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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6013_Библиотеки_им_академика_М_И_Перельмана.pdf
P R O C ED U R E 3
Anterior Odontoid
Resection: The Transoral
Approach
George M. Ghobrial, Eli M. Baron, David Choi,
Harminder Singh, James S. Harrop, J. Patrick Johnson,
Alexander R. Vaccaro, and H. Alan Crockard
Indications
n
Generally, for the correction of irreducible, ventral compression of the
cervicomedullary junction.
n
Specifically, for ventral extradural, midline pathology from the lower clivus to
the C2-3 disk. Anticipated dissection should not extend laterally more than
11 mm on either side of the midline, as this may result in damage to the eustachian tubes, hypoglossal nerves, or vertebral arteries.
n
Commonly used to decompress neural elements, typically in patients with rheu-
matoid arthritis. Cervicomedullary neural compression may be due to
• Craniovertebral settling resulting from rheumatoid or degenerative disease
• Pseudotumor or rheumatoid pannus
• Extradural primary bone or soft tissue tumors
• Congenital basilar invagination
• Irreducible chronic nonunion of a fractured odontoid process causing neural
compression
n
As part of a staged procedure, may be used to excise a chordoma or other
midline extradural tumor at the craniocervical junction
n
May very occasionally be used for midline intradural pathology, such as menin-
giomas and schwannomas, usually as part of a staged procedure.
Examination/Imaging
n
Neurologic and musculoskeletal examination
• Rotary subluxation is a relative contraindication to this procedure, as is irreducible torticollis.
• Careful examination of the oral and pharyngeal region
◆
The relationship of the hard palate to the pathology must be studied: a
hard palate located above the level of pathology allows for good access.
◆
The mouth should be able to be opened more than 25 mm. This is required
to obtain adequate visualization of the pathology, and provide adequate
access for surgical instruments.
◆
Close attention must be paid to the patient’s teeth: Root abscesses and
periodontal sepsis may be significant risk factors for postoperative infection. Any irregularities in dentition should be noted, as they may make
retractor placement difficult.
Procedure 3 | Anterior Odontoid Resection: The Transoral Approach 17
A
FIGURE 3-1, A-B
T R E A T M E N T OP T I O N S
• Anterior odontoid resection through
the transoral approach (transoraltranspharyngeal, with or without
palatotomy)
• Combined anterior odontoid resection
through the transoral approach,
followed by posterior stabilization with
possible decompression
• Standalone posterior stabilization with
possible decompression
• Adjunctive traction reduction (in setting
of reducible basilar invagination or
atlantoaxial subluxation), followed by
posterior stabilization
B
◆
A gum guard, which fits both the irregular dentition and the retractors,
can be fashioned before surgery.
◆
Temporomandibular pathology should be taken into consideration as this
may limit mouth opening and hinder a transoral approach.
• Good neck extension is required. Fixed flexion deformities of the neck can
prevent sufficient mouth opening, and limit surgical access.
• A preoperative otorhinolaryngologic assessment should be performed to rule
out any lower cranial nerve dysfunction. If there is vocal cord, pharyngeal,
or brainstem dysfunction, then a preoperative tracheostomy should be
considered.
n
Preoperative imaging should include multiplanar radiographs of the cervical
spine, computed tomography (CT) with sagittal and coronal reformatting, and
magnetic resonance imaging (MRI) to clearly define any soft tissue pathology
and the degree of neural compression (Figure 3-1).
n
CT reformatted images provide detailed information about the bony elements
and can be beneficial in planning posterior instrumentation procedures.
n
Image guidance has been used as an adjunct for anterior odontoid resection,
including frameless stereotaxy and intraoperative MRI. However, frameless
stereotaxy may be inaccurate because of the mobility of the craniocervical
junction.
n
Magnetic resonance angiography (MRA) may be beneficial in defining the vas-
cular anatomy and relationship of the vertebral arteries to the midline, as well
as dominance of one vessel.
n
In the treatment of patients with rheumatoid arthritis, it is suggested that anti-
tumor necrosis factor be held 2 to 4 weeks before surgery and up to 2 weeks
after. There is no definitive evidence to suggest methotrexate should be discontinued perioperatively.
18 Procedure 3 | Anterior Odontoid Resection: The Transoral Approach
Surgical Anatomy
n
Understanding the ligaments of the craniovertebral junction is vital when oper-
ating in this region.
n
The atlas is united to the occipital bone by the anterior and posterior atlanto-
occipital membranes.
n
The atlantoaxial joint consists of four articulations and two key ligaments. Two
synovial joints for each lateral mass and two odontoid joints, on the anterior
and posterior aspects.
n
The alar ligament arises laterally from the odontoid to attach to the occipital
condyles. The apical ligament runs from the odontoid process to the anterior
margin of the foramen magnum. Disruption of any of the aforementioned ligamentous structures runs an increased risk for basilar invagination.
n
The cruciate ligament runs from the atlas to the axis anteriorly. Atlantoaxial
dissociation results from damage to this ligament, requiring surgical
intervention.
n
Below the foramen magnum, the oropharynx is separated from the prevertebral
fascia by a well-defined areolar plane (Figure 3-2). The oropharyngeal mucosa
heals remarkably well after surgical incision and repair.
n
The most important bony anatomic landmarks for the transoral approach are
the midline structures: rostrally, the septal attachment to the sphenoid, the
pharyngeal tubercle on the clivus; and caudally, the anterior tubercle of the C1
arch. The longus colli muscles flank the dens on each side and, more laterally,
the longus capitis muscles.
n
The anterior longitudinal ligament extends caudally in the midline.
• Knowledge of the location of the vertebral arteries is requisite before performing a transoral procedure.
• The vertebral arteries are located 24 mm laterally from the midline at the
level of the arch of C1, and approximately 11 mm from the midline at the
C2-3 disk space as well as the level of the foramen magnum.
• Pathology such as atlantoaxial rotary subluxation can significantly distort the
relationship of the vertebral arteries to the midline.
• Visually, the anatomic midline can be accurately defined by examining the
symmetry of the anterior longitudinal ligament and the longus colli muscles.
P O S I TI O N I N G PE A R L S
• Because many patients have inherent
spinal instability, perisurgical neck
immobilization may be required. Halo
immobilization, however, will limit neck
extension and surgical exposure.
• The placement of topical 1%
hydrocortisone on the oral mucosa,
before and after surgery, may reduce
the incidence of lip and tongue
swelling.
Positioning
n
Neurophysiologic monitoring electrodes for somatosensory-evoked potential
and transcranial motor-evoked potential monitoring are placed first.
n
Fiberoptic nasotracheal intubation is then performed.
n
A nasogastric tube should also be placed for intraoperative gastric drainage and
postoperative feeding.
n
The patient’s head can be fixed in a three-pin fixation system with slight exten-
sion. Alternatively, a horseshoe with Gardner-Wells traction or the head resting
on a circular headrest can be used.
n
Extension should not be used in patients with fixed cervical kyphosis. Rather,
they should be placed in slight Trendelenburg position to assist in the rostral
extent of the dissection. One caveat to this would be the limitations in positioning caused by cervical instability or cervicomedullary compression; in this case,
positioning is done cautiously with neuromonitoring.
Procedure 3 | Anterior Odontoid Resection: The Transoral Approach 19
Superior articular facet of C1;
articulates with the occipital condyles
Transverse process C1
Lamina C1
Posterior arch C1
Body C2
Transverse foramen C2
Lamina C2
Anterior arch C1
Dens C2
Groove for vertebral artery
Spinous process C2
View from above
Anterior tubercle C2
Posterior tubercle C2
Pedicle C2
Inferior articular facet C2
Spinous process C2
View from below
Dens C2
Transverse process C1
A
FIGURE 3-2, A-C
Lateral masses
Atlas C1
Axis C2
View from anterior
Atlantoaxial articulation
Spinous process C2
View from posterior
Continued
20 Procedure 3 | Anterior Odontoid Resection: The Transoral Approach
Base of skull
Tectorial membrane,
Anterior atlantooccipital ligament
Articular capsule
Lateral atlantoocciptal ligament
Articular
capsule
Base of skull and upper cervical vertebrae
with ligaments viewed from in front
Long. fascia of cruciform ligament
Atlantoepistrophic
ligament
Anterior longitudinal
ligament
Ligament nuchae
Supraspinous
prominens
Interspinous
B
Tectorial membrane,
Apical ligament of dens
Anterior arch of atlas
Median atlantoaxial joint
Transverse ligament of atlas
Anterior longitudinal ligament
deep layer
Dens
Body of axis
ligament
Vertebra
ligament
Base of skull and upper cervical vertebrae
with ligaments viewed from the right side
superfical layer
Hypoglossal canal
Anterior
longitudinal
ligament
Articular capsule
Vertebral artery
Posterior atlantooccipital membrane
Occipital bone
Posterior arch
of atlas
Vertebral artery
First cervical nerve
Intervertebral
foramen
Ligamentum
flavum
Arch of axis
FIGURE 3-2, cont'd
Intervertebral disk
Body of vertebra C3
C
P O S I TI O N I N G PI T FA L L S
• Inability to widely open the mouth
is a relative contraindication to this
procedure. As a general rule, in the
adult population, if you cannot place
three fingers into the mouth of a
patient with his or her mouth fully
opened, the transoral approach should
be avoided. Otherwise, splitting the
mandible and tongue may be needed
for adequate exposure.
• Alternatively, patients may be
positioned laterally in a Mayfield clamp
(Figure 3-3). The advantages of this
position are that blood and washings
drain out of the operative field. The
head is placed in slight extension,
which improves exposure. The table
may be tilted laterally, allowing optimal
positioning for the patient and surgeon.
After the initial procedure, a posterior
stabilization can be performed after
reversing the lateral tilt.
• A fluoroscopy unit is then brought
in following positioning to confirm
adequate positioning and spinal
alignment.
Procedure 3 | Anterior Odontoid Resection: The Transoral Approach 21
FIGURE 3-3
Portals/Exposures
n
Oral swabs can be obtained for culture to identify bacterial colonization before
preparation of the mouth and oropharynx with 1% Betadine or cetrimide.
n
The upper esophagus should be packed with a collagen sponge or gauze to
minimize the ingestion of saline and blood.
n
The midlines of the oropharyngeal mucosa and soft palate are infiltrated with
1% lidocaine with epinephrine (1:100,000). A Crockard transoral retractor
system (Codman, Raynham, Mass.) is used to maintain adequate exposure of
the posterior oral cavity and to keep the nasotracheal and nasogastric tubes to
one side, out of the surgeon’s way (Figures 3-4 and 3-5).
n
A tongue blade and soft palate retractors maximize the exposure.
n
To extend superior and lateral exposure, the soft palate may be split at the
midline from hard palate to the uvula.
n
The uvula may be secured with a red rubber catheter and retracted along with
the soft palate through the nares to avoid problems with swallowing and phonation postoperatively. After incision of the posterior pharyngeal wall, a Crockard toothed self-retaining retractor is inserted for lateral retraction to expose
the underlying anterior longitudinal ligament and longus colli muscles.
n
With or without the aid of lateral fluoroscopy, the extent of the incision is from
the base of the clivus to the upper border of the C3 vertebra.
n
Alternative techniques
• Another technique is to use endotracheal intubation with the SpetzlerSonntag retractor system (Aesculap, San Francisco). This system protects and
retracts the endotracheal tube and tongue, whereas the Crockard system
displaces the nasotracheal tube out of the way.
• The soft palate may also be retracted using sutures through the soft palate,
which are brought out via the nares after they are secured to vessel loops
that were passed through the nostrils into the nasopharynx (Spetzler technique) (Hadley et al, 1988). Alternatively, the soft palate may be divided in
the midline (offset to avoid the uvula) and retracted with sutures hanging
out of the mouth (Crockard, 1995).
22 Procedure 3 | Anterior Odontoid Resection: The Transoral Approach
A
FIGURE 3-4, A-B
B
FIGURE 3-5
Procedure 3 | Anterior Odontoid Resection: The Transoral Approach 23
S T E P 1 P IT FA L L S
• Great care should be taken to avoid
cerebrospinal fluid (CSF) leakage
in order to minimize the risk of
postoperative meningitis. A
preoperative lumbar drain should be
placed when an intradural approach
is anticipated. In such procedures, fat,
muscle, fascia lata, or a dermal fat graft
should be used in the repair of any
dural opening, followed by the
application of fibrin glue.
• With an incision from the inferior
clivus to the superior border of C3,
an operating field of 15 to 20 mm
bilaterally can be exposed. Beyond that,
there is an increased risk of trauma to
the eustachian tube, hypoglossal nerve,
vidian nerve, and vertebral artery at
the C1-2 interspace.
• Given the large vascular channels
and venous sinusoids in this region,
postoperative hematoma formation
may be a problem. This can be
minimized by meticulous hemostasis,
using Avitene, Surgicel, Gelfoam, or
fibrin glue, and postoperative nursing
in the head-up position. Bleeding from
the rheumatoid pannus or small arterial
feeders can be controlled with bipolar
electrocautery. If an intradural
procedure is performed, watertight
dural closure is very important to
minimize the risk of infection. Suturing
or clipping the dura will rarely close the
defect completely. A free dermal fat
graft, pharyngeal mucosal rotation
flaps, or nasal septal mucosal flaps help
provide a watertight closure, and a
lumbar drain may also be used.
Procedure
Step 1
n
The anterior ridge or tubercle of the atlas is palpated. At this point, a confirm-
atory lateral localizing image may be taken. An operating microscope can
then be used, or a surgeon may choose loupe magnification with directed
illumination.
n
A vertical incision is made extending approximately 2.5 cm superiorly and 2.5
to 3.0 cm inferiorly along the midline of the posterior oropharynx (Figure 3-6).
n
The extent of the exposure obtained with this incision will be approximately 15
to 20 mm bilaterally from the midline incision.
n
Dissection is taken through the posterior pharyngeal mucosa, the superior
constrictor muscles of the pharynx, and the anterior longitudinal ligament.
n
Incising the soft (and sometimes hard) palate can provide additional visualiza-
tion of the lower clivus if needed.
n
Using periosteal elevators and electrocautery, a subperiosteal dissection exposes
the arch of C1, as well as the anterior bodies of C2 and C3.
n
The longus colli and longus capitis muscles are detached medially to laterally
from the cervical vertebra.
n
In the presence of instability, there may be a large amount of granulation tissue
at the level of the inferior margin of the atlas and its junction with the anterior
odontoid peg. Toothed retractor blades are then used to retract the dissected
soft tissues laterally. This allows excellent visualization of the midline inferior
clivus, the atlas, and the axis.
FIGURE 3-6
24 Procedure 3 | Anterior Odontoid Resection: The Transoral Approach
A
FIGURE 3-7, A-B
B
Step 2
n
A match-head burr is used to remove the anterior arch of the atlas out laterally
approximately 1 cm to each side of the midline (about two thirds of the arch,
exposing the shoulder of the dens bilaterally) (Figure 3-7). The odontoid mass
and pannus (if present) are then resected in a rostrocaudal direction (starting
at the top of the odontoid process) using a combination of drilling and
curetting.
n
Alternatively, the odontoid process may be initially drilled at its base and disar-
ticulated from the C2 body. The odontoid peg is hollowed out gradually with a
3-mm cutting burr down to the cortical bone, which is then thinned and
removed with a match-head or diamond burr. The alar and apical ligaments are
sharply divided, taking care not to cause a CSF leak. The proximal peg is then
removed after circumferentially elevating off all soft tissue attachments. This is
facilitated by grasping the odontoid peg with special forceps and pulling it down
from the foramen magnum while elevating the dura off it. This allows complete
removal of the dens. This technique has a greater potential for durotomy, particularly in the pediatric population, in whom the odontoid process may have a
hook at its apex that can tear the dura during peg removal.
n
The posterior longitudinal ligament is seen behind the dens, which has now
been removed. The fibers of the transverse ligament are also visualized at the
level of the removed C1 anterior arch. With division of these ligaments, the dura
should be clearly seen. Ligament and soft tissue removal can be accomplished
with a series of small angled curettes, transsphenoidal punches, and transoral
bayoneted forceps. Typically, a gap exists between the ligaments and dura.
Decompression is considered adequate when the dura pulsates freely and the
lateral curvature of the dura is seen bilaterally. Fluoroscopy may be used to
confirm adequate decompression.
Procedure 3 | Anterior Odontoid Resection: The Transoral Approach 25
A
FIGURE 3-8, A-B
B
n
Any venous bleeding can be controlled with Surgicel and fibrin glue (Figure
3-8, A).
n
Extended approaches
• In addition to the standard transoral technique, extended approaches can be
performed to widen the surgical exposure of the craniocervical junction.
• A mandibulotomy can be made to increase the cervical exposure by first
incising the lip in the midline, then more inferiorly through the gingival,
mandible, and finally the hyoid. The mucosa is divided beneath the tongue,
sparing the submaxillary ducts, with retraction of the mandible laterally to
allow for the depression of the tongue to maximize the exposure of the
craniocervical junction superiorly and inferiorly.
• A mandibuloglossotomy extends the above approach to include the middle
clivus to the C3-4 vertebral bodies inferiorly.
• A palatotomy can be made by extending the midline incision of the soft
palate, sparing the uvula. The posterior connection of the vomer can be
disconnected, as well as the hard palate separated then retracted laterally.
• A more extensive bilateral mucogingival extension can be performed along
the maxilla, with a subperiosteal dissection, effectively degloving the face.
The superior limit of muscle and mucosa dissection off of the maxilla is the
infraorbital nerve. Bilateral osteotomies are made from the piriform aperture
to the maxillary alveolus. The maxilla is disarticulated from the pterygomaxillary fissure. An inferior turbinectomy is made. The nasal mucosa is reflected
off of the nasal septum as well as the sphenoid bone for a superior exposure.
Concern for this extensive approach is preservation of the vascular supply
namely via the palatine arteries.
Step 3
n
The posterior pharyngeal wall is then closed with a two-layered closure using
3-0 Vicryl sutures (Figure 3-8, B).
n
Despite the presence of bacterial flora in the oral cavity, a low infection rate of
less than 3% is to be expected if the dura is not breeched. In the presence of
a durotomy, great efforts should be made to close the dura in a watertight
manner.
n
A double layer closure of both the pharyngeal musculature and mucosa is less
susceptible to dehiscence.
n
In the presence of durotomy, a watertight closure may be aided with the applica-
tion of fat, fascia, dermal fat graft, and fibrin glue. Additionally, a lumbar drain
should be used for about 5 days with regular drainage of CSF (10 to 15 mL/hr).