Stereotactic surgery

Brain biopsy using a needle mounted on a stereotactic frame

Stereotactic surgery or stereotaxy (not to be confused with the virtuality concept of stereotaxy) is a minimally invasive form of surgical intervention which makes use of a three-dimensional coordinate system to locate small targets inside the body and to perform on them some action such as ablation, biopsy, lesion, injection, stimulation, implantation, radiosurgery (SRS) etc.

In theory, any organ system inside the body can be subjected to stereotactic surgery. Difficulties in setting up a reliable frame of reference (such as bone landmarks which bear a constant spatial relation to soft tissues), however, mean that its applications have been limited to brain surgery. Besides the brain, biopsy and surgery of the breast are done routinely to locate, sample (biopsy) and remove tissue. Plain X-ray images (radiographic mammography), computed tomography, and magnetic resonance imaging can be used to guide the procedure.

"Stereotactic" (another accepted spelling is "stereotaxic") stems from the Greek "stereo" (solid) and "taxis" (arrangement, order).

History

The stereotactic method was first developed by two British scientists in 1908, working at University College London Hospital, Sir Victor Horsley, a physician and neurosurgeon, and Robert H. Clarke, a physiologist. The Horsley–Clarke apparatus they developed was used for animal experimentation and implemented a Cartesian (three-orthogonal axis) system. Improved designs of their original device came into use in the 1930s for animal experimentation and are still in wide use today in all animal neuroscience laboratories.

Using the Horsley–Clarke apparatus for human brains was difficult because of the inability to visualize intracranial anatomic detail via radiography. However, contrasted brain radiography (particularly pneumoencephalography and ventriculography) permitted the visualization of intracranial anatomic reference points or landmarks. The first stereotactic devices for humans used the pineal gland and the foramen of Monro as landmarks. Later, other anatomic reference points such as the anterior and posterior commissures were used as intracranial landmarks. These landmarks were used with a brain atlas to estimate the location of intracranial anatomic structures that were not visible in radiographs.

Using this approach between 1947 and 1949, two American neurosurgeons, Ernest A. Spiegel and Henry T. Wycis, and a Swedish neurosurgeon, Lars Leksell, developed the first stereotactic devices that were used for brain surgery in humans. Spiegel and Wycis used the Cartesian coordinate system (also called the translational system) for their device. Leksell's device used the polar coordinate system (also called spherical) that was far easier to use and calibrate in the operating room. The stereotactic localization system was also used by Leksell in his next invention, a device for radiosurgery of the brain. This system is also used by the Gamma Knife device, and by other neurosurgeons, using linear accelerators, proton beam therapy and neutron capture therapy. Lars Leksell went on to commercialize his inventions by founding Elekta.

In 1978, Russell A. Brown, an American physician and computer scientist, invented a simple technique to guide stereotactic surgery using computed tomography. This technique significantly improves surgical precision because computed tomography permits direct visualization of intracranial anatomic detail. The technique uses fiducials to create extracranial landmarks in each tomographic image or section. These landmarks specify the spatial orientation of that section with respect to the stereotactic device. Brown's invention stimulated intense interest in stereotaxy and radiosurgery. It is widely used today in the Brown-Roberts-Wells (BRW) stereotactic system as well as other stereotactic and radiosurgical devices.

The stereotactic method has continued to evolve, and at present uses an elaborate mixture of image-guided surgery using computed tomography, magnetic resonance imaging and stereotactic localization.

How it works

Stereotactic surgery works on the basis of three main components:

• A stereotactic planning system, including atlas, multimodality image matching tools, coordinates calculator, etc.
• A stereotactic device or apparatus
• A stereotactic localization and placement procedure

Modern stereotactic planning system are computer based. The stereotactic atlas is a series of cross sections of anatomical structure (for example, a human brain), depicted in reference to a two-coordinate frame. Thus, each brain structure can be easily assigned a range of three coordinate numbers, which will be used for positioning the stereotactic device. In most atlases, the three dimensions are: latero-lateral (x), dorso-ventral (y) and rostro-caudal (z).

The stereotactic apparatus uses a set of three coordinates (x, y and z) in an orthogonal frame of reference (cartesian coordinates), or, alternatively, a polar coordinates system, also with three coordinates: angle, depth and antero-posterior location. The mechanical device has head-holding clamps and bars which puts the head in a fixed position in reference to the coordinate system (the so-called zero or origin). In small laboratory animals, these are usually bone landmarks which are known to bear a constant spatial relation to soft tissue. For example, brain atlases often use the external auditory meatus, the inferior orbital ridges, the median point of the maxilla between the incisive teeth. or the bregma (confluence of sutures of frontal and parietal bones), as such landmarks. In humans, the reference points, as described above, are intracerebral structures which are clearly discernible in a radiograph or tomogram.

Guide bars in the x, y and z directions (or alternatively, in the polar coordinate holder), fitted with high precision vernier scales allow the neurosurgeon to position the point of a probe (an electrode, a cannula, etc.) inside the brain, at the calculated coordinates for the desired structure, through a small trephined hole in the skull.

Currently, a number of manufacturers produce stereotactic devices fitted for neurosurgery in humans, as well as for animal experimentation.

Types of Stereotactic Frame Systems

1. Simple Orthogonal System: The probe is directed perpendicular to a square base unit fixed to the skull. These provides three degrees of freedom by means of a carriage that moved orthogonally along the base plate or along a bar attached parallel to the base plate of the instrument. Attached to the carriage was a second track that extended across the head frame perpendicularly.
2. Burr Hole Mounted System: This provides a limited range of possible intracranial target points with a fixed entry point. They provided two angular degrees of freedom and a depth adjustment. The surgeon could place the burr hole over nonessential brain tissue and utilize the instrument to direct the probe to the target point from the fixed entry point at the burr hole.
3. Arc-Quadrant Systems: Probes are directed perpendicular to the tangent of an arc (which rotates about the vertical axis) and a quadrant (which rotates about the horizontal axis). The probe, directed to a depth equal to the radius of the sphere defined by the arc-quadrant, will always arrive at the center or focal point of that sphere.
4. Arc-Phantom Systems: An aiming bow attaches to the head ring, which is fixed to the patient's skull, and can be transferred to a similar ring that contains a simulated target. In this system, the phantom target is moved on the simulator to 3D coordinates. After adjusting the probe holder on the aiming bow so that the probe touches the desired target on the phantom, the transferable aiming bow is moved from the phantom base ring to the base ring on the patient. The probe is then lowered to the determined depth in order to reach the target point deep in the patient's brain.

Stereotactic Surgery Research in Rodents

Stereotactic surgery can be used to aid research in several different types of animal studies. Specifically, it is used to target specific sites of the brain and directly introduce pharmacological agents to the brain which otherwise may not be able to cross the blood-brain barrier. In rodents, the main applications of stereotactic surgery are to introduce fluids directly to the brain or to implant cannula and microdialysis probes. Site specific central microinjections are used when rodents do not need to be awake and behaving or when the substance to be injected has a long duration of action. For protocols in which rodents’ behaviors must be assessed soon after injection, stereotactic surgery can be used to implant a cannula through which the animal can be injected after recovery from the surgery. These protocols take longer than site-specific central injections in anesthetized mice because they require the construction of cannulae, wire plugs, and injection needles, but induce less stress in the animals because they allow for a recovery period for the healing of trauma induced to the brain before injection. Surgery can also be used for microdialysis protocols to implant and tether the dialysis probe and guide cannula.

Stereotactic Surgery Treatments

Stereotactic radiosurgery (SRS) in Cancer treatment

Stereotactic radiosurgery can successfully treat many different types of tumors, both benign and malignant. The malignant brain tumors treated most often are the "brain metastasis" or tumors that have spread to the brain. A study in 2008 by The University of Texas M. D. Anderson Cancer Center indicated that stereotactic radiosurgery (SRS) and whole brain radiation therapy (WBRT) for treatment of metastatic brain tumours have more than twice the risk of developing learning and memory problems than those treated with SRS alone. “While both approaches are in practice and both are equally acceptable, data from this study suggest that oncologists should offer SRS alone as the upfront, initial therapy for patients with up to three brain metastases,” Three of the latest radiosurgery treatments, are CyberKnife, Gamma Knife and the Stereotactic Linear Accelerator with Image Guided Radiotherapy, Respiratory Gating, Cone beam CT, Kv Imaging and RapidArc. Failure to properly focus the powerful radiation beam produced by the linear accelerator or inadequate shielding can result in crippling injuries.

Stereotactic body radiosurgery has also been used to treat cancer by delivering high doses of radiation accurately to tumors within the body. Prior to the recent development of stereotactic body radiosurgery, the best alternative was standard external beam radiotherapy. Yet, the problem with standard external beam radiotherapy is that much is exposed to high doses of radiation, placing patients at risk for radiation damage.

The team at Methodist Hospital under Dr. Robert T. Woodburn have had special training and substantial experience in the field of stereotactic radiosurgery. According to their work done, SBR cancer treatment is not surgery at all. It is an outpatient procedure that requires three visits to the radiation oncology department which utilizes multiple tightly conformed radiation beams converging at the tumor. The low volume exposed to radiation allows very high doses to be given to the tumor leading to cure rates comparable to surgery. Thus, the low volume of exposure SBR has a low risk of long term complications in the treatment of cancer. Although this treatment is given to patients unable or unwilling to undergo surgery for various reasons, surgery remains the gold standard.

Stereotactic Surgery and Parkinson's Disease

Functional neurosurgery comprises treatment of several disorders such as Parkinson’s disease, hyperkinesis, disorder of muscle tone, intractable pain, convulsive disorders and psychological phenomena. Treatment for these phenomena was believed to be located in the superficial parts of the CNS and PNS. Most of the interventions made for treatment consisted of cortical extirpation. To alleviate extra pyramidal disorders, pioneer Russell Mayer dissected or transected the head of the caudate nucleus and part of the putamen and globus pallidus. Attempts to abolish intractable pain were made with success by transaction of the spinothalamic tract at spinal modullary level and further proximally, even at meencephalic levels.

In 1993-1941 Putman and Oliver tried to improve Parkinsonism and hyperkinesias by trying a series of modifications of the lateral and antero-lateral cordotomy. Additionally, other scientists like Schurman, Walker, and Guiot made significant contributions to functional neurosurgery. In 1953, Cooper discovered by chance that ligation of the anterior chorioidal artery resulted in improvement of Parkinson's disease. Similarly, when Grood was performing an operation in a patient with Parkinson’s, he accidentally lesioned the thalamus. This caused the patient’s tremors to stop. From then on, thalamic lesions became the target point with more satisfactory results.

More recent clinical applications can be seen at the University of Virginia School of Medicine, where Deep Brain Stimulation(DBS), Pallidotomy and Thalamotomy are surgeries used to treat Parkinson’s disease. During DBS, an electrode is placed into the thalamus, the pallidum of the subthalmamic nucleus, parts of brain that are involved in motor control, and are affected by Parkinson’s Disease. The electrode is connected to a small battery operated stimulator that is placed under the collarbone, where a wire runs beneath the skin to connect it to the electrode in the brain. The stimulator produces electrical impulses that affect the nerve cells around the electrode and should help alleviate tremors or symptoms that are associated with the affected area.

In Thalamotomy, a needle electrode is placed into the thalamus, and the patient must cooperate with tasks assigned to find the affected area- after this are of the thalamus is located, a small high frequency current is applied to the electrode and this destroys a small part of the thalamus. Approximately 90% of patients experience instantaneous tremor relief.

In Pallidotomy, an almost identical procedure to thalamotomy, a small part of the palladium is destroyed and 80% of patients see improvement in rigidity and hypokinesiia and a tremor relief or improvement comes weeks after the procedure.

See also

• Cyberknife
• Gamma knife
• Interventional radiology
• Novalis radiosurgery
• Psychosurgery
• Radiosurgery
• Stereotaxic atlas

References

• Robert Levy, A Short History of Stereotactic Surgery, Cyber Museum of Neurosurgery.
• Patrick J. Kelly, "Introduction and Historical Aspects", Tumor Stereotaxis, Philadelphia: W.B. Saunders Company (1991)
• Philip L. Gildenberg, "Stereotactic Surgery: Present and Past", Stereotactic Neurosurgery, (Editor: M. Peter Heilbrun) Baltimore: Williams and Wilkins (1988)
• William Regine; Lawrence Chin (2008). Principles of Stereotactic Surgery. Berlin: Springer. ISBN 0-387-71069-8. http://www.springer.com/medicine/surgery/book/978-0-387-71069-3. 
• van Manen, Jaap (1967). Stereotactic Methods and their Applications in Disorders of the Motor System. Springfield, IL: Royal Van Gorcum. 
• Zapata, A., Chefer, V. I. and Shippenberg, T. S. (2009). Microdialysis in Rodents. Current Protocols in Neuroscience.. 47:7.2.1–7.2.29.. 

External links

• Tasker RR, Organ LW, Hawrylyshyn P (1976). "Sensory organization of the human thalamus". Applied Neurophysiology 39 (3–4): 139–53. PMID 801856. 
• Tasker RR, Hawrylyshyn P, Rowe IH, Organ LW (1977). "Computerized graphic display of results of subcortical stimulation during stereotactic surgery". Acta Neurochirurgica (Suppl 24): 85–98. PMID 335811. 
• Stereotactic Apparatus.
• Praezis Plus: stereotactic planning software.
• Mevis Stereotactic Planning System.