Surgical Management of Sphenoid Wing Meningiomas

En-Plaque Meningiomas

Also known as spheno-orbital meningiomas or hyperostotic meningiomas of the sphenoid wing, en-plaque meningiomas refer to tumors with a carpet-like dural growth, which are associated with a reactive hyperostosis that, in most cases, is marked and principally responsible for clinical manifestations (see Fig. 27.1A ). ^, Sphenoid wing hyperostosis has been reported in as many as 42% of all meningiomas in this area. ^, Due to its extensive bone involvement, differential diagnosis should include fibrous dysplasia, osteoma, osteoblastic metastasis, Paget’s disease, hyperostosis frontalis interna, erythroid hyperplasia, and sarcoidosis. ^{, ,} It frequently extends posteriorly toward the cavernous sinus and anteriorly toward the orbital apex, where it causes proptosis and oculomotor deficits, the primary clinical manifestations of these lesions. Hyperostosis in meningiomas was initially described by Brissaud and Lereboullet in 1903. Theories regarding the cause of hyperostosis include vascular disturbances, irritation of bone without actual invasion, previous trauma, bone production by tumor cells, or osteoblastic stimulation of normal bone. Currently, the most widely accepted theory is that this bone growth is actually bone invasion by tumor cells. ^{, ,}

Globoid Meningiomas

Globoid meningiomas have traditionally been classified into three groups: (1) deep, inner, or clinoidal; (2) middle or alar; and (3) lateral, outer, or pterional (see Fig. 27.1B ). Middle or alar meningiomas have radiologic characteristics similar to lateral or pterional meningiomas. Surgical resection and clinical results of both types are almost identical. For this reason, some authors suggest that globoid meningiomas of the sphenoid wing can be classified into only two groups: deep, inner, or clinoidal and lateral, outer, or pterional, discharging the middle or alar variety. Deep, inner, or clinoidal meningiomas represent the most complex variety of these tumors, whose resection, in most cases, implies increased morbidity and a high rate of recurrence. In this region, the cavernous sinus is the most critical area; therefore, clinoidal meningiomas are subclassified into two groups: tumors without extradural growth and tumors with extradural growth into the cavernous sinus. ^,

There is a third and debatable variety of SWMs. These are tumors that grow within the diploë without an epidural, subdural, or subcutaneous component and are referred to as intraosseous or intradiploic meningiomas. ^, The origin of these tumors in the skull base is controversial. Arachnoid cells have been described, following the vessels and nerves in bone foramina or trapped within the sutures. However, some authors doubt the existence of these tumors, proposing that they are really a variety of en-plaque meningiomas in which the dural component of the tumor is not well identified on preoperative imaging studies, mostly considering that many of these tumors were described before the era of magnetic resonance imaging (MRI).

Computed Tomography

Computed tomography (CT) is predominantly useful in en-plaque meningiomas because it provides more precise information regarding the extent of bone invasion, also allowing correct planning for reconstruction (see Fig. 27.2A ). The dural component of these tumors is typically found as an isodense image with contrast enhancement, being contiguous with the surrounding dura mater. However, it is not always possible to observe this, due to its carpet-like appearance. Also, it may be occulted by the high hyperdensity of the contiguous bone growth. There is no correlation between size of the hyperostosis and size of the meningeal tumor. In fact, small dural components are frequently found associated with large bone masses. A bone window algorithm is mandatory in terms of obtaining better definition of bone thickening. Performing axial and coronal projections, as well as three-dimensional (3D) reconstruction, also facilitates both complete resection and reconstruction. The most common locations of hyperostosis of en-plaque meningiomas are, in order of frequency, the lesser wing of the sphenoid bone, the greater wing of the sphenoid, the roof of the orbit, the inferior orbital fissure, the infratemporal fossa, and the orbital rim.

Globoid tumors appear on CT as well-defined isodense lesions that present an intense and homogeneous contrast enhancement. Even though they are usually slow-growing masses, it is not uncommon to find perilesional edema invading the temporal lobe and centrum semiovale, which is attributed to compression or occlusion in the superficial middle cerebral vein or sphenoparietal sinus; there is no direct relationship between the grade of edema and the size of the tumor. Clinoidal meningiomas usually show hyperostosis of the anterior clinoid process (ACP), causing narrowing of the optic canal and the superior orbital fissure. CT has some limitations when these tumors infiltrate the cavernous sinus; however, CT angiography may help by providing more precise information about blood supply and vascular relations of the tumor.