J Neurosurg 125:779–786, 2016 Neurosurgical Forum Letters TO THE EDITOR Reduced incidence of CSF leak domized study to remove the confounding factors would be ideal to determine the superiority of one method of cra- following complete calvarial nioplasty over other. reconstruction of craniectomies Chinmaya Dash, MCh Kanwaljeet Garg, MCh TO THE EDITOR: We read with keen interest the ar- ticle by Eseonu et al.2 (Eseonu CI, Goodwin CR, Zhou Bhawani Shankar Sharma, MCh X, et al: Reduced CSF leak in complete calvarial recon- All India Institute of Medical Sciences, New Delhi, India structions of microvascular decompression craniectomies using calcium phosphate cement. J Neurosurg 123:1476– References 1479, December 2015) regarding the reduced incidence 1. Barker FG II, Jannetta PJ, Bissonette DJ, Larkins MV, Jho of CSF leaks following complete calvarial reconstruction HD: The long-term outcome of microvascular decompres- of craniectomies done for microvascular decompression sion for trigeminal neuralgia. N Engl J Med 334:1077–1083, (MVD) using calcium phosphate cement. 1996 MVD is a very fruitful surgery and provides symptom- 2. Eseonu CI, Goodwin CR, Zhou X, Theodros D, Bender MT, atic relief in up to 95% of patients with trigeminal neural- Mathios D, et al: Reduced CSF leak in complete calvarial re- 4,5 constructions of microvascular decompression craniectomies gia. CSF leakage following MVD can be devastating. using calcium phosphate cement. J Neurosurg 123:1476– We commend the innovative idea of the authors in their 1479, 2015 efforts to reduce the incidence of CSF leaks following ret- 3. Hutter G, von Felten S, Sailer MH, Schulz M, Mariani L: rosigmoid craniectomy for MVD. The authors report on Risk factors for postoperative CSF leakage after elective 221 patients who underwent retrosigmoid craniectomy for craniotomy and the efficacy of fleece-bound tissue sealing MVD to treat trigeminal neuralgia. Of 221 patients, 116 against dural suturing alone: a randomized controlled trial. J consecutive patients received polyethylene titanium mesh Neurosurg 121:735–744, 2014 4. Shibahashi K, Morita A, Kimura T: Surgical results of incomplete cranioplasty and the subsequent 105 patients microvascular decompression procedures and patient’s post- received calcium phosphate for complete cranioplasty. operative quality of life: review of 139 cases. Neurol Med They reported a statistically significant higher incidence Chir (Tokyo) 53:360–364, 2013 of CSF leaks in the incomplete-cranioplasty group and no 5. Sindou M, Leston J, Decullier E, Chapuis F: Microvascular leaks in the calcium phosphate group. We would like to decompression for primary trigeminal neuralgia: long- bring few important points in this article to the kind atten- term effectiveness and prognostic factors in a series of 362 tion of the readers. consecutive patients with clear-cut neurovascular conflicts who underwent pure decompression. J Neurosurg 107:1144– Dural closure was augmented with a collagen dural 1153, 2007 substitute, which was sutured to the dura and reinforced with collagen matrix and fibrin sealant. However, the ar- Disclosures ticle did not mention the number of patients in whom du- The authors report no conflict of interest. ral substitute was required for dural closure (in patients in whom primary dural closure was not possible) in each group, and this could be a cause of bias.3 Other causes of poor wound healing like diabetes, steroid use, and mal- Response nutrition were not evaluated and can be a very important No response was received from the authors of the origi- cause of bias and need to be accounted for. Moreover, the nal article. rate of CSF leak reported in one of the largest series of MVD was 1.5%.1 There might be some other factors re- sponsible for a high CSF leakage rate in the patients who INCLUDE WHEN CITING received polyethylene titanium mesh–augmented incom- Published online June 17, 2016; DOI: 10.3171/2016.3.JNS16514. plete cranioplasty (CSF leakage rate 4.5%). Hence, a ran- ©AANS, 2016 J Neurosurg Volume 125 • September 2016 779 Unauthenticated | Downloaded 09/30/21 11:55 AM UTC Neurosurgical forum Endoscopic endonasal approach for necessarily mean ample exposure of the aneurysm. For example, the authors mention that for ophthalmic artery clip ligation of cerebral aneurysms aneurysms, an ophthalmic artery with medial origin can be exposed through an endoscopic endonasal corridor. TO THE EDITOR: We read with interest the article by However, one cannot be certain that an aneurysm is safely Szentirmai et al.9 (Szentirmai O, Hong Y, Mascarenhas L, exposed through this route. While we agree with the au- et al: Endoscopic endonasal clip ligation of cerebral aneu- thors that “patient series are needed to clarify the safety of rysms: an anatomical feasibility study and future direc- endoscopic endonasal corridor” for aneurysm surgery, we tions. J Neurosurg 124:463–468, February 2016). The au- think that multiple cadaveric studies are needed to define thors performed a cadaveric study on 9 specimens to study the advantages and disadvantages of this approach for ev- the vascular anatomy through the endoscopic endonasal ery possible aneurysm location. Such studies need to com- approach. They also aimed to assess the possible maneu- pare the classic transcranial approach(es) used for each verability of anterior and posterior circulation vessels specific aneurysm with the tailored alternative EEA in through the endoscopic approach to simulate the surgical terms of instrument maneuverability, perforator exposure, treatment of aneurysms through the nose. They calculated extent of proximal and distal vessel control, and possible the “maximal surgical corridor” areas and assessed the risks to the neural structures. Without these investigations, visibility of adjacent vessels and perforator anatomy. We it seems too unsafe to proceed with case series in which would like to congratulate the authors for the selection of the EEA is used for aneurysm clipping, because there is this interesting topic and performing this study and add little scientific evidence to base the indications for the use several comments. of the EEA for each particular aneurysm. Such studies have been performed to compare different transcranial The authors calculated the maximal surgical corridor 3,6,11 to approach different anatomical regions. It is not clear approaches and are also in evolution for the compari- how they define the maximal surgical corridor. Although son of the EEA with transcranial approaches to address the anterior circulation vessels can be exposed through the specific pathologies in specific locations. There are also 2,5,10 several studies that evaluate the role of EEAs in cerebro- transtubercular approach, we believe the area of expo- 2,7,8,10 sure needs to be defined specifically for different surgical vascular surgery. We think that more work still needs targets (i.e., aneurysm locations). Such definition should to be done to further delineate this role, especially as com- include clear anatomical landmarks as boundaries. There- pared to the classic transcranial routes. fore, considering internal carotid artery (ICA) and ante- The authors stated that the EEA exposures gave them rior communicating artery (ACoA) aneurysms in a single sufficient space to deploy 2–3 clips in different vascular surgical area seems an oversimplification. Exposure of the areas. We agree that the ability to place a clip (temporary clinoidal segment of the ICA and the ophthalmic artery or permanent) is very important in aneurysm surgery, es- pecially when it is done through an endoscopic endonasal complex requires a different trajectory from that of the 4,8 route, but we strongly believe that the fact that the surgeon ACoA complex. This is exceptionally important in en- is able to apply a clip does not mean that exposure is sat- doscopic endonasal approaches (EEAs), where the area of isfactory for aneurysm clipping. The distance of the vessel exposure needs to be as large as necessary and as small as “exposed” needs to be compared to the distance between possible to minimize the risks of a CSF leak while provid- the proximal and distal locations of the clips that can be ing optimal results. safely applied to evaluate the surgeon’s ability to maneu- In the Results section, the authors state that “…anter- ver through that specific corridor. In our opinion the safety osuperiorly projecting aneurysm dome would offer the of clip application (i.e., one with adequate visualization of most favorable access…best visualization of the aneurysm the target vessel, surrounding perforators, and clip tongs neck…perforators…and minimal risk of sac rupture.” We during placement) is as important as the ability to apply agree with the authors that anterosuperiorly projecting an- it. An EEA offers good visibility; however, we still do not eurysms of the ACoA complex would be good candidates know how much we can exactly do through that approach for clip ligation through an EEA. An EEA provides ample for different targets. In addition, the implicit limitation of midline exposure along the tuberculum sellae and does al- the cadaveric model does not allow the placement of clips low control of adjacent structures like the optic chiasm. simulating a real-life scenario, as the absence of the aneu- Also, there may be no need to resect the gyrus rectus to rysm leads to overestimation of the results. In our opinion, expose the aneurysm, as there may be in open surgery.12 targeted cadaveric studies on each aneurysm location and However, we cannot see the link between the methods and feature are required before reaching conclusions on the results of the study and such an interpretation of the re- feasibility or role of the EEA in cerebrovascular surgery. sults. The effect of expected anatomical variations, such The authors propose that angled endoscopes provide as the pre-fixed optic chiasm and midline position of the “a special opportunity for visualizing perforating arter- anterior bend of the ICA (known as kissing carotids), may ies.” We agree completely with this statement.