Characteristics of optic canal invasion in the large midline non-tuberculum sellae anterior skull base meningiomas and the surgical outcomes

Abstract

Objective: There is a lack of available data regarding the incidence and characteristics of optic canal invasion (OCI) in large midline non-tuberculum sellae anterior skull base meningiomas (NTSAM), specifically those originating predominantly from the olfactory groove and planum sphenoidale. This study aims to describe the incidence and characteristics of OCI as well as clinical and visual outcomes following extensive tumor resection with optic canal exploration in intra-optic canal tumor removal. In addition, the predictive performance of OCI by preoperative magnetic resonance imaging (MRI) is investigated.

Materials and methods: From 2016 to 2024, we retrospectively reviewed 24 patients with large midline NTSAM who underwent extensive tumor resection in our institution. The OCI was evaluated and compared between preoperative MRI and intraoperative findings. The OCI was classified as follows. Type 1 represented no invasion, type 2 represented secondary invasion, type 3 represented partial wall invasion (two subtypes), and type 4 represented invasion into the superior-medial-inferior walls of the optic canal. Visual functions were assessed before and after surgery.

Results: Among 24 patients, a mean tumor size of 57.2 mm (range 39.0-79.0). The OCI was observed intraoperatively in 22 cases (91.7%), with 19 cases exhibiting bilateral OCI. Among the 48 optic canals in the 24 patients, 18 (37.5%) were type 4, 12 (25.0%) were type 3-inferomedial, 9 (18.8%) were type 3-superomedial, and 2 (4.2%) were type 2, where 7 (14.6%) optic canals were without OCI. A significant correlation was observed between intraoperative OCI and the tumors that exhibited involvement of the tuberculum sellae (TS) on MRI (p < 0.001). For patients with visual impairment, the vision in 27 of 38 (71.1%) eye sides showed improvement following the surgery. There was 1 (4.2%) case of tumor recurrence at the mean follow-up time of 27.3 months (range 4-73 months).

Conclusions: A high incidence of OCI was observed in the large midline NTSAM. The identification of TS involvement on MRI can serve as a strong predictor of OCI. Therefore, optic canal exploration to remove the optic canal invasion during the surgical removal of these particular tumors should be contemplated to attain radical tumor resection to enhance the possibility of improving visual function and reduce the risk of recurrence.

Keywords: Meningioma; Olfactory groove; Optic canal invasion; Outcome; Planum sphenoidale.

Fig. 1

Illustration of classification of the optic canal invasion. This illustration demonstrates the example of the unilateral optic canal invasion by large NTSAM (partially removed of large tumor bulk). a Type 1: no invasion. b Type 2: secondary invasion c Type 3: superior-medial (SM). d Type 3: inferior-medial (IM). e Type 4: superior-medial-inferior (SMI)

Fig. 2

A T1-weighted image with gadolinium in sagittal view a Large OPM without the involvement of the tuberculum sellae (red arrowhead). b Large OPM with tumor base extends beyond the tuberculum sellae area (red arrowheads)

Fig. 3

Bar chart showing the correlation of the preoperative MRI findings with the intraoperative optic canal invasion. Abbreviations; MRI, magnetic resonance imaging; OCI, optic canal invasion; TS, tuberculum sellae

Fig. 4

a A preoperative T1-weighted image with gadolinium in sagittal view showing a large anterior skull base meningioma which base of the tumor extended to tuberculum sellae. b Preoperative visual field assessment showed mild impairment on the right whereas the left side was noted with low reliability due to severe visual function disturbance. c, d After adequate partial debulking of the tumor, the hyperostosis of planum sphenoidale, tuberculum sellae, bilateral optic roof, and medial part of the bilateral anterior clinoid process was completely drilled until a 180-degree identification of bilateral optic canals was obtained. (Dark plus sign indicates the base of falx cerebri, a yellow asterisk indicates sphenoid sinus, a dark asterisk indicates the right optic canal, a blue asterisk indicates the left optic canal, blue dash line indicates falciform ligament).e Left optic canal exploration started with a sharp cutting of the medial part of the falciform ligament to avoid an injury to the intra-canal optic nerve (blue asterisk). f Demonstrates type 4 optic canal invasion by the tumor (yellow arrow) in relation to the left optic nerve (green asterisk). g After intra-canalicular tumor invasion was totally removed, the left posterior clinoid process (red asterisk), and an extracranial optic nerve were identified (green asterisk). h Right optic canal (dark asterisk) exploration started with a sharp cutting of the medial part of the falciform ligament to avoid an injury to the intra-canal optic nerve. i Demonstrates type 4 optic canal invasion by the tumor (yellow arrow) and an extracranial optic nerve was identified (green asterisk). j The right ophthalmic artery (yellow plus sign) was identified following the complete removal of an intra-canalicular tumor. k A postoperative T1-weighted image with gadolinium in sagittal view showing complete tumor removal without recurrence. l Postoperative visual field assessment showed improvement in both eyes

Fig. 5

Preoperative MRI a, b Sagittal and coronal view showing large planum sphenoidale meningioma extended beyond the TS region. c Preoperative visual field assessment of both eyes. Intraoperative findings. d OCI in the left optic canal was observed as type 4 (yellow arrows) (green asterisk indicates the optic nerve). e Type 3-SM OCI was noted after the opening of the right optic canal which the medial part of the tumor was flipped over due to attachment to the falciform ligament (yellow arrows) (green asterisk indicates the optic nerve) f Postoperative visual field assessment showing improvement on both sides. Postoperative brain MRI T1-weighted with gadolinium. g, h Sagittal and a coronal view showing complete removal of the tumor Follow-up brain MRI at 41 months. i Axial and j coronal views showing recurrent tumor (red arrows) at the frontal lobes without attachment of the cranial base. k, l Axial and coronal views show no residual or recurrent tumor at 60 months following the second surgery and radiation therapy