Cavernous Sinus Meningiomas
Keywords: cavernous sinus, meningiomas, microsurgical resection
Meningiomas involving the cavernous sinus (CS) are some of the most challenging lesions of the skull base due to the dense surrounding neurovasculature, including the internal carotid artery (ICA) and plexus, cranial nerves (CNs) II through VI, and important venous pathways that run deep within this compact region. As such, resection of cavernous sinus meningiomas (CSM) is complicated by their location and high potential for neurovascular injury. This chapter provides an exhaustive review of the diagnosis, management, and treatment of CSMs with an emphasis on microsurgical resection, including a stepwise explanation of the different surgical approaches and techniques available and a detailed description of cavernous sinus exploration. In an extensive experience with these lesions, the authors believe that the best outcomes are achieved from a multidisciplinary approach from a team of neurosurgeons, neuro-oncologists, and radiation oncologists who can evaluate the patient-specific risks and benefits of different treatment modalities.
Cavernous sinus meningiomas (CSMs) are classified as either primary tumors arising from the meningeal wall of the cavernous sinus (CS) or extensions of extracavernous tumors—often meningiomas of the lesser sphenoid wing, orbit, middle fossa, clivus, or petrous bone. 1, 2, 3, 4 In children, intracranial meningiomas are rare and represent only 1.0–4.2% of central nervous system tumors. 5 Meningiomas arising from the lateral wall of the CS represent less than 1% of all intracranial meningiomas. 6
The CS is an anatomical space located on both sides of the sella turcica at the convergence of the anterior fossa, middle fossa, sphenoid ridge, and petroclival ridge (▶ Fig. 16.1). The contents of the CS are contained within a membranous structure. Inferiorly and medially, this membrane is composed of periosteum and is contiguous with the periosteal layer of dura covering the middle fossa and sella turcica. The superior and lateral portion of this outer cavernous membrane is contiguous with the connective tissue sheaths of cranial nerves (CNs) III, IV, and V. The outer cavernous membrane forms the outer boundaries of the CS. CNs III, IV, and V are located within this membrane and are thus within the lateral wall of the CS. This rich venous plexus maintains connections to the ophthalmic veins, pterygoid plexus, superior and inferior petrosal sinuses, basilar venous plexus, and middle and inferior cerebral veins (▶ Fig. 16.1).
Fig. 16.1 Membranous structure of the cavernous sinus. The lateral wall of the cavernous sinus consists of two layers, the superficial layer and deep layer. The superficial layer is the dura propria of the temporal lobe; the deep layer is the inner cavernous membrane that is a fusion of the epineurium of the oculomotor, trochlear, and trigeminal nerves. (Reproduced from Fukuda H., Evins A. I., et al. The meningo-orbital band: microsurgical anatomy and surgical detachment of the membranous structures through a frontotemporal craniotomy with removal of the anterior clinoid process. J Neurol Surg B Skull Base. 2014; 75(2):125–132.)
The CS can be divided into three distinct venous spaces, namely, the medial compartment between the internal carotid artery (ICA) and the lateral wall of the sella, the anteroinferior compartment which is the space anterior to the ICA, and the posterosuperior compartment which is delimited by the ICA and the posterior portion of the roof of the CS. The CS is approximated by four walls, anterior, posterior, lateral, and medial, as well as by its roof and floor. The anterior wall mostly corresponds to the superior orbital fissure (SOF), which separates the CS from the orbit anteriorly. The medial wall corresponds to the pituitary gland and sella turcica superiorly and sphenoid bone inferiorly. The lateral wall is formed by CNs III, IV, and V—including the Gasserian ganglion—and faces the medial surface of the temporal lobe. The posterior wall separates the CS from the posterior cranial fossa and corresponds to the Dorello’s canal inferiorly, Gruber’s ligament laterally, and the posterior petroclinoid ligament superiorly. The roof of the CS faces the basal cisterns, extending from the anterior clinoid process (ACP) to the posterior clinoid process (PCP).
The ICA and its branches, accompanied by a sympathetic plexus of nerves, pass through the sinus, along with CN VI on its course to the SOF under the ophthalmic division of CN V (CN V1). The meningohypophyseal trunk (MHT) usually arises from the posterior bend of the intracavernous ICA and has three branches, the tentorial (Bernarconi-Cassinari), dorsal meningeal, and inferior hypophyseal arteries—all of which display some degree of variability. The inferolateral trunk usually arises from the lateral aspect of the ICA as it courses anteriorly. The ICA exits the cavernous at the level of the ACP, piercing the outer cavernous membrane which forms a ring around the vessel, known as the proximal dural ring.
CSMs can arise from the dura of the CS itself—true CS meningiomas—or from the dura of the sphenoid ridge, clinoid processes, or petroclival region and extend into or infiltrating the CS. CSMs that are not wholly located within the CS can grow to considerable size before becoming symptomatic. Meningiomas originating outside the CS can easily invade the CS through the anatomical openings created by CNs III and IV.
The oculomotor canal is the most common CS entry point for meningiomas arising from the PCP, ACP, lateral portion of the diaphragma sellae, anterior portion of the edge of the tentorium, area of the oculomotor trigone, and/or the area of the tuberculum and dorsum sellae. Most meningiomas originating in this perisellar area invade the optic canal when extending anteriorly (▶ Fig. 16.2).
Meningiomas originating from the tentorial edge, posterior to the PCP along the petrous ridge, and from the dura of the clivus can invade the CS along the course of CNs IV and V and through Dorello’s canal. These lesions can become large in size but the majority of the tumor grows in the posterior fossa, and thus, it is important to distinguish these lesions from petroclival meningiomas which require a different surgical strategy (▶ Fig. 16.3).
Meningiomas arising in the middle fossa can also invade the CS directly through the lateral wall of the CS. These meningiomas can also become large in size and invade the sella and optic canal before becoming symptomatic.
Meningiomas that extend throughout the entirety of the CS including the superior, anterior, posterior, and inferior compartments, up to the foramen rotundum and foramen ovale, encasing the ICA, CN VI, and the MHT, very likely infiltrate the adventitia of the vessel (▶ Fig. 16.4). These lesions, although benign histologically, pose substantial surgical challenges and should be treated as malignant lesions, with subtotal surgical resection and adjuvant radiotherapy.
Fig. 16.2 MRI showing a meningioma originating in the perisellar area and invading the cavernous sinus thorough the anatomical openings created by cranial nerves III and IV.
Fig. 16.3 MRI showing a meningioma originating from the tentorial edge at the petrous ridge and invading the cavernous sinus likely along the course of cranial nerves IV and V and through Dorello’s canal.
Fig. 16.4 MRI of a meningioma extending through the entire cavernous sinus and encasing the internal carotid artery.
Symptoms at presentation depend on the specific neurovascular involvement and may often include oculomotor nerve deficits (ptosis, diplopia, anisocoria, ophthalmoplegia), Horner’s syndrome, proptosis, sensory loss or pain in one or more trigeminal divisions, visual field deficits, and/or ischemic events due to compression of the ICA. Palsy of CNs III, IV, or VI is extremely common as are trigeminal nerve deficits. Pituitary dysfunction rarely manifests at initial presentation, but can occur and should be considered. 7, 8 Assessment of cerebellar function and coordination may provide useful information on tumor extension into the posterior fossa with compression of the brainstem. Differential diagnosis should include other lesions known to invade the CS, including metastatic lesions, pituitary adenomas, perineural spread of head and neck malignancies, hemangiomas, and other neurogenic tumors. Additionally, non-neoplastic pathologies, such as thrombophlebitis, infections, vascular lesions including ICA aneurysms, carotid-cavernous fistulas, dural arteriovenous shunts, and inflammatory lesions (Tolosa-Hunt syndrome, inflammatory pseudotumor) should be considered. 8
CSM often present radiologically as hypointense to isointense lesions with enlargement of the CS, thickening of the lateral wall of the CS, and homogeneous contrast enhancement with nonspecific dural tail sign (▶ Fig. 16.2). Calcifications may be seen as hypointense regions within the tumor and CT may also demonstrate associated hyperostosis. In cases where CSMs invade the walls of the sphenoid sinus, it is most often the unique results of bony thickening rather than destructions. 9 Magnetic resonance angiography often provides useful information about vascular relationships and involvement without the risks of conventional angiography. In patients with extensive lesions who are at high risk for ICA involvement, conventional angiography should be considered with assessment of the collateral circulation by a balloon occlusion test. Patents with poor collateral circulation are good candidates for vascular bypass.
Treatment of CSMs has considerably evolved over the past three decades. Initially, CSM were not considered surgically, however, the emergence of microneurosurgical techniques, coupled with a better understanding of CS anatomy and increasing microsurgical experience, opened the door for surgical management. Currently, there are three main options for the management of CSMs: observation, microsurgical resection, and/or stereotactic radiosurgery (SRS). Patients with asymptomatic or minimally symptomatic CSMs without observed growth may be candidates for observation. 7 However, up to 25% of conservatively managed meningiomas described in the literature show some degree of growth. Hashimoto et al. reported that skull base meningiomas have slower growth rates compared with non-skull base meningiomas, with growth around 0.67–1.2 cm3/year. 4, 10, 11 Different attempts at pharmacological treatment, including hydroxyurea, mifepristone, or tamoxifen regimens, have all failed to sufficiently treat meningiomas. 7 Intervention, either microsurgical resection or SRS, is indicated in patients with progressively worsening symptoms or demonstrated growth on serial imaging. 7 In general, large symptomatic, or increasingly symptomatic, lesions or those that demonstrate early growth are often surgically resected with or without SRS.
A number of reports have demonstrated significant postoperative neurological deficits, the difficulty of achieving gross-total resections, and the continued need for follow-up due to the possibility of recurrence. Many surgeons opt for a more conservative approach that involves removal of the tumor from the lateral aspect of the CS without entering the sinus proper, due to the high potential for postoperative morbidity. 6
In 1999, Levine et al proposed the so-called Levine-Sekhar grading system to predict the resectability and prognosis of skull base meningiomas, 12 and a 2016 study by Nanda and colleagues confirmed this to be a good predictor of surgical resectability in finding that ICA encasement significantly reduced complete resection rates. 1, 13 Additionally, Nanda et al found that tumor recurrence was significantly lower in patients who underwent adjuvant SRS. 1 Despite the growing body of data, there remains no consensus on an optimal treatment strategy for CSMs, and some authors have even advocated for Gamma Knife radiosurgery as the first line treatment. 14
It is our belief that tumors with significant extracavernous components that demonstrate brainstem compression and hydrocephalus necessitate surgical intervention. Tumors compressing the optic nerve or chiasm should also be considered prime candidates for resection in order to avoid the risk of radiation-induced optic neuropathy. Although aggressive resection of CSMs has not proven to be the optimal treatment option, it must be considered for tumors greater than 3.0–3.5 cm in diameter and are not ideal candidates for SRS.
We believe that the best outcomes in patients with CSMs are achieved from a multidisciplinary approach from a team of neurosurgeons, neuro-oncologists, and radiation oncologists who can evaluate the patient-specific risks and benefits of different treatment modalities.
16.7 Surgical Approaches
Several different surgical approaches have been described for the resection of lesions involving the middle fossa. In tumors that extend significantly into the CS from adjacent areas, the addition of an orbitozygomatic osteotomy to a standard pterional approach may be required to improve surgical exposure and to provide vascular control of the ICA (▶ Fig. 16.5). When lesions are confined to the lower compartment of the CS, a pterional approach with removal of the zygomatic arch may be sufficient to expose the posterior and inferior compartments of the CS (▶ Fig. 16.6), however, with poor visualization of the more distal compartments. For lesions involving the CS, parasellar region, upper clivus, and adjacent neurovascular structures, we prefer to use a fronto-orbitozygomatic approach—a pterional approach with removal of the zygomatic arch and lateral wall and roof of the orbit—to achieve a wide angle of surgical exposure.
Fig. 16.5 The orbitozygomatic osteotomy. A pterional craniotomy is extended by removing the zygomatic arch and the lateral wall and roof of the orbit.
Fig. 16.6 A fronto-temporo-zygomatic craniotomy. This consists of a pterional approach with additional removal of the zygomatic arch to reach lesions confined to the lower compartments of the cavernous sinus.
16.7.1 Preoperative Preparation
Mild hypocapnia is recommended, however, profound hypocapnia should not be induced unless indicated for control of edema or increased surgical exposure. Intraoperative somatosensory evoked potential, motor evoked potential, and electroencephalography monitoring is recommended. As a precaution, a lumbar drain should be placed, but should remain closed for the entire extradural portion of the approach, and in most cases is not needed at all throughout the procedure.
16.7.2 Positioning and Incision
Initial patient positioning is the same as that used in the pterional approach, wherein the head is extended, rotated 25–35° away from the lesion, oriented with the vertex slightly downwards. A curvilinear incision should be planned beginning just anterior to the tragus, at the level of the inferior margin of the zygomatic arch, up to the superior temporal line, curving to terminate at the hairline superior to the contralateral midpupillary line (▶ Fig. 16.7). A narrow strip of hair along the planned incision should be shaved and the skin prepped. During the incision, care should be taken to preserve the superficial temporal artery in the event that intracranial bypass is needed.
Following the incision, the skin flap can be elevated, and the underlying temporalis fascia exposed. The fascia can then be sharply incised along the margin of the superior temporal line and elevated separately to perform a subfascial dissection. This technique protects the frontal branch of the facial nerve, which lies in the subgaleal fat pad and runs along the superficial surface of this fascial plane. The dissection can then be continued anteriorly to expose the orbital rim, malar eminence, and zygomatic arch. The temporalis muscle is then raised independently, exposing the root of the zygoma and pterion. The muscle flap is left attached to the cranium at its vascular pedicle in the infratemporal fossa. The skin flap and temporalis muscle are then retracted anteriorly and inferiorly with surgical fish hook retractors attached to a bar (▶ Fig. 16.8).
Fig. 16.7 Patient positioning and incision. The head is extended, rotated 25 to 35° to the contralateral side, and the vertex is angled slightly down. The incision extends from the tragus to the contralateral midpupillary line