Extended Pterional Approach for Medial Sphenoid Wing Meningioma: A Series of 47 Patients

Abstract

Background  To describe our operative strategy and analyze its safety and effectiveness for the removal of medial sphenoid wing meningiomas (MSWMs) through the extended pterional approach.

Method  We identified 47 patients with MSWMs who were operated using this approach between 1986 and 2016. Medical charts, operative reports, imaging results, and clinical follow-up evaluations were reviewed and retrospectively analyzed.

Results  No surgical mortality was observed in this sample. Gross total resection was achieved in 30 (63.8%) patients. Intradural clinoidectomy was performed in 16 (34%) patients. The median length of follow-up was 8.5 years (range, 1–30 years).

Conclusion  The extended pterional approach associated with microsurgery techniques provided excellent results for the removal of MSWMs.

Introduction

In 1938, Cushing and Eisenhardt ¹ classified sphenoidal meningiomas into outer (pterional), middle (alar) and inner (deep, clinoidal) lesions according to their site of dural attachment on the lesser sphenoid wing. Medial sphenoidal wing meningiomas (MSWMs) are closely related to the optic nerve (ON), internal carotid artery (ICA), and middle cerebral artery (MCA). ^{1 2 3 4 5 6 7 8 9 10 11 12 13} The distance between the lateral portion of the tuberculum sellae (TS) and the medial wall of the sphenoidal wing is a scanty 1 cm. Therefore, MSWMs and TSMs usually have features in common, particularly in cases of large meningiomas with invasion of the surrounding structures. Bassiouni et al ¹⁴ have suggested that symptoms of meningioma may vary depending on the direction of tumor spread. However, on the basis of clinical findings, preoperative imaging and intraoperative inspection, it is often difficult to determine the exact origin of the meningioma. ^{2 3 7 10 11 12 13 14}

Of all intracranial meningiomas, the incidence of MSWM varies from 17 to 43.9%. ^{1 9 11 14} Despite the anatomical understanding of the anterior and middle skull base and great advances in skull base surgery and microsurgery, the complete removal of MSWMs remain one of the most challenging because of their propensity to encase the ON, ICA, and its branches and to invade the cavernous sinus (CS). ^{1 2 3 4 5 6 7 8 9 10 11 12 14 15 16 17 18 19 20 21} This report reviews our experience in the surgical treatment of 47 patients with MSWM over a 30-year period using the modified pterional approach. We outline several key advantages provided by this approach.

Patients and Methods

Study Design

We conducted a retrospective review of 47 patients with MSWMs who underwent surgery by the modified pterional approach between 1986 and 2016 (a 30-year period) performed by two senior authors (J.C.L. and C.E.P.). Intraoperative videos and photos of 39 patients were retrospectively analyzed to observe nuances in the microsurgical technique. The Simpson grade of meningioma resection was determined through review of the operative report, surgeon's assessment, and postoperative images. Pathological review was conducted according to the World Health Organization (WHO) guidelines. The need for informed consent was waived because of the retrospective nature of the study. In this series, neuronavigation was recently introduced.

Extended Pterional Approach

Under endotracheal general anesthesia, a patient's head is secured in the Mayfield three-point fixation system, positioned in extension, and rotated 20 to 30 degrees away from the side of the tumor. A frontotemporal skin incision is initiated approximately 1 cm anterior to the tragus, ascending from the zygomatic arch, staying behind the hairline, and extending to the midline. Hemostasis is achieved using hemostatic clamps. The temporal muscle and fascia are sectioned in a single layer; dissected and detached from the frontotemporal bone; anteriorly turned to expose the junction of the zygomatic, sphenoidal, and frontal bones; and then maintained in this position with the help of several rubber bands. One burr hole is made in the superior-lateral aspect of the orbital rim, above the intersection of the zygomatic bone and the supraorbital ridge. Craniotomy is performed anteriorly extending, touching the ipsilateral supra orbital prominence but not the orbital rim, resulting in a low subfrontal craniotomy. In older patients, the dura mater is usually adherent to the bone and may tear if not carefully separated from the bone; in this situation, more than a single burr hole may be necessary ( Fig. 1 ). The lesser wing of the sphenoid bone and orbital floor are flattened using a high-speed drill and a fine rongeur until the meningo-orbital band is completely exposed ( Fig. 2A ). The dura mater is then opened in a curvilinear fashion over the Sylvian fissure and a second incision is directed toward the falciform ligament. The operating microscope is introduced in the surgical field. After the splitting of the Sylvian fissure, the meningioma directly comes into view ( Figs. 2B , 2C , 3B ). A self-retaining retractor can now be placed to keep the frontal lobe in the correct position and protect the brain surface from the surgical manipulation. In large lesions that obstruct sight and access to the carotid cistern, the tumor capsule is bipolar coagulated and progressively debulked. The dissection of the tumor begins from the frontotemporal operculum and branches of MCA ( Figs. 3B , 3C , 4B ) and proceeds toward the ICA bifurcation. At this point, the prechiasmatic portion of the ON should be identified and protected. The remaining portion of the meningioma is removed and only after the tension in the optic apparatus decreases, careful manipulation and dissection of ICA and ON begins. The basal dura with tumor invasion is bipolar coagulated and stripped off the underline hypertrophic anterior clinoid process (ACP). If necessary, the ACP is drilled away and removed using a small Leksell rongeur. To remove a tumor that extend into the optic canal (OC) and compress the intracanalicular segment of the ON, the roof of the OC is drilled away with a diamond drill with copious irrigation to prevent optic nerve damage from the heat generated by drilling. ( Figs. 2C , 4B , 4C ). The bone of the OC is made paper-thin and is easily elevated. The falciform ligament is sectioned. The tumor located lateral to the ON and medial to the ICA is carefully dissected, preserving the ophthalmic artery and perforators on the undersurface of the optic apparatus. We do not violate the walls of the CS; only the portion of the tumor located outside the walls of the CS is removed, and any tumor inside the CS is left in situ. In case of inadvertently opening the ethmoidal sinus, a muscle graft is plugged into the bone defect and covered with biological glue. The dura mater is sutured watertight and the bone flap is replaced with a skull-fixation device. Finally, the temporal muscle and superficial layers are routinely closed.

Fig. 1.

Preoperative sagittal ( A ) MRI detected a MSWM with encasement of ICA in a 57-year-old man with progressive visual decline. ( B ) The extended pterional craniotomy. ( C ) Initial exposure revealed a vascularized meningioma. ( D ) After GTR, clinectomy, and OC opening the decompression of ICA and ON. GTR, gross total resection; ICA, internal carotid artery; MRI, magnetic resonance imaging; OC, optic canal; ON, optic nerve.

Fig. 2.

CT scan ( A ) showing a large MWSM in a 77-year-old woman with seizure and cognitive decline. Intraoperative photographs ( B and C ) show the meningioma occupying the Sylvian fissure. After removal of the tumor, the MCA branches were dissected free. ( D ) MRI confirming the GTR. CT, computed tomography; GTR, gross total resection; MCA, middle cerebral artery; MRI, magnetic resonance imaging.

Fig. 3.

Preoperative axial ( A ) gadolinium-enhanced T1-weighted MRI revealed a MWSM that spread along the sphenoidal ridge. Intraoperative photographs ( B ) revealed that MCA was completed encased by the meningioma. ( C ) Postoperative image showing a small fragment of tumor attached to the MCA. MCA, middle cerebral artery; MRI, magnetic resonance imaging.

Fig. 4.

( A ) Preoperative CT scans in a patient with visual decline. ( B ) Intraoperative photographs after GTR, the opposite of ICA; the posterior communicating artery and anterior choroid are clearly seen. ( C ) T1-weighted MRI with contrast enhancement confirming GTR. AChA, anterior choroid artery; CT, computed tomography; GTR, gross total resection; ICA, internal carotid artery; MRI, magnetic resonance imaging; PCA, posterior communicating artery.

Patients Follow-up

Computed tomography (CT) was performed for all patients in the immediate postoperative period to observe any early postoperative changes, such as intracranial hematoma or brain infarction. Patients were followed-up with magnetic resonance imaging (MRI) 3 and 12 months after surgery. The median length of follow-up was 8.5 years (range, 1–29 years). Thereafter, patients were reexamined every year. The Glasgow Outcome Scale (GOS) was used to define the outcome.

Results

Histological Features

The pathology, as defined by the WHO classification of meningiomas, was benign in 44 (93.6%) of cases. Three (6.3%) meningiomas were WHO grade 3. The most frequent pathology subtypes were meningothelial and fibroblastic meningiomas.

Tumor Volume

Tumor volume varied from 4.3 to 364 cm ³ (average, 55.3 cm ³ ). We considered MSWMs < 33 cm ³ as small, 33 to 112 cm ³ as medium, and > 112 cm ³ as large. Eight tumors (17.0%) were small, 17 (36.1%) were medium, and 22 were (46.8%) large.

Relationship with ICA, MCA, and ON

MSWMs are closely related to the ICA, MCA, and ON. Anterior clinoidectomy creates an extra space, thereby widening the surgical corridor, facilitating tumor removal, and decompressing the ON and ICA ( Figs. 1C , 2D , 4C ). We performed intradural clinoidectomy in 16 (34%) cases. Four meningiomas completely encased the ICA. We noted that the MSWM enveloped the MCA in eight patients and encircled the ON in 16 patients.

Clinical Presentation

We are in agreement with researchers who claim that MSWMs occur more commonly in the fifth and sixth decades of life (3, 9, 10, 14, 18). Our patient population showed definite gender predilection for women. Ophthalmologic examinations were routinely performed in the pre- and postoperative periods. The most common presenting symptom was decreased visual acuity which was noted in 31 (65.9%) patients ( Table 1 ).

Table 1. Patient demographics and neurological picture.

Age at treatment:

15–83 y (mean, 58.0 y)

Sex:

Male: 9 (19.1%)

Female: 38 (80.8%)

Symptoms:

Visual impairment: 31 (65.9%)

Headache: 24 (51%)

Seizures: 15 (31.9%)

Motor signs: 14 (29.7%)

Diplopia: 7 (14.8%)

Decreased cognition: 5 (10.6%)

Note : More than one symptom may occur in one patient.

Mortality and Morbidity

There was no operative mortality in this sample (until 30 days after surgery). Overall mortality was 12.7%. One male patient died due to a pulmonary embolism 45 days after being discharged from the hospital. A female patient died 16 months after discharge from the hospital because of a colon carcinoma. Another patient died of cardiac failure 2 years after the operation. A 75-year-old female died 7 months after surgery due to an acute subdural hematoma. In two patients, the cause of death could not be determined. Although surgery is generally safe and effective, notwithstanding complications occurred in seven (14.8%) patients. There were three (6.3%) patients with postoperative cerebrospinal fluid (CSF) leaks from the scalp incision. We did not observe a single case of rhinorrhea. The condition of two patients worsened after surgery because of the appearance of a massive hemiplegia due to an avulsion of the lenticulostriate artery during tumor dissection.

In two patients, hydrocephalus was diagnosed in the postoperative period; these patients required a ventricle peritoneal shunt. An excellent or good outcome was achieved in 36 (76.5%) patients. The excellent category includes patients whose status was normal and had a neurological examination without persistent symptoms. For the good category, the patient's condition should reveal minor residual deficits or symptoms with a normal life. At the time of final follow-up, 24 (51.0%) patients were GOS 5, 12 (25.5%) were GOS 4, five (10.6%) were GOS 3, and six (12.7%) were GOS 1.

Extension of Resection and Recurrence

Gross total resection (GTR) was achieved in 30 (63.8%) patients ( Figs. 1 2 3 ) and subtotal removal (STR) occurred in 17 (36.1%) patients. During the follow-up period, all patients underwent serial MRIs. Any residual tumor was managed with the classic policy of wait and scan. In these series, recurrence was detected in three individuals (6.3%), all of them originating from the STR group. Adjuvant external radiation was administered with a total dose of 54 Gy with 1.8 Gy/fraction in opposite three portals during the postoperative course in the three patients with recurrent lesions. Two meningiomas were WHO grade 2 and one patient was WHO grade 1. The demographic and clinical profiles of the patients are summarized in Tables 1 2 3 .

Table 2. Surgical outcome and follow-up.

Surgical mortality: 0

Recurrence: 3 (6.3%)

GTR: 30 (63.8%)

GOS 5: 24 (51.0%)

GOS 4: 12(25.5%)

GOS 3: 5 (10.6%)

GOS 1: 6 (12.7%)

Clinoidectomy: 16 (34%)

Unroof OC: 9 (19.1%)

Complications:

CSF leak: 3 (6.3%)

Hydrocephalus: 2 (4.2%)

Wound infection: 2 (4.2%)

Pulmonary complications: 4 (8.5%)

Follow-up: 8.5y (range, 1–31 y)

Abbreviations: CSF, cerebrospinal fluid; GOS, Glasgow Outcome Scale; GTR, gross total resection; OC, optic canal.

Table 3. Tumors characteristics.

Volume

Small: 10 (21.2%)

Medium: 29 (61.7%)

Large: 8 (17.0%)

Grade (WHO)

Grade 1: 44 (93.6%)

Grade 2: 3 (6.3%)

Vascular relationship

Encase ICA: 6 (12.7%)

Encase MCA: 8 (17.0%)

Encase ACoA: 1(2.1%)

Laterality:

Right: 28 (59.5%)

Left: 19 (40.4%)

Multiples: 3 (6.3%)

Abbreviations: ACoA, anterior communicating artery; ICA, internal carotid artery; MCA, middle cerebral artery; WHO, World Health Organization.

Discussion

The Extended Pterional Approach

Traditionally, MSWMs are resected through the pterional approach and its variations. ^{4 6 8 9 11 14 15 17 18 19 20 21 22 23 24} or cranial base approaches. ^{1 2 3 7 10 12 13 25 26 27 28}

While this operative corridor is sufficient many lesions, it provides a limited angle of view for the ICA and ON. Resecting MSWMs through the classical pterional approach can be technically challenging, in large and giant lesions. In the extended pterional approach, the frontal bone cut is performed touching the ipsilateral supra orbital prominence but not the orbital rim. We obtained an eccentric fronto-pterional-temporal craniotomy with extension toward the frontal bone; this variation possibility accesses through the subfrontal route besides the usual anterolateral view provided for the pterional approach. In the standard pterional craniotomy, the anterior frontal cut is approximately 3 cm superior to the orbital ridge. In contrast, in the extended pterional approach, the craniotomy reaches the frontal skull base, giving the surgeon a direct and unobstructed line of vision for the frontal base. Therefore, the retraction, if necessary, is kept to a minimum. The extended pterional approach improves the angle of vision by 1.5 cm which is maintained over the full range of the craniotomy. It also increases the angle of view and decreases the working distance. Therefore, the extended pterional approach improves maneuverability, provides sufficient workspace for fine instrument movement, decreases the amount of frontal lobe retraction, and consequently reduces the incidence of venous infarction, edema, and contusion. This allows for the possibility of employing several operative microscopy angulations and multiple surgical corridors which are particularly important in cases of large or giant tumors. The disadvantage of this approach is that it is difficult to establish adequate visualization under the surface of the ipsilateral ON and optic chiasm (OCH). By shifting the surgical microscope medially and laterally by tilting the operative table, we can partially circumvent this problem.

This nuanced surgical technique has not previously been published.

In cases of small tumors, early exposure of the ON and OCH is straightforward.

The anterior clinoidectomy create an extra space, widening the surgical corridor, facilitating tumor removal, and decompressing the ON and ICA. Anterior clinoidectomy can be performed by the intradural ^{8 9 12 13 14 15 20 21 22 23 24 25} or the extradural approach. ^{1 2 3 7 9 10 12 13 18 25 26 27 28 29 30} We prefer to perform a tailored anterior clinoidectomy from the intradural route ( Figs. 2B , 4B ). Romani et al ³¹ stated that the amount of ACP removal can be partial, intermediate, or complete, depending on the local anatomy of ACP and size and spread of the meningioma. We performed intradural clinoidectomy in 16 (34%) patients and unroofing of the OC in 31 patients (65.9%).

As reported by Dolenc ^{26 27} and others, ^{3 17 25} extradural resection of the ACP may result in ON injury and entail a risk of vascular lesions in cases with bone bridges to the middle and/or posterior clinoid processes. Extradural drilling of the OC around an already stretched ON can directly pose a risk to the nerve or its vascularity. On the other hand, intradural exposure of the ON and following it proximally toward the OC may be a safer alternative than extradural bone removal. ^{8 9 12 13 14 15 20 21 22 23 24 31}

Mortality, Morbidity, and Outcomes

Cushing and Eisenhardt ¹ reported an overall operative mortality rate of 53.8%, while Behari et al published a 43% mortality rate. ⁴ The incidence of mortality has ranged from 0 to 27% in recent series. ^{2 3 5 10 11 14 15 18 20} In this sample, there was no operative mortality (until 30 days after surgery). The overall mortality was 12.7%, with 35 (74.4%) patients obtaining GOS 4 or 5.

At present, preservation or improvement of vision is an important goal of treatment. Visual improvement or stabilization after tumor removal ranges from 40 to 71% in published series. ^{9 10 12 14 15} In this study, three (9.6.%) patients showed improvement in visual acuity. Five (10.6%) patients with preoperative amaurosis did not show any improvement which implicates ischemia as the cause of visual loss rather than ON compression. We observed stabilization of visual acuity in 39 (82.9%) patients. In the literature, stabilization of vision has been reported to occur in 46 to 84% of cases. ^{9 10 14 15}

Extent of Resection and Recurrence

Neurosurgical papers on MSWMs have reported GTR rates ranging from 5.8 to 100%. ^{1 2 3 4 5 7 9 10 11 14 18 20 23 31} In this series, GTR was accomplished by complete macroscopic lesion removal (Simpson's grade II) in 30 (63.8%) patients; STR was obtained in 17 patients (36.1%). In 10 patients, tumor remnants were left in the CS. To reduce regrow, Al-Mefty et al ^{2 5} and others ²⁸ advocate cranial base approaches with routine unroofing of the foramina rotundum and oval, as well as performing a posterolateral orbitotomy and removing the tumor from inside the CS. However, GTR may be dangerous for some patients and it is difficult to achieve because tumors may be adherent to or encase vital vessels. At diagnosis, many lesions are already large or giant. In this sample, 60.7% of lesions were large or giant. If the surgeon persists to remove every last residual piece of tumor, then it could result in an unwarranted cranial nerver (CN) or arterial injury; consequently, GTR is not always a reasonable goal, particularly in elderly patients. ^{32 33 34} Several surgeons prefer more conservative tumor removal because of the risk of postoperative CSF leakage, ocular motor nerve palsies, vascular occlusions, and infection. In our series, meningiomas are invading the CS were not removed; rather, only the portion of the tumor located outside of the CS wall was resected. In published microsurgical series, the recurrence rate for MSWMs, with a follow-up period ranging from 2 to 9.3 years, varied from 0 to 41%. ^{10 11 14 15} The recurrence rate of this sample, with a median follow-up of 8.5 years (range, 1–31 years), was 6.3% (three patients). We are willing to acknowledge that more conservative tumor resection could be associated with recurrence and progression of tumors. On the other hand, the most convincing argument in favor of conservative tumor resection is the association between increased surgical morbidity and extensive operations. Finally, this study is subject to limitations. Specifically, the results should be interpreted with caution due to the small sample size and lack of a control group.

Conclusions

The extended pterional approach is a versatile, safe, and effective approach for MSWMs. It improves the angle of visualization of the area ventral and medial to the ON and ICA, revealed by a low sub frontal corridor to the chiasmatic space, and minimizes brain retraction, facilitating the dissection of the interface between the ON and vascular structures and the tumor. We achieved GTR in most patients without mortality and with a relatively low rate of complications.