Procedures and technology

Brain laser ablation, safety procedures in spinal surgery, safety procedures in brain surgery, intraoperative monitoring.

Brain laser ablation surgery

Laser ablation surgery, also referred to as Laser interstitial thermal therapy (LITT) is a novel technique for treating a wide range of tumours, radiotherapy injuries, areas that cause epilepsy refractory to medical treatment, cavernomas, and many other conditions. Over the last decade, very small laser probes (1.3 mm) have been developed that also feature an integrated cooling system. Using precision methods known as stereotaxy, 1 to 3 of these laser probes are placed after planning the entry point, trajectory and target point inside the brain, tumour or lesion to be treated.

Once the laser probes have been positioned in the operating theatre, the patient is transferred to the MRI scanner, where a series of images are taken to show where the heat generated by the laser at the tip of the probe is deposited. We use the Medtronic Visualase system at the Institute of Neurosciences to define a series of safety points on the MRI images where we do not want the temperature to rise, and automatically stops the laser if these temperatures are reached in risk areas. It also assesses how heat is deposited in the lesion. Temperatures between 40°C and 60°C degrade proteins in a manner dependent on the duration of exposure to heat, a process known as ablation. It is a highly controlled process that uses thermographic sequences to determine where the heat generated by the laser is deposited at any given moment, with information accurate to temperature changes of less than one degree Celsius.

Not all lesions can be treated with laser therapy. Heat opens the blood-brain barrier locally, and in cases of ablations of a certain size, it can cause unwanted cerebral oedema, so it is generally not used on lesions larger than 3 cm. For this reason, mixed conventional surgical procedures combined with laser ablation are increasingly being performed for large lesions and deep areas, in order to minimize risks and take advantage of the benefits of both procedures.

PROGRAMMES

Laser ablation for:

Drug-resistant epilepsy (amygdalo-hippocampectomy, cortical dysplasias, deep brain lesions, etc.)
Hypothalamic hamartomas
Malignant glioma
Brain metastases
Cavernomas
Meningiomas
Radiation necrosis

Safety procedures in spinal surgery

A series of integrated procedures has been developed to ensure maximum safety in all spinal surgery procedures.

Before surgery

The essential elements of patient safety prior to surgery are an accurate diagnosis and a proportionate and appropriate diagnostic recommendation, carefully planned. For this purpose, the specialities of neurosurgery (NS) and orthopaedic surgery and traumatology (OST) are integrated into a mixed surgical unit. All cases undergo assessment in clinical sessions, benefiting from an integrated view of each patient. Surgical risks and ways of limiting them are also given special consideration in the process we call prehabilitation. For example, treatment for osteoporosis, obesity, anxiety, depression, or injections to minimise pain while waiting for surgery to be prepared may be of interest. Surgery planning may include processing imaging tests in stereoscopic virtual reality systems, or in simpler planners that show corrections to the balance and curves of the spine with prosthetic material. All of this allows us to select the ideal material, the degrees of correction required in each segment of the spine, etc.

During surgery

There are basically three technologies that increase safety in the operating theatre: neuronavigation, intraoperative tomographic imaging and intraoperative monitoring (see specific section below).

Specifically, in our workflow, the patient is initially monitored by neurophysiologists. Proper synchronisation with the neuroanaesthetists is essential to obtain good recordings throughout the procedure. The patient is then placed in the surgical position and a CT (computed tomography) image is obtained using the O-Arm system (Medtronic). This is the position in which the surgery will be performed, and the O-Arm is placed in position in the surgical field. The robotisation of the table system and O-Arm allows you to work in the surgical field and obtain images with great ease. The CT imaging in these conditions ensures optimal precision.

The neuronavigator is a state-of-the-art S8 system (Medtronic) that automatically registers new O-Arm CT imaging scans. The navigator records the movements of the surgical instruments using a camera system, just as satellites detect our cars with navigators on road maps. For lumbar procedures, a localisation ‘star’ for the neuronavigation system is placed on the patient's iliac crest, or, once the surgical incision has been made, on the spinous process of one of the vertebrae.

When, for example, screws are placed in the pedicles of the vertebrae, the neuronavigator records the movement of the instruments as they enter the vertebra through the pedicle in real time. In turn, the neurophysiologist assesses that there is no damage to any nerve roots, and also checks that there is no stimulation of any roots by electrically stimulating the head of the implanted screw below the established safety parameters. With these precautions in place, all of the prosthetic material is positioned, and then a CT scan is performed using the O-Arm system. These images will enable us to assess whether the placement is indeed optimal. Otherwise, a suboptimal position is modified at that time, and it is not necessary to perform further surgery at a later date.

Additional advantages: 1.) Neuronavigation also reduces radiation exposure for the patient and surgical team, as it is not necessary to continuously use the X-ray image intensifier; 2.) Monitoring allows for surveillance not only of the placement of prosthetic material, but also of any traction or compression of nerve roots or spinal cord during surgical procedures. The neurophysiologist helps guide the surgical procedures, which enables surgeons to adapt the procedure and even the overall strategy during surgery.

With these systems, the rate of misplacement of prosthetic material, such as pedicle screws, is less than 1%, compared to 8-12% with conventional fluoroscopic control.

Safety procedures in general surgery

The neurology and neurosurgery department has developed a series of integrated procedures to ensure maximum safety in its brain surgery procedures.

Before the procedure

A proper planning for brain surgery enables the integration of an increasing amount of anatomical, physiological, and functional information that can be incorporated into a stereoscopic 3D model of the skull and brain. This model can be viewed in virtual/augmented reality and in 2D, and can also be printed on 3D printers. We can segment a tumour or brain resection, simulate a cranial opening, take rectilinear and curvilinear measurements, integrate physiological information about the tumour or brain (PETs - positron emission tomography activity maps -, SPECT and SISCOM (especially in epilepsy surgery), MR perfusion sequences), functional (functional MRI maps of tasks and resting state, and TMS), as well as morphological connectivity sequences (HARDI tractography).

Ultimately, the goal is to obtain optimal safety margins and surgical approaches for the removal of tumours and other brain lesions or abnormalities. For example, locations of language and sensory-motor areas, as well as their fibres and connectivity tracts around or within the planned resection.

During the procedure

Advanced neuronavigation allows all of the aforementioned planning elements to be integrated, co-registered in the operating theatre with each patient's actual anatomy, and visualised during surgery. Anatomical elements in the surgical field often shift, which in extreme cases can be up to 2 cm, referred to as cerebral ‘shift’. To correct this, intraoperative ultrasound is used, which can be co-registered with the neuronavigator image. To further minimise the risk to functions such as motor skills or sensitivity, neurophysiological monitoring systems are used with the patient under general anaesthesia. To minimise the impact on language function, the patient undergoes surgery while awake, which allows this function to be mapped in the cerebral cortex and also subcortically during removal in the white matter, while a neuropsychologist with highly specific training monitors this function. Using these techniques, Dr Conesa has operated on more than 700 patients since 1989, with a morbidity rate of less than 4% for these procedures.

In addition to these functional safety features, the Institute of Neurosciences has a complete Kinevo (Zeiss) robotic platform, which also enables an additional Quevo support endoscope with integrated vision directly on the surgical microscope viewer or the built-in screens. In addition, brain tumours can be marked with red fluorescence using 5-ALA (Gliolan®) or yellow fluorescence using fluorescein. The cerebral vascular network can also be viewed using fluorescence. This 4K platform also allows these surgeries to be performed in exoscopic mode and surgical recordings of the highest quality to be made.

The laser brain ablation system (Visualase by Medtronic) has ushered in a paradigm shift in brain surgery. Access to the target lesion is achieved through a minimal cranial opening of 1.6 mm. The precision in positioning the laser probe is optimal with the innovative Leksell Vantage stereotactic system, which is compatible with MRI as it is made of carbon. The functional safety and efficacy of ablation on the target tissue is observed online in the MRI room by superimposing the synchronous recording of highly detailed morphological sequences with high-precision sequences in the recording of temperature changes (thermographic).

Finally, the possibility of performing surgeries in the hybrid operating theatre allows for mixed endovascular and microsurgical procedures to be carried out on cerebral aneurysms, cerebral arteriovenous malformations (AVMs) and arteriovenous fistulas. It also allows verification of the microsurgical closure of the operated aneurysm and the excised AVM or interrupted AVF.

Intraoperative monitoring

Intraoperative neurophysiological monitoring is a technique applied in real time during surgeries where there is a potential risk of injury to the central and/or peripheral nervous system. It is performed by applying various neurophysiological techniques (electroencephalography, somatosensory evoked potentials, motor evoked potentials, brainstem evoked potentials, visual evoked potentials, brain and peripheral nerve mapping, etc.) that measure the response of the brain, spinal cord, and peripheral nerves to different stimuli. Certain changes in these responses allow us to detect complications such as lack of oxygen, nerve stretching, and mechanical problems, etc. Rapid detection, interpretation, and secondary intervention can reduce and/or prevent neurological damage, increasing the likelihood of a favourable outcome during surgery.