A variety of standard microsurgical approaches and techniques have been developed over decades to deal with anterior skull base pathologies. The most feared complication of anterior cranial base surgery is vascular injury and its consequences. This chapter provides an overview of relevant surgical anatomy of the anterior skull base, common anterior, and anterolateral skull base approaches, pathologies involving anterior cranial base vasculature, relevant vascular challenges, common vascular complications, and microsurgical techniques to avoid such complications.
Key wordsVascular – skull base – anterior – complications – tumor
12 Vascular Challenges in Anterior Skull Base Open Surgery
I profess to learn and to teach anatomy not from books but from dissections, not from the tenets of philosophers but from the fabric of nature. William Harvey (De Motu Cordis, 1628)
12.1 Key Learning Points
Among the various microsurgical approaches, the common approaches which help in the surgical management of anterior cranial base lesions are transbasal, frontotemporal, and transsphenoidal approaches.
Vascular complications are the most feared complications in anterior skull base surgery and include both arterial and venous (channels/sinus) complications.
Vascular complications may manifest via hemorrhage, vasospasm, embolism or thrombosis, pseudoaneurysm, or vessel stenosis.
The selection of the ideal approach is the most crucial step in anterior skull base surgery.
The anterior cerebral artery (ACA), its branches, and the anterior communicating artery (AComA) complex are often involved in anterior skull base and suprasellar tumors.
The incidence of internal carotid artery (ICA) injury during transsphenoidal surgery varies from 0.2 to 2%.
Anatomic proximity, tumor infiltration, surgical error, prior radiotherapy, inadequate preoperative imaging or interventions like cerebral angiogram or embolization, and suboptimal use of neurosurgical adjuncts such as neuronavigation or micro-Doppler are common reasons for vascular injury.
The indications for surgery should be clear, surgical strategies must be tailored according to the pathology, and goals of surgery well-defined.
Avoiding direct injury to the brain and vessels involves the use of surgical adjuncts, adequate exposure via skull base approach, minimal brain retraction, and optimum brain relaxation.
Internal debulking of tumor and bimanual, extracapsular dissection are among the most important microneurosurgical techniques to avoid devastating vascular complications.
Careful patient selection, meticulous preoperative planning, proper understanding of the regional anatomy, firsthand radiological knowledge of anatomical variations, safe handling of critical neurovascular structures, intraoperative anticipation of vascular injury, and strict postoperative surveillance are the keys to avoid such complications and achieve the best overall outcome.
Skull base approaches are designed to expose and treat complex skull base pathologies optimally while reducing the extent of retraction and manipulation of normal neurovascular structures. A complete understanding of the complex vascular anatomy of the anterior skull base is crucial prior to attempting surgical treatment of any vascular or skull base pathologies in this region. The anterior approaches to the skull base include transsphenoidal, transbasal or extended transbasal, transmaxillary or extended transmaxillary, and transoral approaches. The anterolateral approaches include frontotemporal orbitozygomatic, subtemporal transzygomatic and preauricular subtemporal-infratemporal approaches. The major complications arising out of skull base surgeries are vascular injury, cranial nerve injury, brainstem damage, cerebrospinal fluid (CSF) leak, and varying extent of cosmetic deformity among which vascular complications might be the most dreadful nightmare for a neurosurgeon. In this chapter we focus on the vascular challenges which can be encountered while performing an anterior skull base open surgery and the techniques to prevent it.
12.3 Surgical Vascular Anatomy of Anterior Cranial Base
The anterior cranial base is formed by ethmoid, sphenoid, and frontal bones. It has endocranial and exocranial surfaces which are connected by canals and foramina, through which numerous vascular structures pass. The anterior cranial fossa faces the frontal lobes with gyri recti medially and the orbital gyri laterally, along with the branches of the anterior cerebral arteries (ACAs) medially and middle cerebral arteries laterally. 1 Another set of vessels traversing the anterior cranial base are anterior and posterior ethmoidal arteries, supraorbital arteries, and supratrochlear arteries through the anterior and posterior ethmoidal foramina, supraorbital foramen, and supratrochlear foramen, respectively. The optic canal transmits the ophthalmic artery along with the optic nerve. The main arterial supply to the orbit is the ophthalmic artery. The wide collateralization network of ophthalmic artery makes its sacrifice well tolerated in most situations as long as the collateral vessels are intact. These collateral vessels include leptomeningeal collaterals, duro-arteriolar collaterals, and periventricular collaterals commonly arising from anterior ethmoidal, posterior ethmoidal, and lacrimal arteries. 2 The collateralization is also enhanced by the orbital plexus linking the ophthalmic artery with facial, middle meningeal, and maxillary arteries and the rete mirabile caroticum connecting internal and external carotid arteries. 3 The main venous drainage of the orbit is through the superior and inferior ophthalmic veins. The intracranial view of the anatomical bony landmarks of the anterior cranial base is demonstrated in Fig. 12.1. The sellar region is very much related to the main trunk and early branches of internal carotid artery (ICA). The distance separating the medial margin of the carotid artery and the lateral surface of the pituitary gland is an important consideration in anterior cranial base approaches (transsphenoidal surgery). 4 The distance between the gland and artery varies from 1 to 7 mm (average, 2.3 mm). The intercarotid distance between cavernous carotid arteries is 15 to 17 mm in normal individuals and increases from 20 to 22 mm in patients with pituitary adenoma. 3 , 4 , 5
The perforating branches of the ACA include the recurrent artery of Heubner (RAH) and subcallosal-hypothalamic perforating branches, while the cortical branches include fronto-orbital artery (FOA) and frontopolar artery (FPA). Its anatomical course and variations are particularly relevant when performing microsurgical resection of meningiomas located at tuberculum sellae, planum sphenoidale, and olfactory groove. The FOA is the first cortical branch of the ACA, typically arising within the first 5 to 10 mm of the A2 segment, and runs along the orbital surface of the frontal lobe to supply the olfactory bulb and tract, gyrus rectus, and orbital gyri, while the FPA is the second cortical branch, larger in diameter, and courses in the interhemispheric fissure to supply the medial and ventral surfaces of the frontal pole. 5 The FOA is related to the olfactory tract and sulcus while the FPA relates to the interhemispheric fissure. A normal anterior communicating artery (AComA) could be defined as an anastomosis between the left and right ACA through a single lumen. Najera et al report the location of AComA above the anterior half of the optic chiasm in 20% of cases, an anatomic variation that could increase the risk of vascular injury. 5 The authors also mention the origin of RAH within 5 mm of the AComA in most cases. RAH could be encountered anterior to the A1 segment in almost half of the cases, while in the remaining the RAH may be positioned above or behind the A1 segment. 5
In the endocranial surface of the anterior cranial base, the foramen caecum in the midline provides the passage of the emissary vein. 1 The inferior frontal veins drain the orbital surface of the frontal lobe. They are mainly divided into two groups—anterior group and posterior group. The anterior group veins take their course toward the frontal pole and empty into the superior sagittal sinus. The anterior veins comprise both anterior orbitofrontal and frontopolar veins. The posterior group drains to join the veins at the medial part of the sylvian fissure which later converge on the anterior perforated substance to form the basal vein. The posterior group comprises the olfactory and posterior orbitofrontal veins. The inferior frontal veins and the areas they drain are as follows: the anterior orbitofrontal vein drains the anterior part of the gyrus rectus and the anteromedial part of the orbital gyri, the posterior orbitofrontal veins drain the posterior portion of the orbital surface of the frontal lobe, and the olfactory vein drains the olfactory sulcus and the adjacent part of the gyrus rectus and medial orbital gyri. 6 The cavernous sinuses are located on either side of the sphenoid sinus, sella, and pituitary gland. 4 Venous sinuses that interconnect the paired cavernous sinuses may be found in the margins of the diaphragma and around the gland and termed anterior/posterior intercavernous sinus based on location. If both anterior and posterior intercavernous sinuses coexist, they together constitute the circular sinus. 4
12.4 Pathologies Involving Anterior Cranial Base, Surgical Approaches, and Associated Vascular Challenges
A large spectrum of neurosurgical disorders affects the anterior cranial base. The common pathologies affecting the base include benign and malignant tumors, arteriovenous fistula/malformations, CSF fistula, congenital malformations, traumatic brain injury, bony lesions, and infectious pathologies. The benign tumors such as planum sphenoidale meningioma (PSM), olfactory groove meningioma (OGM), tuberculum sella meningioma (TSM), and malignant tumors like esthesioneuroblastoma, chondrosarcoma, and other sinonasal malignancies can also involve the skull base. Osseous pathologies such as fibrous dysplasia, congenital malformations such as encephalocele, infectious pathologies like tuberculous osteomyelitis or meningitis, or paranasal fungal infections extending to the anterior cranial base are other possibilities. Many of these lesions can reach enormous size and result in encasement of major vessels and other neural structures. The management strategy of each pathology varies and may not always be primarily surgical.
Various intracranial approaches to the anterior skull base have been described before. Among these, the common approaches we use for the microsurgical management of the aforementioned lesions include transbasal, pterional, or frontotemporal, and transsphenoidal approaches. In transbasal or subfrontal approaches, the anatomical variations of the anterior ethmoidal artery (AEA) create a big challenge. Abdullah et al reported that AEA is closely related to the skull base in 62.7% of cases (grades I and II) and courses freely in the ethmoid sinus below the skull base in the remaining 37.3% (grade III). In the former group, 42.5% of the artery is completely within the skull base (grade I) while another 20.2% course at the level of skull base with some degree of bony protrusion (grade II). Sometimes, the AEA is located below the skull base with a mesentery connecting it to skull base. If the AEA is not recognized as being in a mesentery, the artery might be accidentally injured while clearing sinonasal septations at the skull base, especially in sinonasal infiltrative malignant or infective pathologies. 7
The ACA, its branches, and the AComA complex are often involved in anterior skull base and suprasellar tumors. 5 The ACAs become separated as far as the AComA complex allows as the tumor enlarges. As a result, the ACAs could be found posterosuperior and lateral to OGMs. 8 The medial orbitofrontal and frontopolar branches may become incorporated into the tumor capsule. The FOA is the most frequently involved vessel in anterior skull base meningiomas, particularly in OGMs, since this artery runs along the olfactory sulcus. We have observed that OGMs may initially displace the FOAs laterally and then later encase them, while the FPAs are typically attached to the upper pole of the tumor within the interhemispheric fissure. 5 Apart from the common sources of blood supply such as anterior/posterior ethmoidal arteries and sphenoidal branch of middle meningeal artery, the pial branches of ACA and AComA also constitute potential additional vascular challenges in giant anterior cranial base tumors. The anterior and posterior ethmoidal arteries provide the major blood supply in olfactory groove meningioma. Early dissection of the tumor from the frontal lobe and visualization of the ACAs are the key steps to avoid catastrophic vascular complications in such scenarios. However, the absence of an arachnoid plane between the tumor and the surrounding vessels may predict more difficult resection and higher risk of vascular injury.
Tumors that originate from the tuberculum sellae or planum sphenoidale displace the optic nerves superiorly and laterally, the optic chiasm superiorly and posteriorly, the ICAs laterally, the anterior cerebral and communicating arteries superiorly, and the pituitary gland inferiorly. 9 The blood supply for TSM is typically from the posterior ethmoidal arteries; with increasing size, arterial supply is parasitized from the AComA, ACA, McConnell capsular arteries, and dural hypophyseal vessels. 10 The approach selection (microsurgical/endoscopic) in TSM is largely guided by the involvement of internal carotid, anterior cerebral, or AComA. 11 Bifrontal or pterional/orbitozygomatic approaches are better in vessel encasement cases. While resecting esthesioneuroblastoma or other sinonasal malignancies with intracranial extension, it is critical to understand both the neurovascular structures involved (especially the ACAs and their branches) and the presence of subpial invasion to avoid inadvertent injuries. 9 When operating in the suprachiasmatic region, injury to the AComA branch, subcallosal artery (ScA), can lead to severe cognitive and memory dysfunction due to basal forebrain involvement. ScA can be considered as one of the most important perforators of the AComA complex, apart from hypothalamic and chiasmatic arteries. 12
In a frontotemporal approach, after opening the sylvian fissure, the stem of the ICA and its branches, the ACA complex, middle cerebral artery complex and optic nerve need to be identified and meticulously preserved while operating the lesion. Circumferential encasement of the major arterial complex or perforator vessels stands as a major challenge in any skull base surgery, especially in large or giant meningioma resection. 13 Also, the identification of perforator vessels versus tumor feeders is crucial in avoiding complications. A preoperative angiogram may give a fair clue of the vascularity and anatomy of tumor feeders and also help to differentiate them from the perforators which should be preserved intraoperatively. Tracing the vessel to the parent artery and dissection along the subarachnoid plane also help to preserve the perforator vessels. The transsphenoidal approach to midline sellar and suprasellar lesions is limited laterally by bilateral ICAs, and the common vascular structures which may sustain inadvertent injury are the sphenopalatine artery and branches, ICA, basilar artery, and intercavernous sinus. Ectasia of the cavernous ICA and kissing carotids are significant challenges to the transsphenoidal approach, making the surgical corridor narrow and the dural opening difficult. 14 The use of micro-Doppler and careful dural opening help to overcome such challenges. This dolichoectasia may be seen in the pituitary fossa, sphenoid bone, or sinus and is commonly seen in acromegaly patients. Protrusion of the ICA into the sphenoid sinus is also relatively common (25–30%). Dehiscence of the bony sphenoidal wall of the ICA is seen in 10% cases. 15 Another rare challenge that needs to be anticipated is the association of aneurysm (ICA or its branches) and pituitary adenoma. The variations in the anatomy of the intercavernous sinus also pose significant surgical challenge in microsurgical transsphenoidal approaches. This can often be managed with injection of flowable Gelfoam or tissue glue.
In the subfrontal approaches, the anterior superior sagittal sinus (SSS) is commonly ligated to release the anterior falx. The anterior SSS includes veins that drain the medial, lateral, and basal surfaces of the frontal lobe. 16 The frontopolar veins have a single trunk, but variations such as multiple tributaries near the SSS also exist. 17 Many approaches require ligation of the anterior one-third of SSS for resection of midline anterior cranial fossa meningiomas. However, it is not safe in all cases. The length, caliber, and tributaries probably determine the area of frontal lobe drained by a vein into the anterior one-third of SSS. Longer, larger veins and veins with more tributaries drain a larger area. Acutely angulated veins also carry more blood from the posterior and eloquent areas of frontal lobe. 18 So the quantification of venous drainage based on preoperative contrast-enhanced magnetic resonance (MR) venogram could provide information on choosing midline basal versus lateral approaches.
12.5 Vascular Complications in Anterior Cranial Base Surgery
Vascular complications are the most feared complications in anterior cranial base surgery and includes both arterial and venous (channels/sinus) complications. Ischemic complications are caused by hemodynamic insufficiency, embolization, vasospasm, radiation vasculopathy, and venous anomaly. 19 Arterial injuries are frequently evident in the immediate postoperative period, whereas venous injuries typically present days later, resulting in congestive edema, hemorrhage, and seizures. Close anatomic proximity of the lesion with vessels is the main reason for inadvertent injury. Other causes are infiltration of tumor into adjacent vasculature, error in surgical technique, prior radiotherapy, inadequate preoperative imaging or interventions like cerebral angiogram or embolization, and suboptimal use of neuronavigation or micro-Doppler. 20 Intraoperative arterial injury may lead to catastrophic sequelae, which may range from hemorrhage, vasospasm, embolism or thrombosis, and sometimes delayed complications like pseudoaneurysm or arterial (ICA) stenosis. Carotid pseudoaneurysmal formation and eventual rupture may occur as a result of excessive adventitial dissection. This complication is usually sudden and fatal and may occur intraoperatively or postoperatively. Tuchman et al report the interval to diagnosis following surgery varied between 0 days and 10 years. 21 Performing computed tomography (CT) angiography 2 to 3 days after surgery in suspected cases may detect the pseudoaneurysm as immediate postoperative imaging may be negative in many cases except for active extravasation. Stroke arising due to thrombotic occlusion of the ICA or embolism into distal vessels can also be a major concern. Sometimes the blunt injury of perforator vessels during dissection may lead to its vasospasm of varying severity in the postoperative period. Meticulous sharp dissection, maintaining arachnoid plane, avoiding vessel traction, and placement of papaverine-soaked Gelfoam over the perforator vessels are some of the techniques which can be used to avoid the postoperative vasospasm. The stagnation of arterial flow is common after surgical resection of basal arteriovenous malformation (AVM) and may result in retrograde thrombosis of feeding arteries leading to hypoperfusion. This happens especially if the AVM is large, patient is old, or the feeding arteries long. Similar stagnation can affect the venous system as well, though the neurologic deficit from venous thrombosis may be reversible, unlike arterial occlusion.
The incidence of ICA injury during transsphenoidal surgery varies from 0.2 to 2% in large series. 22 , 23 Arterial bleeding can also come from ICA branches such as the inferior hypophyseal artery or small capsular artery. 24 , 25 Injury to the sphenopalatine or posterior nasal artery is not rare in this approach (3.4%) though it is usually manageable with careful localization and coagulation of these arteries if transected. 26 Sometimes torrential bleed may happen while opening the sellar dura due to the venous channels over the entire face of the sellar dura in cases of pituitary microadenoma. As the bleeding may be in the form of diffuse ooze and difficult to localize to any specific vessel, flowable Gelfoam or glue may be the most beneficial tools in such situations. The anatomic relationship between the AComA complex/proximal ACA branches and tumors is a fundamental issue when dealing with large suprasellar lesions. 5 The main source of permanent neurological deficit after suprasellar meningioma surgery, other than visual loss, is intraoperative injury to the ACA or its branches. 5 Kassam et al reported a case of avulsion of FOA during the resection of an OGM in which the patient developed a delayed A2 pseudoaneurysm which ruptured and resulted in permanent right hemiparesis and cognitive deficits. 27
The RAH supplies key territories including the anterior part of caudate nucleus, putamen, outer segment of the globus pallidus, and even the anterior limb of internal capsule. Inadvertent injury or occlusion may cause faciobrachial monoparesis, if the branch supplying the anterior limb of the internal capsule is compromised, and aphasia, if the artery is on the dominant side. 5 The neurological deficits associated with the injury of posterior perforating arteries from the AComA include incapacitating memory deficits and personality changes. Fortunately, there is a very low risk of injuring these vessels whenever the pathology is ventral to the AComA; lesions such as complex adenomas with subarachnoid invasion or meningiomas may occupy the space behind the AComA putting the subcallosal perforating arteries at risk. 5
Obliteration of a patent SSS may impair venous return and induce edema in the part of the brain where venous drainage is obstructed, especially in tumors with significant peritumoral frontal lobe edema. Even in the anterior third of the sinus, long considered to be less critical, sinus ligation could result in sacrifice of the draining veins, leading to significant frontal lobe venous congestion, edema, or infarction. Furthermore, in these patients with large anterior cranial base tumors, there is increased intracranial pressure due to the presence of a large mass and secondary decreased venous return. Preoperative contrast-enhanced MR venogram provides necessary information on the status of the location/caliber of draining veins and their tributaries which helps in choosing the ideal approach and further surgical planning.
12.6 How to Avoid Arterial and Venous Complications?
Surgeons must be proficient with various surgical approaches to the anterior skull base and knowledgeable of their specific potential risks and benefits. The selection of the ideal approach is one of the most crucial steps in skull base surgery. Surgical strategies must be tailored according to each case based on location, nature and size of the lesion, relationship with surrounding neurovascular structures, extent of dural attachment (meningioma), and surgeon’s expertise. The approach should also achieve the goals of minimal brain retraction, proper exposure of the lesion/neurovascular structures, especially toward the tumor base at the skull base surface, and also the ability to cut off or reduce tumor blood supply. Preoperative angiogram provides the opportunity to perform embolization prior to the lesion resection, especially in highly vascular lesions. If major vessel injury or sacrifice is anticipated, the patient should be well prepared for possible arterial clip reconstruction or bypass surgery or sinus reconstruction surgeries. In hypercoagulable high-risk conditions such as Cushing’s disease, perioperative anticoagulant prophylaxis may help in reducing the incidence of thrombotic or embolic complications. 28 Minimal handling of vessels and avoiding prolonged brain retraction can avoid these complications to a great extent. The regional cerebral blood flow can decrease to the point of ischemia when brain retraction pressures exceed 20 mm Hg. 29 , 30 Clinical studies demonstrated CSF drainage as an effective method in decreasing the retraction pressure required. Also, the use of multiple retractors reduces the pressure applied by each retractor. The vigilant monitoring of retraction pressures using strain-gauge retractors may also be helpful, especially while applying over arteries and cranial nerves. Strict airway and oxygenation maintenance as well as adequate fluid and electrolyte balance are yet other preventive measures to avoid complications in skull base surgery and may play a role in venous infarct management.
Internal debulking of tumor and bimanual, extracapsular dissection are the most important microneurosurgical techniques to avoid devastating vascular complications in anterior cranial base lesions. Meningiomas of the anterior cranial fossa represent 12 to 20% of all intracranial meningiomas. 31 While performing a frontotemporal approach for OGM, the initial debulking and exposure of the basal dura mater provide the opportunity to coagulate and divide the feeding arteries. This, as well as splitting of the sylvian fissure, provides better visualization of the ICA bifurcation at the posterolateral aspect of tumor, with subsequent identification of the ACA complex, optic chiasm, and optic nerves. Changes in head rotation intraoperatively provide varying angles of visualization of ACA complex and thereby its preservation. In the subfrontal transbasal microsurgical approach, the dura mater of the anterior cranial base is dissected free from the underlying bone and the dural basal vessels can be then coagulated and divided. This is a very crucial step for early devascularization of an anterior skull base tumor. Comparing the lateral approach to anterior bifrontal approach, the senior author reported the experience from the personal series of 57 patients and suggested that lateral (pterional/frontotemporal) approaches resulted in less frontal lobe damage, less encephalomalacia (as measured by ratio of porencephalic cave volume to tumor volume) in the hemisphere contralateral to the tumor, and better olfactory preservation in comparison to anterior approaches. 32 Preoperative ethmoidal artery ligation can play a major role in the surgical excision of large-to-giant anterior skull base meningiomas. 33
The advantages of sharp arachnoid dissection over blunt dissection have already been reported. Zygourakis et al in their study report that following the arachnoid plane and dissection along the arachnoid planes in the suprasellar cistern to protect the AComA complex, often separated from the tumor capsule by an arachnoid sheath, may help prevent complications. Also, when portions of the tumor are wrapped around the A1 and AComA, a small portion of tumor can be left unresected if it cannot be easily separated from the associated perforating arteries. ACA encasement and sagittal sinus invasion may be the predictive factors favoring open microsurgical resection over endonasal approach and should be weighed more heavily than tumor size, distance to optic chiasm, sellar invasion, or surgical approach when predicting the morbidity of a surgery for PSMs or OGMs. 34
Based on diameter alone, the RAH could be mistaken for the FOA. The RAH, FOA, and FPA can be differentiated according to their origin, course, and destination. The key landmarks for these three arteries are the A1 segment, the olfactory tract, and the interhemispheric fissure, respectively. While the FOA distally drifts away from the A1 segment, the RAH remains parallel to A1. 5 In cases of giant olfactory groove meningiomas with complete encasement of the FOA, its intraoperative sacrifice may have little clinical consequences as the vascular territory may have already been compromised by the tumor growth. 5 Suprasellar meningiomas with potential vascular encasement are a relative contraindication for endoscopic endonasal surgery. The FOA is the most commonly encountered vessel when resecting sinonasal tumors with anterior skull base invasion, and selective coagulation of its feeders to the olfactory tracts is required for complete oncological resection. As 20% of FOAs supply the frontal pole, care should be taken to preserve the FOA when possible; this is not always simple or possible given the tendency (85%) of the FOA to cross the olfactory tract. 5
Preservation of normal vasculature, while maintaining the ability of the surgeon to attain the greatest visibility, is an important factor when choosing an approach. The transbasal approach allows access to the origin of the anterior SSS, allowing for maximum draining vein preservation, thereby avoiding venous infarction. Maximal preservation of the draining veins should be considered while resecting large anterior skull base lesions. Borghei-Razavi et al reported the advantage of removing the orbital bar while performing the transbasal approach as it offers a trajectory allowing ligating the most anterior aspect of the SSS without risking injury to any of the veins draining into the sinus. 16 The other techniques for avoiding basal venous injury are providing adequate extension of the patient’s head, release of CSF, and using epidural dissection so that the dura can be opened in a low subfrontal fashion rather than over the frontal pole, thereby preserving the majority of venous integrity. The complication rate of venous infarctions can also be decreased by performing extended bifrontal craniotomies with bilateral orbital osteotomies rather than traditional bicoronal craniotomies. 16 The technique of extradural posterior mobilization of the sphenoparietal sinus has been described to achieve adequate retraction of the frontal lobe intradurally without sacrificing the frontobasal bridging veins. 35 Goldschmidt et al reported the use of near-infrared vein finder technique to define cortical veins, pathological dural veins, and venous sinus anatomy prior to dural opening, and it offers a real-time image independent of brain shift. 36 Consideration of venous drainage is important when selecting the approach for patients with midline anterior cranial fossa meningiomas, since removal of such tumors would require a low trajectory to gain access to the base of the tumor. The variation in the origin of the first and second veins draining into SSS should also be an important factor when deciding the approach. 16 Although the transbasal approach can be performed with the preservation of the SSS, a unilateral approach such as the pterional approach can bypass the risk to injure SSS or basal draining veins entirely. Consequently, these results are important to consider when choosing an optimal approach for resection of such tumors as these patients are at increased risk of venous infarction.
There may not be a single best approach for the resection of anterior cranial base lesions. Multiple different approaches may be used for anterior cranial base tumor or AVM resection including pterional, subfrontal, and orbitofrontal approaches. Each approach has its own benefits and disadvantages. Avoiding direct injury to the brain and vessels involves the use of surgical adjuncts, adequate exposure, and optimum brain relaxation. Minimizing the use of retractors to preserve veins is essential. Intraoperative imaging modalities such as digital subtraction angiography (DSA), indocyanine green video angiography, or micro-Doppler are efficient adjuncts to check for the patency of vessels after tackling the pathology. There exists no precise vascular assessment today which can predict the occurrence of vascular complications accurately. Postoperative adjuncts include DSA, transcranial Doppler, CT/MR angiography, and physiologic modalities such as positron emission tomography (PET), hexamethylpropyleneamine oxime (HMPAO SPECT), 133Xe clearance, xenon-enhanced CT (Xe/CT), perfusion CT (PCT), and diffusion-weighted/MR perfusion imaging. 37 Significant limitations remain in the management of cerebrovascular anatomy and physiology in anterior cranial base microsurgery. Patient-related factors (age, comorbidities, medications), pathology-related factors (symptoms, size, location, configuration), anticipation of potential cerebrovascular complications, and, most importantly, the experience of the surgeon are paramount to successful outcome. Most importantly, as in the case of any skull base surgery, the natural history of disease and the effectiveness of alternate mode of treatments must be weighed against the morbidity of surgical procedure.