Introduction

Olfactory groove meningiomas (OGMs) constitute 4-13% of all intracranial meningiomas, originating from the dura of the anterior cranial fossa over the cribriform plate and frontosphenoidal suture.^[1], ^[2], ^[3], ^[4], ^[5] Typically, OGMs manifest with hypo/anosmia, visual deterioration, mental changes, and headaches due to compression of the olfactory or optic nerve and frontal lobe. Seizures are also prevalent in these patients. ^[6], ^[7] Despite their slow growth, OGMs often remain clinically silent in their early stages, resulting in substantial tumor sizes at the time of diagnosis. ^[6], ^[7], ^[8], ^[9]

Distinguishing OGMs from other midline meningiomas in the anterior cranial fossa, such as those in the planum sphenoidale and tuberculum sellae, is not merely an anatomical exercise but holds clinical significance. Meningiomas in these locations are commonly diagnosed earlier due to visual impairment.

The classical bifrontal craniotomy proves inadequate for safe exposure of large OGMs, evident from the incidence of life-threatening complications related to brain retraction. ^[1], ^[4], ^[5] Alternative surgical routes, including the pterional and subfrontal approaches, ^[1], ^[10], ^[11], ^[12], ^[13], ^[14], ^[15] expose the posterolateral surface of the tumor from a lateral view. The fronto-basal-orbital approach ^[5], ^[16] accesses the tumor from underneath, exposing its dural attachment first.

In our retrospective analysis of 30 OGM cases, we assessed clinical presentation, tumor characteristics, surgical approaches, and follow-up results following microsurgical intervention through a unilateral (pterional/subfrontal) or bilateral (bifrontal) craniotomy.

Materials and Methods

We scrutinized the records of patients treated for olfactory groove meningioma at our department (RMLIMS, Lucknow) through unilateral and bilateral approaches. A total of 30 patients who underwent OGM removal were reviewed, and their clinical data, radiological findings, and surgical outcomes were retrospectively analyzed.

We identified 30 patients with olfactory groove meningioma (18 females and 12 males), aged between 33 and 54 years, with a mean age of 41.4 years in the unilateral group and 40.4 years in the bilateral group. The preoperative median Karnofsky Performance Score (KPS) was 100 (range, 60-100). Headache was the most frequent complaint (40%), followed by visual impairment (26.6%), anosmia/hyposmia (16.6%), and mental changes (6.6%). In 2 patients (6.6%), OGMs were associated with seizures ([Table 1]). Tumor diagnosis was based on magnetic resonance imaging (MRI) and/or computed tomography (CT) with a contrast agent, with two patients undergoing cerebral digital subtraction angiography (DSA) for embolization purposes. A total of 16 surgical procedures were conducted, utilizing both the pterional (n=16, 53.3%) and bifrontal (n=14, 46.6%) approaches. The pterional approach closely adhered to the technique originally described by Yaşargil. In this method, the frontal bone's lateral part, the anterior segment of the squamous part of the temporal bone, and the lateral aspect of the greater wing of the sphenoid bone were mobilized and excised. To facilitate improved access and manipulation of the anterior fossa from a broader perspective, the frontal part of the bone flap was extended medially and inferiorly. [Figure 1] illustrates the intraoperative steps following dural opening for this approach.

The bifrontal approach, closely mirrors the technique delineated by El Gindi. After a bicoronal scalp incision and periosteum dissection, a bifrontal bone flap was lowered to the orbital rim. The frontal sinus was opened, and its posterior wall and mucosa were excised, with subsequent closure of the frontonasal duct using muscle. Bilateral dural openings were performed, and tumor resection predominantly occurred from one side, with careful retraction of the non-dominant frontal lobe. The dominant frontal lobe's retraction was minimized as much as possible. In summary, a bifrontal craniotomy was executed after the release of supraorbital nerves. Subsequently, a bilateral orbitotomy was conducted, encompassing 2–2.5 cm of orbital roof crossing the midline just anterior to the crista galli. Post-procedure, the anterior skull base underwent reconstruction using a pedunculated flap of galea and abdominal fat to fill any residual dead space. ([Figure 2]).

Results

A total of 30 patients diagnosed with olfactory groove meningioma were included in the study, comprising 18 females and 12 males. The age distribution ranged from 33 to 54 years, with a mean age of 41.4 years in the unilateral group and 40.4 years in the bilateral group.

In our series, total removal was achieved in 27 patients, while partial removal occurred in three patients. Of the 30 OGMs, 16 (53.3%) were treated with the pterional -subfrontal approach, and 14 (46.6%) with the bifrontal transbasal approach. The pterional approach was significantly more frequent for small and medium-sized OGMs (p <0.05).

Overall, gross total resection (GTR) was achieved in 27 procedures (90%), with 10% classified as subtotal resection (STR). The pterional approach allowed a significantly greater percentage of GTR than the bifrontal approach (p<0.05). Simpson’s grade I-II resection was achieved in 27 procedures (90%), with the pterional approach showing a significantly higher percentage of Simpson I-II removal compared to the bifrontal approach.

Postoperative cerebral edema occurred in 12 patients, with a rate of 25% in patients with a unilateral approach and 57.14% in patients with a bilateral approach. The mean surgical length was 2 hours for the unilateral approach and 3 hours for the bilateral approach.

Discussion

Francesco Durante successfully performed the first Olfactory Groove Meningioma (OGM) resection in 1885 through a left frontal craniotomy. ^[17] In 1938, Cushing and Eisenhardt outlined OGM resection principles in a series of 22 patients, using a unilateral subfrontal approach. ^[18], ^[19] Despite numerous publications on OGM treatment, the optimal surgical approach remains controversial. Pterional, frontal, bifrontal, and their variations are the most reported open transcranial procedures for OGMs. ^[1], ^[2], ^[3], ^[4], ^[5], ^[13], ^[15], ^[18], ^[20], ^[21], ^[22], ^[23], ^[24], ^[25], ^[26], ^[27], ^[28]

Nevertheless, the extensive dataset and long follow-up of OGM cases facilitate comparison of results with various surgical strategies. Key findings include: 1) higher mortality and severe complications with the bifrontal approach; 2) the pterional approach achieving a significantly greater percentage of Simpson I-II removal compared to bifrontal; 3) no retraction-related brain swelling in pterional cases, although postoperative CSF leak probability was higher with the bifrontal approach. Simpson grade I-II and WHO grade I were significant prognosticators for longer overall survival, with age and WHO grade being independent factors.

The pterional approach, introduced by Yaşargil, is widely used for vascular and neoplastic lesions in the anterior and middle cranial fossa. ^[29] Its advantages include early control of neurovascular structures, minimal damage to frontal lobes and olfactory nerves, and avoidance of frontal sinus transection, reducing the risk of CSF leak. ^[11], ^[13], ^[22], ^[30] However, it has a narrow working angle. The unifrontal approach, described by Olivecrona and Urban, spares the contralateral frontal lobe and superior sagittal sinus, avoiding bifrontal retraction and potential cognitive dysfunction. ^[5], ^[26] However, it has drawbacks like late exposure of distant neurovascular structures and the risk of CSF leak from frontal sinuses. ^[5], ^[22], ^[31]

The ongoing debate on surgical strategy focuses on tumor resection extent and safety. Our study showed a GTR rate of 90%, with no significant difference between pterional (93.75%) and bifrontal (85.7%) approaches. Optic canal involvement was associated with tumor diameter, while vascular encasement occurred in 8.2% of cases. Postoperative complications varied, with life-threatening complications more frequent in bifrontal cases. No mortality was observed in our series.^[32], ^[33], ^[34], ^[35], ^[36], ^[37], ^[38], ^[39]

The most critical factor in preventing recurrence was the extent of initial resection, supported by a median follow-up of 60 months. Paranasal sinus infiltration increased recurrence risk, especially when involved bone was not removed.

Conclusion

In conclusion, our extensive series highlights the higher risk associated with the bifrontal approach and identifies age and WHO grade as independent factors affecting overall survival in OGM patients. While Simpson grade I-II's prognostic power may be influenced by other variables, it should continue to be the standard for OGM care.

Source of Funding

None.

Conflict of Interest

None.