Transcortical transcatheter ultrasound-assisted technique for deep-seated brain tumors. Technical note

Abstract

Purpose

Surgery of deep-seated brain tumors can be challenging. Several methods have been described to facilitate transcortical approaches, including ultrasound-assisted resection. Ultrasound-guided placement of a standard ventricular catheter is a widely reported technique and has been used to approach these lesions via the transcortical route. We describe how we usually perform this useful technique to assist and enhance the transcortical resection of some deep-seated brain tumors.

Methods

Standard electromagnetic frameless navigation (S8 Neuronavigation System, Medtronic, Minneapolis, USA) was employed to focus the craniotomy and to plan the trajectory of the ventricular catheter. After dural opening, an ultrasound device (Arietta 850, Hitachi-Aloka Medical, Tokyo, Japan) was used for intraoperative ultrasound (IOUS) assessment. A ventricular catheter was placed from the cortex to the lateral wall of the tumor under direct real-time IOUS visualization to guide the further transcortical dissection.

Results

Transcortical transcatheter ultrasound-assisted technique involved minimal time and infrastructure requirements. There were no major technical difficulties during its use, providing confidence and improving subcortical white matter dissection by guiding the route to the tumor.

Conclusions

Recent improvement of IOUS image-quality devices offers several attractive options for real-time navigation. The combination of conventional neuronavigation systems with real-time IOUS assessment during the intradural step provides a higher degree of control by improving the execution of the surgery. We hope this description may be a useful tool for some selected cases and contribute to the further enhancement and improvement of this widely used technique.

Introduction

Surgical resection of deep-seated brain lesions can be challenging. When the transcortical approach is used, accurate tumor location and the surgical corridor employed to reach the tumor are two of the paramount points of the procedure [1]. Ultrasound-guided placement of one ventriculostomy catheter from the cortex to the tumor is an easy and well-described technique which simplifies the white matter dissection step along the transcortical route. This technique, based on subcortical dissection along a previously placed catheter which serves as a landmark to reach the tumor, has several variants, and has been used not only for deep-seated brain tumors [2–4]. Among its other possibilities, we also find described transcortical approaches to lateral ventricle and intracerebral hematoma evacuation surgery [5, 6].

In this paper we describe, step by step, an illustrative case of how we usually perform this feasible technique to facilitate the transcortical resection of some deep-seated brain tumors.

Material and methods

We present a case of a 54-year-old woman with a history of previous breast cancer, who after being free of disease for 7 years presented a lesion compatible with metastasis in the initial cranial scan. Magnetic resonance imaging (MRI) showed a single deep-seated lesion in the right caudate nucleus (Fig. 1). The patient was neurologically intact. After considering the transcallosal approach, we finally decided to use a right frontal transcortical approach. An ultrasound device (Arietta 850, Hitachi-Aloka Medical, Tokyo, Japan) was used for intraoperative ultrasound (IOUS) assessment. A convex transducer ultrasound probe (C42, Hitachi Medical, Tokyo, Japan) with a bandwidth of 8 to 4 MHz was selected for epidural and transcortical evaluation (Fig. 2a–c). A standard ventricular catheter was employed to guide the further transcortical dissection from the cortex to the tumor wall. Standard electromagnetic frameless stereotactic navigation (S8 Neuronavigation System, Medtronic, Minneapolis, USA) was employed to focus the craniotomy and to plan the trajectory and the entry and target points of the ventricular catheter. An electromagnetic stylet (Stealth-Station electromagnetic stylet, Medtronic, Minneapolis, USA) was also employed as a ventriculostomy catheter guide (Fig. 2d–e).

Fig. 1.

Preoperative study. The initial radiological diagnosis was a right caudate nucleus breast cancer metastasis. A Contrast-enhanced axial T1-weighted MRI shows a single contrast-enhancing lesion on the right caudate nucleus. B, C Coronal and sagittal images provide a better tridimensional picture of the lesion showing how deep the tumor is located

Fig. 2.

Materials and infrastructure required. Intraoperative photos. A–B The ultrasound device and a convex probe are taken from the neonatal intensive care unit. C The ultrasound probe is sterilely assembled. D A standard ventricular catheter is cut to fit the length of the electromagnetic frameless neuronavigation stylet. E: The electromagnetic stylet replaces the standard ventricular catheter guide to navigate the ventricular catheter

Operative technique

The procedure was performed using MRI-based electromagnetic neuronavigation. Entry and target points, from the anterior third of the superior frontal sulcus to the lateral wall of the tumor, were planned on the navigation software. Based on preoperative scans and intraoperative navigation, a right frontal craniotomy was performed over the anterior third of the superior and medial frontal gyrus. The trajectory from the entry point to the lesion was not the shortest but rather the route with the least transgression of white matter fascicles.

First of all, the ultrasound probe was sterilely assembled for epidural evaluation. Copious normal saline was used. Correct identification of the lesion by ultrasound was verified and the findings were correlated with the preoperative MRI studies (Fig. 3). After the dura was opened, the arachnoid over the previously selected entry point was split and the sulcus was minimally deepened.

Fig. 3.

Correlation of preoperative MRI with IOUS findings. A Preoperative contrast-enhanced T1-weighted MRI coronal cut. Note that the right and left sides are inverted for a better correlation with the intraoperative findings. B Initial epidural IOUS evaluation of the tumor shows information and details comparable to the preoperative MRI study. The frontal horn of the left lateral ventricle, septum pellucidum, interhemispheric fissure, the tumor and even the surrounding edema are clearly identified

The navigation stylet was then inserted into the ventricular catheter and the entry point was restarted directly over the surface of the entry point. Using the extrapolated data from the navigation system, the distance between the entry point (sulcus) and the target (tumor wall) was marked with a sterile skin marker on the surface of the catheter. Following the trajectory provided by the navigator, the catheter was introduced for approximately 1 cm until it was visible on the ultrasound monitor. Under direct real-time IOUS visualization and while keeping the planned trajectory, the catheter was advanced until its tip reached the external wall of the tumor (Fig. 4a–c).

Fig. 4.

Intraoperative photographs. A Initial IOUS evaluation. A coronal cut is selected to guide the ventricular catheter placement from the cortex to the external wall of the tumor. B Under direct IOUS visualization, the catheter is advanced until the navigation system wrongly reports that it has reached the tumor. C Brain shift is confirmed. Thus the catheter is advanced under direct real-time IOUS vision until the external wall of the tumor is reached. D Intraoperative view of the placed catheter without the navigation stylet. E–G Transcortical white matter dissection along the catheter surface until the external wall of the tumor is reached. H When the external wall of the tumor is identified, the ventricular catheter is further removed

The navigation stylet was then removed and the catheter was cut and fixed (Fig. 4d). Next, transcortical microsurgical dissection was carried out along the catheter, which worked as an internal fiducial guiding the route to the tumor. As the transcortical dissection progressed deeper, the distance remaining to reach the external wall of the tumor was directly estimated by the conventional marks and holes of the standard ventricular catheters (Fig. 4e–g). At this point, retraction systems were placed if needed and the surgical corridor was subsequently secured with fine patties. When the external wall of the tumor was identified (Fig. 4h), the ventricular catheter was removed and the tumor resection began using standard microtechniques. Once the tumor resection was completed, in order to monitor and anticipate potential postoperative complications, a standard ventricular catheter was left in the frontal horn of the right lateral ventricle.

Results

The transcortical transcatheter ultrasound-assisted technique took minimum operative time and entailed minimal infrastructure requirements. Although not absolutely indispensable, during the extradural time, conventional navigation was useful for centering the craniotomy and planning the trajectory and the ideal entry point. During the intradural step, the IOUS imaging was very valuable for verifying the correct catheter placement and improved control over tumor resection in a real-time fashion.

When the entry point was restarted over the opened sulcus, the distance between the entry point (sulcus) and the target (tumor wall) decreased by 0.9 cm with respect to the initial plan. This was due to brain shift. When we restored the entry point, we observed that the navigator wrongly projected 0.9 cm deeper when the stylet was really still directly placed over the cortex. Thus, when we introduced the catheter and the navigator supposedly informed us that we had reached the tumor, we found by means of IOUS imaging that there was really still a distance of approximately 0.9 cm to reach the lateral wall of the tumor (Fig. 4b). After we noticed this, insertion of the catheter proceeded under direct IOUS visualization until the lateral wall of the tumor was truly reached (Fig. 4c). Another important point during IOUS examination is to avoid blood clots and hemostatic materials. By using copious normal saline irrigation and while keeping the field clean, we can obtain better images. Once correct placement of the catheter was confirmed, further transcortical dissection to reach the tumor was developed more securely and rapidly, solving one of the paramount points in the surgery of deep-seated brain lesions.

In our patient, the entire tumor resection was successfully performed with no additional difficulties (Fig. 5a). Ultrasonography also enabled us to check the proper final placement of the ventriculostomy catheter and carry out a last inspection after dural closure in order to exclude any hemorrhagic complication. The ventriculostomy catheter remained closed until it was removed on the second postoperative day. The patient’s postoperative period was uneventful and was discharged neurologically intact on the fourth postoperative day. The final histological study confirmed the initial diagnosis of breast cancer metastasis (Fig. 5b–e).

Fig. 5.

Macroscopic and microscopic images. A Macroscopic appearance of the resected tumor. Intraoperative photo after complete tumor removal. B Panoramic histological section of the tumor. C Histological appearance of the breast metastatic carcinoma. Clearly delimited tumor-central system interface. Ductal carcinoma (bottom) and cerebral white matter (up). D Only astrocytic elements mark with glial fibrillary acidic protein (up) E Immunostain for Gata 3 in metastatic carcinoma. Strong nuclear positivity of the tumor cells is shown

Discussion

Ultrasonography has its origin in the development of sound navigation and ranging (SONAR) technology during World War I. In the 1930s, Karl T. Dussik theorized the application of ultrasonography for brain tumor diagnosis [7, 8]. The next step came from John J. Wild who identified gastric and breast cancer by ultrasonography. Wild was also responsible for introducing IOUS in neurosurgery, since in 1950 he identified a brain tumor after bone removal. Since then, IOUS indications in neurosurgery have kept growing and now include cranial, spine, vascular and peripheral nerve surgery [7, 9, 10].

Accurate location of intracranial pathology has turned navigation techniques into a basic tool for neurological surgery. However, conventional systems are not able to reflect brain shifts and the progressive extent of tumor resection. IOUS is a real-time imaging tool. In addition, it is cheaper and requires less infrastructure and operative time than other alternatives like intraoperative MRI [11]. These issues, together with the significant image-quality improvement of the new ultrasound systems, are the main reasons why IOUS is playing an important role as a powerful additional tool for conventional neuronavigation systems [12, 13].

Particularly for deep-seated brain tumors, IOUS offers a very wide range of attractive possibilities. The widely described technique of ultrasound-guided ventriculostomy catheter placement can be modified to use the catheter as a surgical corridor for the transcortical approach [2–4, 14]. There are multiple variations and many applications of this versatile technique. In our proposal, frameless navigation is initially used to plan the craniotomy, the entry point and the catheter’s trajectory. Then, the catheter is placed under real-time IOUS guidance, turning it into an extremely simple and helpful tool to guide the further white matter dissection along its length. This is one of the options for employing this well-described and widely employed technique.

Regarding the management of deep-seated brain lesions, there are many studies that describe how to perform the resection via minimally invasive approaches using of tubular retractors. Some of them show some large series where the resection is achieved with excellent results in a very elegant fashion [15–17]. Most of these reports use frameless navigation for the retractor placement, with fewer cases describing the employment of IOUS guidance. Probably, if the craniotomy is large enough, both frameless navigation and real-time IOUS could be used complementarily, facilitating some initial steps of placement of the tubular retractor. Either way, the core philosophy of the abovementioned proposals emphasizes the need to achieve a safe corridor that accurately locates and exposes the lesion. Because these are the inherent characteristics of the transcortical approach for deep-seated brain tumors, navigation is paramount regardless of whether it is carried out via conventional neuronavigation, via IOUS or ideally by a combination of both methods.

Conclusions

Recent improvement of IOUS image-quality devices offers several attractive options for real-time neuronavigation. The transcortical transcatheter ultrasound-assisted technique is an accurate, rapid and suitable additional tool during the transcortical approach to deep-seated brain tumors. The steps to follow are simple, feasible and can be easily performed with minimal infrastructure and operative time. In our patient, the transcortical transcatheter ultrasound-assisted technique facilitated the subcortical dissection and provided a higher degree of real-time control over the tumor resection. The IOUS assessment allowed us to notice and correct brain shift, securing the proper final catheter placement.

We believe that this technique can be feasibly performed in any operating room using generally available materials. We hope that this description of how we usually perform this widely used procedure may be useful for some selected cases and contribute to the further enhancement and improvement of this technique.

Abbreviations

IOUS

Intraoperative ultrasound

MRI

Magnetic resonance imaging

SONAR

Sound navigation and ranging

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Mario Gomar Alba, Antonio José Vargas Lopez, Francisco Javier Velasco Albendea, Gaizka Urreta Juárez, María José Castelló Ruiz and José María Narro Donate. The first draft of the manuscript was written by Fernando García Pérez and José Javier Guil Ibáñez and all authors commented on previous versions of the manuscript. The project was directed by José Masegosa González. All authors read and approved the final manuscript.

Funding

No funding was received to assist with the preparation of the manuscript.

Declarations

Conflict of interest

The authors declare that they have no conflict of interest to declare that are relevant to the content of this article. The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Ethics approval

This study was approved by the local ethics committee. All procedures performed were in accordance with ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standard.

Consent to participate

Signed informed consent was obtained from all patients involved in this study.

Consent to publish

Signed informed consent regarding the use and publication of the results of the performed procedures was obtained from all individual participants included in this study.