INTRODUCTION

Olfactory groove meningiomas, which account for 10% of all intracranial meningiomas, arise from the cribriform plate or the frontosphenoid suture. Their microscopic appearance, pathologic classification, and female preponderance reflect the characteristics of meningiomas found elsewhere.¹ An olfactory groove meningioma was successfully resected by Durante in 1885, and this constitutes the first reported successful removal of a meningioma.²

Olfactory groove meningiomas are usually midline, but as their size increases they may become asymmetric. The frontal lobes are always displaced superiorly and posteriorly, and in larger tumors, inferior and lateral displacement of the optic nerves and chiasm is observed. Their growth can also occur inferiorly through the cribriform plate into the ethmoid sinus, through the planum sphenoidale into the sphenoid sinus, or laterally through the orbit.^3,4

Olfactory groove meningiomas can be highly vascularized tumors, as observed in meningiomas in other locations. Their main blood supply is derived from contributions of the external carotid artery. Olfactory groove meningiomas typically receive their blood supply from the anterior and posterior ethmoidal arteries as well as branches of the middle meningeal artery and meningeal branches of the ophthalmic artery.^5,6 As they enlarge, variable contributions from the anterior cerebral arteries are observed.

Olfactory groove meningiomas develop insidiously and their diagnosis is commonly made late, when tumors are large. Their treatment is therefore mostly surgical. Surgical results have continued to improve since the introduction of the surgical microscope, combined with the use of more refined skull base approaches and microsurgical techniques.

The clinical presentation, radiologic characteristics, and treatment options of olfactory groove meningiomas, as well as outcomes of patients who have received this diagnosis, are reviewed in this chapter.

CLINICAL PRESENTATION

Olfactory groove meningiomas are commonly diagnosed when their size is significant and causes local mass effect.^7,8 The initial complaints of many patients are nonspecific, leading to a high rate of misdiagnosis. The slow progression of symptoms in many cases may be accompanied by apathy in these patients, which decreases the likelihood they will seek medical care. The time frame noted from the development of initial symptoms to the time of diagnosis varies substantially between different series and has been reported to be up to 14 years.⁹

Hyposmia or anosmia is one of the earliest presenting symptoms, but few patients seek medical care for this isolated symptom. At the time of diagnosis, anosmia is noted in more than 50% of cases (Table 27-1). In a rare case, cacosmia has been reported secondary to an olfactory groove meningioma.¹⁰ Later aspecific symptoms consist of headaches and personality changes, such as apathy and akinesia, which are commonly misdiagnosed as being associated with depression or aging. Occasionally, an early stage of aggressiveness has been reported.^11,12 Exceptional cases of euphoria have also been described.¹³ Patients then develop a flat affect as well as some short-term memory problems from subtle frontal lobe dysfunction. Later progression can lead to dementia and urinary incontinence. The symptoms usually progress over several months to years, and the impact on the social and professional lives of patients can be dramatic. Mental disturbance is the most commonly reported presenting symptom in published series and occurs in more than 50% of cases (see Table 27-1).

Late findings may include visual symptoms from compression of the optic nerve or optic chiasm. Less frequently, visual symptoms may be due to an intraorbital invasion of the tumor. Varying degrees of visual field cuts as well as loss of visual acuity have been reported in about one third of patients at the time of diagnosis (see Table 27-1).^14,15 The presence and severity of a visual defect seems to correlate to the size of the tumor. The triad of anosmia and unilateral optic atrophy with contralateral papilledema first described in the Foster Kennedy syndrome is rare and can be observed in other conditions.^16–19 In addition to the Foster Kennedy syndrome, optociliary shunting may be found on funduscopic examination.²⁰

Seizures are an uncommon presenting symptom (8%), but their presence prompts the use of imaging studies, which leads to more rapid diagnosis. Rare cases are diagnosed secondary to the effects of local invasion in the paranasal sinuses and consist of nasal obstruction, epistaxis, spontaneous cerebrospinal fluid (CSF) leaks, or meningitis.

PREOPERATIVE EVALUATION

Magnetic resonance imaging (MRI) with and without gadolinium enhancement is the study of choice to confirm the diagnosis of an olfactory groove meningioma. The appearance of these tumors on MRI is similar to that of meningiomas found in other regions of the intracranial cavity or spinal canal. Olfactory groove meningiomas classically appear as a homogeneously enhancing lesion with a dural attachment centered on the cribriform plate (Fig. 27-1). They are usually isointense to gray matter on T1-weighted sequences and iso- to hyperintense on T2-weighted sequences. Ethmoidal or intranasal extension of the tumor can be ascertained as well, and the relationship of the optic nerve and chiasm is visible. The visual apparatus is displaced posteriorly and inferiorly in olfactory groove meningiomas. The anterior cerebral arteries are usually displaced posteriorly and superiorly, and their relationship to the capsule is noted. Encasement of the anterior cerebral arteries within the tumor is rare. Frontal lobe edema is observed to varying degrees. Cerebral edema is present preoperatively in up to 58% of case, prompting the use of steroids.⁹

FIGURE 27-1 Sagittal (left) and coronal (right) view of MRI with gadolinium enhancement demonstrating large dural based mass centered on the cribriform plate.

A computed tomography (CT) scan with fine cuts through the anterior skull base is useful to evaluate the extent of the paranasal sinus or orbital involvement. The location and degree of hyperostosis may influence the surgical aggressiveness used. Paranasal sinus involvement seems to occur in about 19% of cases (Table 27-2). Intraorbital involvement through erosion of the medial orbital wall is uncommon but has been reported in up to 5% of cases.⁹

A cerebral angiogram is seldom required for diagnosis or definition of the relation to normal vasculature because the anterior cerebral arteries are easily visible on the MRI study. A cerebral angiogram demonstrates a vascular blush at the anterior skull base with posterior and superior displacement of the anterior cerebral arteries. A flow-related saccular aneurysm of the anterior ethmoidal artery has been reported in association with an olfactory groove meningioma, with resolution of the aneurysm on resection of the tumor.²¹

The size of the tumor at time of diagnosis is highly variable. Tumor sizes of up to 10 cm have been reported at the time of diagnosis.⁹ At diagnosis, most olfactory groove meningiomas are large and have a diameter greater than 4 cm (see Table 27-2). They can also present as incidental findings on imaging in up to 10% of cases.⁹

DIFFERENTIAL DIAGNOSIS

The differential diagnosis is usually limited, and the MRI findings are usually very characteristic of these tumors. An olfactory nerve schwannoma or subfrontal schwannoma not associated with any cranial nerves is a rare tumor that can arise in that location.^22–25 Key preoperative imaging findings include the presence of bone scalloping as well as the absence of bone sclerosis and a dural tail.²⁶ In one case, a nasal schwannoma has been found in conjunction with an olfactory groove meningioma.²⁷ Occasionally, olfactory groove meningiomas can be difficult to distinguish from esthesioneuroblastomas. A young patient can alert to the possibility of these tumors. An olfactory groove meningioma can also develop after radiation for therapy for the treatment of an esthesioneuroblastoma.²⁸ Dural-based metastases must also be considered in the differential diagnosis. In this regard, rare cases of subdural metastatic disease, notably breast carcinoma, have been reported, sometimes metastasizing an associated meningioma.²⁹ With improved screening and local tumor control for breast carcinoma, this situation has become exceptional.

It is important to differentiate olfactory groove meningiomas from tuberculum sellae meningiomas, which arise from the planum sphenoidale or the tuberculum sellae and present with visual symptoms earlier in the disease. The visual apparatus is displaced superiorly and laterally in cases of tuberculum sellae meningiomas. A sagittal view on the MRI should be able to differentiate these two tumors preoperatively.

MANAGEMENT OPTIONS

The treatment of olfactory groove meningiomas usually requires surgery at the time of diagnosis because of their size. An increase in incidental findings is expected because of the increased availability of neurologic imaging. In cases of small lesions devoid of mass effect, continued observation may be an option until growth is documented. The choice between treatment and expectant management also heavily relies on the patient’s life expectancy. Radiosurgery may also have a larger role in some incidental cases.

Management options for recurrent disease include reoperation as well as radiosurgery. Rare cases of olfactory groove meningiomas progress to atypical or malignant meningiomas, prompting aggressive surgery with radiotherapy.

SURGICAL APPROACHES FOR THE RESECTION OF OLFACTORY GROOVE MENINGIOMAS

Olfactory groove meningiomas usually require surgical treatment at time of diagnosis because of their size and associated mass effect. Several surgical approaches are commonly used when treating olfactory groove meningiomas: the subfrontal,^6,30–36 pterional,^{33,35,37–42} or interhemispheric approaches.⁴³ Cases with extensive paranasal sinus involvement require a craniofacial approach.^16,44,45 The transsphenoidal approaches are also an option in selected cases.^46,47

The best approach combines early access to the basal attachment of the tumor and its vascular supply. The approach should also minimize any frontal lobe retraction, which can be judiciously avoided with the use of gravity. Good visualization of the optic nerve, chiasm, anterior cerebral arteries, as well as the anterior skull base floor is necessary to limit morbidity and optimize the chances of a complete resection. Little consensus exists among surgeons about the superiority of any approach.

Subfrontal Approaches

The bifrontal subfrontal approach was the first approach described for the treatment of olfactory groove meningiomas. It remains the most widely used approach and different surgeons have developed additions to the approach (see Table 27-2).

The standard bilateral subfrontal approach is performed through a bicoronal skin incision with the patient’s head placed in slight extension in rigid head fixation. The head is optimally positioned to permit unobstructed venous return and to provide maximal separation of the frontal lobes from the tumor. A pericranial flap is harvested and reflected anteriorly, with preservation of the supraorbital nerves and arteries. An interfascial dissection is performed anteriorly over the temporalis muscle to protect the frontalis branch of the facial nerve. The standard bilateral subfrontal approach is made through two burr holes on either side of the superior sagittal sinus, anterior to the coronal suture, as well as burr holes at the anatomic keyhole (Fig. 27-2). The temporalis muscle is cut at the level of the keyhole to the cranium along the direction of the planned craniotomy, permitting muscle closure over the keyhole burr holes for better cosmesis. The craniotomy is completed when adequate lateral exposure is ensured. The lower limit of the craniotomy is approximately a centimeter above the orbital rims. Resection of the frontal sinus mucosa is performed early, and the remainder of the frontal sinus is cranialized, increasing the frontal exposure.

FIGURE 27-2 Anatomic views (A, lateral; B, anteroposterior) of common surgical approaches used for the resection of olfactory groove meningiomas.

The extent of the low frontal exposure facilitates the resection of the tumor by offering early access to its vascular supply (ethmoidal arteries and meningeal branches of the middle meningeal and ophthalmic arteries). It also shortens the working distance and limits the need for frontal lobe retraction.

The dura can be opened horizontally in the low frontal area. Bilateral dural opening with ligation of the superior sagittal sinus can be performed anteriorly. The tumor is easily accessible, and its capsule is coagulated anteriorly and inferiorly to achieve maximal devascularization.³⁶ Internal debulking of the tumor is then accomplished. The superior and posterior aspects of the tumor are addressed last. The capsule is dissected off the optic nerves, chiasm, and anterior cerebral arteries using microsurgical techniques. A reasonable arachnoid plane is usually found posteriorly and should be followed for dissection. It is important to dissect the feeding arteries before coagulating them so as to clearly visualize and preserve the anterior cerebral arteries and the perforating branches to the hypothalamus. Frontal lobe retraction is usually necessary at this stage of the operation for good visualization.

Complete resection of the tumor should be possible. Dura mater that is involved with the tumor should be resected when feasible and balanced against the risk of developing a postoperative CSF leak. The anterior skull base should then be inspected, and the crista galli or any areas of hyperostotic bone should be drilled with a high-speed diamond burr drill. Dura should be closed in a watertight fashion to prevent the formation of a postoperative CSF leak. Dural patching may be necessary. The pericranium is used to reconstruct the floor of the anterior skull base and is sutured in place to the dura posterior and inferior to the posterior edge of the frontal sinus. The bone flap is secure to the skull by leaving a sufficient ridge at its inferior surface to prevent necrosis or edema of the pericranial flap.⁴⁸ Sufficient inferior fixation is also necessary to prevent the bone flap from sinking in and providing an unsatisfactory cosmetic result.

The subfrontal approach can be complemented by the addition of orbital osteotomies as a means of improving access to the tumor and limiting the need for any brain retraction. The keyhole burr hole is extended anteriorly to permit entry into the orbit. A subperiosteal orbital dissection is performed, and control of the anterior and posterior ethmoidal arteries can be accomplished before any tumor dissection.⁴⁹ The orbital osteotomies are completed with a cut at the frontozygomatic and frontonasal sutures (see Fig. 27-2). The orbital osteotomies can be performed in a unilateral as well as bilateral approach.⁵⁰

Other variations to the subfrontal approach limit the craniotomy to the size of the patient’s frontal sinus.⁵¹ The anterior table of the frontal sinus is resected at the limit of the sinus with an oscillating saw. Cranialization of the frontal sinus is then performed. The dura is opened in a transverse fashion in the low frontal area with sacrifice of the superior sagittal sinus, and resection of the tumor is completed in a similar fashion. The theoretical advantages to this approach consist of exposing less of the superior sagittal sinus. Some debate has arisen as to the safety of surgically dividing the superior sagittal sinus, even in its anterior portion.⁵² Variations to these approaches have been developed that preserve the superior sagittal sinus while maximizing exposure by incising the inferior part of the falx.⁵³

A less invasive subfrontal approach can be performed through a unilateral craniotomy in the frontolateral approach. Entry into the frontal sinus is not always mandatory and the craniotomy size is smaller (see Fig. 27-2). The approach has a more lateral angle, enabling early CSF drainage by splitting the sylvian fissure proximally. The need for frontal lobe retraction is minimized, and the superior sagittal sinus is preserved. The major limitation to the approach is the limited view offered into the paranasal sinuses or toward the orbits. Reconstruction of the anterior skull base is possible with a free pericranial graft but may be more challenging. The vascular structures are encountered toward the final stages of the operation as in the bifrontal approach. A unilateral osteotomy can also be included in this approach.^30,54

Most of the subfrontal approaches are time consuming because of the additional steps involved with controlling the frontal sinus or performing additional osteotomies. The risk of a postoperative CSF leak is increased with wide opening and exposure of the frontal sinus. A theoretical increase in infection exists as well with a breach in the paranasal sinuses. In all subfrontal approaches the neurovascular structures are visualized and dissected last, compared with the pterional and interhemispheric approaches.