Meningiomas of the Frontal Skull Base and the Orbit Intracranial meningiomas are very common, accounting for 25 to 30% of all primary intracranial tumors; they frequently involve the orbital structures or grow intraorbitally. 2, 3, 4 Meningiomas commonly arise intracranially from the frontal skull base and are classified according to their localization and dural attachment and as well as to their histological differentiation. Histologically they are mostly benign tumors classified as grade I and infrequently as grade II tumors (atypical meningiomas). Malignant meningiomas are rare and classified as grade III tumors (anaplastic meningioma) and are characterized by a poor prognosis. 5 The most common localization with orbital involvement is the medial and lateral sphenoid wing, the anterior clinoid process, the tuberculum sellae, and the frontal skull base. In contrast to these localizations, meningiomas of the orbit and optic sheath meningiomas are rare. 2, 4, 6, 7, 8, 9, 10 Whereas meningiomas arising from the sphenoid wing, the anterior clinoid process, and optic sheath result in unilateral symptoms, midline tumors arising from the sellar tubercle or sphenoidal plane lead frequently to bilateral symptoms and visual impairment due to their close correlation and affection of both optic nerves and the optic chiasm. 9 Imaging studies and intraoperative findings show infiltration of the optic canal, optic nerve involvement, or infiltration of the cavernous sinus by meningiomas with “en plaque” growth pattern 7, 11, 12, 13 ( ▶ Fig. 12.1). Fig. 12.1 Tuberculum sellae meningioma with optic nerve involvement. (a, b) MRI of a tuberculum sellae meningioma with extension to the sphenoidal plane and distinct compression of the optic chiasm. Homogeneous contrast enhancement is characteristic of the circumscribed tumor with contact with the dural matrix and invasion into the sellar region. (c–e) Intraoperative delineation of the tumor after right-sided frontal craniotomy and subfrontal approach. The surgeon reaches the surface of the tumor after exposure of the cisterns and release of CSF (c). The tumor causes significant medial compression of the ipsilateral optic nerve within optic canal. The orbital roof can be exposed extradurally and intradurally with this approach. Tumors arising from the sphenoid wing with extension to the lateral orbital wall are defined as spheno-orbital meningiomas. These tumors grow slowly with absent or minor symptoms, but they can achieve enormous sizes and consequently involve important neurovascular structures 14 ( ▶ Fig. 12.2). Radical resection of these tumors is related to high risks, so that an incomplete resection is preferred to preserve neurovascular functions. 2, 3, 7, 9, 11, 13 Magnetic resonance imaging (MRI) is the most important diagnostic method for imaging of meningiomas. These tumors are characterized by a mass with clearly defined borders and typical homogeneous contrast enhancement ( ▶ Fig. 12.3 and ▶ Fig. 12.4). Meningiomas of the sphenoid wing can infiltrate the osseous structures or can grow entirely intraosseously. The osseous elements with tumorous infiltration appear enlarged and can involve the lateral orbital wall. High-resolution computed tomography with three-dimensional reconstruction is recommended in these cases for the delineation of the osseous structures involved and for surgical planning of osseous resection and preoperative planning of necessary cranio-orbital reconstruction. Fig. 12.2 Meningioma of the left anterior clinoid process with optic canal infiltration. Intradural delineation of a left-sided meningioma (asterisk) laterally to the optic nerve (arrows) arising from the anterior clinoid process after left-sided supraorbital “keyhole” craniotomy. Note the compression of the left optic nerve in the proximity and within the optic canal by the meningioma. Although the tumor has a size of a few millimeters, it affects the optic nerve by compression at the entrance to the orbit, with visual impairment and visual field disturbance. Fig. 12.3 Optic sheath meningioma. (a) MRI of a patient with an optic sheath meningioma with hypointense depiction in the T2-weighted transversal slices. Note the distinct proptosis caused by the intraorbital mass effect. (b) The contrast enhanced sequences show the typical homogeneous enhancement of the tumor. The affected and compressed optic nerve can be seen in the center of the tumor inside the complete intraorbital course. Fig. 12.4 Invasive meningioma of the frontal base. (a, b) Amaurotic patient with an invasive meningioma of the anterior and middle skull base with demonstrated calcification of the tumor. Calcifications with this pattern tend to be high risk, so that an extended biopsy or partial resection with optic canal decompression is recommended. The transversal (c) und coronal T1-weighted MRI slices (d, e) show the extension of the tumor after contrast enhancement on the frontal skull base spreading to the suprasellar region with infiltration of the cavernous sinus and surrounding of the internal carotid artery. Memorize Meningiomas are mostly benign tumors and can reach large sizes due to their slow growth pattern. If they are localized in the optic canal, they can cause loss of visual acuity in the early onset of the disease. Optic canal tumors can grow in the circumference of the optic nerve. These tumors can be approached and resected via the subfrontal route. If necessary, the complete course of the optic nerve can be delineated and decompressed. Complete tumor resection is achieved and both optic nerves, the chiasm, and the contralateral internal carotid artery are delineated after meticulous mobilization of the tumor and decompression of the optic nerve ( ▶ Fig. 12.1d). Both optic nerves, the optic chiasm, and the contralateral internal carotid artery are exposed ( ▶ Fig. 12.1e). Carcinomas of the paranasal sinuses, metastases, esthesioneuroblastomas, sarcomas and malignant melanomas are the most common malignant tumors of the frontal skull base with infiltration of the orbit. 15, 16 Both orbits can be involved and infiltrated because of their close anatomical relationships, so that surgical resection can be significantly aggravated. 17 Contrast-enhanced MRI and high-resolution CT are the diagnostic methods of imaging with sagittal and coronal reconstructions and are employed for proper surgical planning. The possibilities and the dimension of surgical resection should be evaluated very precisely and discussed thoroughly with the patient as part of an interdisciplinary treatment protocol with the focus on the risks to visual function and the prognosis. The resection of tumorous osseous structures such as the orbital roof or the lateral orbital wall is not associated with resulting functional deficits. In contrast, a higher functional risk is seen in tumors with infiltration of the periorbita or the ocular muscles. The osseous elements can be reconstructed using various methods and materials. Autologous tissues can be used, such as calvarial split bone of the healthy tabula interna of a frontal bone flap, or industrially produced materials such as titanium mesh or computer-aided design implants. Malignant tumors often infiltrate the frontobasal dura, so that meticulous duraplasty and cranioplasty should be undertaken maximally ( ▶ Fig. 12.5, ▶ Fig. 12.6). 17 Fig. 12.5 Malignant intranasal, intracranial, and intraorbital tumor. (a–d) Malignant tumor of the rhinobase (spindle cell tumor) with osseous destruction and left-sided infiltration of the orbit and infiltration of the periorbita in a 27-year-old woman shown in the contrast enhanced transversal and coronal T1-weighted MRI sequences (a, b) and in the coronal reconstruction of the CT scan (c). High-resolution CT imaging for the evaluation of the osseous destruction and planning for reconstruction should be done regularly. Note the left-sided proptosis and left paramedian subcutaneous tumorous swelling of the nasal root (d).
12.3 Malignant Tumors of the Frontal Skull Base and the Orbit
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