Olfactory groove meningiomas represent approximately 10% of all intracranial meningiomas. Because these tumors originate at the ventral skull base, the endonasal route provides direct access to the tumor blood supply for early devascularization and removal of the underlying hyperostotic bone at the cranial base. In carefully selected patients, these tumors can be totally removed without additional brain retraction or manipulation. In this report, we describe the surgical technique and operative nuances for removal of olfactory groove meningiomas using the endoscopic endonasal approach, and also discuss the indications, limitations, complication avoidance and management, and postoperative care.
Key points
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Olfactory groove meningiomas are midline skull base lesions that represent approximately 10% of all intracranial meningiomas.
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Radical resection including the dural attachment and involved hyperostotic bone (Simpson grade I) offers the best chance of minimizing recurrence.
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Although surgical resection via a transcranial approach remains the mainstay of treatment, in carefully selected cases, the endoscopic endonasal approach via the transcribriform corridor provides direct access to the tumor blood supply (ethmoidal arteries) for early devascularization and removal of the underlying hyperostotic bone at the cranial base, so that radical Simpson grade I resection can be achieved without additional brain retraction or manipulation.
Introduction
Olfactory groove meningiomas represent approximately 10% of all intracranial meningiomas. These midline skull base lesions arise from the dura of the cribriform plate and planum sphenoidale. Hyperostosis of the adjacent underlying bone is not uncommon, and occasionally, tumor extension can be found in the ethmoid sinuses and nasal cavity in approximately 15% to 25% of cases. Radical resection, including the dural attachment and involved hyperostotic bone (Simpson grade I), offers the best chance of minimizing recurrence. Incomplete removal can result in tumor recurrence, usually at the cribriform plate, ethmoid sinuses with extension into the paranasal sinuses.
The most common surgical approaches for resecting olfactory groove meningiomas are the bifrontal transbasal approaches and pterional approaches. Additional cranial base extensions may be used, if desired, such as orbital rim (orbitopterional or modified orbitozygomatic) or supraorbital bar removal (extended transbasal) to minimize brain retraction and gain additional exposure. These transcranial approaches generally require some degree of brain retraction or manipulation, but can adequately access and resect the tumor. Complications can include cerebral edema, venous infarction, hematoma, cerebrospinal fluid (CSF) leakage, bone flap infection, with a mortality of up to 5%.
Recently, there has been increased interest in the use of the endoscopic endonasal approach (EEA) via the transcribriform corridor for resection of olfactory groove meningiomas. Nevertheless, this continues to be a topic of debate. Because these tumors originate at the ventral skull base, the endonasal route provides direct access to the tumor blood supply (ethmoidal arteries) for early devascularization, and removal of the underlying hyperostotic bone at the cranial base so that radical Simpson grade I resection can be achieved. In carefully selected patients, these tumors can be totally removed without additional brain retraction or manipulation.
In this report, we review the surgical technique and operative nuances for removal of olfactory groove meningiomas using the EEA. We also discuss the indications, limitations, complication avoidance and management, and postoperative care.
Introduction
Olfactory groove meningiomas represent approximately 10% of all intracranial meningiomas. These midline skull base lesions arise from the dura of the cribriform plate and planum sphenoidale. Hyperostosis of the adjacent underlying bone is not uncommon, and occasionally, tumor extension can be found in the ethmoid sinuses and nasal cavity in approximately 15% to 25% of cases. Radical resection, including the dural attachment and involved hyperostotic bone (Simpson grade I), offers the best chance of minimizing recurrence. Incomplete removal can result in tumor recurrence, usually at the cribriform plate, ethmoid sinuses with extension into the paranasal sinuses.
The most common surgical approaches for resecting olfactory groove meningiomas are the bifrontal transbasal approaches and pterional approaches. Additional cranial base extensions may be used, if desired, such as orbital rim (orbitopterional or modified orbitozygomatic) or supraorbital bar removal (extended transbasal) to minimize brain retraction and gain additional exposure. These transcranial approaches generally require some degree of brain retraction or manipulation, but can adequately access and resect the tumor. Complications can include cerebral edema, venous infarction, hematoma, cerebrospinal fluid (CSF) leakage, bone flap infection, with a mortality of up to 5%.
Recently, there has been increased interest in the use of the endoscopic endonasal approach (EEA) via the transcribriform corridor for resection of olfactory groove meningiomas. Nevertheless, this continues to be a topic of debate. Because these tumors originate at the ventral skull base, the endonasal route provides direct access to the tumor blood supply (ethmoidal arteries) for early devascularization, and removal of the underlying hyperostotic bone at the cranial base so that radical Simpson grade I resection can be achieved. In carefully selected patients, these tumors can be totally removed without additional brain retraction or manipulation.
In this report, we review the surgical technique and operative nuances for removal of olfactory groove meningiomas using the EEA. We also discuss the indications, limitations, complication avoidance and management, and postoperative care.
Preoperative considerations, indications, and limitations
The anatomic limits of the endonasal transcribriform corridor are the posterior table of the frontal sinuses anteriorly, the medial orbits (lamina papyracea) laterally, and the planum sphenoidale and tuberculum sellae posteriorly. A panoramic view of the ventral skull base can be obtained of this transcribriform corridor with a 30-degree angled endoscope aimed superiorly. Early devascularization of the tumor can be performed because the site of dural attachment and the primary tumor blood supply (anterior and posterior ethmoidal arteries) are adjacent to the paranasal sinuses. In carefully selected patients, a Simpson grade I resection of the tumor, including its dural attachment and involved hyperostotic bone, can be achieved ( Figs. 1 and 2 ).
Choosing the appropriate surgical approach is largely determined by careful study of the preoperative imaging, particularly the size of the tumor, location, site and extent of the dural attachment, degree of involvement of neighboring vascular structures (tumor encasement of vascular structures), degree of T2 changes (pial invasion), and surgeon’s preference. If the basal dural attachment is confined between the medial walls of the orbit, then the EEA may be considered a suitable approach. If, however, the dural attachment and associated tumor extends laterally over the orbital roofs, a complete Simpson grade I resection is not feasible. Some laterally extending tumors may be difficult to access through the transcribriform corridor, which can result in residual tumor and a site for future recurrence. Although extending the bone removal laterally over the orbits can be performed, skull base reconstruction becomes more challenging and the risk of postoperative CSF leakage increases. Significant anterosuperior tumor extension behind the posterior wall of the frontal sinus may also prohibit safe complete removal, as this is often a “difficult-to-reach” area. If a radical resection is the desired goal, a transcranial approach should be considered in these cases.
The presence of tumor encasement of major vessels is very important to identify on preoperative imaging, as this may preclude complete removal regardless of surgical approach. Whether the tumor is approached transcranially or endonasally, it is often safer to leave a small tumor remnant adherent to critical neurovascular structures to avoid a major catastrophic vascular injury. However, in the event of a vascular injury, such as a vessel tear or avulsion, it is more feasible to gain vascular control with temporary clips and perform direct vessel repair or bypass in an open approach than with an endonasal approach. Thus, in cases with vascular encasement, we strongly prefer an open transcranial approach, particularly if a near-to-gross total removal is desired. In our opinion, it is technically safer to dissect tumor off of the A2 vessels in the interhemispheric fissure from a transbasal interhemispheric approach than an endonasal approach with current instrumentation. Therefore, it is important to identify a “cortical cuff” (rim of neural tissue that separates the tumor capsule from the A2 vessels and anterior communicating artery complex) or an arachnoid CSF cleft between the tumor and the vessels, when considering an EEA for olfactory groove meningiomas.
The patient’s preoperative olfactory function is also an important factor to consider when choosing the optimal surgical approach. It is paramount to counsel patients that olfactory function is invariably lost after an EEA by nature of the transcribriform approach (removal of olfactory mucosa, transection of olfactory nerves/tracts). Therefore, if preoperative olfaction is already compromised, an EEA should be considered, given all other surgical factors are favorable. If, however, olfaction is intact and the patient strongly wishes to preserve this function, a transcranial approach (pterional, transbasal) should be considered because it has a better chance at sparing the olfactory nerves.
The EEA also is suitable for patients presenting with recurrent meningiomas at the cribriform plate extending into the paranasal sinuses ( Fig. 3 ). This is not uncommon in patients who have had previous craniotomy for olfactory groove meningiomas where the cribriform plate was not previously drilled out at the initial surgery. The EEA has the advantage of removing the sinonasal portion of the tumor, drilling out the hyperostotic cribriform plate, and providing a solution for skull base reconstruction with the vascularized pedicled nasoseptal flap, especially in patients who have had previous craniotomy where the pericranial flap is unavailable for reconstruction.
In some cases, a combined transcranial/EEA strategy can be considered for some tumors with significant tumor extension laterally and paranasal sinus involvement ( Fig. 4 ). Although an EEA alone offers the advantage of removing the sinonasal tumor and hyperostotic cribriform plate, the addition of a transcranial approach (bifrontal transbasal approach) offers wider exposure of the anterior skull base over both orbital roofs and shorter access to interhemispheric fissure to dissect tumor off of critical vessels. Conversely, the visualization afforded by the endoscope can detect tumor in the nasal cavity that is often hidden from the transcranial view from above.
Surgical technique
Preparation and Patient Positioning
The patient is placed in the supine position with the head in 3-pin skull fixation under general anesthesia. The head is rotated slightly toward the right side to facilitate comfortable access to the nose when the surgeon stands on the patient’s right side. In addition, the neck is extended slightly to facilitate access to the cribriform region. We generally do not use lumbar drains in EEA transcribriform procedures. Intravenous antibiotics, antiepileptics for seizure prophylaxis, and 10 mg dexamethasone are administered at the start of the operation. Intraoperative navigation is used with either an MRI, computed tomography angiography (CTA), or both modalities merged. This is helpful in determining the extent of bony opening along the sagittal and coronal planes, as well as predicting the proximity of critical neighboring vasculature.
The nose and nares are prepped with betadine solution, and Oxymetazoline (Afrin)-soaked pledgets are placed into the nasal cavity to decongest the nasal mucosa. The thigh is also prepped for harvesting of an autologous fascia lata graft. We use a standard 2-surgeon, 3-handed to 4-handed binaural technique with a neurosurgeon and otolaryngologist. Intraoperative neurophysiologic monitoring of somatosensory and motor evoked potentials is performed throughout the case.
Endoscopic Endonasal Transcribriform Approach
In our practice, we prefer to use a 30-degree endoscope as our workhorse for extended EEA approaches because it provides additional viewing angles in multiple directions by simply rotating the scope. Our clinical experience is consistent with the findings in an anatomic study by Batra and colleagues, in which the 30-degree endoscope provided the best view of the ventral skull base from the frontal sinus to the planum sphenoidale with the least distortion in comparison with the 0-degree and 70-degree endoscopes.
The nasal septum and tail and anterosuperior attachment of the middle turbinates are injected with 1% lidocaine with epinephrine (1:100,000 dilution). The inferior turbinates are lateralized with a Goldman elevator and both middle turbinates are resected to create access to the cribriform plate. Bilateral maxillary antrostomies are performed to expose the orbital floor, an important anatomic landmark. Bilateral sphenoidotomies are performed with care taken to preserve the vascular pedicle (along the arch of the choana) to the nasal septum.
A large vascularized pedicled nasoseptal flap is then harvested from either side and rotated into the posterior nasopharynx until the reconstruction phase. It is important to design the flap in such a manner to maximize the surface area of the flap to provide adequate coverage of the anticipated skull base dural defect. The anterior margin of the incision is made at the septocolumellar junction to maximize the sagittal reach of the flap. The incision is extended laterally along the floor of the nose to increase the coronal dimension of the flap. It is better to overestimate the defect size and oversize the flap than to have a smaller flap with suboptimal coverage. Care is taken to protect the vascular pedicle from inadvertent trauma to prevent vascular compromise of the flap.
The sphenoidotomy is widened and bilateral total ethmoidectomies are performed with a tissue microdebrider to expose the junction of the lamina papyracea with the fovea ethmoidalis. An extended frontal sinusotomy (modified Lothrop procedure) is performed to expose the anterior extent of the transcribriform corridor. A superior septectomy is performed to provide a panoramic view with binostril access to the ventral cribriform plate. An additional posterior septectomy can be made to allow triangulation of instrumentation through both nostrils to the surgical target. The Lothrop cavity (common frontal sinus cavity) is widened and the nasofrontal beak is thinned down with up-angled curettes and a high-speed drill to expose the posterior frontal sinus wall. The endoscopic modified Lothrop procedure is an important step in the exposure of the transcribriform corridor because it provides exposure of the posterior table of the frontal sinus, a key landmark to delineate the anterior border of the transcribriform corridor. This also serves as a ledge to tuck inlay graft material and a platform to lay down the nasoseptal flap.
Next, a transcribriform craniectomy of the ventral skull base is performed using a high-speed drill with copious irrigation ( Figs. 5 and 6 ). The boundaries of the craniectomy are largely determined by the size of the tumor and the extent of the dural attachment. In general, the craniectomy extends from the posterior wall of the frontal sinus at the level of the crista galli to the planum sphenoidale in the sagittal plane, and from lamina papyracea to lamina papyracea in the coronal plane. After thinning down the fovea ethmoidalis and cribriform plate, the crista is drilled down and dissected away from the dural reflections. The anterior and posterior ethmoidal arteries are coagulated and divided bilaterally to devascularize the tumor. Care is taken to avoid retraction of the proximal end of these arteries back into the orbit before they are adequately coagulated so as to avoid orbital hematoma and proptosis. The exposed dura is further coagulated to devascularize the basal attachment of the tumor.
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