Minimally invasive thumb-sized pterional craniotomy for aneurysm clipping has afforded our patients with a shorter hospital stay at a lower cost compared to the national average.
Less invasive surgical approaches for intracranial aneurysm clipping may reduce length of hospital stay, surgical morbidity, treatment cost, and improve patient outcomes. We present our experience with a minimally invasive pterional approach for anterior circulation aneurysms performed in a major tertiary cerebrovascular center and compare the results with an aged matched dataset from the Nationwide Inpatient Sample (NIS). From August 2008 to December 2012, 22 elective aneurysm clippings on patients ≤55 years of age were performed by the same dual fellowship-trained cerebrovascular/endovascular neurosurgeon. One patient (4.5%) experienced transient post-operative complications. 18 of 22 patients returned for follow-up imaging and there were no recurrences through an average duration of 22 months. A search in the NIS database from 2008 to 2010, also for patients aged ≤55 years of age, yielded 1,341 hospitalizations for surgical clip ligation of unruptured cerebral aneurysms. Inpatient length of stay and hospital charges at our institution using the minimally invasive thumb-sized pterional technique were nearly half that of NIS (length of stay: 3.2 vs 5.7 days; hospital charges: $52,779 vs. $101,882). The minimally invasive thumb-sized pterional craniotomy allows good exposure of unruptured small and medium-sized supraclinoid anterior circulation aneurysms. Cerebrospinal fluid drainage from key subarachnoid cisterns and constant bimanual microsurgical techniques avoid the need for retractors which can cause contusions, localized venous infarctions, and post-operative cerebral edema at the retractor sites. Utilizing this set of techniques has afforded our patients with a shorter hospital stay at a lower cost compared to the national average.
Surgical clip ligation had been the mainstay of treatment for intracranial aneurysms but has been recently supplanted mostly by less invasive endovascular techniques.1,2 Clinical trials including the International Study of Unruptured Intracranial Aneurysms (ISUIA-1 and ISUIA-2), and the International Subarachnoid Aneurysm Trial (ISAT) have demonstrated lower morbidity and mortality, reduced length of hospital stay, and lower overall expense, with endovascular treatment compared to surgical clip ligation.3–5 However, the higher aneurysm recurrence rate after endovascular therapy has led to the examination of the cumulative risk to the patients compared to surgical clip ligation.3,4 Surgical treatment remains an important modality for aneurysm therapy, particularly for anterior circulation aneurysms that have morphologies that may be difficult to treat with endovascular means.
Unlike advancements in endovascular devices, few advances in surgical techniques have been made recently. Techniques to make surgical treatment less invasive have included the supraorbital craniotomy combined with the eyebrow incision for anterior circulation aneurysms and “retractorless surgery” to minimize surgical trauma to the brain during aneurysm clipping.6–8 These less invasive surgical approaches may reduce length of hospital stay, surgical morbidity, treatment cost, and improve patient outcomes.9
Here, we present our experience with a minimally invasive approach to surgical clip ligation of unruptured intracranial aneurysms using a pterional approach for anterior circulation aneurysms performed in a major tertiary cerebrovascular center and compare the results with an age matched dataset from the Nationwide Inpatient Sample (NIS). The surgical technique will be reviewed, including patient preparation, brain relaxation, sylvian fissure dissection, and closure. Post-operative care and discharge requirements will also be outlined.
NOTE: Prior to performing this procedure, obtain all required institutional approval and patient consent.
1. Surgical Technique
2. Brain Relaxation
3. Sylvian Fissure Dissection
4. Post-treatment Care
Currently, at our institution over 150 aneurysms are treated annually. From August 2008 to December 2012, 22 elective aneurysm clippings using this minimally invasive thumb-sized pterional craniotomy technique for supraclinoidal aneurysms on patient’s ≤55 years of age were performed by the same dual fellowship-trained cerebrovascular/endovascular neurosurgeon that developed this technique (EMD) (Table 1). This age group was chosen as earlier trials have shown that surgical treatment of aneurysms in patients above this age result in worse outcomes than endovascular treatment and hence, few patients older than 55 are treated with surgical clip ligation at our institution.
Only one patient (4.5%) treated for a right MCA aneurysm experienced a post-operative complication. A head CT scan was obtained due to decreased left upper extremity movement and revealed ischemic changes in the distribution of a right MCA branch most consistent with a thromboembolic event during clip ligation or transient vasospasm. The patient improved with physical and occupational therapy and was at baseline at two-month follow-up. 18 of 22 patients returned for follow-up imaging and there were no recurrences through an average duration of 22 months.
To represent the national average, we utilized the Nationwide Inpatient Sample (NIS) from 2008 to 2010. The NIS is a hospital discharge database that represents approximately 20% of all inpatient admissions to nonfederal hospitals in the United States. We obtained the NIS database from the Agency for Healthcare Research and Quality’s Healthcare Cost and Utilization Project (Rockville, MD). Detailed information on the design of the NIS is available at http://www.hcup-us.ahrq.gov.
Hospitalizations for clipping of unruptured cerebral aneurysms were collected from the NIS by cross-matching the International Classification of Diseases (ICD-9-CM) diagnosis code for an unruptured cerebral aneurysm (437.3) with the procedure code for clipping (39.51) of a cerebral aneurysm. The ICD-9-CM codes used for aneurysm clipping have been previously studied and validated.10–16 Only patients under 55 years of age were included, as to age-match the cases with our internal dataset. We excluded patients with “subarachnoid hemorrhage” (ICD-9-CM 430) and “intracerebral hemorrhage” (ICD-9-CM 431). In comparing total hospital charges across the years we assumed a 3% annual inflation rate for each year and used the adjusted charges in the analyses.
1,341 hospitalizations for surgical clip ligation of unruptured cerebral aneurysms were identified. Inpatient length of stay and hospital charges at our institution using the minimally invasive thumb-sized pterional technique were compared to NIS using Mann-Whitney U tests. Both outcome measures were significantly reduced at our institution in comparison to the national average (Table 2).
Age, yrs | 47.5 (44-52) |
Male | 4 (18%) |
Aneurysm maximum dimension, mm | 6.3 (5.6-9.0) |
Location | |
Internal carotid artery | 4 (18%) |
Middle cerebral artery | 7 (32%) |
Anterior cerebral artery | 2 (9%) |
Anterior communicating artery | 6 (27%) |
Posterior communicating artery | 3 (14%) |
Craniotomy size, mm2 | 1,835 (1,370-2,133) |
Postoperative complications | 1 (4.5%) |
Duration of follow-up, months | 22 (14-28) |
Recurrence | 0 (0%*) |
Continuous variables presented as median (intequartile range) | |
Categorical variables presented as n (%) | |
*4 patients were not available for follow-up imaging |
Table 1: Internal Dataset Patient Characteristics
Internal dataset | NIS | P Value | |
Age, yrs | 47.5 (44 – 52) | 47 (42 – 52) | 0.561 |
Length of stay, days | 2 (1 – 3) | 4 (3 – 6) | <.001 |
Hospital charges, $ | 49,040 (42,550 – 58,767) | 77,178 (55,778 – 121,461) | <.001 |
Continuous variables presented as median (interquartile range) |
Table 2: Internal Dataset compared to Nationwide Inpatient Sample (NIS)
Surgical clip ligation of intracranial aneurysms remains a relevant and important option in treating certain types of aneurysms, though this role has been diminishing over the past several years as endovascular technology becomes safer and more efficacious. Endovascular treatment has surpassed surgery for cerebral aneurysms, yet the higher recurrence rate after endovascular treatment, the occasional need for surgical treatment after aneurysm recurrence from failed endovascular treatment, specific morphologies making endovascular therapy higher risk requiring stent placement, and some recent literature reviewing the cumulative risk of endovascular treatment being higher than for surgical treatment, all keep surgical clip ligation relevant to aneurysm treatment.17
The subfrontal approach was first described as a unilateral approach by Krause in 1908, and then modified by Dandy and Heuer for lesions of the pituitary gland and optic canal.18 In 1933, Dott used this approach for clipping an aneurysm.19 Through this technique there is minimal brain exposure and wide access to the suprasellar region with minimal need for brain retractors. Dandy and later Yasargil modified and used this technique to clip anterior communicating artery aneurysms.20,21 Many other neurosurgeons have modified this technique describing it by different terms and have used this approach not only to reach vascular, but also anterior skull base lesions. Al-Mefti and Fox modified the supraorbital approach to the supero-lateral orbital exposure.22 This extends the supraorbital craniotomy to include the lateral and superior orbital wall. This approach was used for orbital and skull base tumors as well as for complex anterior circulation aneurysm clipping. The advances in neurosurgery have been reflecting the size of the craniotomy and exposure not only for the cosmetic advantage but also to avoid complications such as epidural hematomas, unintended cortical injury, brain retraction, and the time of exposure to room air.
Van Lindert et al. reported a series of 139 patients with a total of 197 aneurysms that were treated with clipping through the supraorbital keyhole approach.18 In this study no complications related to the exposure were reported, and only four patients experienced aneurysmal rupture during clipping. The ruptures were attributed to aneurysm dissection or a result of clip application, and not due to brain retraction. The authors describe that multiple aneurysms can be safely clipped in the same procedure and that contralateral aneurysms can be safely reached. Petraglia et al. reported a series of 28 patients with anterior communicating artery aneurysms that were treated with clipping through the subfrontal approach.8 They describe this technique as safe and with fewer complications compared to the traditional pterional approach.
Some of the limitations related to the keyhole supraorbital approach are: (1) the keyhole is not always performed in the same anatomical location. The small incision and craniotomy requires good preoperative planning with MRI and CT reconstructions that depict the aneurysm orientation and the bony structures. In this way the incision and craniotomy need to be individualized for each patient’s anatomy. (2) The direction of the instruments and light must be in the same plane and may require special clips that allow better visualization of the target. (3) There is a higher risk of opening of the frontal sinus, which may negate any cosmetic advantages compared to the pterional approach.23 (4) Requires a well trained vascular neurosurgeon.
At our institution, the senior author’s (EMD) approach for clipping anterior intracranial aneurysms involves thumb-sized pterional craniotomies without brain retractors. It is important to use a mouthpiece on the operative microscope for continuous readjustment of focus and angle of view to maintain constant bimanual manipulation of the brain tissues without retractors. This is considered less invasive than the standard approach and prevents many post operative complications and provides a faster recovery. We believe this is reflected in the shorter post-operative length of stay and lower total hospital charges, in comparison to the national average from NIS.
It is important to note that the patients treated at our institution had supraclinoid aneurysms. We do not treat aneurysms below the communicating segment of the internal carotid artery using the described clipping technique because drilling of the anterior clinoid process would require a larger craniotomy and cervical carotid cut-down for proximal arterial control. Additionally, none of the aneurysms treated in this study were considered giant aneurysms (>20 mm). In our experience, these larger aneurysms typically require more extensive exposure to allow bypass and dissection to identify inflow and outflow zones and would not be treated well with a mini-craniotomy. Additionally, this smaller-sized craniotomy does readily allow for multiple clip placements when needed and provides adequate exposure for proximal and distal control of the parent arteries associated with supraclinoid aneurysms in preparation for possible aneurysm rupture during dissection or clip placement. It avoids using the standard sized craniotomy flap to minimize any unnecessary exposure of the cortical surface which can be damaged during the approach. It also minimizes potential space for fluid and blood collections to form in the subdural and epidural spaces.
It is important to recognize however, that this is a single-center, single surgeon, retrospective study with a relatively small sample size. Treatment was not randomized and this could be a potential for selection bias. We tried to minimize bias by matching the groups with only patients under 55 years of age; knowing that advanced age is a contraindication to clipping of an unruptured cerebral aneurysm.3 However, due to limitations of the NIS, we could not control for important confounders such as aneurysm size and location, limiting the conclusions that can be drawn in our comparisons with the national average. The lower costs and shorter length of stay at our institution, in comparison to the national averages, can also be partially attributed to institutional resources. Centers handling a large volume of cases for aneurysm treatment likely have a dedicated staff and a standardized set of protocols. A prospective randomized multicenter trial that includes the cost of long-term follow-up, recurrence rates, and return to work will better address these limitations and expand the scope of the study.
Lastly, we emphasize that this technique is being reported for the surgical treatment of unruptured supraclinoid anterior circulation aneurysms measuring no larger than 20 mm. Larger or ruptured aneurysms, were not evaluated in this study because these aneurysms frequently require larger craniotomies for bypass and proper exposure and in the case of subarachnoid hemorrhage, larger craniotomies are required because of brain swelling, potential craniectomy, and access to lobar intraparenchymal hemorrhages. Though this exposure has been used in low Hunt-Hess grade subarachnoid hemorrhage patients with small and medium sized anterior circulation aneurysms in the locations described above, these data were not studied here and are not recommended until the surgeon has established a degree of comfort with surgical exposure first, with the unruptured aneurysms. The minimally invasive thumb-sized pterional craniotomy allows good exposure of small and medium-sized supraclinoid anterior circulation aneurysms. Additionally, minimal to no Sylvian Fissure dissection can be acquired with this craniotomy when approaching anterior communicating artery aneurysms. The senior author has found this approach to be very effective when approaching both ruptured and unruptured anterior communicating artery aneurysms, particularly those pointing inferiorly and anteriorly where the neck and inflow and outflow vessels could be readily identified. This thumb-sized craniotomy allows a subfrontal approach with minimal to no dissection of the Sylvian Fissure or resection of the Gyrus Rectus.
We recommend that neurosurgeons who do not routinely employ these surgical techniques, judiciously and progressively incorporate these minimally invasive and less tissue damaging maneuvers into their approach based upon comfort level. Cerebrospinal fluid drainage from key subarachnoid cisterns and constant bimanual microsurgical techniques avoid the need for retractors which can cause contusions, localized venous infarctions, and post-operative cerebral edema at the retractor sites. Utilizing this set of techniques has afforded our patients with a shorter hospital stay at a lower cost compared to the national average.
The authors have nothing to disclose.
The authors have no acknowledgments.
Mayfield Infinity skull clamp | Integra | A-1114 | |
Mayfield table attachment | Integra | A-1018 | |
4-French Fukishima suction tip | Integra | R-8986 | |
Periosteal elevator (Langenbeck) | Codman | 65-1116 | |
Metzenbaum scissors | Codman | 36-5023 | |
Malis dissector, round angled | Codman | 80-1541 | |
Penfield dissector, style 1 | Codman | 65-1015 | |
Lempert bone rongeur | Codman | 19-1232 | |
Malis Irrigation Module | Codman | Module 1000 | |
Bovie monopolar electrocautery device | Codman | ||
Insulated blade for electrocautery device | Covidien | E1455 | |
Fish-hook retractors | Lone Star | 3350-8G | |
Pneumatic drill | Medtronic | Midas Rex MR7 | |
Side-cutting drill | Medtronic | F2/8TA23 | |
Fluted legend match head tool | Medtronic | 10MH30 | |
Surgical scalpel No. 10,11,15 | Bard-Parker | 0029064 (No.10), 0018291 (No.11), 0018043 (No.15) | |
Intra-operative microscope with mouthpiece | Leica | ||
Microscissors | V. Mueller | NL3785-034(st), NL3785-035(cvd) | |
Rhoton dissector, #2 | V. Mueller | NL3785-002 | |
Telfa strips | American Surgical | #80-09 (1/2×3), #80-04 (1/4×3) | |
Aneurysm clip | Aesculap | ||
Raney clip applier | Aesculap | FF012R | |
Synthes Matrix metal plating system | Synthes | ||
Braided absorbable surgical sutures (Vicyrl) | Ethicon | J790D (3-0), J743D (4-0) | |
Braided nylon nonabsorbable surgical sutures (Nurolon) 4-0 | Ethicon | C584D | |
Doppler System | Mizuho | 07-150-02 |