Intracranial meningiomas can be classified into two types by its configuration; global and flat. In 1938, Cushing and Eisenhardt first introduced the terms “meningioma en masse” and “meningioma en plaque” to differentiate them.1 Meningioma en masse is the most common type. Meningioma en plaque represents a morphological subgroup defined by a thin, widespread, carpet or sheet-like lesion that infiltrates the dura and sometimes invades the bone with the intraosseus tumor growth leading to significant hyperostosis. The sphenoid wing is the most common location of meningioma en plaque. For this tumor two synonyms are most used in the literature: sphenoid wing meningioma en plaque and spheno-orbital meningioma.1–4 Differential diagnosis includes fibrous dysplasia, osteoma, metastasis, etc. Because of the rarity of this tumor, only a few published studies about surgical treatment of sphenoid wing meningioma en plaque are available in the literature.1–8 Complete surgical resection is difficult because of the involvement of the orbital apex, superior orbital fissure and cavernous sinus, so it has a higher recurrence rates. Between Sep. 1998 and Apr. 2009, 37 patients underwent resection for sphenoid wing meningioma en plaque in Beijing Tongren Hosipital. In this retrospective series transcranio-orbital approaches and surgical outcomes are discussed.
Thirty-seven patients were treated surgically using a transcranio-orbital approach for resected sphenoid wing meningioma en plaque. Fifteen were men and 22 were women, with a mean age of 45.5 years (range: 16-67 years). Average medical history was 31 months (range: 1 month-8 years). Nineteen lesions were found in the right side and 18 were in the left side. One patient complicated by neurofibromatosis type II, another patient complicated by parasagittal and falcine multiple meningiomas.
The most common presenting signs were proptosis (37 cases). Other symptoms and signs included deficits of visual acuity (26 patients, 70%)), headache (9 patients) and seizure (1 patient). Seven patients presented with recurrent tumors and two patients had undergone two operations previously.
Ophthalmological examinations: the degree of proptosis was measured by a Hertel exophthalmometry in all patients, mean proptosis was 6.2 mm (range, 4 mm-13 mm). Opthalmoplegia were present in 15 patients, mainly upside and abduction movement disorder. Visual acuity measurements of affected eyes revealed 26 patients were less than normal: 11 patients were 0.5-1.0, 8 patients were 0.1-0.5, 5 patients were less than 0.1, and 2 patients were no light perception.
All patients received orbital computed tomography (CT) and magnetic resonance Imaging (MRI) scans. Axial and coronal CT bone window scans were excellent for visualization of the hyperostosis. On CT scans, the typical features were significant hyperostosis of the great wing of sphenoid bone and involving adjacent bone, including the middle cranial fossa bone, the lateral orbital wall and the orbital roof, the walls of the sphenoid sinus and ethmoidal cells. The edges of hyperostosis were rough and brush-like. On CT scans, the soft-tissue component of meningioma was carpet-like, isodense and homogeneously enhanced after contrasted (Figure). The great wing of sphenoid bone was destroyed in only three patients.
MRI showed T1 intensity was isointensity or hypointensity, T2 intensity was hyperintense. Gadolinium enhancement showed typical features for meningioma. The dura in the soft-tissue component was homogeneously enhanced, but the hyperostotic bone was not enhanced. Postcontrast fat suppression T1-weighted MRI was useful to evaluate the extension of dural enhancement and soft-tissue involvement of the orbital content in those patients with tumor extending into the orbit.
Ipsilateral fronto-temporal craniotomy with general anesthesia was used for all patients. Patients were placed in a supine position with the head tilted 20 degrees-30 degrees to the contralateral side. The scalp incision began 1cm superior to the anterior aspect of the auricle and curved anteriorly, ending at the hairline, 1 cm shy of the midline. Care was exercised during this part of the incision to avoid injury to the temporal branch of the facial nerve. In most patients the extracranial soft tissue was involved, extracranial soft-tissue tumor of the infratemporal fossa or the temporal muscle was resected first. After removal of the extracranial part of the tumor, a high-speed drill was used for expeditious removal of any thickened bony prominence of the lesser and greater sphenoid wings. Removal of the lesser sphenoid wing opened the optic canal and upper part of the superior orbital fissure, removal of the greater sphenoid wing opened the lateral and lower parts of the superior orbital fissure, and removal of the lateral wall and roof of the orbit exposed the periorbita. The superior orbital fissure was unroofed to expose the fascia. The greater sphenoid wing (i.e., the base of the middle cranial fossa) was removed with a high-speed drill between the periorbita, temporal dura, and fascia of temporal muscle. It was drilled down to the opening of the foramen rotundum, then the infratemporal fossa was exposed and the maxillary nerve was decompressed. If there is a marked hyperostosis around the optic canal, the optic canal should be opened and decompressed. It was mandatory to open the dura to identify the optic nerve intradurally before unroofing the optic canal.
The blood supply of this tumor was usually from branches of the middle meningeal artery. During the greater sphenoid wing resection, those branches were coagulated and resected. All infiltrated dura 10 mm away from the main tumor should be resected. But in the superior orbital fissure, the orbital apex and cavernous sinus, the infiltrated tumor must be left in situ in some patients for complete resection was not possible without a significant risk of further neurological deficits. And the residual tumor was coagulated. The intraorbital procedures should be accompanied by an ophthalmologist. Intraorbital tumor nodules were resected under meticulous avoidance of intraorbital nerves, areas of the periorbita involved by the tumor were also removed.
After tumor removal, the dura and periorbita were reconstructed with fascial grafts or artificial dura. In some cases, a muscle graft was required at the middle cranial base, augmented with fibrin glue, to achieve a watertight closure and prevent cerebrospinal fluid leak. The superior orbital rim was important for a good cosmetic appearance, so it should be preserved or reconstructed. After bony resection of the orbital roof and lateral orbital wall, the eye bulb can remained in place if the superior and lateral orbital rims remain intact, so further bony reconstructions of orbital walls were not performed. The sphenoid ridge did not need reconstruction, but the temporal bone defect could be reconstructed with titanic mesh.
Extent of resection
Total tumor resection was not achieved according to the Simpson classification Grade I (total tumor resection with excision of infiltrated dura). Subtotal tumor resection (STR) was achieved in 31 patients (9 patients were Simpson grade II, 22 patients were Simpson grade III), giving a STR rate of 83.8%. Gross tumor resection (Simpson grade IV) was done in 6 patiants. Complete surgical resection was difficult because of the involvement of the orbital apex, superior orbital fissure and cavernous sinus. Six tumor residuals in the cavernous sinus were treated by gamma knife therapy.
Histopathological examinations showed 33 patients were benign meningioma (WHO grade 1): 27 patients (73%) were meningothelial meningiomas, 4 were fibrous meningiomas, 2 were psammomatous meningioma, 2 were atypital meningiomas (WHO grade 2), and 2 were malignant meningiomas (WHO grade 3). Atypital and malignant meningiomas were treated by postoperative radiotherapy.
After surgery, proptosis was improved in all patients, reduced to an average value of 3.6 mm (0 mm-6.8 mm). Eight patients (21.6%) showed temporary ophthalmoplegia, 6 patients had abducens deficits, 7 patients had ptosis. Those symptoms were all improved in 2-3 months. CSF leak was found in 1 patient and was resolved by continuous lumbar drainage for 1 week. There were no cases of loss of sight, intracranial hematomas, meningitis, or pulsating exophtalmos.
There were 30 patients followed up with an average follow-up time of 36 months (range: 3 months-9 years). Of the remaining tumors, 7 patients were progressive during the follow-up period, and 5 patients underwent second surgery, including two trans-nasal endoscopic surgeries to resect sphenoid-involved tumor. One recurrent patient received gamma knife treatment. There were no operative deaths in our series.
Meningiomas are the most common nonglial intracranial primary tumors. Meningiomas en plaque are presumed to account for 2%-4% of intracranial meningiomas.4 These tumors are defined by an intraosseus tumor growth leading to significant hyperostosis and a widespread, carpet-like, soft-tissue growth at the dura. Bony tumor growth usually involves the greater and lesser sphenoid wing, the orbital roof, the lateral orbital wall, and the middle cranial base. The sphenoid ridge involving the orbit is the most common location, so sphenoid wing meningioma en plaque also known as spheno-orbital meningioma.1
Meningioma en plaque is mainly found in middle aged females, usually in the fourth to fifth decade of life. The female-to-male ratio was 3-5:1.5 Proptosis is the most common presentation, it's the tumor invasion orbit and hyperostosis that causes forward displacement of the eyeball, so the proptosis is painless, non-pulsating, and irreducible. Other symptoms and signs include decreased visual acuity or blindness, headache, extraocular movements disturbances, seizures, ect.1–6
Morphologically, meningioma en plaque consists of two major components: the hyperostosis component and soft-tissue component.1 The hyperostosis component includes the greater and lesser sphenoid wings, the lateral orbital wall and orbital roof, the middle cranial fossa, the anterior clinoid process, and the optic canal, the walls of the sphenoid and ethmoidal sinus can also be involved. The soft-tissue component or en plaque component is extensive carpet-like dural involvement, including dura over the greater sphenoid wing, cavernous sinus and convexity. The tumor can infiltrate the periorbita, temporal fossa, infratemporal fossa, pterygoplatine fossa and temporal muscle. The extent of both components can vary considerably.
Meningiomas en plaque are more likely to provoke adjacent bony hyperostosis than the larger globular tumors, however, the size of tumor is independent of associated hyperostosis.1,3 The cause of associated hyperostosis in meningiomas at the sphenoid bone remains a point of controversy: specifically regarding whether this represents a secondary change of the bone without tumor invasion vs direct infiltration of the bone by a tumor.3,9 Most authors agree with Cushing's conclusion that the infiltration of meningioma cells into bone stimulates osteoblastic activity with hyperostosis. New bone growth probably resulted from periosteal stimulation by tumor invasion, histopathological examination of hyperostotic bone revealed the tumor cells invading the Haversian system of the overlying bone, so hyperostosis is part of the tumor. In all patients in our series, the hyperostotic bone samples were sent for histopathological examination, and all of them were confirmed to have tumor invasion.
CT scan is excellent for showing the hyperostosis, while MRI shows the soft-tissue component of tumor and involved dura much better than contrast CT scan. Postcontrast fat suppression T1-weighted MRI is useful to evaluate the presence and degree of meningeal enhancement especially in those patients extending into the orbit.4 In three patients CT scans showed that the greater wing of sphenoid was destroyed and absorbed, so the preoperative diagnosis was “malignant meningioma” or “metastatic tumor”.8 But the postoperative histopathological examination revealed meningothelial meningiomains in 2 patients and atypital meningioma in 1 patient. One meningothelial meningioma recurred two years after operation.
The surgery of sphenoid wing meningioma en plaque poses a great technical challenge to neurosurgeons and ophthalmologists, because of the complicated anatomical boundaries of the orbits, the cavernous sinus, and the cranial nerves and vascular structures in the medial aspect of the sphenoid wing.6,7 Different surgical approaches have been proposed for the removal of sphenoid wing meningioma en plaque, including pterional, fronto-tempo-orbito-zygomatic, cranio-orbital, combined transcranial-transmalar approaches, etc.1–7 All patients in our series underwent fronto-temporal craniotomy, this approach provides a sufficient access to the orbit apex and the middle fossa base to accomplish bony and soft-tissue tumor resection and decompression of the superior orbital fissure, the optic canal and the foramen rotundum. In our opinion, removal of the zygomatic arch is not necessary, because additional space provided by removal of the hyperostotic bone can increases tumor exposure. The greater wing of sphenoid bone is removed with a high-speed drill between the periorbita, temporal dura, and fascia of temporal muscle. The foramen rotundum is opened carefully, the foramen rotundum is a important anatomic landmark, the cavernous sinuses are located inner to it.1
All the tumor-infiltrated bone in the cranial base should be resected, especially the hyperostotic bone of anterior clinoid process, to prevent the tumor recurrence.7 If there is a obvious hyperostosis around the optic canal, the optic canal should be opened and decompressed, it is recommended to open the dura to identify the optic nerve intradurally before unroofing the optic canal and incising the dural cuff of the optic nerve for a short distance.3 The blood supply of the tumor is from branches of the middle meningeal artery, during the greater sphenoid wing resection, those branches are coagulated and resected.
After completion of the bony removal, and removal of all the intracranial tumor, the dura is opened beyond the area of carpet-like tumor infiltration, and all infiltrated dura should be resected, including the second layer over the cavernous sinus, the dura over the sphenoid wing, and the temporal and frontal bone. Jesus et al4 found that the hypervascular dura contained neoplastic cells more than 10 mm away from the main tumor, so he recommend that an extensive amount of dura be removed with the main tumor and the margins should be pathological studied. An intraorbital tumor nodule displaces rather than infiltrates the orbital context, so areas of the periorbita involved by the tumor are also removed. The close co-operation between the neurosurgeons and the ophthalmologists is important for this surgery.
To avoid recurrences, all of the involved bone should be removed, so many patients' lateral orbital wall and/or roof are defective. Many authors propagate a firm reconstruction of the orbital walls to avoid enophthalmus, pulsating eye bulb, or oculomotor muscle fibrosis, which may result in ophthalmoplegia.1,5,10–12 The superior orbital rim is important for a good cosmetic appearance, so it should be preserved or reconstructed.11 The reconstruction of sphenoid wing bone is not needed, but the temporal bone defect can be reconstructed with titanic mesh. After bony resection of the orbital roof and lateral orbital wall, the eye bulb remains in place if the superior and lateral orbital rims remain intact. Maroon et al6 reported 200 patients of orbital wall and roof resections without reconstruction, resulting in no patient of permanent pulsating enophthalmus. DeMonte concluded that a partial or complete orbital roof resection, isolated or combined with lateral or medial orbital wall defects, does not require routine reconstruction if the periorbita remains intact.1,3 Only 6 patients in our series underwent reconstruction of the orbital walls with titanic mesh, however, no patient of enophthalmus and pulsating eye bulb occurred.
The best surgical outcome of sphenoid wing meningioma en plaque is depended on early diagnosis and complete removal.1,5,7,13 But complete removal of meningioma en plaque is often difficult because of their extensive involvement of the orbital apex, the superior orbital fissure, and the cavernous sinus. The total tumor resection is almost impossible according to the Simpson classification Grade I (total tumor resection with excision of infiltrated dura). Invasion of the cavernous sinus is considered the main cause of recurrences. Recurrence rate of sphenoid wing meningiomas en plaque was reported to be about 35%-50% in the literature.5,14 Ringel et al1 reported 63 patients of spheno-orbital meningioma, 76% of which had tumor residuals. Follow-up data was collected for up to 17 years (median, 4.5 years), of which 61% were stable and 39% were progressive.
In summary, sphenoid wing meningiomas en plaque mainly are benign meningothelial meningiomas, and more than half of residual tumors remained stable during the follow-up period, so the aim of surgery should be the relief of leading symptoms rather than radical resection. All the hyperostosis bone of the great wing of sphenoid bone should be removed to decrease recurrence. Extensive tumor removal with bony decompression at the orbital apex produces satisfactory cosmetic and functional results. Radiosurgery (e.g. gamma knife) can control eventual regrowth of residual tumor in the cavernous sinus.1–5,13,15
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