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News -> February, 1999 News
The advent of computer technology along with the advances in fiber optic
imaging has resulted in dramatic improvements in instrumentation available
for endoscopic sinus surgery.
Recently various image-guided surgical systems with instruments have become
available. Each of the systems provide real-time positional feedback of an
instrument's location within the patient as correlated to either a CT scan
or MRI scan image.
The Instatrak system (Visualization Technologies Inc., Woburn, Mass.) our
group has experience with uses axial, sagittal, and coronal CT scan images
to identify instrument location. Preoperatively a standardized headset is
placed on the patient as a reference device. The axial CT scan is imaged
with the device in place and is then loaded into a computer. The workstation
reconstructs the 3mm axial scans to 1 mm cuts in three orthogonal planes.
The same standard headset reference device is used during the surgery so
that positional instrumentation can be zeroed and standardized. The
free-standing computer and CT scan reviewing apparatus sits on a rolling
column so that it can be moved from room to room. The system is accurate
to within 2 mm when the headset reference device is appropriately zeroed.
The level of accuracy of these instruments is extremely important as a few
millimeters in one direction or another is imperative knowledge in the
sinonasal anatomy.
The indications for image guided endonasal endoscopic surgery includes
revision sinus surgery, optic nerve surgery (like optic nerve decompression)
sinus surgery in cases with bone dehiscence in the lamina papyracea, and/or
cribiform plate, CSF leak repair osteoplastic frontal sinus surgery without
a template, endonasal tumor surgery (especially of the skull base),
transphenoidal hypophysectomy (to replace the C-arm), and in any patient
with distorted anatomy secondary to abnormal development or previous
surgery. A case in which the image guided system is especially useful
is the revision anterior ethmoid, frontal recess and frontal sinus
surgery done endoscopically where turbinate tissue has been ressected
such that the normal landmarks are not present.
Our experience with the Instatrak system has convinced us of its utility
in endoscopic nasal surgery. In the past the only instrument that could be
used for positional feedback with the Instatrak was a probe. Recently,
other instruments including powered sinus instrumentation, suctions, and
various sinus forceps have been fitted so that they can provide positional
feedback. This is a useful advance to save in operative time and improve
the utility of the system. Unfortunately, the most limiting factors of
this technology is the extreme cost of the system. Hopefully in the years
to come, the cost of these machines will come down. Other drawbacks of the
systems available include increased CT scanning time and costs, increased
operating room setup time and imperfect accuracy with the present technology.
As each of these drawbacks is addressed in the future generation image
guided surgical systems, their use will expand to more centers. Until
that time, image-guided endoscopic nasal surgery will not be adopted
universally. Yet, these systems will eventually become the gold standard
of treatment in many endoscopic nasal procedures.
David A. Sherris, M.D., Assistant Professor and Consultant
Division of Rhinology, Department of Otolaryngology
Mayo Clinic Rochester, Minnesota
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