32 Managing Carotid Injury During Transsphenoidal Surgery
The transsphenoidal approach is a routine, widely accepted, and safe operative procedure; however, serious vascular injuries may occur during both the approach and the resection of pathology. Rates of complication are related to surgical volume, with incidences directly correlated with the surgeon’s experience. Carotid injury is a rare but potentially life-threatening complication of the transsphenoidal approach. Although an uncommon occurrence, approximately 12% of pituitary surgeons have experienced this complication at some point in their practice.1 A detailed preoperative knowledge of the sphenoid and sellar anatomy as well as the use of intraoperative neuronavigation help to prevent pitfalls during the transsphenoidal approach, yet arterial injuries can still occur, particularly in the management of complex lesions. The ability to quickly and effectively treat vascular injuries is imperative in attaining a satisfactory outcome. This requires the support of multiple medical subspecialties as well as access to available endovascular technologies. This chapter reviews the vascular anatomy of the sellar and suprasellar region and discusses the types of vascular injuries most commonly seen with the transsphenoidal approach and their immediate intraoperative and postoperative endovascular management.
Vascular Anatomy of the Pituitary Region
The cavernous segment of the carotid artery originates lateral to the posterior clinoid process, where it enters the sinus and traverses it in a forward and horizontal direction for approximately 2 cm. It then turns upward medial to the anterior clinoid process as it exits the roof of the cavernous sinus and the dural ring. It is the most medial structure within the cavernous sinus. In approximately 14% of reviewed cases, the shortest distance between the bilateral carotid arteries was within the sellar component of the cavernous-carotid artery.2 In 4% of cases, the shortest distance was within the sphenoid component of the cavernous-carotid segment.2
The relationship between the sella and the cavernous segment of the carotid artery, specifically the distance separating the medial edge of the carotid artery and the lateral surface of the pituitary gland, is a crucial factor to consider during transsphenoidal surgery. In a review of cadaveric cases, the distance between the lateral aspect of the pituitary and the artery varied from 1 to 7 mm (average, 2.3 mm).2 However, a separation between the gland and the artery is not always present, and in one fourth of reviewed cases the cavernous segment of the carotid artery protruded through the medial wall of the cavernous sinus to directly abut and indent the pituitary gland.3,4 This results in not only herniation of the gland in a contralateral position but also conforming of the pituitary to the wall of the artery, with protrusion both above and below the vessel. The same phenomenon applies to a sellar tumor, in which the artery may become invaginated by the expanding mass, even if the tumor is small and does not invade the cavernous sinus.
Multiple arterial branches arise from the cavernous segment of the internal carotid artery. The meningohypophyseal trunk, the most proximal branch, arises lateral to the dorsum sellae just as the artery turns anterior from the foramen lacerum. The meningohypophyseal trunk gives rise to three arteries: the tentorial artery; the inferior hypophyseal artery, which supplies the pituitary capsule and anastomoses with the contralateral vessel; and the dorsal meningeal artery. The inferolateral trunk arises from the lateral side of the horizontal segment of the cavernous-carotid artery in 84% of cases but may infrequently branch from the meningohypophyseal trunk as well.3,5
Given the ability to extend the transsphenoidal approach across the planum sphenoidale and into the suprasellar compartments, the suprasellar relationship and morphology of the anterior circulation to a large sellar tumor are of crucial importance during preoperative planning. Numerous arteries, including the internal carotid and basilar artery, as well as the circle of Willis and its branches, may be deformed from mass effect by the expanding tumor. In 82% of cadaveric cases, the shortest distance between the bilateral internal carotid arteries was noted in the supraclinoid segment.4 The internal carotid artery exits the cavernous sinus along the medial aspect of the anterior clinoid process as it reaches the anterior incisural space. It then proceeds posteriorly, superiorly, and laterally to its bifurcation below the anterior perforated substance. As it courses lateral to the optic nerve, creating the opticocarotid space in between, it feeds multiple small arterial branches to the optic nerve, chiasm, tract, and floor of the third ventricle. The superior hypophyseal artery, which courses medially below the floor of the third ventricle to anastomose with the contralateral vessel around the infundibulum, is a branch from the ophthalmic segment of the internal carotid artery. The next intradural branch of the internal carotid artery is the ophthalmic artery, which enters the optic canal below the optic nerve. This is followed by the posterior communicating artery, which branches from the posterior wall of the internal carotid artery and travels posteromedially below the optic tracts and floor of the third ventricle. Finally, the anterior choroidal artery originates immediately above the posterior communicating artery, also from the posterior wall of the internal carotid artery, but takes a posterolateral course below the optic tracts. The internal carotid artery ends in a bifurcation with the anterior cerebral artery coursing medially above the optic nerve and chiasm to the interhemispheric fissure, where it joins its contralateral vessel via the anterior communicating artery. The anterior cerebral artery is of particular importance when performing extended suprasellar approaches for tumors as they will likely be displaced or encased by the lesion.
Vascular Injuries to the Carotid Artery
Vascular injury during transsphenoidal surgery can occur during both the surgical approach as well as the resection of tumor. The most effective management of vascular injury is prevention through detailed preoperative and intraoperative technique. It is critical for the operative surgeon to remain in the midline during the approach and have an intimate knowledge of the relationship between the vasculature and the surrounding bony structures. Entry into the sphenoid sinus may be complicated by a carotid artery that bulges into the space or is actually exposed to the sinus without any bony protection, a phenomenon seen in 4% of specimens.4 Preoperative magnetic resonance imaging and computed tomography angiography (CTA) are noninvasive methods to accurately assess the relationship among vascular, bony, and soft tissue structures. Vascular abnormalities on these studies can then be followed by digital subtraction angiography (DSA) for further elucidation. In addition, these imaging modalities can be coupled to intraoperative neuronavigation to ensure that a midline approach is adhered to beyond the vomer, an especially important tool in abnormal sphenoid sinus anatomy such as cases of honeycomb configuration, nonpneumatized sphenoid bone, and oblique sphenoid septum. Other predisposing surgical difficulties include cavernous sinus invasion by the tumor, previous transsphenoidal surgery, radiation therapy, and bromocriptine therapy. Patients with acromegaly may also be at higher risk for injury secondary to distortion of nasal and sinus anatomy as well as a tendency to have tortuous ectatic arteries that may protrude into the sella.6 In addition, previous inflammatory conditions in the vicinity of the sella such as cerebrospinal fluid rhinorrhea or meningitis may weaken the carotid wall, predisposing it to iatrogenic injury.
Surgical Control of Intraoperative Hemorrhage
Despite proper preoperative planning and meticulous intraoperative technique, injuries to the vascular structures of the anterior circulation will inevitably occur, especially if one performs many surgeries for complex sellar pathology. The early recognition of such an injury as well as the coordinated and effective steps taken from that point are critical in limiting the morbidity and mortality associated with these events.
The first step is to control the hemorrhage to prevent excessive blood loss. Upon encountering the torrential arterial bleeding from inadvertent laceration or perforation, the natural first step is aspiration of blood with the appropriatesize sucker and application of a cottonoid with pressure to the site of injury. Concomitantly, the anesthesiologist should resuscitate the patient with intravenous fluids, pressors, and blood products as needed. In addition, direct manual compression on the cervical carotid artery ipsilateral to the side of injury can help to diminish the proximal pressure on the arteriotomy, potentially facilitating hemostasis. With endoscopic surgery, the endoscopic view may become obscured by blood. The use of two suctions, one in each nostril, and constant irrigation of the lens will facilitate visualization. If the endoscope is on a scope-holder, it is important to have an extra set of hands to control the scope so that it can be removed and cleaned or moved above the rising pool of blood or down toward the arteriotomy as needed.
Fukushima and Maroon7
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