A new image-guided surgical system is under development at Vanderbilt University, Nashville, TN, that employs steerable needles to penetrate the brain with minimal damage and suction away the blood clot that has formed. Part of an ongoing collaboration between a team of engineers and physicians, the steerable needle system could, they say, prevent substantial damage during surgery to remove a clot, or intracerebral hemorrhage. Neurosurgeons know that removing a clot, unless it is small and lies on the brain’s surface where it is easy to reach, could create more damage to the surrounding tissue when the clot is removed. So they usually prefer watchful waiting when a serious clot is detected in the brain, and administer drugs to decrease the swelling around the clot to help the patient improve without surgery.
But, for the past four years, the Vanderbilt team has been developing a steerable needle system for “transnasal” surgery to remove tumors in the pituitary gland and at the skull base that traditionally involve cutting large openings in a patient’s skull and/or face. Studies have shown that using an endoscope to go through the nasal cavity is less traumatic, but the procedure is so difficult that only a handful of surgeons have mastered it.
The system uses an active cannula consisting of a series of thin, nested tubes, each with a different intrinsic curvature. By precisely rotating, extending, and retracting these tubes, an operator can steer the tip, allowing it to follow a curving path through the body. The single needle system required for removing brain clots was actually much simpler than the multi-needle transnasal system, they said.
The brain-clot system needs just two tubes: a straight outer tube and a curved inner tube. Both are less than one twentieth of an inch in diameter. When a CT scan has determined the location of the blood clot, the surgeon determines the best point on the skull and the proper insertion angle for the probe. The angle is dialed into a fixture attached to the skull immediately above a small hole that has been drilled to enable the needle to pass into the patient’s brain.
The surgeon positions the robot so that it can insert the straight outer tube through the trajectory stem and into the brain. He also selects the inner tube with the curvature that best matches the size and shape of the clot, attaches a suction pump to its external end and places it in the outer tube.
Guided by a CT scan of the patient, the robot inserts the outer tube into the brain until it reaches the outer surface of the clot. Then it extends the curved, inner tube into the clot’s interior. The pump is turned on and the tube vacuums out the material. The robot moves the tip around the interior of the clot, controlling its motion by rotating, extending, and retracting the tubes. According to the feasibility studies the researchers have performed, the robot can remove up to 92 percent of simulated blood clots, they said.
The goal of a future project is to add ultrasound imaging combined with a computer model of how brain tissue deforms to ensure that all of the desired clot material can be removed safely and effectively.