Intracranial meningiomas can be grossly distinguished into supratentorial and infratentorial locations. Regarding its treatment, the approach depends on the case: wait and watch is an option for small cases or nongrowing tumors; stereotactic radiosurgery (SRS) has been advocated as a growth-control therapy, with relatively good results. Also, endovascular embolization plays its role, mainly as a surgical adjuvant. However, surgery remains the only curative treatment (1).

For those meningioma emerging from the cranial base, depending on the tentorium or occupying the cerebellopontine angle (CPA), it is mandatory to avoid injury to the capital surrounding structures (main intracranial vessels, cranial nerves) and limit traction from brainstem structures, which could cause microvascular disruption and major morbidity. Thus, a necessity for innovative tools emerges, which could improve outcomes and reduce risks in complex meningioma surgery.

Laser surgery has the advantage of reducing mechanical trauma and intraoperative bleeding, valuable characteristics for meningioma resection. The first use of lasers in neurosurgery dates back to 1966 (2, 3). Interest in them has been fluctuating throughout history because of the lack of refinement of the initial laser technologies, which implied large equipment and some troublesome characteristics. However, this technology has been improved, and several models were developed. Initial pulsed-wave lasers were largely replaced by continuous-wave lasers (4), capable of delivering focused and nondispersive energy to dissect and vaporize histological targets. Another significant landmark was its presentation as a handheld fiber since the development of the flexible CO₂ laser in 2005 (5).

Since 2015, the 2-μm thulium laser has been used in medicine, thanks to its promising characteristics (6). Although initially developed for urological surgery, recently it has been adopted for neurosurgical procedures. It is capable of delivering focused and nondispersive energy to dissect and vaporize histological targets, proving coagulation and cutting capacities. The equipment consists of a standard size console connected to an optical fiber cable that transmits the wave. This fiber can be then inserted in different terminals: a handheld piece or an endoscope (Figure 1). When required, the laser is activated by a pedal switch, by the operator, who handles the terminal and directs it toward its objective. Distance of application will depend on the desired effect: closer for cutting, slightly further for superficial coagulation, but will range approximately between 2 and 10 mm. The device does not pose space problems in the operating room, has no particular maintenance or refrigeration needs, and offers easy and intuitive operation.

Its appliance has already been described for endoscopic third ventriculostomy as well as for schwannoma microsurgery (7, 8). Some initial reports showed its feasibility for meningioma surgery (9, 10). Our group began using it in 2014, particularly for resection of cranial base and posterior fossa meningiomas.

This paper intends to depict our experience with the first 75 cases operated on with this tool, which constitutes the largest series up to the date in the literature.

Technology in neurosurgery has the aim of improving outcomes, helping the surgeon and limiting complications. Lasers and neurosurgery relationship is coming back now stronger than ever in our times, thanks to the many advantages of modern devices which resolve previous issues, such as the 2-μm thulium laser.

First, it allows bloodless tissue coagulation and ablation (depending on the power intensity and distance of application). Its anti-edema and vasoconstrictive potential allows for delicate cytoreduction maneuvers that facilitate exeresis, avoiding excessive bleeding in those lesions supplied by abundant arterial feeders. Second, energy is transported through thin optical fibers, which allows flexible configurations for an endoscopic or handheld device. Third, due to its particular wavelength (2 μm), it is strongly absorbed by the surrounding aqueous medium, avoiding dispersion and damage to the surrounding structures; finally, it is presented as a small device the size of a standard console, which does not usually pose space problems in the operation room. Thanks to all those treats, it constitutes a useful tool for meningioma microsurgery, helping avoid mechanical traction and continuous aspiration, facilitating capsule opening, intralesional debulking, and dissection. In addition, in case of incomplete resection, it is appropriate to safely coagulate tumor remnants and the dural implant base. We show a brief experience in the Supplementary Video.

As potential inconvenient traits, it would require a learning curve and proper carefulness by the surgeon during its application, but we have found this curve to be short and easy to undergo. It might be argued that laser would be a redundant technology, as other classical instruments, like the diathermic loop or monopolar cautery would already accomplish the same function. However, compared with it, the 2-μm thulium laser avoids electrical and thermal dispersion effects, can be applied in a more wide range of angles and positions and comes perfectly regulated for coagulation or cut. Its coagulation capacities reduce the need of bipolar forceps, so the changing of instruments gets reduced. It makes a good surgical partner to the ultrasonic aspiration device, to achieve proper debulking. In short, it is a complement to the usual instruments that offers several possibilities. Indeed, cost-effectiveness for the medical institution is favorable, as is not a very expensive tool and can be employed by several specialties.

As shown by previous studies, it causes very limited tissue penetration (around 2 mm maximum), with a cleaner and more precise cut than bipolar forceps. This is also superior to previous laser devices. The lesion that it causes can be stratified into three main areas: (a) central area or microsurgical crater, (b) honeycomb zone originated by the vaporization of cells, and (c) shrunken zone consisting of cells with pyknotic nucleus. Interestingly, the depth of the crater varied from 0.8 mm (6 W) to 1.2 mm (12 W), and in all three layers, there were no areas of microhemorrhage, confirming the focused coagulative power of the device. An in vivo study on murine brain performed by Katta et al. (12) highlighted how the use of 15-W thulium fiber laser allowed sharper bloodless cutting, both linear and curvilinear, with a thermal injury less than 100 µm and a removal rate of around 5 mm³.

As mentioned, lasers have been used in neurosurgery for different purposes. Third ventriculostomy has been performed by some groups in big series with optimal results and no damage to the basilar and related arteries (7, 9). However, for this purpose, the power should be limited to 4 W. The use of a 2-µm thulium laser has also been developed in vestibular neurinoma surgery by our group, being especially suitable for capsule opening (“V cut”), central debulking, and internal auditory canal opening. That accounts mainly for the large ones (Koos grades III and IV) and those with a cystic necrotic component, characterized by abnormal hypervascularization (8, 13, 14). Passacantilli et al. reported a 20-patients series of meningioma operated with this specific laser (10, 15, 16). Otherwise, some other laser models are currently being investigated for neurosurgical procedures, such as the 980-nm diode laser and the thulium-doped yttrium aluminum perovskite (Tm:YAP) crystal laser (17, 18). Colasanti et al. show the appliance of a modern CO₂ laser in a variety of cases (19). As we found it more useful for hard or fibrous tissues, this group interestingly has applied laser to pial opening and final excisional bed coagulation among other surgical steps.

In our series, which comes from 2014 to 2021, we have a high representation of posterior fossa meningiomas (40 out of 75 cases). Particular attention is paid for uses arising from the tentorium (20). Some of them present as occupying the pontocerebellar angle, as the T6-T7 type [according to the classification of Yasargil modified by Al-Mefty (21)], and thus presenting symptomatology characterized by hypoacusia, tinnitus, and vertigo. Other meningiomas with subtentorial development mimicking CPA lesions are those involving the foramen lacerum, superior and inferior petrosal sinuses, sigmoid–transverse junction, and the inner dura of the acoustic porus. In those cases, a retrosigmoid or lateral suboccipital approach is usually indicated. Importantly, it is mandatory to avoid injury to the capital surrounding structures (SCA, AICA, PICA, V to XII cranial nerves), and limit the traction on brainstem structures, which could cause inadvertent microvascular disruption and major morbidity.

As a group with a broad experience in CPA tumors, we have observed that, as well as for vestibular schwannomas, the use of this laser in tentorial, CPA, and petroclival meningioma is favorable to the aforementioned objectives. We used 2-µm thulium laser under microscopic guidance: It allowed a precise cut to demarcate the area within the capsule and continue with the intralesional debulking, allowing the coagulation of microhemorrhagic spots resulting from an intraoperative break of neoangiogenic bed, thus facilitated dissection of the capsule without thermal energy transfer in nearby nerves.

In this series, that constitute the biggest in literature with 75 patients, the use of a handheld flexible thulium laser has been proved as a safe and helpful instrument for meningioma resection. In particular, we appreciated the use of a handheld flexible laser fiber appeared to be safe and easy to handle. We concluded that thulium laser does not suppose a particular risk for healthy brain or neurovascular structures around the working space. Power regulation allowed us to regulate intensity according to the particular moment requirements.

We could establish that, in our series, the degree of resection and neurological outcome were not different from previous series (20). Our impression is that handheld thulium laser fiber shortens and facilitates the duration of the steps where it is involved. Consequently, expertise in using the 2-μm thulium laser may lead to better results and shorter interventions.

Our study has several limitations: It is a longitudinal study based on a retrospective cohort and performs a descriptive analysis of the patients. Further randomized studies with a control group about surgical time, blood loss, and neurological outcome will have to be performed in the future. Also, the expansion of this laser's fields of applications (as, for instance, soft tissue dissection or different tumors, or for endonasal skull base surgery) should be explored. What is certain is that, if properly considered, many groups will progressively find different utilities for it in neurosurgery.

Intracranial meningiomas can represent a neurosurgical challenge because of several factors such as their source site, the region toward which they extend, their more or less vascularized pattern, and the relationships with delicate neurovascular structures. As found in this retrospective study, the 2-μm thulium laser has proven to be a safe and useful assistant to the surgery, especially in complex cases. It has allowed us to perfect the dissection techniques and microsurgical exeresis, ensuring excellent control of bleeding and avoiding any harmful dispersion of thermal energy into the surrounding healthy tissues. Consequently, we deem it very useful and will continue to work with it.