Manual Instruments as an Alternative to Drilling for Bony Exposure in Skull Base Surgery: Concept and Technique

Abstract

Background  Drilling in neurosurgery is an integral part of surgical exposure, especially in skull base approaches and craniovertebral junction (CVJ) surgeries. Most of such drillings are done in close proximity to the neurovascular structures in skull base surgeries and cervical-medullary junction or facet/pedicle in CVJ surgeries. Reluctance to drilling among young neurosurgeons is due to less hands-on experience during training and also, in the early part of the career, due to fear of injury to neurovascular structures.

Methods  Five commonest bone removals for skull base region and CVJ surgeries that can be safely done using manual instruments were identified based on experiences of senior authors. The authors highlight key technical nuances to widen surgical corridors using manual instruments safely for skull base surgical approaches.

Results  Basic neuroanatomical concepts and basic physics help in using manual instruments safely for bone removals in various skull base surgical approaches.

Conclusions  Manual instruments may be used for bone removals in selected skull base surgical approaches, which help young neurosurgeons to perform these surgeries in limited-resource settings.

Introduction

Drilling in neurosurgery is being used mainly for skull base surgery, especially for vascular lesions such as aneurysms and neoplastic lesions of the skull base and spine including craniovertebral junction (CVJ). ^{1 2} The commonest regions of drilling include the sphenoid ridge, anterior and posterior clinoids, petrous bone (anterior or posterior), occipitomastoid region over transverse/sigmoid sinuses, internal auditory meatus (IAM) in acoustic schwannoma, and C1–C2 joint space for CVJ surgeries. Recently, drilling is being used very frequently for standard and extended endoscopic surgeries for sellar/suprasellar and parasellar lesions, respectively. ³ In 1895, the first portable handheld drill was created by brothers Wilhelm and Carl Fein of Stuttgart, Germany, ⁴ and in 1917 the first trigger-switch was invented; pistol-grip portable drill was patented by Black and Decker. ⁵ This was the start of the modern drill era. Over the last century, drill equipment and also their attachments have evolved, which have allowed their use even in earlier “difficult-to-access” regions safely. ⁶ Ultrasonic bone scalpel and bone aspirators too are being used in neurosurgery for osteotomies and bone work in deeper locations. ^{7 8} The literature suggests that both drill and bone scalpel have their own set of complications. ^{9 10 11 12 13} Usually, drilling in the skull base surgical approaches is done only by senior neurosurgeons and rarely a trainee or young neurosurgeon gets sufficient hands-on practice for drilling. ¹⁴ This leads to fear of damage to neurovascular structures in the minds of young neurosurgeons and most often they do surgeries without sufficient bony exposures resulting in inadequate surgical corridor. As opposed to experienced neurosurgeons, young neurosurgeons need wider surgical corridors, due to not so steady hands and limited experience to maneuver surgical instruments in deep and narrow surgical corridors. ^{14 15} There are reports of anterior clinoidectomy without use of high-speed drill, but detailed technique of anterior clinoidectomy without drill, which actually is a mechanical thing, has never been discussed in detail. ¹⁶

The authors highlight key technical points to use manual instruments for bony exposures (without high-speed drill), especially in selected surgical approaches of skull base surgeries, to widen surgical corridors even in deep and narrow surgical corridors, which may help young neurosurgeons and those working in the settings of limited resources, especially in low- and middle-income countries (LMICs), to perform these surgeries safely.

Technique

Bony removals in neurosurgery in addition to craniotomies are done to enhance surgical access and exposure. The authors selected the following five commonest surgical approaches where bony removals in neurosurgery may be done without high-speed drill:

• Joint preparation in CVJ surgeries for fusion with or without fixation.

• Osteotomies for skull base approaches.

• Removal of bone in retromastoid approaches for cerebellopontine angle (CPA) lesions:

  • – Occipitomastoid bone over sigmoid sinus.

  • – Posterior lip of IAM in surgery for acoustic schwannomas.

• Extradural anterior clinoidectomy for skull base approaches.

• Floor of sphenoid sinus and sella in transsphenoidal surgeries.

Joint Preparation in CVJ Surgery for Fusion with or without Fixation

All joints of spine (including CVJ) have facet joints and intervertebral joints (which contain intervertebral discs and other ligaments). There is a distinct plane between bone of the vertebra and other structural components of the joint such as joint capsule, end plate cartilage, or similar structures (longitudinal ligaments, annulus fibrosus, nucleus pulposus). It is always feasible to dissect all joint structures from the bone of the vertebra if the plane of the dissection is accurate ( Fig. 1 ) and can be done with the help of sharp instrument in the beginning followed by separating the plane by using appropriate sharp or blunt instrument. Facet joint preparation of C1–C2 joint ( Fig. 2 ) or disc space preparation in cervical ( Fig. 3 ) or other spine levels can be done using sharp instruments such as blade/chisel to remove these nonbony joint structures to help prepare the joint spaces for fusion. One needs to use appropriate size of the blade (surgical blade number 11 or 15) in C1–C2 joint or disc spaces of other spine levels. Sharp chisel of appropriate size is equally capable of doing the job. It is important to select low-profile chisels of different lengths, thicknesses, and widths per available space for dissection. Most commonly, 2- to 3-mm-thick, 3- to 7-mm-wide, and 15- to 25-mm-long chisels are appropriate according to joint spaces available. Smooth bend of 10- to 15-mm distal end to approximately 20 degrees is quite useful for dissection as it allows the surgeon to see the dissection plane without difficulty due to the shaft of the chisel ( Fig. 2a, 2b and 2c ). Using dissection in anatomical plane is always better than drilling, mainly because drilling can never be as uniform as the existing anatomical plane and is bound to either incompletely remove of nonosseous tissue of joint structures or remove more of the actual bone of the vertebra, either of which is not required.

Fig. 1.

(a) Anterior view of cadaveric C5–C6 disc space dissection using a curved chisel to dissect bone from other structures with a well-defined plane. (b) Right C1–C2 joint space dissection showing partially dissected bone of C2 superior articular surface from other joint capsule structures. (c) Anterior view of C5–C6 vertebral body during C5–C6 anterior discectomy showing separation of all joint/disc structures from inferior surface of C5 vertebral body using a sharp chisel.

Fig. 2.

Sharp chisels of 4-mm (middle) and 5-mm (on both sides) width (a) with distal 10- to 15-mm curved ends ( b ) of 5-mm chisels (on both sides in the image), so that vision is not interfered while using. Chisel lengths are around 15 to 25 cm (c) .

Fig. 3.

Right inferior (a) and right superior (b) views of the right side of the skull with frontotemporal craniotomy showing inferior (a) and superior (b) surfaces of right orbital roof with marked ( arrows ) portions where a chisel is used to break it for passage of Gigli wires from inferior aspect to the surface burr holes of craniotomy (c) . Left anteroinferior view of postoperative three-dimensional volume rendering of CT scan showing cuts ( arrows ) over the orbital rim of frontotemporal craniotomy with modified orbitozygomatic osteotomy using a chisel and Gigli wire. Miniplates, used for rigid fixation of the bone flap, too are visible.

Osteotomies for Skull Base Approaches

Osteotomies in the form of orbitozygomatic (OZ) osteotomy, either standard or modified, and lateral or median orbital osteotomies are the commonest, which are used for middle and anterior skull base surgeries, respectively. Oscillating saw attachment, of the high-speed drill or bone scalpel, is used for these purposes nowadays. Gigli saw wire, instead of the equipment, can be used if one can make a hole in the orbital roof by chisel from inferior aspect ( Fig. 3–c ) through which Gigli wire can be passed to either burr hole made over the convexity of the skull or the cut edge of the convexity bone flap near the osteotomy margin (for single-piece craniotomy and osteotomy) ( Fig. 3c ). Safeguarding periorbita or muscle adjacent to the orbit or zygoma, respectively, is required by either chisel or drill/bone scalpel by using flat spatula or retractor ( Fig. 3c ).

Removal of Bone in Retromastoid Approaches for CPA Lesions

Occipitomastoid Bone over Sigmoid Sinus

Retromastoid craniotomy or craniectomy is the workhorse for the lesions in the CPA region. Exposing sigmoid sinus partially or fully provides 5 to 8 mm (average width of the sigmoid sinus) ( Fig. 4a ) more lateral angle of view into CPA region merely by pulling the stay sutures laterally perpendicular to the course of the sinus after dural opening parallel to the sigmoid sinus. It can be done with the help of chisel by gradually removing thin pieces of bone from over the surface. It is important to keep slanting edge of the chisel parallel to the surface of the bone to safeguard against injury to the sigmoid sinus ( Fig. 4a ). Once bone overlying the sinus becomes too thin, it can be separated using blunt dissectors and removed using nibblers or Kerrison punches. Another technique is to make a groove lateral to the sigmoid sinus over mastoid air cells using sharp chisels followed by using nibblers to gradually remove the bone overlying the sigmoid sinus ( Fig. 4a, b ). Principles of bone removal remain the same as used for drilling, which is making the overlying bone as thin as possible (egg-shelling), so that it can be removed safely by nibblers or Kerrison punches ( Fig. 4a, b ).

Fig. 4.

Line diagram of axial view of the sigmoid sinus (ss) (a) with corresponding cadaver image (b) showing overlying occipitomastoid bone, which can be thinned by using a chisel with slanting edge inferiorly (toward dura) (upper image of a and horizontal arrow in b). It can also be done by making a groove over mastoid bone by chisels lateral and parallel to the sigmoid sinus (lower image of a and vertical arrow in b). Once the groove is made, bone overlying the sigmoid sinus can be gradually removed using nibblers.

Posterior Lip of the Internal Auditory Canal

The usual distance of dura over sigmoid sinus to the internal auditory canal (IAC) is 35 to 45 mm ( Fig. 5a ) and the bone of the posterior lip of the IAC makes an angle of less than 90 degrees ( Fig. 5b ), which can be removed using Kerrison punch of 1 or 2 mm. Cauterization and curvilinear elevation of dural flap over the IAC is done as it is done before drilling ( Fig. 5c ). The posterior lip of the IAC can be removed bit by bit using standard Kerrison punches (up cutting, 90-degree angle). It is usually feasible to remove 4 to 5 mm of the posterior lip of the IAC using standard Kerrison punches alone ( Fig. 5b ). However, Foraminotomy Kerrison (which has forward-angled distal end) with thin foot plate ( Fig. 5d ) can be used to remove additional 1 to 2 mm of the posterior lip of the IAM, which usually is sufficient to decompress the meatal part of the schwannoma to identify the facial nerve anterosuperiorly in the IAM. It is pertinent to mention that partial decompression of the lesion at the introitus of the IAM should be done to avoid pressure injury to the facial nerve by inserting foot plate of the Kerrison punch. It allows identification and preservation of the facial nerve and removal of the schwannoma. However, per current trend, one should leave part of the lesion if it is adhered to the facial nerve and further dissection seems to compromise its function (physiologically).

Fig. 5.

(a) Cadaver specimen of the right-sided posterior fossa dura showing distance between surface dura over sigmoid sinus and internal auditory meatus. (b) Axial section of bone window of computed tomography (CT) scan of the right-sided IAC with line diagram of Kerrison punch representing feasibility of removal of posterior lip of IAC. (c) Superior view of cadaveric specimen of the right-sided IAC showing exposure of bone needed lateral to the IAC ( arrow ), before bony removal. (d) Foraminotomy Kerrison punch with thin foot plate, which has a forward-angled distal end, which is helpful in removing additional 2 mm of posterior lip of IAC.

Extradural Anterior Clinoidectomy for Skull Base Approaches

The anterior clinoid lies in close proximity to the optic, oculomotor, trochlear, and ophthalmic cranial nerves and internal carotid and ophthalmic arteries. It is connected to the sphenoid ridge laterally, the orbital roof medially, and the optic strut inferiorly. One needs to remove two bony attachments, lateral (sphenoid ridge) and superomedial (roof of the optic canal), so that it can be removed safely and easily. Removal of the sphenoid ridge is a routine process done by the neurosurgeons. The anterior clinoid, which is practically the medial extension of the sphenoid ridge, can be safely removed by manual instruments by adopting the following steps:

• Step 1 : Free margin of the orbital roof to be prepared by OZ (either standard or modified) osteotomy. It allows Lempert's micronibbler ( Fig. 6a ) or any similar micronibbler to hold the free bony margin of the orbital roof to be caught between its jaws. Gradual removal of the orbital roof is to be done till the roof of the optic nerve is removed. The optic nerve can be identified as continuation of the basifrontal dura continuing to the orbital apex ( Fig. 6b ). Division of meningo-orbital band may be required for proper exposure of the bone in the deep aspect of the orbital roof. If OZ osteotomy is not done, a small part of the roof just deep to the orbital rim may be broken using chisel to get free edge of the orbital roof so that it can be held between the jaws of the nibblers to remove the orbital roof till the optic nerve roof. One must not use Kerrison punch in the optic canal, as it will lead to compression of the optic nerve. Micronibbler's jaws are used to hold the bony edges over the optic nerve only without actually putting any pressure on the optic nerve to remove the roof of the optic foramen.

• Step 2 : The anterior aspect of the temporal bone along with the sphenoid ridge is removed gradually with the help of nibblers toward the deroofed optic nerve and superior orbital fissure. This step cannot be done without dividing meningo-orbital band. The end point of this step is to remove the lateral border of the superior orbital fissure, where temporal polar dura will appear entering into the orbit ( Figure 6b ).

• Step 3 : After completion of the above-mentioned two steps, the anterior clinoid is left attached to the optic strut only but its tip remains hidden in the cavernous sinus. The third and most critical step is to mobilize temporal polar dura posteriorly (peeling off) from lateral wall of the cavernous sinus to expose parts of V1 and V2 nerves entering into the superior orbital fissure (Dolenc's technique), ¹⁷ which exposes tip of the anterior clinoid completely ( Fig. 6c ). Venous bleeding from the cavernous sinus can be taken care of by using fibrin glue, gelatin/thrombin compound (Surgiflo or Floseal), or oxidized cellulose (preferably fibrillar type). Oxidized cellulose may be used instead of cottonoids to separate the tip of the anterior clinoid from the dura and other structures (including cavernous part of the internal carotid artery [ICA]). Gentle retraction of the orbit inferiorly or stay sutures over perisylvian dural folds to retract it superiorly helps to expose the anterior clinoid better. At this stage, micronibbler is used to remove the anterior clinoid bit by bit without twisting or pulling ( Fig. 6d ). Evaluation of preoperative imaging studies especially presence of middle clinoid is important, in which case only removal of the body is done and the tip has to be left as it continues as middle clinoid. ¹⁸

Fig. 6.

Intraoperative images of extradural right anterior clinoidectomy using micronibbler (Lempert's nibbler). (a) Removal of the right orbital roof with deroofing of the right optic nerve ( arrow ). (b) Removal of the right sphenoid ridge along with removal of anteromedial temporal base till removal of the lateral wall of the superior orbital fissure ( arrow ). (c) Right temporal polar dura mobilized posteriorly off the cavernous sinus (Dolenc's technique) to clearly expose the optic nerve (Optic N); the tip of the anterior clinoid (Ant. Clinoid) shown by arrows. Right V1 and V2 ( arrows ) are also exposed while doing it, which are visible. (d) Last bit of the anterior clinoid is being removed bit by bit using micronibbler.

Floor of Sphenoid Sinus and Sella in Transsphenoidal Surgeries

Removal of the sphenoid sinus floor is usually done using the Kerrison punch, starting from openings of the sphenoid sinuses on both the sides. Midline bone of the roof, which is attached to the keel of vomer, can be broken easily with the help of blunt dissectors, or, if it is thick, microchisel available in the pituitary set does the job satisfactorily ( Fig. 7a ). Sellar floor is usually thinned out in most of the space-occupying lesions of sella and can be broken using blunt dissectors. Even if it is thick, gentle strokes of the microchisel to make a hole on the floor to negotiate foot of the 1-mm Kerrison punch is quite easy ( Fig. 7b ). One has to know the patient's specific anatomy beforehand and must be aware of the locations of the septa within the sphenoid sinus. ^{18 19 20 21} More often than not, either of the septa goes superiorly or inferiorly to the cavernous part of the ICA. Lateral wall of the sphenoid sinus too are not covered at places by bony wall and it is better to palpate before trying to remove bone on the extreme lateral aspects of the sellar floor. Using the foot of the Kerrison as hook to remove lateral part of the floor is safer than trying to bite it. Additionally, instead of keeping the foot of the Kerrison punch exactly lateral (3 o'clock or 9 o'clock position), it is better to keep the direction of the foot oblique (10 or 11 o'clock or 7 or 8 o'clock position on the left side and 1 to 2 o'clock or 4 to 5 o'clock position on the right side) and then to use it to remove it under direct vision (of endoscope). One can use blunt hooks to palpate the space between the dura and bone for additional safety. If the lateral wall is deficient at some place, it may be used to create a plane between the medial wall of the cavernous sinus and the bone of the lateral wall of the sella and then remove it by pushing it medially to break it. Dural opening should be started from midline and then followed laterally. It is important to recognize that distal most part of the ICAs is fixed to the dura by proximal and distal dural rings and one has to be extra cautious while working in those areas (10 o'clock and 2 o'clock positions). Except at the dural rings, the dura is not attached to the ICAs and therefore one can see by lifting the dura before cutting it toward the lateral extremes. Conventional surgical approach to the sellar/suprasellar lesions can be done easily with the help of manual instruments only. However, drill is required for extended transsphenoidal surgeries. The authors have found that even conchal sphenoid sinus, sharp chisel in the midline and long straight curettes for the lateral part, can be used safely to expose sellar floor, in which case all the bone within the sella is cancellous bone (dark brownish) and soft ( Fig. 7c ), except cortical bone just superficial to the sellar dura, which can easily be identified by its color (yellowish white like cortical bone) ( Fig. 7d ).

Fig. 7.

Endoscope-assisted transnasal transsphenoidal approach for sellar lesion. (a) Two horizontal cuts made by a chisel over the floor of the sphenoid sinus for its removal. (b) Sellar floor is being removed using Kerrison punch with exposed sellar dura. (c) Conchal type of sphenoid, where a sharp chisel is being used as a curette to remove the soft spongy cancellous bone ( brownish colored ). (d) Cortical ( whitish ) bone of sellar floor exposed using a sharp chisel and curette by gradual removal of cancellous bone of conchal sphenoid.

Discussion

Manual instruments were being used for neurosurgery for centuries and actually dates back to the Neolithic age. ^{1 22} Microneurosurgery, propagated by Yasargil and practiced now around the world, actually did not give much importance to the drilling as is being given to it now. ²³ Use of high-speed drills is relatively a new phenomenon over the last two decades and now slowly and progressively replacing manual instruments to such an extent that maybe after a decade or so, it will be difficult to find manual instruments for bone work in neurosurgery. ^{24 25} However, despite tremendous developments in the techniques and technologies in neurosurgery, access to even basic neurosurgical services in the LMICs is still dismal. ²⁶ Cost of these high-speed drill equipment and their consumables are more than 100 times the cost of the manual instruments for performing the same job. ²⁷ An example of it is disappearance of stainless steel (SS) spine implants from the market for more than a decade, replaced by titanium implants, which are approximately 50 to 100 times costlier than SS implants. ^{28 29} Its implications on patients affordability in LMICs, where most of the cost is born by the patients as out-of-pocket expenditure of health care services, is usually 65 to 85%. ^30-31 Interestingly, significant numbers of patients never undergo magnetic resonance imaging (MRI) study in their lifetime, as MRI compatibility is one of the most important considerations in favor of titanium implants. Market/industry works on profit and their interest is better taken care of by high-end sophisticated instruments and equipment. ²⁴ Lots of neurosurgeons in LMICs, especially in tier 2 or tier 3 cities, work in financially constrained situations, which do affect patient care. ^{32 33 34} These are highly unattended issues mainly because those working in such circumstances have practically no say in modern rapidly advancing neurosurgical world where neurosurgical care is getting costlier at a fast pace. The authors intend to highlight that manual instruments are still capable of performing most of the so-called bone works required in advanced skull base surgical approaches, where otherwise drill is considered necessary or at least equipment manufacturers are trying to create an impression similar to this. The authors feel that clinical skills and thorough knowledge of the patient specific neuroanatomy is more important than the advanced equipment including drill itself for bone work in skull base surgeries or many other surgeries where drill is considered mandatory. Most of the trainees, working at well-equipped institutions, especially in the LMICs, need to work after completion of their trainings at centers, where facilities are limited and it is not feasible to bear the cost of the high-speed drill and their consumables. Lack of training of using manual instruments such as Hudson brace, Gigli wires, chisels, osteotomes, nibblers, and Kerrison punches makes lots of trained neurosurgeons unable to work at resource-scarce centers. ²⁴ The authors feel that, over the last decade, the use of manual instruments for craniotomies has decreased and the procedures are done using only power tools (pneumatic/electrical) at majority of tertiary care institutions where neurosurgical training is given. We feel that even if equipment market is driving increasing use of high-speed drills in neurosurgery, neurosurgical community should understand that it will be premature to do away with the training of using manual instruments in neurosurgery. ^{32 33 34}

Of nearly 125 centers in India, where neurosurgical services are provided, only 10 to 12 have access to cadaver dissection facility. ^{32 33} With approximately 350 to 400 neurosurgical trainees passing out every year, most of them work in tier 2 or tier 3 cities where only basic neurosurgical facilities are available and many of them do not have even operating microscope or drill. ^{34 35} Cadaver dissection courses organized in various scientific conferences/meetings for 1 to 2 days are insufficient for proper training for young neurosurgeons, as the authors believe that attending such cadaver dissection workshops do help them understand neuroanatomy to some extent but are insufficient for surgical training, for which it should be a regular and integral part of neurosurgical training. Unfortunately, a neurosurgeon working at a tertiary care hospital or well-equipped intuitions is unaware of challenges faced by neurosurgeons working at poorly equipped neurosurgical center. Providing the best possible neurosurgical services with available facilities can help most of the patients living at smaller places to have access to neurosurgical services, who often fail to travel to distant places due to various reasons, the most important of which is usually financial implications. ^{34 35 36}

Manual instruments work on basic physics principles and one should analyze the act of bone work required at the deep-seated surgical corridors. Humans are most proficient in using their hands mainly because use of hand starts even before birth (intrauterine stage). ³⁷ Using hands in combination with some foot-controlled equipment to perform an act needs greater coordination and will always be more difficult than using hand instruments alone. Drilling needs lot of practice to become proficient to actually use it on the patients safely. It will be better for both the trainee and young neurosurgeon to start using manual/hand instruments to start with and then gradually shift to the drills after some experience, not the opposite, which is the modern trend. This is the responsibility of the experienced neurosurgeons working at well-equipped centers to explain and propagate detailed technical nuances of using manual instruments, which will help in increasing access to neurosurgical care at large part of the world where people struggle to get even basic neurosurgical services. ^{26 34 35 36}

A chisel has two surfaces, one flat and another slanting. A vertical tap on the top of the chisel will cut the bone toward an angle of slanting edge, whereas an osteotome will always cut in the direction of the tap over its head. This property of chisel is utilized by wood workers or designers and the same principle can be utilized for bone work too. Similarly, making 15- to 20-mm distal segment of an osteotome angled to 15 to 20 degrees will make it work like a chisel mainly due to change in the cut produced after a tap over its top. Thin superficial layers of surface bone can be shaved off bit by bit by using low-profile long chisels in deep locations if one is aware of the patient's specific anatomy. The authors use this principle to expose sigmoid sinus with the help of manual instruments alone. Similarly, appropriate-sized chisel or curved osteotomes can be used to change the bone morphology, so that manual instruments such as nibblers or Kerrison punches work where otherwise these do not work. A Kerrison punch or nibbler does not work to expose sigmoid sinus mainly because after removing bone laterally up to the medial edge of the sigmoid sinus, the bone overlying it is too thick and its medial surface is obtuse so that neither of these instruments is able to hold the bone between their jaws. Creating a gutter beyond (lateral to) sigmoid sinus over the mastoid air cells, which is a safe region, nibblers can easily hold the bone between free medial edge of occipitomastoid bone and medial edge of the gutter created by the chisel. This allows one to gradually remove the bone to expose the sigmoid sinus safely. ^{38 39 40} The authors have been using manual instruments for exposing part transverse/sigmoid sinus for retromastoid approaches for more than 6 years with no difference in complications related to sinus injury or postoperative thrombosis. ⁴¹

The posterior lip of the IAM has an acute angle (less than 90 degrees) and can always be removed using thin foot plate of the Kerrison punch. A Foraminotomy Kerrison has long bayoneted shaft with thinned foot plate and can be used safely to do the job that is done by the drill. However, it is important to partially decompress the lesion at the introitus of the IAM so that inserting foot plate of the Kerrison punch does not exert pressure over the facial nerve. This technique usually is able to remove 5 to 7 mm of the posterior lip of the IAM, which provide space to decompress intrameatal part of the lesion and identify the facial nerve. Identification of the facial nerve is the most important step to safely preserve it in acoustic schwannoma surgeries.

Removal of the anterior clinoid is a key surgical step. A young neurosurgeon should do it routinely to expand surgical corridor whenever one needs to use interoptic, opticocarotid, and retrocarotid spaces for sellar, suprasellar, and parasellar lesions. It is also quite useful for transcavernous approaches for petroclival lesions such as meningiomas and vascular lesions such as aneurysms of the cavernous and pararclinoid ICA and basilar top aneurysms. ^{42 43 44} The authors feel that a young neurosurgeon needs wider surgical corridors, especially in deep locations, mainly because they have difficulty in maneuvering instruments in narrow corridors and do not have their hands as steady as the experienced neurosurgeons. The key point is to expose the anterior clinoid including its tip properly. It needs thorough knowledge of the anatomy of this location and following surgical steps as described. Once exposed properly, one can use appropriate manual instruments and remove it safely and easily. Barring one report by Chang, ¹⁶ most of the literature and lectures/videos available online give the impression that these bone works can only be done using high-speed drill, which is not true and makes young neurosurgeons and neurosurgeons working at limited-resource centers hesitant to use this important step to make their surgeries easier. Manual instruments alone (no drill technique) have been mentioned in the literature. ¹⁶ The anterior clinoid lies between the optic nerve and V1 in the superior orbital fissure and removing bone on both sides of the anterior clinoid. Proper exposure of the anterior clinoid is the key point in exposing it completely in the surgical field by mobilizing (peeling off) temporal pole dura from the V1 and V2 in the cavernous sinus. The authors do anterior clinoidectomy without drill routinely for various pathologies, where it is indicated with the help of micronibblers, and have faced no difficulty. Cavernous sinus bleeding, while peeling of temporal dura and after removing the anterior clinoid, is easily controlled by oxidized cellulose, flowable sealants, or fibrin glue.

Manual instruments were routinely used for transsphenoidal surgeries; however, recently high-speed drills are used more in cases where standard pituitary chisel and hammer, Kerrison punches, and curettes were being used initially and usually are sufficient except for extended transsphenoidal approaches. ^{21 45 46} The authors do understand that high-speed drills are an important equipment for neurosurgery and reduce operative times; however, most of the advanced microneurosurgical procedures can be safely done with the help of manual instruments. ⁶ There are bone works required in few surgeries such as extended transsphenoidal surgeries, translabyrinthine approaches, and Kawase's approach where the role of drill is important. ^{47 48 49}

We conclude that manual instruments are effective to perform most of the microneurosurgical procedures. Strong concepts of neuroanatomy and fundamentals of mechanism of actions of manual instruments are important to keep basic surgical techniques of using manual instruments alive, so that microneurosurgical skills can propagate even at centers of developing countries where resources are limited.

Authors' Contributions.

	Author
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Clinical studies	√	√	√	√	√	√	√	√	√	√
Data acquisition	√	√	√	√	√	√	√	√	√	√
Data analysis	√	√	−	−	−	−	−	−	−	−
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The manuscript has been read and approved by all the authors, the requirements for authorship as stated earlier in this document have been met, and each author believes that the manuscript represents honest work.