In the next century this will be totally different. The emphasis will be on real time functional localization and minimally invasive or non invasive procedures. Today surgery means physical, mechanical removal of a brain tumor. Tomorrow energy in the form of both ionizing and non ionizing radiation will also be used.
Preoperative simulation
The neurosurgeon of tomorrow will switch on a computer and see his patient’s head on a giant color screen. The head will be displayed in three dimensional color with every single facial contour and even the superficial temporal arteries clearly displayed. The skin and skull can be made transparent and the tumor located in the depths of brain. The head is rotated 360 degree in any direction and plane. The contour of the tumor is visualized. The relationship of the tumor to the adjacent vascular and neural structures is displayed. A complex picture in which is fused a CT, MRI, PET scan, cerebral blood flow and a host of other neurophysiological functions is displayed. The optimum least invasive angle of entry is determined. Using the left button of the mouse, the incision is made. Hemostasis is secured with the right mouse button. If the frontal branch of the facial nerve has been cut accidentally the postoperative facial appearance is immediately displayed. The computer can even be programmed to say, “Ouch, the hurts”. The entire surgery is carried out on screen with a mouse.
Superb computer graphics ensure that the surgeon sees exactly what he would see, under the microscope in the actual surgery. Alterations in blood pressure, cerebral blood flow and neurological function at every step is displayed with warning signals. The CT/MRI picture is periodically superimposed over “The operative area” so that the exact amount of tumor remaining can be seen. No longer can the surgeon claim to have removed the entire tumor! In a few hours the surgeon has optimized the best treatment plan. In the real theatre the next day, there will be no rehearsals. As all the errors have already been committed, there is time for correction. Obviously on D–day there would be no room for flaws.
Intraoperative functional localization
One of the major drawbacks in brain surgery is the limitations in precisely localizing brain functions intraoperatively. Even the MRI only demonstrates structure. While we know precisely where Broca’s area is situated in the normal person, it is often forgotten that when there is a tumor adjacent to the speech area, the speech area itself gets shifted. Post operative neurological deficit can be avoided and tumors removed more aggressively in the future. Thanks to functional MRI, Magnetoencephalography, Thermoencephaloscopy, SPECT, PET, Magnetic Source Imaging (MSI) and so on. In MSI special detectors, detect the infinitely small magnetic field produced by current flowing in neurons. Thus, it will eventually be possible to identify groups of neurons firing when a particular action takes place.
Robots in neurosurgery
Robot guided stereotactic surgery is now available in a few centers. Advances in engineering, optics, biomaterials, artificial vision and micro miniaturization have resulted in flexible robots holding sensors (ultrasonic, barometric or visual). Today’s robot has a trunk, shoulder, arm, elbow, forearm, wrist and hand inter–connected with angular joints. The fingers can introduce a probe towards a target with an accuracy of 0.1 mm. Tomorrow’s robot will have AI (Artificial Intelligence) – a PC piloting the robot. The command module is an IBM computer in which a robot programming card is inserted. It houses the software used to pilot the robot. A calibration file translates the Cartesian coordinates, forbidden areas which the robot’s trajectory must avoid. Once the trajectory is computed it is displayed and submitted for validation to the surgeon. On approval, the robot, which has been wrapped in a sterile plastic bag, starts its approach. X–ray controls check that the current position is correct. Correction is made through small displacements triggered from a keyboard. The robot assumes the final position, through automatic detection of the image of the probe holder on digitized radiograms, and comparison with the theoretical target. Once the correct position is reached, the power of the command module is shut down, so that unwanted movement of the robot cannot take place. Intelligent stereostactic robots, flexible enough to support microscopes, endoscopes, telesurgery, needle biopsies and aspiration will eventually be available. A robot used in the neurosurgical theatre should have:
- Precision and reliability.
- Be capable of performing every kind of routine stereostactic procedure using the same frame and equipment.
- Be driven from various types of neuroradiological image.
- Safe and permanently submissive to human control.
- Capable of sophisticated but stereotyped work like electrode implantations.
- Have user friendly human computer interfaces.
- Have versatility towards future applications.
- Be reasonably cost effective.
Surgery without a knife
Today’s buzz words are “Non invasive/minimally invasive surgery”. Tomorrow it will be “Surgery without a knife”. The traditional method of physically removing a tumor may be given to achieving highly selective tumor destruction using ionizing and non ionizing radiation. Using stereostactic techniques, a high dose of radiation (X–ray or gamma rays) can be selectively delivered to a tumor or arterio venous malformation. Very high precision ensures that the adjacent brain is not injured. Radiation therapy will no longer be restricted to malignant tumors.
The photon radiosurgery system is yet another innovative technique. Here, a needle that emits X–rays at its tip can be inserted into a brain tumor. The needle is 3 mm in diameter and 100 mm long. X–rays are generated by forming and focusing an electron beam in an electron gun. The beam is accelerated through a high voltage region. The beam then travels down the evacuated needle. X ray are emitted from the needle tip in a spherically symmetric pattern. 100 rads can be delivered per minute at a distance of 1 cm from the tip of the needle. The needle is kept in position for an hour. Preliminary results are encouraging.
Non ionizing radiation like local hyperthermia and photoradiation may also be used as treatment options. Computer controlled heat energy distribution exclusively within a brain tumor is possible. Heat generating catheters and antennas can be selectively implanted to produce local temperatures of 45 to 50 degrees centigrade. Experimentally it has been shown that tumor cell kill is maximum above 42 degrees centigrade. Unfortunately, the normal body cells cannot withstand this internal temperature. Hence, highly selective hyperthermia is required.
Photoradiation may stage a comeback in the next few decades. A photosensitizer is a substance which preferentially concentrates in malignant tissue. In the presence of oxygen, when activated by light of the appropriate wavelength and intensity, these photosensitizers selectively destroy malignant tissue. Clinical studies are now under way using hematoprophyrin derivative.
