Surgery techniques

The Intraoperative magnetic resonance imaging (MRI) system at Klink Hirslanden has been specially developed for neurosurgery. Coupled to a computer-assisted navigation system it enables an MRI scan to be done at any point during an operation. This is particularly helpful when operating on certain types of brain tumors – allowing to precisely delineate the margin between tumor and healthy tissue.

Current research suggests that using this technique can improve the outcome for patients. In cases of malignant brain tumors, particularly glioblastomas, we use intraoperative MRI in combination with a fluorescent dye (Gliolan) in order to further optimize the likelihood of a maximal resection.

When operating on pituitary tumors, intraoperative MRI offers a valuable adjunct to endoscope-assisted microsurgery, particularly in order to visualize hidden or difficult-to-access parts of the tumor and assist in its definitive and total removal.

The intraoperative computed tomography (CT) at Klinik Hirslanden is integrated with the “BrainSuite” system – a neurosurgical operating room equipped with

• the most up-to-date spatial navigation technology and
• microsurgical instruments

At any point during an operation we can perform a CT scan – this is particularly useful in the area of the skull base, for certain brain tumors, for vascular neurosurgery and for selected spine surgery in order to gain precise spatial orientation.

Using CT intraopertively in this way, the precision and thus the safety of an operation can be significantly improved. In operations for spine stabilization, intraoperative CT provides exact confirmation of the position of prosthetic discs or screws, which may be implanted.

Our intraoperative angiography system allows us to perform the most advanced vascular neurosurgery for aneurysms and arterio-venous fistulae or malformations. Every angiographically-assisted operation is performed by an experienced, interdisciplary team of neuroradiologists and neurosurgeons.

Using angiographic monitoring, it is possible to measure particular flow parameters in the blood vessels during the operation, facilitating and optimising intraoperative decision-making, like clip selection and positioning.

Intraoperative electrophysiological monitoring (neuromonitoring) is used to keep track of important neurological functions while operating. In the brain this is especially important when operating near areas, which process motor functions or vision or near tracks of nerve bundles, which convey electrical signals in the deep brain, brain stem or spinal cord. During spinal surgery, especially in complex cases containing scar tissue or during the placements of implants, electrophysiological monitoring is applied to avoid damage to nerves traveling in and next to the spinal canal.

Depending on the structures and functions to be monitored a variety of methods of monitoring are available and often a combination of techniques is applied (Somatosensory evoked potentials (SSEP), Motor evoked potentials (MEP), Acoustic evoked potentials (AEP), Electroencephalogram (EEG), Visual evoked potentials (VEP) and direct tissue micro-stimulation). In all cases a neurologist is present in the operating room to interpret to electrical impulses while they are obtained. In case of tumour surgery, bi-polar or mono-polar micro probes are used to measure functional activity before and while tumour tissue is removed. Comparable to real-time 3D radar, electrical currents are sent from the tip of the stimulation probe into the surgical field in a spherical fashion and with varying intensities, allowing visualization of distances to eloquent structures in all directions and in real time. Especially at tumour boarders or tumour-infiltrated zones, this allows precise differentiation between tumour and healthy tissue.

In nature, bats use ultrasonic waves at a frequency above 20 kHz to locate prey or obstacles. Intra-operative ultrasound is based on the same principle: Waves are emitted by a transducer, reflected individually by tissue structures and detected again by the transducer. In this way different tissues can be visualised. Ultrasound waves are risk-free because, similar to sound waves, they leave no lasting effects in the body.

In neurosurgery, ultrasound allows real-time navigation in the depth of the central nervous system. Ultrasound is used before and after opening of the meninges in order to localize lesions in depth of the brain. During a tumour operation ultrasound enables to visualize and observe the progress of tissue removal in real time.

Intraoperative real-time navigation with ultrasound is a complementary method to intraoperative computer-assisted navigation and can also be linked to it. This is particularly relevant in the event of displacement of brain structures during surgery, which can occur after the drainage of cerebro-spinal fluid (CSF) or the removal of tumour tissue. Intraoperative ultrasound always provides an online and real-time image of tissue, irrespective of its deformation and hence allows for continuous and precise spatial orientation. This is particularly valuable for the detection of tumour borders or anatomical structures such as cortical sulci or ventricles.

For microsurgery of tumors in and around the spinal cord, the use of ultrasound is also enormously helpful: the opening of the dura can be made more precise and, when resecting a tumour in the spinal cord, tumour boundaries can be displayed exactly.

In our center we use most modern and high-resolution ultrasound technology with a series of ultra-sound probes, some of which being so small that they can be placed directly on tissue even inside a small surgical cavities.

Solitary EBV-associated Lymphoma, left parietal, post-central. Minimally invasive trans-sulcar dissection with intra-operative ultrasound.

Computerized neuro-navigation creates an interface for the surgeon between pre-operative imaging and the actual operation. Before surgery 3D MRI (Magnetic Resonance Imaging), CT (Computed Tomography) and catheter angiography diagnostic data are used to produce images of a for example tumor, the skull base or vessels with very high resolution. Already during the 3D planning of the operation, we assess the position of the target area in relation to other important structures that we want to protect during the operation, such as important nerve tracts (represented in the MRI by fiber tracking), speech areas, motor areas or venous and arterial supplying vessels of the brain.

During the operation, the patient's head is fixed in a suitable position and the processed 3D data from the surgical planning procedure are brought into alignment with the head surface. This is done with the help of a laser detector. The stereo camera of the navigation system detects the position of the head in 3D space and an algorithm automatically performs an exact co-registration between the virtual 3D data of the surgery planning and the actual surgical area. 

Once this process is completed, we are able to display the current point of surgery in relation to the surrounding brain structures at any time during the operation, using a tracked instrument or a laser beam in the center of the optical axis of the microscope. If intra-operative MRI or CT is employed, that data may also be directly fed into the navigation system. The risk of an operation can thus be kept to a minimum, since the route to the surgical target area is optimized, risky areas are recognized early and injury to essential structures is avoided.

Studies have shown, that the prognosis after surgery of high-grad gliomas is directly linked to the extent of resection. Therefore neurosurgeons and neuroscientists continuously try to optimize resection techniques. In this context, 5-aminolevulinic acid (5-ALA) has taken an important role over the last twenty years of glioma surgery.

5-ALA is an amino acid, that is formed by Succinyl-CoA and the amino acid glyicn. Amino acids are the components of human proteins. In particular, 5-ALA is part of the production of the blood pigment haemoglobin as a precursor of the hem protein. Via various intermediates 5-ALA is enzymatically converted into hem. Among other things, protoporphyrin IX is produced, that has the property to glow under UV-light.

In the 1990s several scientific groups were able to show, that 5-ALA specifically accumulates in tumor-tissue after external administration. Altered metabolic mechanisms make it harder for tumor cells to process 5-ALA and protoporphyrin IX appropriately. As a result, proteins are accumulating in cancerous tissue, which can be made visible by UV-light. The tumor shows fluorescence.

During surgery the surgeon switches from normal light to UV-light by using a specially equipped operating microscope and the glioblastoma will then light up – whereas healthy brain tissue will not fluoresce.

The tumor fluorescence enables a real-time view of the cancerous tumor areas. Thereby high-grade gliomas (glioblastomas and anaplastic astrocytomas) can be resected far more precisely and effectively. In some cases, 5-ALA even unmasks tumor areas, that are barely visible on MRI, thus improving the extent of resection.

Several studies have shown, that the prognosis in high-grade gliomas is directly linked to the extent of resection. It was demonstrated in over 250 patients that the use of tumor fluorescence allowed removal of all areas of the glioma that had previously picked up contrast on MRI imaging in twice as many cases as with the standard approach (without fluorescence). As a result, 41% of patients were progression-free six months after surgery compared with 21% in the control group.

In glioma surgery the margin of the tumor is of special relevance. In this transition zone between the tumor center and the healthy brain tissue gliomas grow diffusely infiltrating. Here the gliomas can hardly be distinguished from healthy tissue, but can be made visible by inspecting the fading shades of 5-ALA- fluorescence. The transition zone cannot be resected without hesitation in every case. The art of glioma surgery is the individual definition of the resection border and the balancing of radicality versus risk of deficit. In simple terms: the tumor including the transition zone should be resected as radical as possible if no functional areas of the brain are put in danger. Therefore, in this delicate transition zone additional techniques like electrophysiological monitoring, brain mapping, ultrasound and 3D-neuronavigation are employed. The surgical outcome and especially the prognosis can be significantly improved by this synergistic use of advanced surgical, imaging and visualization techniques.