26 Sphenoorbital Meningiomas
Cushing and Eisenhardt1 first described meningioma en plaque as “the flat spreading tumors (meningiomas en plaque) which provoke hyperostosis chiefly of the greater wing of the sphenoid.” Cushing described that the infiltration of the bone by meningioma cells stimulates osteoblastic activity resulting in hyperostosis.2 This hyperostosis is typical of the sphenoid bone, and is less frequent at other cranial sites.3 These tumors have been referred to in the literature as sphenoid wing meningioma en plaque, pterional meningioma en plaque, hyperostosing meningioma of the sphenoid ridge, invading meningioma of the sphenoid ridge, or more generically as sphenoorbital meningiomas (SOMs).4
SOMs constitute up to 9% of all intracranial meningiomas.5 They originate from the dura of the sphenoid wing, and they can extend into the cavernous sinus, superior orbital fissure (SOF), orbital apex, and convexity dura. Soft tissue growth can spread to extracranial compartments, including the orbit, the infratemporal fossa, and the temporal fossa. Bone involvement may extend to include the anterior clinoid process and lesser sphenoid wing, the orbital roof, the lateral orbital wall, and the middle fossa base. Tumor may also extend to the optic canal and the paranasal sinuses.4,6–8
Most patients with SOM are middle-aged women whose symptoms are primarily attributable to the hyperostosis.9 Earlier reports concluded that SOMs were not usually resectable because of their extensive bone and soft tissue involvement, and surgical treatment was discouraged.10–12 Seminal to our understanding of these tumors and to the development of the surgical techniques for their resection was the work of Guiot, Derome, and Tessier.3,13,14 With further development of microsurgical techniques, skull base approaches, new neuroimaging techniques, and the use of image-guided surgery, more complete resection of SOMs has become technically feasible and safe. Recent studies report that successful results can be achieved in the majority of patients.3,4,6–9,15–19 Even so, with efforts to preserve neurological function, residual tumor involving the cavernous sinus, orbital apex, and SOF remains a problematic surgical limitation. These areas are major sites for residual tumor, recurrence, and continued neurological deterioration. Adjuvant radiotherapy for residual tumor or recurrence commonly forms part of modern management plans.
Clinical Presentation
The most common symptom is unilateral, nonpulsating, progressive proptosis (80 to 90%) ( Fig. 26.1A,B ). Optic neuropathy, evidenced by decreased visual acuity, loss of color vision, and a constricted visual field with an enlarged scotoma has been identified in 27 to 80% of patients in published series.5 Other cranial nerve (CN) deficits (CN III, IV, V, VI, and VIII) are seen in 20 to 25% of patients. Even though the oculomotor nerve is the most commonly affected CN besides the optic nerve,4,6–8,15,20–23 diplopia is usually on the basis of extraocular muscle restriction due to intraorbital tumor rather than secondary to neuropathy of the ocular motor nerves.
Radiological Evaluation
Although plain roentgenograms routinely demonstrate the hyperostosis, both computed tomography (CT) and magnetic resonance imaging (MRI) are critical for tumor diagnosis and management planning. CT scans show the characteristic periosteal pattern of hyperostosis, surface irregularity of the hyperostotic bone, and remodeling of the orbital roof and sphenoid wing7,20 ( Fig. 26.2A,B ). MRI demonstrates tumor extension to the soft tissues and the dura much better than contrast-enhanced CT ( Fig. 26.3A,B ). MRI, especially with postcontrast fat-suppression techniques, best identifies soft tissue involvement of the orbital contents, the infratemporal fossa, and the temporalis muscle.4,7,20,24
Histopathology
Most reports on the surgical treatment of SOMs describe these meningiomas as typically being of low grade (grade I) and most commonly of the meningothelial variant.3,4,6,7,9,20,25 Atypical and anaplastic meningiomas have been reported.7,24 Pathological analysis of the hyperostotic bone typically identifies direct tumor involvement and meningothelial cells within Haversian canals.27
Differential Diagnosis
Fibrous dysplasia, osteoma, osteoblastoma, Paget disease, hyperostosis frontalis interna, osteoblastic metastases, erythroid hyperplasia, and sarcoid may mimic hyperostosing meningiomas and should be considered in the differential diagnosis.9,20,28–30
Management
The management of a patient with SOM should be individualized based on considerations of the patient’s age, symptom complex, presence or absence of neurological findings, presence of comorbidities, and desired outcomes of intervention. Observation, radiation therapy or surgical resection can be options for management of SOMs.
Observation
Almost all patients without evidence of optic neuropathy can be managed nonoperatively, at least initially. Should observational management be chosen, close clinical follow-up with detailed cranial nerve testing and ophthalmological examination of visual acuity, visual field, and degree of proptosis (Hertel exophthalmometry) are necessary in addition to follow-up MRI. Tumor growth, progressive proptosis, and the onset of neuropathy are all indications for intervention.
Surgical Resection
Preoperative Evaluation
A comprehensive ophthalmological and neurological examination should be completed for all patients with the diagnosis of SOM. A detailed visual evaluation, with visual field testing, assessment of visual acuity, fundus examination, and quantification of the degree of exophthalmos using Hertel measurements, is crucial. Radiological assessment including high-resolution CT scans to assess degree and extent of hyperostosis and contrast-enhanced MRI are performed. These are complementary studies and together optimally identify the full extent of the tumor.
The surgical approach should be tailored according to the extent of tumoral involvement of the orbit and adjacent anatomical compartments. Different surgical approaches, including pterional, frontotemporal, transzygomatic, frontotemporal orbitozygomatic, and fronto-temporal-orbital, have been described for SOM resection. The approach selected must allow access to the orbit and the middle fossa base for resection of the tumor-infiltrated bone and soft tissue. Decompression of the SOF, the optic canal, and the cavernous sinus should be possible, and brain retraction should be minimal.
Surgical Technique
The patient is positioned supine with the head rotated to the contralateral side. A large frontotemporal or bicoronal skin incision is recommended to provide access to enough pericranial tissue to repair the dural defect and the cranial base.31 The extent of the craniectomy and the size of the craniotomy are “right-sized” intraoperatively based on feedback from CT and MRI coregistered stereo-tactic navigational data. These systems are very helpful in the delineation of the extent of hyperostotic bone and dural involvement. The temporalis fascia is incised 2 cm above the “keyhole” region, from the superior temporal line to the root of the zygoma. The periosteum and the superficial and deep layers of the temporalis fascia are elevated off of the frontal bone, orbital rim, and zygoma as one, thus protecting the frontalis branch of the facial nerve ( Fig. 26.4A ) Subperiosteal dissection is utilized to elevate the temporalis muscle laterally and inferiorly, carefully preserving the blood supply and innervation. When infratemporal fossa exposure is required, a zygomatic osteotomy is performed, leaving the zygomatic arch attached to the masseter muscle ( Fig. 26.4B,C ). Tumor-infiltrated temporalis muscle is excised. The hyperostotic bone of the lateral sphenoid wing is usually encountered during elevation of the temporalis muscle ( Fig. 26.4D ). This tumor-infiltrated bone is removed with a high-speed cutting burr and rongeurs. This allows entry into the orbit and intracranial spaces to allow for removal of tumor extensions to these spaces ( Fig. 26.5A ). If more extensive dural or orbital exposure is necessary, a frontotemporal craniotomy can be elevated. If necessary, osteotomies of the orbital rims can be cut, and the supralateral orbital rim elevated, either separately or in continuity with the frontotemporal bone flap ( Fig. 26.6 ).31 All hyperostotic bone of the lesser sphenoid wing, middle fossa floor, lateral orbital wall, orbital roof, and anterior clinoid process is removed extradurally using a high-speed drill under magnification and constant irrigation. As the lesser sphenoid wing and anterior clinoid are removed, the optic canal and upper part of the SOF are opened. The foramen ovale and rotundum are opened as the floor of the hyperostotic middle fossa is removed ( Fig. 26.5B ). Intradural tumor involvement is removed with sharp dissection and microscopic techniques ( Fig. 26.5C ). Dural resection is extended to include the medial temporal dura of the lateral cavernous sinus wall if necessary. Meningioma extension within the cavernous sinus and SOF can directly invade the cranial nerves and the connective tissue planes between the cranial nerves and is typically left in place to avoid neurological complications. Once the intracranial portion of the tumor has been excised, attention is turned to the intraorbital involvement. The dura is repaired with pericranium, temporalis fascia, or allograft material before the commencement of intra-orbital tumor resection.
Often, tumor extension into the orbit is extraconal and extraperiorbital. This extent is removed when the bone of the lateral orbit is removed. When involved, the periorbita is resected, and intraorbital tumor invasion is removed. The lateral rectus can be tagged with a suture transconjunctivally at the beginning of the case to help identify the muscle once tumor resection has started. All intraorbital, extraconal tumor can be removed. Invasion into the orbital apex, annulus of Zinn, or SOF is left in place due to the high risk of injury to the cranial nerves.
If the sphenoid or ethmoid sinuses are entered, these are obturated with autologous fat graft to prevent cerebrospinal fluid (CSF) leakage. If a periorbital defect is present, it is closed with locally harvested temporalis fascia. The pericranial graft is then rotated over the orbit. This helps to compartmentalize the orbit from the intracranial space and to avoid adhesion of the orbital tissues to the dura.
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