|Home | About | Journals | Submit | Contact Us | Français|
Paraclinoid segment internal carotid artery (ICA) aneurysms have historically been a technical challenge for neurovascular surgeons. The development of microsurgical approach, advances in surgical techniques, and endovascular procedures have improved the outcome for paraclinoid aneurysms. However, many authors have reported high complication rates from microsurgical treatments. Therefore, the present study reviews the microsurgical complications of the extradural anterior clinoidectomy for treating paraclinoid aneurysms and investigates the prevention and management of observed complications.
Between January 2004 and April 2008, 22 patients with 24 paraclinoid aneurysms underwent microsurgical direct clipping by a cerebrovascular team at a regional neurosurgical center. Microsurgery was performed via an ipsilateral pterional approach with extradural anterior clinoidectomy. We retrospectively reviewed patients' medical charts, office records, radiographic studies, and operative records.
In our series, the clinical outcomes after an ipsilateral pterional approach with extradural anterior clinoidectomy for paraclinoid aneurysms were excellent or good (Glasgows Outcome Scale : GOS 5 or 4) in 87.5% of cases. The microsurgical complications related directly to the extradural anterior clinoidectomy included transient cranial nerve palsy (6), cerebrospinal fluid leak (1), worsened change in vision (1), unplanned ICA occlusion (1), and epidural hematoma (1). Only one of the complications resulted in permanent morbidity (4.2%), and none resulted in death.
Although surgical complications are still reported to occur more frequently for the treatment of paraclinoid aneurysms, the permanent morbidity and mortality resulting from a extradural anterior clinoidectomy in our series were lower than previously reported. Precise anatomical knowledge combined with several microsurgical tactics can help to achieve good outcomes with minimal complications.
The paraclinoid segment of the internal carotid artery (ICA) has been named the area from where it exits the cavernous sinus and enters the subarachnoid space to the origin of the posterior communicating artery1,3,9,22,29).
Aneurysms arising from the paraclinoid segment have presented unique challenges in both diagnosis and microsurgical management because of their unique anatomic location, and these types of aneurysms have been associated with high morbidity and mortality5,9,11,36). Before the development of skull base techniques, the approach for these aneurysms was difficult because the anterior clinoid process (ACP) obstructed the surgical field and restricted the surgeon's working space. The clipping of paraclinoid aneurysms, while attempting to preserve the ophthalmic artery and maintain patency of the ICA, is a technically difficult procedure. A significant number of paraclinoid aneurysms present as giant aneurysms1,22,26,41), lesions that may further add to the difficulties of management.
However, advances in skull base approaches10,11), especially the extradural anterior clinoidectomy8,16,24), have greatly improved surgical outcomes for patients with paraclinoid aneurysms. Furthermore, endovascular procedures have become alternative treatments for paraclinoid aneurysms17,27,31). However, microsurgery continues to result in a larger percentage of total occlusions compared to other methods, especially for large and giant aneurysms, because total obliteration with endovascular treatment is not as likely as it is with surgery14,20,39), and coiling procedures have been associated with a higher rate of recurrent aneurysms compared with that of surgical treatment5,19). Although the extradural anterior clinoidectomy was developed specifically to improve outcomes for paraclinoid aneurysms, many authors still report high complication rates resulting from this approach3,4,6,9,11,19,25).
The purposes of this study are to review our recent experiences using a extradural anterior clinoidectomy to surgically repair paraclinoid segment aneurysms and to analyze the microsurgical complications we have experienced. We also analyzed how to avoid and to manage potential complications based on these results.
Between January 2004 and April 2008, 22 patients with 24 paraclinoid aneurysms underwent microsurgical direct clipping by a cerebrovascular team at a regional neurosurgical center. We retrospectively analyzed the clinical records in patients with these aneurysms. All paraclinoid aneurysms were confirmed using digital subtraction angiography (DSA), three-dimensional computed tomography angiography (CTA), preoperative temporal bone computed tomography (CT), and magnetic resonance imaging (MRI) (in 12 of the patients). Microsurgery was performed via an ipsilateral pterional craniotomy and with an extradural, extended anterior clinoidectomy8,16,24,35). We retrospectively reviewed the patients' medical charts, office records, radiographic studies, operative records, and videos.
The 22 patients included 5 men and 17 women ranging in age from 42 to 69 years (mean 53.5). The clinical presentations of the 24 paraclinoid aneurysms include headache in four cases (16.6%), subarachnoid hemorrhage in six cases (25%), transient ischemic attack or stroke in one case (4.2%), dizziness in one case (4.2%), diplopia in one case (4.2%) and incidental findings including three cases with ruptured other aneurysm in 11 cases (45.8%) (Table 1). In nine patients with subarachnoid hemorrhages, the Hunt and Hess grade was II in five patients, III in one patient, and IV in three patients. Among 22 patients, seven (31.6%) had multiple intracranial aneurysms and three (13.6%) had other aneurysms in the paraclinoid segment.
According to an anatomic system based on the aneurysm's presumed vessels of origin and location on the ICA30), the locations of the 24 paraclinoid aneurysms were as follows : 12 superior hypophyseal (50%), two carotid cave (8.3%), eight ophthalmic (33.3%), one posterior carotid wall (4.2%), and one transitional (4.2%). Aneurysms measuring up to 15 mm were considered small, those from 16 to 24 mm were large, and those measuring 25 mm or more were defined as giant. Twenty patients (83.3%) had small aneurysms, three (12.5%) large aneurysms, and one (4.2%) patient a giant aneurysm. Of the patients with multiple aneurysms, two had contralateral ICA aneurysms. No patient had any other types of vascular malformation.
All 24 paraclinoid aneurysms were treated using an ipsilateral pterional approach with an extradural, extended ACP removal. First, prior to the craniotomy, proximal control of the ICA was obtained through routine exposure of the cervical ICA, which was then isolated using a rubber loop band. A frontotemporal craniotomy was performed (slightly larger than usual) with a high-speed drill in the lateral end of the superior orbital fissure (SOF). The ACP was partially drilled away, and the frontotemporal dural fold (FTDF) that passes the bony SOF and attaches to the periorbita was exposed. The dura of the anterior and middle fossa was dissected to expose the FTDF superomedially and the SOF inferolaterally. The FTDF and the periorbita-dura junctions were hence uncovered at the anterior limit of the lateral wall of the cavernous sinus (Fig. 1). Then, the FTDF was divided with a sharp scissors, and the outer dura layer of the lateral wall of the cavernous sinus was carefully peeled from the inner layer to expose easily and safely the entire dimension of the ACP. The peeling was performed from the foramen ovale, inferolaterally, and to the SOF-periorbita junction, superomedially. In this way, we were able to uncover the deepest inferolateral surface of the ACP (Fig. 2). The ACP and optic strut were removed extradurally, and an "L" shaped dural incision was performed along the sylvian fissure and frontal base. The dural incision extended anteriorly over the third cranial nerve and toward the opening of the oculomotor foramen. Next, the optic sheath lateral to the optic nerve was opened, exposing the anterior portion of the roof of the cavernous sinus. After the identification of ophthalmic artery, if necessary, the distal dural ring was completely or partially released to allow for mobilization of the ICA segment in order to improve access to the aneurysm for clipping.
The clinical outcomes are expressed using the Glasgow outcome scale (GOS) after six months of follow-up. The outcomes after an ipsilateral pterional approach with extradural anterior clinoidectomy for 24 paraclinoid aneurysms were defined as excellent or good (GOS 5 or 4) in 21 patients, 87.4%; fair (GOS 3) in two patients, 8.4%; and poor (GOS 2) in one patient, 4.2% (Table 2). The fair and poor outcomes resulted from vasospasm-related ischemia and hydrocephalus in one patient of the Hunt and Hess grade III with SAH and two of grade IV with ruptured other aneurysm. All cases of unruptured paraclinoid aneurysms were treated successfully without additional neurological deficits.
The surgical complications related directly to the extradural anterior clinoidectomy included transient cranial nerve palsy (6), cerebrospinal fluid leakage (1), worsened change in vision (1), unplanned ICA occlusion (1), and epidural hematoma (1) (Table 3). Only one of these complications resulted in permanent morbidity, and none resulted in death. No morbidity was related to ischemia from occlusion of the ICA. The cranial nerve palsies occurred at the third cranial nerve; three of the six patients showed partial ptosis, and two patients had limited gaze adduction combined with ptosis. Only one patient showed almost complete ipsilateral palsy, which included ptosis, gaze limitation, and pupil dilatation. All of these patients fully recovered within one to six months. The patient with a worsened change in vision that resulted in permanent morbidity had a history of a previous ophthalmologic problem. The overall complication rate was 41.7%; however, the permanent morbidity rate was 4.2% and there was no case of surgically related mortality.
The paraclinoid segment of the proximal ICA is described using various names, including the ventral internal carotid artery segment15) and the carotid-ophthalmic segment10,11,25). These aneurysms have traditionally been a technical challenge because access to the neck of the aneurysm usually requires ACP removal5,9,11,36). In addition, these aneurysms are frequently large or even giant in size1,22,26,41), while their location provides a restricted working space. However, the development and refinement of new surgical techniques6,10,11) have greatly improved surgical outcomes for paraclinoid aneurysms.
Endovascular procedures have become alternative and effective treatments in the management of these lesions17,27,31). However, obliteration of the aneurysm with endovascular treatment has a lower success rate for total occlusion14,20,37). Furthermore, recurrences are more frequent after endovascular treatment, especially in lesions that were incompletely occluded during the initial procedure5,19). Microsurgery, therefore, remains the primary treatment for paraclinoid segment ICA aneurysms, as it provides a higher long-term success rate9,19), although in some cases, combined surgical and endovascular approaches has been a useful treatment strategy1,21,29,33).
In 1968, Drake et al.13) reported that only 40% of patients (with 14 paraclinoid aneurysms) achieved good outcomes (GOS score of 4 or 5) following microsurgery, while 60% of patients died. However, subsequent clinical series have shown substantial improvements in outcome. In 1994, Batjer et al.3) reported positive outcomes in 87% of cases from a surgical series of 89 paraclinoid aneurysms, with only a 12% morbidity rate. In 2001, Hoh et al.19) reported that combined surgical and endovascular treatment of paraclinoid aneurysms resulted in good outcomes in 90% of the 145 surgically treated aneurysms. In 2004, Beretta4) reported good outcomes in 81% of study patients with a 13% morbidity rate. Recently in 2008, Raco et al.32) reported good outcomes in 81% of patients and a long-term morbidity rate of 20%. The current study reports favorable outcomes similar to these previously published results.
However, although surgical outcomes for paraclinoid aneurysms have demonstrated an overall decrease over time in postoperative mortality and morbidity, many authors still report a higher rates of surgical complications compared to the surgical treatment of other aneurysms3,4,6,9,11,19,25,32,38). The current study also documents a relatively high complication rate of 41.7%. Most of these complications, however, were transient, and permanent morbidity was lower in our study than in previous studies.
The cranial nerves can be injured during ACP removal or clip blade advancement or from excessive retraction or overzealous sinus packing. We experienced a high rate of transient cranial nerve palsies (25%), mostly of third cranial nerve, which has been previously reported6,9,19,38). However, all nerve palsies were transient and recovered fully within one to six months of surgery. Cranial nerve palsies likely occurred as a result of the traction caused by the peeling of the lateral wall of the cavernous sinus. To prevent permanent nerve injuries, when dividing the FTDF for ACP removal, we used a backward-curved pair of scissors11,12) parallel, not perpendicular, to the ACP in order to avoid the injury of the cranial nerves (Fig. 3). We also partially cut only the FTDF and gently retracted its sleeve. When applying the clip, we were careful to confirm whether the end of clip blade injured a cranial nerve. In order to prevent injury while retracting the temporal lobe, the carotid-oculomotor membrane was opened sharply, and the lateral wall of cavernous sinus was peeled back.
Although other groups8,19,32,38) have reported a relatively high incidence of postoperative cerebrospinal fluid leakage, this was not common in our study (4.2%). In our series, 15 incomplete dural closings and three ethmoid or sphenoid sinus openings associated with ACP removal were found. If distal dural rings are completely released and the dura around the ACP is defective, complete closing of the dura will be impossible in almost all cases. In such cases, we suture several points of the incision margin of the dura, and then cover the area with a free graft, such as with a piece of muscle or a small pericranial fascia flap, to prevent cerebrospinal fluid (CSF) leakage through the sphenoid sinus. After this, we reinforce the graft with fibrin glue. This procedure is performed repeatedly until two or three layers of grafting are fixed above the dural defect.
The opening of the ethmoid sinus can also result in postoperative CSF leakage and is associated with injury to the mucous membrane, which can occur during pneumatization of the ACP8,19,28,40). However, this problem can be avoided if the sinus mucous membrane is preserved. In this study, the ethmoid sinus was opened in a few cases (12.5%), although we rarely found injuries to the mucous membrane. The mucous membrane can be preserved through careful preoperative evaluation of the pneumatizations of the ACP and optical strut (OS)28), ACP erosion, and the overall development of the ethmoid sinus2). Through careful preoperative evaluations of the temporal bone CT, we were able to prevent mucosal injury to the ethmoid sinus. We analyzed all of the patients in this study for pneumatization of the ACP and OS, erosion of ACP, and for the development of the ethmoid sinus using a preoperative temporal bone CT. Computed tomography scans with a 0.6-mm thickness were obtained, and coronal and sagittal reconstructions of the images were displayed in all cases (Fig. 4). Mikami et al.28) classified pneumatized patterns as type I, type II, and type III, according to the route of pneumatization, via the OS, the anterior root (AR), and both the OS and AR, respectively. We found only two cases of type I pneumatization of the ACP in our study. In those two cases, extremely careful drilling using a diamond bar was performed with ACP removal. Using this technique, the dissector gradually pushes it into the paranasal sinus if the mucous membrane is exposed (Fig. 5), and it can be packed by betadine gel-soaked Gelfoam. En bloc removal of the ACP is also possible after pushing the mucous membrane into the sinus. If the preoperative CT demonstrates erosion, resection of the ACP should be avoided18) or performed very carefully. In four of our cases the medial margin of clinoidectomy had to be performed carefully according to the development of the ethmoid sinuses on the temporal bone CT images, and the mucous membrane had to be pushed into the ethmoid sinus with a dissector. Nevertheless, it was covered with free graft such as a piece of muscle with a small pericranial flap when sinus mucosa was injured and fibrin glue was applied. We had only one postoperative CSF leakage, treated with these tactics, among all the patients. In this case, we performed lumbar spinal drainage followed by bed rest for a week, and the leakage resolved without any permanent morbidity.
The surgical complication associated with permanent morbidity in our study was worsened vision, which is similar to previous reports11,19,25,32). Rizzo34) found two etiologies of worsened vision, including a fulminant orbital syndrome caused by the compromise of large draining veins of the orbit and a retrobulbar optic neuropathy caused either by direct injury or damage to the small dura vessels of the posterior optic nerve. Kumon25) believed that the occurrence of visual disturbances resulted from injury to the ipsilateral optic nerve caused by excessive retraction or by the heat produced by the diamond drill. Therefore, when the bone is drilled and thinned until only a thin rim remains, care must be taken to avoid heat injuries to the optic nerve. Heat damage can be prevented with the use of continuous cold saline irrigations, and mechanical injury can be prevented with the use of a dissector or a microcurette to unroof the optic canal. Micropunches or microrongeurs are never used until the optic canal is unroofed. Recently, the bone-cutting ultrasonic aspirator has been used in place of a drill for clinoidectomy. Chang et al.7) reported that, with an ultrasonic bone curette, unroofing of the optic canal could be safely completed, with low morbidity and mortality, and it required much less expertise to use the ultrasonic aspirator compared to that required to operate a standard drill. Therefore, there is no need to insert any instrument between the bone and the dura and no danger of thermal injury. Also, during the unroofing procedure, the edge of the bone should always be identifiable. However, the handpiece of the ultrasonic bone curette is somewhat bulky and hinders visibility within the deep and narrow operative field. As the tip of the ultrasonic bone curette is relatively smaller than larger regular drill bits, the resection of a large amount of bone is time-consuming. Finally, the use of this device does not automatically protect the soft tissues. Thus, the angle of the tip and the optic canal should be as close to perpendicular as possible.
Since the inferior lateral wall of the optic canal (situated between the optic nerve and the ICA, also known as the OS) can be removed only by drilling, this portion is drilled intermittently in order to minimize the optic nerve's exposure to heat25). Releasing of the optic nerve sheath at its lateral border reduces the force of retraction, as there is enough space between the nerve and the sheath. This technique allows for the observation of vessel circulation on the surface of the optic nerve, which allows for the detection of excessive retraction40).
Another complication associated with permanent morbidity in previous studies is ICA occlusion, which results in ischemic injury11,19,38). Hoh et al.19) reported morbidity related to ICA occlusion (four patients, 2%) and other surgery-related ischemia (two patients, 1%) in 180 microsurgical treatments of paraclinoid aneurysms. Although we also experienced one unplanned ICA occlusion (4.2%), this occlusion did not result in any permanent neurological deficits. ICA occlusions can be prevented with the use of a variety of clips, including angled fenestrated clips, which are used for these types of aneurysms. If the aneurysm is thrombosed, a thrombectomy is required and an endarterectomy might also be needed. When an aneurysm cannot be clipped because of calcification within the aneurysm neck or because the aneurysm is incorporated into the ICA, a bypass with a vein graft or radial artery should be performed4). Proximal artery control is important in the microsurgical management of paraclinoid aneurysms but also presents a technical challenge. Many different methods have been developed to achieve proximal artery control, including intraoperative balloon occlusion of the ICA35). In this study, we obtained proximal artery control through a cervical exposure prior to craniotomy and found this method to be safe, effective, and practical. Other authors have agreed that this small time investment is well worth the effort3,19,40).
Hemostasis is also a concern in this procedure, as the outer layer of the lateral dural wall of the cavernous sinus must be carefully peeled away from the inner layer in order to expose the deepest inferolateral surface of the ACP; bleeding is common during this peeling procedure. When bleeding occurs, it is important to locate the original focus of bleeding. Bleeding from the cavernous sinus should be distinguished from bleeding from the dural draining vein, as the former can be well controlled with gentle packing with hemostatic agents (packing appears as "cones" made by the hemostatic agent (Fig. 6), while the latter requires bipolar coagulation. Furthermore, with bleeding from the cavernous sinus, overzealous sinus packing must also be avoided because of potential compressive injuries to the cranial nerves. Recently, another method was introduced that consists of injecting fibrin glue to achieve coagulation during cavernous sinus bleeding23). The fibrin glue fills the cavernous sinus by forming a local coagulum within the cavernous sinus. It obliterates the main venous channels that lead into the cavernous sinus space, which safely provides a dry cavernous sinus surgical field.
The surgical treatment of aneurysms that arise from the paraclinoid segment of the ICA has been a technical challenge for cerebrovascular surgeons. The authors have tried to avoid the several complications in extradural anterior clinoidectomy to paraclinoid aneurysms using several tactics. A backward-curved pair of scissors were used parallel to the ACP in order to avoid injuring the cranial nerves. The ACP was drilled carefully until only a thin rim remains with the cold saline irrigations. ICA occlusions can be prevented with the use of angled fenestrated clips. Also, careful attention on the origin of bleeding is advised when peeling the wall of cavernous sinus. Precise anatomical knowledge combined with these microsurgical tactics for preventing and managing potential challenges can help to achieve good outcomes with minimal complications.