23 Lateral and Middle Sphenoid Wing Meningiomas

Introduction

A sizable proportion of meningiomas arise in the sphenoid region. In large surgical series, sphenoid wing meningiomas account for 11 to 18% of cases.1–3 There are no pathological and molecular genetic features specific to sphenoid wing meningiomas. However, malignant and atypical meningiomas are less frequently encountered in the skull base than at the convexity.4 Ionizing radiation can cause sphenoid meningiomas.5,6 Meningiomas are more common in females. This is particularly true for meningiomas en plaque of the sphenoid wing. Between 77 and 94% of these growths are diagnosed in women.7

Surgery for sphenoid wing meningiomas poses a variety of problems reflecting the complex anatomy of the sphenoid region. Tumors of the outer third of the sphenoid ridge and many small middle wing tumors are essentially convexity meningiomas with regard to clinical presentation and surgical treatment ( Figs. 23.1 and 23.2 ). More medially located sphenoid wing meningiomas may compress and encase the carotid artery and its branches, the optic apparatus, and the pituitary stalk ( Fig. 23.3 ). Sphenoid wing meningiomas may show prominent dural involvement (en plaque growth, Figs. 23.4, 23.5, and 23.6 ). Tumors may grow in the dural layer overlying the cavernous sinus and in the cavernous sinus itself ( Fig. 23.7 ). Some sphenoid ridge meningiomas (“sphenoorbital meningiomas”) are characterized by prominent bone invasion and hyperostosis involving the lateral orbital wall, the orbital roof, and eventually the orbit itself, resulting in cosmetic problems and exophthalmos, but also in compression of the optic nerve with subsequent loss of visual function. Bone invasion and hyperostosis are usually associated with meningioma growth along the underlying dura. Tumor growth may extend into the facial and subcranial regions ( Figs. 23.4 and 23.7 ). In some patients, bilateral or multifocal tumors are encountered ( Figs. 23.6 and 23.7 ).

Surgical objectives vary considerably with tumor site and growth pattern. Intradural tumor with significant mass effect usually warrants surgery. Ideally, one should aim for a complete resection. Intracranial tumor close to the optic apparatus should be resected aggressively because even a small regrowth can cause loss of vision and visual field defects, sometimes before an unequivocal mass can be visualized by magnetic resonance imaging (MRI). On the other hand, visual symptoms and exophthalmos due to orbital involvement are often adequately treated by orbital decompression and limited intraorbital surgery. Osseous involvement is often primarily a cosmetic problem.

Most neurosurgeons broadly distinguish between (globular) tumors of the lateral and middle third of the sphenoid ridge, medial wing tumors, and hyperostosing/en plaque (sphenoorbital) meningiomas. This chapter focuses on tumors of the outer and middle sphenoid ridge. However, many sphenoid tumors do not fit very well into these categories ( Figs. 23.4, 23.5, 23.6, and 23.7 ). The concepts of surgery for medial sphenoid wing and sphenoorbital meningiomas often have to be applied to operations for middle wing tumors as well.

Classification of Sphenoid Meningiomas

The first classification for sphenoid wing meningiomas was proposed by Cushing and Eisenhardt. Cushing and Eisenhardt distinguished between globular meningiomas of the deep or clinoidal third, those of the middle (“alar”), and those of the outer third of the sphenoid ridge (“pterional meningiomas”), and en plaque pterional tumors.8 Bonnal et al and Brotchi and Pirotte describe five categories of sphenoidal meningiomas.9,10 Clinoidal tumors are referred to as group A tumors. Invasion of the cavernous sinus is listed as one characteristic of these growths. Globular tumors of the middle and lateral sphenoid ridge are termed group D and E meningiomas, respectively. Meningiomas en plaque with hyperostosis of the sphenoid bone (i.e., sphenoorbital meningiomas) are designated group B tumors. It is recognized that the designation pterional chosen by Cushing for these growths may not be fully appropriate. Large invasive tumors of the sphenoid ridge (“invasion en masse”) are assigned to a separate new category (group C tumors). These tumors are thought to combine features of both group A and B tumors (i.e., globular and invasive growth en plaque). Roser et al further subdivided hyperostosing/en plaque (sphenoorbital) tumors into meningiomas en plaque with and without cavernous sinus infiltration, and purely intraosseous tumors.11

**Fig. 23.1** Two lateral sphenoid wing (pterional) meningiomas. **(A)** Medium-sized meningioma originating from the most lateral aspect of the left greater sphenoid wing (T1-weighted contrast-enhanced axial and coronal, and T2-weighted coronal scans). Surgery for this tumor was no different from surgery for a convexity meningioma. The middle cerebral artery (*arrow*) was protected by a thin layer of brain tissue, and identification and preservation of its distal branches were not difficult. **(B)** A much larger tumor in a similar location diagnosed in a 67-year-old female patient who presented with flattened affect, cognitive decline, a possible seizure, and a mild hemiparesis (triplanar T1-weighted contrast-enhanced scans). The middle cerebral artery (*arrow*) proved relatively easy to dissect; however, several M3 branches were engulfed by the tumor. Copyright M. Simon and J. Schramm, reproduced with permission

**Fig. 23.2** Small middle sphenoid wing meningioma (axial and coronal T1-weighted contrast-enhanced, and T2-weighted axial scans; compare **Fig. 23.4** ). This tumor was diagnosed during the workup for vertigo in a 64-year-old female. There is limited dural involvement (*arrowheads*). Conceptually, drilling of the sphenoid can turn this tumor into an “upside-down” convexity meningioma. The medial surface of the tumor is related to the middle cerebral artery and its branches (*arrows*), but their dissection is virtually never a problem in tumors of this size. Copyright M. Simon and J. Schramm, reproduced with permission.

**Fig. 23.3** Large middle sphenoid wing meningioma. The patient was a 41-year-old woman who presented with a generalized seizure. **(A)** The size and location of the tumor are well delineated by triplanar T1-weighted magnetic resonance imaging. There is only minimal dural involvement. The course of the carotid and the middle cerebral artery and its branches are visible (*arrows*). Tumors of this size may encroach upon and compress the optic apparatus (for comparison see **Figs. 23.6** and **23.9** : optic nerve compression from dural and intraosseous growth). **(B)** The vascular relations (*arrows*) are depicted even more clearly on T2-weighted images. **(C)** At surgery the tumor was found to originate from the middle sphenoid ridge (i.e., this tumor is not a medial wing [clinoidal] meningioma with a large lateral component). Pamir et al have pointed out that clinoidal meningiomas usually infiltrate the bone of the anterior clinoid process.16 There was no bone infiltration in this case. Copyright M. Simon and J. Schramm, reproduced with permission.

**Fig. 23.4** Another small middle sphenoid ridge meningioma (coronal and sagittal T1-weighted contrast-enhanced and axial T2-weighted images; compare **Fig. 23.2** ). **(A)** In contrast to the tumor shown in **Fig. 23.2,** there is more widespread dural growth (*arrow*). **(B)** A computed tomographic scan shows tumorous infiltration of the sphenoid bone (*arrowheads*). Thickening of the lateral orbital wall has already resulted in mild exophthalmos. The bony and dural involvement render this lesion more challenging than the case presented in **Fig. 23.2** . One could argue that this tumor should be classified more precisely as a sphenoorbital meningioma (compare **Fig. 23.7** ). Copyright M. Simon and J. Schramm, reproduced with permission.

**Fig. 23.5** A bilateral sphenoid wing meningioma with a left-sided, medium-sized globular pterional (lateral wing) component. The tumor became symptomatic with seizures. See **Fig. 23.8** for the corresponding intraoperative findings. **(A)** T1-weighted and axial T2-weighted images depicting a tumor mass centered on the left lateral sphenoid ridge, and tumorous infiltration of the ipsilateral as well as the contralateral dura overlying the right sphenoid ridge (*arrowhead*). The dorsomedial border of the tumor mass appears related to the middle cerebral artery and its branches (*arrows*). There is also a (nonneoplastic) cyst located immediately adjacent to the medial surface of the tumor (*). **(B)** Computed tomographic scans show bilateral and extensive involvement of the sphenoid bone largely sparing the left anterior clinoid process. Copyright M. Simon and J. Schramm, reproduced with permission.

**Fig. 23.6** A medium-sized meningioma of the left middle sphenoid wing with extensive dural involvement and intraosseous growth. The tumor was diagnosed in a 73-year-old woman following several seizures. The ophthalmological exam was normal. **(A)** T1-weighted contrast-enhanced magnetic resonance imaging (MRI) scans showing the origin and size of the tumor (upper and middle row). There is extensive carpetlike involvement of the frontotemporal dura (*arrowheads*). The course of the middle cerebral artery and the M2 branches (*thin arrows*) are nicely depicted on T2-weighted images (lower row). At surgery, the vessels could be easily identified and preserved (see **Fig. 23.9** ). Intraosseous growth is already apparent on the MRI scans (*arrows*). Involvement of the lateral orbital wall has resulted in mild exophthalmos. Dural and intraosseous tumor spread will sooner or later lead to optic nerve compression even before MRI will show a definite tumor mass (for comparison see **Fig. 23.3** : tumor mass encroaching upon the optic apparatus). **(B)** Postoperative computed tomographic scans depicting the extent of the bony resection. Copyright M. Simon and J. Schramm, reproduced with permission.

**Fig. 23.7 (A,B)** A sphenoorbital meningioma (compare **Fig. 23.4** ) with a sizable globular tumor component centered on the middle sphenoid wing, bilateral infiltration of the cavernous sinus (*arrows*) and growth in the paranasal sinuses (*arrowheads*). Note that there is a second en plaque tumor in the left temporodorsal/occipital region (*). This growth pattern precludes a surgical cure. Surgical objectives in this case include removal of the intradural globular mass, and decompression of the orbit and the optic canal. **(A)** Triplanar T1 weighted contrast enhanced and coronal T2 weighted images delineating the globular and the en-plaque component of the tumor. **(B)** CT scans depict the rather extensive bony involvement. Copyright M. Simon and J. Schramm, reproduced with permission.

Tumors of the medial sphenoid wing are often subclassified based on the presence of invasion of the cavernous sinus.12–15 Some authors use the term clinoidal meningiomas to exclusively refer to meningiomas originating from the anterior clinoid process rather than as a more general designation for middle sphenoid wing meningiomas.16,17 Al-Mefty has proposed to distinguish between tumors originating proximally to the end of the carotid cistern, which directly enwrap the carotid artery (group I), those with a point of origin at the superolateral aspect of the clinoid process and an arachnoidal membrane interposed between the tumor and the carotid artery (group II), and finally tumors originating medially in the region of the optic foramen (group III).17 This classification has been adhered to by some but not all authors.12,13,15,18 Group I tumors are probably rare, and the lack of an arachnoidal dissection plane between the tumor and the carotid artery may be related to other factors such as repeat surgery. Group III tumors may be more appropriately referred to as optic foramen, optic sheath, or optic canal meningiomas.12,13,18

Tumor classifications should ideally help to choose the surgical strategy and predict the clinical outcome, including the risk of recurrence. To this end it is probably sufficient to broadly distinguish between (globular) lateral and medial sphenoid wing meningiomas, and hyper-ostosing en plaque/sphenoorbital meningiomas, and to note any cavernous sinus involvement. For obvious reasons, size matters and should be well recognized.16 Importantly, one will quite often encounter tumors that do not seem to fit ideally into any of the categories outlined ( Figs. 23.4, 23.5, 23.6, and 23.7 ). The surgical strategy in a specific case will be influenced by the location of the tumor along the ridge (and in particular the corresponding arterial relations), by the extent of bone infiltration (e.g., with or without involvement of the orbital roof or the base of the middle fossa), by the extent of dural involvement, and by invasion of the cavernous sinus beyond the mere infiltration of its outer wall. These factors relate directly to different types of surgical risks (and complications) and to the chances for complete removal.

Clinical Presentation

Patients with sphenoid wing meningiomas may present with loss of vision, visual field cuts and optic atrophy. Visual symptoms result from direct compression or encasement of the optic apparatus but may also reflect tumor growth into and around the optic foramen and canal. Visual symptoms due to optic atrophy and intracranial hypertension may rarely be encountered in very large tumors. Foster-Kennedy syndrome (ipsilateral optic atrophy and contralateral papilledema) has been traditionally associated with large meningiomas of the frontotemporal skull base.

Diplopia is not rare. Tumor growth in the cavernous sinus or superior orbital fissure may lead to ocular palsies. Intraorbital tumor growth characteristically causes diplopia due to restriction of ocular movements rather than oculomotor nerve paresis. Involvement of the cavernous sinus will also sometimes result in sensory loss in the distribution of the ophthalmic (and eventually other) division (s) of the trigeminal nerve. Some patients present with prominent exophthalmos. Exophthalmos reflects the presence of intraorbital tumor, but also intraosseous growth in the lateral orbital wall and orbital roof ( Figs. 23.4, 23.6, and 23.7 ). Exophthalmos may also result from venous stasis. Extracranial tumor growth and hyperostosis can cause cosmetic disturbances, such as frontal and temporal bulging.

Hemiparesis (and aphasia, if the dominant hemisphere is involved) can be encountered in patients with large tumors. Large growths may also present with cognitive and memory deficits, a flattened affect, and personality changes ( Fig. 23.1 ). In general, compression and encasement of the major arteries of the anterior circulation are clinically silent. Seizures are relatively frequent. Uncinate fits, and gustatory and olfactory hallucinations pointing to the temporal lobe as their origin are observed, as well as complex-partial and generalized tonic-clonic seizures ( Figs. 23.1, 23.3, 23.5, and 23.6 ). Psychiatric symptoms may be encountered in some patients.

Clinical signs and symptoms reflect tumor location and growth pattern. Tumors of the lateral sphenoid wing will often become relatively large before the development of a focal deficit such as hemiparesis or aphasia will result in the diagnosis. Neuropsychological disturbances will often only become apparent in retrospect. Tumors of the medial sphenoid ridge commonly cause earlier and more specific symptoms due to the proximity of the optic apparatus and cavernous sinus. Patients with sphenoorbital meningiomas typically present with exophthalmos, deterioration of visual acuity and field cuts, and diplopia. Finally, the number of patients with more or less asymptomatic meningiomas diagnosed during the course of a workup (e.g., for headache or vertigo) is increasing ( Fig. 23.2 ).