General considerations
BSCM is a rare condition. Scientific focus is set on different treatment modalities, the ideal time point of surgery or radiotherapy and surgical approaches[12, 15, 27, 30, 36]. Indication for surgery is mainly given by a symptomatic lesion which is surgically accessible[40]. Al Mefty and Spetzler pointed out, that the definition of “surgically accessible” can be interpreted widely and that it rather depends on the institutions’ experience in treatment of BSCMs[4]. Accordingly, it seems crucial to optimize surgical precision and effectiveness to the highest level possible. Implementation of neuroendoscopic techniques already improved surgical success in various pathologies of the posterior fossa, e.g., in intrameatal vestibular schwannoma resection[16, 19, 22, 24, 35]. Even comparably rare indications such as resection of optic pathway cavernous malformations have been treated successfully under endoscopic guidance[9, 39]. However, reports on endoscopic techniques in procedures for BSCM remain very limited to several case reports and small series (Table 3)[3, 10, 17, 18, 23, 26, 32, 33, 38].
Table 3
List of literature reports on endoscopic techniques in surgery for BSCM
publication
|
type of study
|
patients
|
endoscopy
|
approach
|
Sandalcioglu et al., 200230
|
retrospective, single-center series
|
12
|
partly endoscopic assisted
|
variable
|
Sanborn et al., 201229
|
case report
|
1
|
fully endoscopic
|
transnasal, transclival
|
Linsler & Oertel, 201514
|
case report
|
1
|
fully endoscopic
|
transnasal, transclival
|
Nayak et al., 201523
|
retrospective, single-center series
|
4
|
fully endoscopic
|
transnasal, transclival; retrosigmoidal; supracerebellar
|
He et al., 201624
|
case report
|
1
|
fully endoscopic
|
transnasal, transclival
|
Gomez-Amador et al., 201727
|
case report
|
1
|
fully endoscopic
|
transnasal, transclival
|
Erickson et al., 201828
|
case report
|
1
|
fully endoscopic
|
transnasal, transclival
|
Alikhani et al., 201925
|
case report
|
1
|
fully endoscopic
|
transnasal, transclival
|
Surgery
To preserve eloquent brain tissue and structures, a minimally-invasive approach and manipulation within the brainstem is crucial. The two-point method, published by Brown et. al., aims towards limiting surgical corridors. In some cases of BSCM, when the direct approach crosses eloquent tissue, it even recommends an alternative, sometimes more demanding approach[7]. Moreover, extra- and intralesional bleeding has to be differed precisely to avoid unnecessary preparation[27]. In the presented cases the favourable entry point was defined under endoscopic view (Fig. 5). Thereby the subsequent corticotomy could be limited to an average of 4.5x3.7 (± 1.0x1.1) mm. The minimal invasiveness is strengthened by the small median relation of 9.99% (1.2% − 31.39%) between the surgical entry point and the maximum dimension of BSCM (figures within Table 2). Surgical invasiveness due to preparation on the brainstem surface could subsequently be limited effectively. Unfortunately, there is no systematic analysis on the size of corticotomy and its effect on surgical success or clinical outcome in microsurgical procedures available. Since endoscopically assisted resection of BSCM is the standard procedure for BSCM resection in the authors’ department, neither an internal control group could be assessed. Accordingly, the presented results are lacking statistical proof of significance. However, the authors presume that a definition of convenient entry points under endoscopic and navigational guiding contributes to a less invasive surgical preparation.
In this study, endoscopes were applied free-handed and maneuvered manually at different timepoints of the procedure. While the authors are used to insert the optics purely under endoscopic visualization, modern microscopes enable a synergistic combination of both techniques in order to improve orientation and a safe handling. Such microscopic integration might advance getting familiar with endoscopic techniques in this specific indication. In the presented cases, only 2D-visualization was used. However, with an increasing frequency of endoscopically assisted or purely endoscopic procedures in neurosurgery, technological solutions for a stereoscopic view are demanded. In this context 3D-exoscoscopes turned out to be rather applicable in spinal procedures[8]. Possible advantages of 3D-HD-endoscopic visualization, as described for transsphenoidal pituitary surgery[37], remain elusive regarding BSCM resection. The authors used endoscopy mainly for additional inspection purposes. Only in few cases preparation, coagulation or resection is carried out under pure endoscopic guidance. Implementation of advanced endoscopic visualization technologies may form a basis for future BSCM resection purely under 3D-endoscopic guidance.
The presented cases underline the possibility of a safe implementation of neuroendoscopy in various approaches to BSCMs. There were no intraoperative complications associated to the endoscope in this study. However, precautious maneuvering is essential, since the optics are inserted free-handed and guided manually. Manual handling, especially of angled endoscopes underlies a certain learning curve[34]. Whilst surgical results of endoscopic transsphenoidal procedures could be shown to significantly improve after 20–50 cases[20, 21], it seems obvious, that such numbers can hardly be achieved for BSCM. Thus, endoscopically assisted resection of BSCM should be reserved for extensively trained neuroendoscopists. The senior surgeon (JO) exhibits broad expertise regarding cranial and spinal endoscopic techniques for more than 15 years in daily practice. This may lead to the absence of endoscopy-related complications within the presented series and highlights the necessity of neuroendoscopic experience in this specific pathology.
Achievement of gross total resection remains the fundamental surgical goal. The risk of fatal re-bleeding due to remnant cavernoma cannot be emphasized enough[6, 45]. Especially in deep seated lesions, microscopic insight into the resection cavity can be very limited[33]. This dilemma aggravates by minimizing the surgical entry point into the brainstem as shown in this series. In such cases, endoscopy can be of high value. As shown, endoscopic 360° inspection of the resection cavity was possible in all cases, even through the smallest corticotomy of 2.8x3.2mm. Due to the limited number of patients included and the absence of a statistical control group, a probabilistic analysis on detection rates with the endoscope cannot be provided. However, assurance of a gross total resection might be supported by additional endoscopic inspection and should be evaluated in further studies. Garcia et al. recently reported on a recurrence rate of 6.6% in his large series of 213 patients with BSCM in over 20 years. Blind spots and misinterpretation of the resection cavity’s surface were considered important contributors defining between morbidity and cure[14]. We strongly believe, that the endoscope adds significant information for the neurosurgeon at this point. Especially considering the proposed right-angle-method[14], angled endoscopes might facilitate detailed inspection of potential blind spots. However, in the presented study, one patient (5%) showed re-bleeding due to recurrence 6 months after initial resection. Hence, the endoscopic visualization should not be considered as guarantee for gross total resection. Despite the possibility of circumferential illumination of the resection cavity, undetected residual cavernoma tissue cannot be precluded. Yet, endoscopic inspection might reduce the risk of unidentified remnant BSCM, but the study design, with its limited case numbers and the absence of a microsurgical control group, does not allow a statistically convincing conclusion in this context and further prospective studies are needed.
Clinical outcome
Favorable clinical outcome after surgery for BSCM is reported in a majority of all cases. Improved or stable medical condition can be found in 61–91%[13, 27, 28, 44]. In the presented study 80% of the patients showed an improved, or at least stable, clinical status after surgery. Furthermore, 61.1% improved after another 12 months follow-up. Hence, the presented results seem very representative compared to previous studies.
Wu et al. reported a statistical trend of cavernous malformations involving cerebellar peduncle towards unfavorable short- and long-term outcomes[43]. In this study four patients showed BSCM reaching into cerebellar peduncle. Only one patient showed clinical deterioration after surgery, whilst the others had an excellent clinical outcome after 12 months. Without being able to strengthen it statistically the presented results cannot support this thesis.
Though overall clinical outcome appears to be favorable in the vast majority, intraoperative morbidity should not be despised. With a surgery related morbidity of 20%, the presented study fits in between the reported morbidity rates of 10-37.3%[1, 2, 11, 31, 41]. Compared to literature reports, implementation of endoscopic techniques for BSCM resection does not seem to increase the risk of surgery related morbidity. Taking into consideration that the surgeon’s experience in neuroendoscopy is of high relevance in this context, an interindividual variety in morbidity rates must be assumed.
Limitations
The presented study has several important limitations. Despite the fact, that there is limited literature on endoscopic techniques in BSCM surgery available in particular, this study contains a limited number of patients. The retrospective character makes it susceptible to information and selection bias. Follow-up periods varied noticeably between the presented patients. Although almost all patients underwent clinical and radiological examination after 12 months, subsequent treatment in peripheral or distant hospitals impedes a consequent long-term follow-up in all patients. Major limitation is given by the absence of an internal control group for detailed statistical analysis. Since the endoscopically guided resection is the standard procedure for BSCM surgery within the authors’ department, no internal data for such analysis was available. The presented conclusions must therefore be interpreted with restraint. It is the very purpose of this study to illuminate potential benefits of implementing neuroendoscopy in BSCM surgery. Hopefully, further institutions will be inspired to share their experience, enabling an intensified scientific discourse allowing a strong statistical evaluation.