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Cappabianca et al. Mini-invasive Surg 2020;4:83 I http://dx.doi.org/10.20517/2574-1225.2020.67 Page 3 of 11

impossible, especially in the attempt of minimizing morbidity related to the traits of the tumors [2,4,7,17,18] .
Nonetheless, tumor recurrence can occur, even with radical tumor removal and after long time from
the primary surgery [21-23] . For these reasons, treatment has moved toward more conservative surgical
strategies for meningiomas, opting for a maximum allowed resection, minimizing risks for the neurological
functional status, followed by strict imaging surveillance and eventual adjuvant therapies. This attitude
shift, supported by a conspicuous amount of data demonstrating that tumor recurrence is a function of
tumor biology, have questioned the clinical use of the Simpson grading score [24-28] . This latter, indeed, has
shown a prognostic value not suitable for all meningioma locations, achieving lesser prognostic impact for
skull base and spinal meningiomas as compared to convexity tumors. Furthermore, the histological grade
has recently been related to the location, and it has been observed that there is evidence of higher-grade
meningiomas at hemispheric/convexity locations. This has to be taken into account when considering
surgery for those tumors, which might feature favorable prognostic correlation between location and
regrowth.

The ideal surgical approach should allow for maximum extent of resection, i.e., tumor mass removal in
addition to infiltrated dura and bone, while minimizing the risk of morbidity. The choice of the most
appropriate approach greatly depends on the anatomic features of the meningioma, its relationship with
critical neurovascular structures, and the site of dural attachment.

Although the role of surgery for meningiomas might appear to be fairly standardized, class I scientific
[16]
evidence is uncommon and surgical indications are mainly defined by experience-based practice : the
surgical management of a meningioma, indeed, should be tailored upon its nature, symptomatology,
patients’ characteristics, and risk of morbidity. The observational management for asymptomatic,
[7]
incidentally discovered meningiomas has been validated by many retrospective series and reviews ,
while surgery is the main choice in cases of radiologically confirmed growth or in the presence of clinical
symptoms. In the case of elderly patients and when lesions involve eloquent areas or deep and complex
regions such as the cavernous sinus, radiotherapy can be considered as first-line treatment according to
tumor size and signs [16,29] .

Finally, in the case of spinal meningiomas, the negligible benefits of an aggressive surgical strategy -
that includes a wide removal of the dural attachment - do not seem to outweigh the risk of surgical
complications and patients’ morbidity, especially for ventrally located meningiomas or with calcified dural
attachment [23,28,30] .

Meningioma surgery was revolutionized in the 1960s by the advent of the use of the operating microscope:
the advancement of microsurgical techniques brought terrific improvement in terms of outcomes and
definitely opened the era of modern neurosurgery [31-33] . A new level of precision in the surgical removal
of tumors, particularly skull base meningiomas, was reached and novel surgical routes have been
experimented, with emphasis on a deep understanding of anatomy [34,35] . Subsequently, further enthusiasm
was brought by the advent of the endoscope in the late 1990s [36-39] . The intrinsic optical properties of the
endoscope, allowing for a wide and close-up view of the surgical field, added extra value to the safety of
meningiomas surgical treatment, either as unique visualization tool or as an adjunct to the microscope.

The evolution of the surgical techniques and visualization tools moved along together with instrument
development and technological advancements. From the bayonet-shaped instruments used for
microsurgical approaches where the lens of the microscope is far from the surgical field, the endoscopic
technique requires straight instruments that slide along the endoscope, whose lens is near the surgical
target [40,41] . Today’s visualization tools are upgraded with sophisticated imaging technologies that
enhance the capabilities to better identify the tumor-vessels interface, such as infrared technology,