|
Craniovertebral junction, and the upper cervical spine can be approached
through the neck, either through an antero-lateral or posterior approach.
But when the pathology is anterior and also requires wide exposure on
either side of mid line in the upper cervical spine, the trans oral route
helps us to reach it directly.
The
transoral route is chosen ideally for extradural lesions confined to the
clivus, the C-V junction, and the upper cervical vertebrae. The most
common indication is odontoidectomy. Basilar invagination, Rheumatoid
arthritis with A-A subluxation, odontoid fractures with A-A subluxation,
Koch's spine, Chordoma, Myeloma, Metastasis, and Lymphoma are the common
problems encountered. The intradural lesions, such as Schwannomas,
Epidermoids, and Meningiomas can also be dealt with through approach by
experienced hands. Clipping of lower and middle third basilar artery
aneurysms through this route is also possible.
Surgical anatomy:
The
atlanto-axial joint is formed between the dens of the axis and the atlas,
and, one on each side, between the lateral masses of the two vertebrae.
The dens articulates with the back of the anterior arch of the atlas by a
small synovial joint.
Behind
the prevertebral fascia are the median raphe between the longus colli
muscles and then the anterior atlanto-occipital membrane which is the
continuation of the anterior longitudinal ligament. The longus colli
muscles and anterior longitudinal ligament are inserted to the anterior
tubercle of C1. The longus capitis muscles run lateral to the longus colli
muscles.
The
apical ligament is attached to the apex of the odontoid process
and the alar ligaments are attached laterally on either side
of it, and then to the occipital condyles.
The
vertical limb of the cruciate ligament joins the body of the axis
to the foramen magnum. The transverse limb is a main component of the
cruciate ligament and attached to the posterior surface of the arch of the
arch of the atlas.. This thick ligament surrounds the odontoid process
posteriorly; between the two is a large synovial cavity, or bursa.
There is an interface between the alar and transverse ligament. The
direction of the alar ligaments is oblique and they are located anterior
to the transverse limb of the cruciate ligament.
Posterior to the transverse limb is the slightly dark yellow to light
brown colored tectorial membrane, which is the continuation of the
posterior longitudinal ligament in front of the dura.
Surgical approaches:
We can plan the extent
of exposure step by step orienting it centrally first and extending it to
the periphery as required depending on individual requirement.
Transoral-pharyngeal approach:
Click
for intraoperative video clippings
| The
patient is positioned supine with the head extended and skull traction
in place. Alternatively, the head may be immobilized in the Mayfield
frame. Some recommend lateral position with the head immobilized in
the Mayfield frame, especially when a posterior fixation is planned in
the same sitting. This avoids unnecessary movements while positioning
for posterior fixation.
Endotracheal
intubation with a flexometallic tube positioned at the side of the
mouth is adequate; some prefer routine tracheostomy. The mouth is kept
open with a gag that rests against the upper dental arch and depresses
the tongue (tonsillectomy retractor). Several types of transoral
retractors such as Crockard, Dingman, Davis-Crowe, McGarwer etc. are
available. Care is taken to ensure that lip or tongue is not caught
between the tongue blade and the teeth. A rubber catheter should be
used sometimes to retract the uvula and soft palate. Oral irrigations
with an antiseptic solution is carried out.
The soft palate may be
retracted with stay stitches and the posterior pharyngeal wall is
exposed. This gives adequate exposure for lesions at the foramen
magnum and in patients with minimal basilar invagination. Many prefer
to split the soft palate to gain better exposure; this predisposes
to troublesome, though transient, post operative nasal regurgitation
in my experience.
The posterior wall of
the pharynx is incised with cutting diathermy from the roof down to
C2-C3 disc or as required. Palpation of the anterior tubercle of the
anterior arch of the atlas helps to keep the incision to midline.
The prevertebral
muscles are carefully dissected from the lower clivus, the arch of the
atlas, and the C2 body on the subperiosteal plane.
The arch of the atlas,
and the dens of the axis are drilled away. There may be some soft
tissue (such as rheumatoid pannus) behind the arch and in front of the
dens which needs to be removed to get to the dens. Lateral exposure at
this level should not exceed 1.5 cm to avoid injury to the
vertebral arteries. A median corpectomy of the body of C2 (about 1
inch in diameter) down to the C2-C3 disc level is recommended as a
routine. |
|
Removal of the dens will
expose the transverse limb of the cruciate ligament and apical ligament.
This may be removed along with the lower most tip of the clivus for
presumed better decompression as recommended by some. This step is better
avoided in my opinion and adds to instability.
Additional extradural/
intradural pathology is dealt with as required.
The pharyngeal wall may be
closed in a single layer with absorbent suture material. The palate is
closed in a single layer as well, if it had been split.
Post operatively,
nasogastric tube feeding is established for a week and the patient is
mobilized with a 'Philadelpia' cervical collar to restrict the atlanto-axial
joint movements.
Extended approaches:
Extended transoral
approaches include maxillary osteotomy, mandibulatomy and other skull base
approaches.
Bilateral LeForte
maxillary osteotomy can be done through a trans oral sulcus
incision and the maxillae can be pushed down as a single piece and by
resecting a part of nasal septum we can have adequate exposure superiorly.
If necessary we can further split the maxilla in the center and swing both
the halves of maxillae on either side outward and a wide access can be
achieved.
|
This approach is
particularly useful for lesions of the upper and midclivus. The roof
of naso pharynx is another area, which is difficult to reach, and
trans oral route combined with splitting the maxilla gives wide
access. |
 |
 |
 |
|
Leforte
osteotomy |
Osteotomy
completed |
Hard plate
split |
If access is required
inferiorly a mandiblotomy may be added. The mandible can be split
in the mid line or para sagittaly and the floor of mouth and tongue can be
split in the mid line .The mandibular halves can be swung outwards gaining
excellent exposure. No significant post operative functional or esthetic
problems are expected.
 |
 |
 |
 |
|
Mandible split |
Tongue split |
Floor of the mouth split |
C2 Tumor bulge |
| |
|
|
|
 |
 |
 |
 |
|
after excision |
Mandible closure |
Tongue closure |
Skin closure |
This approach is useful
for a radical excision of upper cervical spine lesions with lateral
extensions.
In the same way if the
lesions are to one side of mid line, we can combine the central oral
exposure with maxillary osteotomy of one side. If further superior access
is required we can include the nose, floor and lateral walls of orbit
along with this as zygomatico maxillary osteotomy. Care must be taken not
to jeopardize the vascularity of the maxillary segment.
Stabilization:
Most surgeons recommend
some form of stabilization either in the same sitting or as a second
stage. Another school feel that stabilization is not required in selected
patients.
Absolute indications for
stablization are
History of precipitating
trauma,
Symptoms suggestive of
instability, such as suboccipital pain (occipital neuralgia), and
worsening deficits on neck flexion,
Radiological suggestion
of instability,
Patients under 40 years
of age,
Post operative
suboccipital pain (occipital neuralgia).
Postoperatively the
patient may be mobilized with a 'Philadelphia' collar or an 'Halo' frame
for about 6 weeks.
Complications:
Transient nasal
regurgitation is common; retraction of the soft palate instead of
splitting reduces this risk. Continued nasogastric tube feeding is
recommended to tide over this problem.
Dural tear may lead
to CSF leak and meningitis; careful drilling and use of fine up-cutting
punches help to prevent this. A continuous lumbar CSF drainage in a closed
system for a week will help seal off the leak. If persists, an occult
hydrocephalus should be thought of.
Pharyngeal wound
dehiscence is rare; healing is surprisingly good in the oral cavity.
Continued nasogastric tube feeding is indicated untill satisfactory
healing.
Snapping of posterior
wiring has been reported and requires refixation.
Oral edema may be
avoided with large dose of dexamethasone at the time of incision and
topical application of steroid cream at the operated site; may warrant a
tracheostomy.
Infection is a
dreaded problem; may require removal of fixation system and nursing the
patient with a Halo frame of skull tongs for 2-3 months.
The outcome depends
on the preoperative neurological status, duration of illness, and the
nature of the pathology. |
