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Computer-Assisted Navigation System in Pediatric Intranasal Surgery
Florence Postec, MD;
Denis Bossard, MD;
François Disant, MD;
Patrick Froehlich, MD
Arch Otolaryngol Head Neck Surg. 2002;128:797-800.
ABSTRACT
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Objectives To introduce a computer-assisted navigation system and to evaluate its
application in pediatric sinusonasal surgery.
Methods A commercially available wireless passive marker system that allows
the calibration and tracking of virtually any instrument was adapted to children
and used during pediatric endoscopic sinusonasal surgery.
Results The headset localizer that was initially used in computed tomographic
scanning was not well accepted by children. Correlation of the preoperative
computed tomographic scan to the actual patient was made possible by a laser
device. Setup time was able to be decreased from an initial 20 minutes to
3 minutes. The average recording accuracy was 1.1 mm. The advantages of the
system became apparent as experience increased in cases involving sinus polyposis,
choanal atresia, nasopharyngeal fibroma removal, tumor biopsy, and minimally
invasive maxillary, frontal, and sphenoidal surgery.
Conclusions The computer-assisted navigation system was used first as a control
system and then, as experience increased, as a true surgical guide. Indications
for its use also increased. Pediatric intranasal surgery was performed using
2 complementary guides: an endoscopic view and a computed tomographic view
of the instrument's position.
INTRODUCTION
SINUSONASAL SURGERY for children has progressed technologically over
recent years, aiding in the application of an endoscopic approach and minimally
invasive surgery.1 Even so, anatomical markers
are not adequate for proper perioperative assessment of normal areas and pathological
areas. Surgical accuracy could be enhanced by the use of an image guidance
system in association with endoscopy.
Computer-assisted navigation systems (CANSs) are based on stereotaxic
recording and have long been used by neurosurgeons as a surgical guide for
minimal craniotomy or for tumors that are hard to locate.2
Two main types of image guidance systems have been developed. Optical-based
image guidance systems use an infrared camera array to monitor instruments
and head position. Unlike electromagnetic-based systems, these devices do
not have problems of signal interference from metallic objects near the surgical
field. However, a clear line of sight must be maintained between the infrared
camera and light-emitting diodes during surgery.
Over the past few years, these systems have been developed in functional
endoscopic sinus surgery (FESS) for adults3-4
as a surgical control in difficult cases5 or
as a surgical guide for minimal conservative surgery.6
The objectives of the present report were to adapt an image guidance system
for use in children and to evaluate its application in pediatric nasal and
sinus surgery.
PATIENTS AND METHODS
COMPUTER-ASSISTED NAVIGATION SYSTEMS
The sinus navigation system (VectorVision; BrainLAB, Heimstetten, Germany)
used in this study was previously developed for neurosurgery2
and FESS in adults.7 It was a noninvasive system
that linked a freehand probe tracked by a passive-marker sensor system to
virtual computer image space on the patient's preoperative computed tomographic
(CT) images. It was based on infrared flashes with passive markers that reflected
infrared light–emitting diodes positioned around 2 cameras that detected
object positions.
Software was used by the surgeon with a sterile remote control. The
CANS that was used initially was replaced by a more compact system (VectorVision
Compact System; BrainLAB). The compact design, which was developed exclusively
for otorhinolaryngology, was optimized for operating rooms with space constraints.
PREOPERATIVE PROCEDURE
Computed tomographic scanning was performed before surgery. Initially,
a headset and fiducial markers were required both during preoperative CT scanning
and during surgery. A headset that would be well tolerated was positioned
with a noninvasive flexible fixation system and firmly fitted onto the nasal
dorsum and parietal area and into the outer ear canals (Figure 1). The headset included 6 passive infrared markers, allowing
reliable correlation of the preoperative and perioperative phases, so that
the headset could be secured in the right position during surgery. The markers
were positioned in the nasal and ethmoidal areas to limit irradiation by CT
scanning. The headset that was initially necessary during CT scanning was
no longer required. The CT images were transferred from the magnetic optical
disk to the navigation system. Because the CT scanning was performed on a
1-mm basis, the accuracy of the system could not exceed 1 mm.
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Figure 1. The headset fits with 2 earplugs
into the external ear canals and rests on the bridge of the nose.
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PERIOPERATIVE PROCEDURE
Initially, the headset was placed on the patient's head in the same
position as during the preoperative CT scan. The 6 markers had to be accurately
correlated to the 6 fiducial markers on the preoperative images. To optimize
the accuracy of the navigation system, the exact position of the headset was
checked by a pointing instrument positioned on the nasion.
When the headset was no longer required during CT scanning, a preoperative
correlation with preoperative image data was achieved semiautomatically. A
cordless laser device sent 2 different laser beams that communicated with
the passive camera system during scanning. While the surface points were being
acquired, an algorithm matched the position of the acquired laser points to
the preoperatively scanned data sets. The navigation system allowed simultaneous
display of the coronal, sagittal, and axial views, as well as 3-dimensional
reconstruction of the endoscopic image, simultaneously on the same screen.
A passive infrared sensor was set on the intranasal surgical instrument.
The instrument could be calibrated in diameter and length, so that its tip
could be located with accuracy.8-9
Several instruments could be referenced and used simultaneously during navigation.
STUDY POPULATION
The CANS was used in 34 pediatric cases (14 boys and 20 girls; age range,
4 days to 15 years). Surgical procedures were performed in cases involving
polyposis (n = 10), choanal atresia (n = 5), nasopharyngeal fibroma (n = 3),
and tumor biopsy (n = 1); there were also 8 cases in which minimally invasive
sinus surgery was performed.
RESULTS
CANS COMPATIBILITY WITH PEDIATRIC SURGICAL INSTRUMENTATION
During surgery, the CANS could be used to reference all surgical instruments,
including a microdebrider and its various blades and suction tubes. The initial
extra installation and calibration time of 20 minutes decreased to 3 minutes.
ACCURACY OF PEROPERATIVE RECORDING
The mean reference accuracy for the anatomical marker ranges averaged
1.1 mm using the system with only a perioperative headset. A loss in accuracy
was noticed during surgery in the first cases, owing to slight changes in
headset position. This was probably due to stretching of the skin by the headset
itself.
REVISION SURGERY FOR POLYPOSIS
A CANS was first used in revision surgery for polyposis in cystic fibrosis
(Figure 2) to help complete ethmoidectomy
and polyp resection. It was used as a surgical guide in the 5 difficult cases
reported herein, in which the anatomical markers defined by endoscopy were
modified by previous surgery. Ethmoidectomy could be completed with respect
to the integrity of the orbit wall and ethmoidal roof.
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Figure 2. Computer-assisted navigation system
in revision surgery for polyposis guides instruments in areas where anatomical
information from endoscopy is insufficient.
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SURGERY FOR POLYPOSIS IN CYSTIC FIBROSIS
A CANS was then used in the first surgical procedures (Figure 3) in cases involving polyposis in cystic fibrosis (n = 8).
The system was again helpful during ethmoidectomy, and the operation was able
to proceed under inflammatory conditions involving blood and purulent secretions.
It was particularly useful in cases of cystic fibrosis, allowing quicker surgery:
the duration decreased to an average of 20 minutes per side, compared with
45 to 60 minutes per side without CANS.
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Figure 3. Computer-assisted navigation system
for first polyposis in cystic fibrosis helps in the performance of surgery
in which there are blood and purulent secretions in association with endoscopic
guidance.
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The CANS enabled the ethmoidal roof to be distinguished from the floor
of ethmoidal cells, despite their similarity during FESS. Completion of ethmoidectomy
at the end of procedure was ensured by tracking the tip of the referenced
pointer along the orbit wall and ethmoidal roof.
CHOANAL ATRESIA
The CANS allowed the position of the instruments to be visualized in
relation to bone atresia (n = 7). In cases of recurrent stenosis, it was used
to complete vomer and pterygoid bone resection (Figure 4). It was found that bone resection was insufficient during
the first procedure, being one possible factor of recurrent stenosis. The
CANS could also be used as a surgical guide when endoscopic control was made
difficult by the presence of blood.
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Figure 4. Computer-assisted navigation system
in choanal atresia helps achieve more extensive bone resection than can be
achieved without guidance.
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NASOPHARYNGEAL FIBROMA
Recurrent nasopharyngeal fibroma was managed by endoscopic resection
in 3 cases. Two recurrences were removed from the sphenoidal sinus. Direct
guidance allowed exact location and conservative resection. The other case
was on the external part of the choana. The CANS helped ensure complete removal.
TUMOR BIOPSY
A child with midface osteosarcoma was treated by surgery and chemotherapy.
A CT scan showed possible residual tumor invading the sphenoidal sinus. The
endoscopic view was insufficient to allow secure biopsy, avoiding internal
carotid artery and optic nerve. During the procedure, the CANS was used to
guide instruments to the area. In 2 other cases, the CANS guided the biopsy
instruments directly to the tumor in the sphenoidal area.
MINIMAL CONSERVATIVE SURGERY
The use of CANS in these pediatric cases enabled surgery to be limited
to the pathological area. The system was also helpful for removing polyps
in the frontal (Figure 5) or maxillary
sinus (n = 5) and for guiding instruments into the sphenoidal sinus using
a more conservative approach (Figure 6),
without excision of the posterior portion of middle turbinate (n = 3). To
carry out this conservative approach, the surgeon had to rely on an endoscopic
view and direct guidance from the position of the instruments on the CT images.
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Figure 5. Surgery is performed directly
in the limited pathological area of the frontal sinus.
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Figure 6. The computer-assisted navigation
system was used to guide instruments directly into the sphenoidal ostium without
removing any part of the middle turbinate.
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COMMENT
The most difficult task in adapting the passive infrared CANS to pediatric
intranasal surgery was the development of a noninvasive10
pediatric headset that would fit accurately both during preoperative CT scanning
and during surgery. Still, having to wear a headset during preoperative CT
scanning was uncomfortable and often painful for children; therefore, the
CT scans were often inadequate. Then, an attempt was made to eliminate the
headset during preoperative CT imaging. A laser device allowed perioperative
semiautomatic matching between surface points and CT scan data.
Unlike electromagnetic systems,11 the
CANS did not require modification of the instruments. Using a remote control,
the surgeon was able to operate the whole system alone during surgery. The
indications for CANS' use increased, initially from revision surgery for polyposis
to the first procedure for polyposis in cystic fibrosis and then to various
types of procedures for which it was previously not thought to be helpful.
CANS appeared as a useful surgical guide for completion of bone resection
in recurrent choanal atresia. Insufficient bone resection appeared as one
possible factor of restenosis. It is now used during the first procedure for
choanal atresia to allow efficient bone resection. It has not yet been proved
to decrease risk of restenosis. In the minimally invasive approach, CANS was
able to limit surgery to the pathological areas.12
It was also used to endoscopically remove limited recurrent nasopharyngeal
fibromas and to guide tumor biopsies. Its applications increased as experience
increased, demonstrating its utility in pathological cases in which it did
not seem initially useful.
At first, CANS was used in children as a surgical control and not as
a surgical guide. With accuracy of 1.1 mm, adaptation of the system to pediatric
surgery and increasing experience, the system was progressively used as a
real surgical guide. Surgery relied on endoscopic and/or CT views of the instruments.
This system appeared to be a useful guide for experienced surgeons, and could
be of help in teaching FESS to residents and fellows, but it was not a substitute
for perfect endoscopic anatomical knowledge.13-14
Orbital and meningeal complications during intranasal surgery are the main
sources of litigation in otolaryngology. It is possible that CANS can be used
to assess potential hazards.15 Nevertheless,
it cannot yet be asserted that the system reduces the risk of surgical complication
and certainly not that CANS should be a legal requirement in difficult cases
of pediatric FESS. Indeed, CANS might encourage the surgeon to take more risks,
with the temptation to perform a more complete procedure than would otherwise
be attempted.
It is probable that in the near future there will be more demand for
CANS in pediatric sinusonasal surgery. The main problem is that at the present
time CANS is too expensive for its profitability to be ensured in a pediatric
otolaryngology department; however, its cost is likely to decrease in the
future.
CONCLUSIONS
CANS was used in pediatric intranasal surgery and appeared to be a helpful
surgical guide and not just a control tool. Indications for the use of CANS
have extended to various types of surgery for which it was not initially thought
to be helpful. Surgery previously relied on endoscopic and preoperative CT
scan views of the instruments. However, CANS is not a substitute for perfect
endoscopic anatomical knowledge, and it cannot yet be asserted that CANS reduces
meningeal and orbital risk.
AUTHOR INFORMATION
Accepted for publication December 5, 2001.
This study was presented in part at the 15th Annual Meeting of the American
Society of Pediatric Otolaryngology, Orlando, Fla, May 17, 2000.
Corresponding author and reprints: Patrick Froehlich, MD, Département
d'ORL, Hôpital E. Herriot, Place d'Arsonval, 69437 Lyon CEDEX 03, France.
From the Department of Otorhinolaryngology, Hôpital E. Herriot,
Lyon, France.
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