate from the superior or lateral aspect of the anterior clinoid process and, as they grow, come into contact with the carotid artery, with interposition of an arachnoid membrane deriving from carotid and sylvian cisterns; group III included tumors that originate from the optic foramen in which the arachnoid membrane is present between vessels and tumor, but may be lacking between tumor and optic nerve. 11 Therefore, it is quite clear that meningiomas originating from the medial region of the sphenoid wing are more challenging for neurosurgeons, given their proximity to the optic nerve, to the cranial nerves entering the superior orbital fissure, and to the cavernous sinus (▶ Fig. 8.1). On the contrary, lateral SWMs push the sylvian fissure medially, and for this reason the optic nerve is less at risk. Fig. 8.1 Growth pattern of medial sphenoid wing meningiomas. The dark area is the site of origin while the shadowed area represents the area involved when the tumor progressively grows. Pterional or lateral SWMs arise from the dura covering the outer sphenoid wing. Headache and psychological deficit represent the most common clinical presentation due to the fact that they are slowly growing tumors and their diagnosis is often delayed until they reach quite a large size. Seizures and other symptoms suggestive of increased intracranial pressure such as blurring of vision and vomiting were also common symptoms. Less frequent symptoms are gradual progressive diminution of vision, usually affecting the same side of the tumor, motor weakness, and altered consciousness. This group includes both globular and hyperostotic en plaque tumors (also called “spheno-orbital” meningiomas). Large tumors with middle cranial fossa extension compressing the temporal lobe or brainstem result in seizures or hemiparesis, respectively. Such tumors may also cause cognitive and memory deficits, personality changes, and dysphasia. Tumor-induced hyperostosis of the sphenoid wing and lateral orbit may present with proptosis, diplopia, and orbital pain. En plaque meningiomas of the sphenoid wing, also called spheno-orbital meningiomas, present with such ocular manifestations (▶ Fig. 8.2). These tumors can invade the lateral wall of the cavernous sinus, superior orbital fissure, floor of the middle cranial fossa, and the extracranial infratemporal fossa. These tumors carry a high rate of recurrence, due to frequent bone involvement, cavernous sinus, or infratemporal fossa invasion. Also for these reasons, the most appropriate surgical treatment should be total removal, including the dural attachment and bone that is involved with the tumor. 12 For this reason, bone reconstruction, orbital repair, soft tissue repair, and esthetic, represent fundamental steps of surgical techniques. Moreover, large tumors may have considerable surgical difficulties because of their possible close relationship with MCA and its branches. Usually an arachnoidal plane may be recognized and sharply dissected. In some cases, the arachnoidal plane between the tumor and artery is not clearly present; in these cases, a small fragment might be left in place, whereas needed to avoid direct damage to the main arterial trunk or even to small branches. Fig. 8.2 En plaque lateral sphenoid wing meningioma. (a) Preoperative CT scan demonstrating bone involvement and invasion. (b) Postoperative CT scan demonstrating surgical removal including the involved bone and reconstruction with a titanium plate.
8.1 General Considerations and Definition
8.2 Lateral or Pterional Sphenoid Wing Meningiomas
8.2.1 General Aspects and Clinical Presentation
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