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The craniofacial
approach has gradually evolved over the past five decades into a safe and
reliable technique for resecting both benign and malignant tumors involving
the anterior cranial base. It can be extended and incorporated as a part
of a more complex resection involving the infratemporal fossa and
anterolateral cranial base, as well as the middle cranial fossa,
cavernous sinus etc.
INDICATIONS:
The tumors most commonly requiring combined anterior
craniofacial surgery usually begin in the nose or sinuses. Many of these
tumors to a greater or lesser degree are malignant .
Inverting papilloma is an example of transitional type of tumor that is
locally invasive, does not metastasize, but must be resected aggressively
to avoid recurrence. Esthesioneuroblastoma
varies from a very indolent to a highly aggressive tumors. Most tumors of
nasal or para nasal sinus origin are squamous cell or adenocarcinomas of
the maxillary or ethmoid sinuses.
Tumors with a primary intracranial origin such as
meningioma, chordoma or chondrosarcoma require
combined resection when they clearly violate the anterior fossa floor.
SURGICAL TECHNIQUE:
General anesthesia should be performed by a team experienced
in neurosurgical procedures. A lumbar drain is routinely placed and
patients are given prophylactic per operative antibiotic. The patient is
then placed in a Mayfield head holder and positioned to optimize both the
neurosurgical and facial approaches. The leg is propped to obtain a skin
graft and fascia lata if needed.
The anterior craniofacial approach incorporates a
combination of transfacial and transcranial
procedures. The facial approach consists of a graduated greater exposure
depending on the extent of disease. The basic is done through a lateral rhinotomy approach coupled with a low craniotomy. The
lateral rhinotomy incision may be extended into
a Web-Ferguson incision if a more extensive maxillary excision is
required.
Craniotomy:
The craniotomy is tailored according to the extent of
involvement of the anterior fossa floor, the sub cranial tumor location,
and the degree of dural or frontal lobe
invasion. A bicoronal scalp incision is made
running 2 to 3 cms behind the hairline. The
flap is elevated in the subgaleal plane down to
the eyebrows , then to the lateral orbital walls laterally and just below
the nasal globella medially. A large flap of pericranial tissue is created that will be used for
later reconstruction. As the dissection proceeds the brows, the
supratrochlear and supraorbital neurovascular bundles are exposed and
preserved.
The anterior cranial fossa is then exposed by removing a
segment of bone which may be pedicled on the
temporalis muscle or completely separated. The lower horizontal bone cut
should be kept low to lessen the need for subsequent brain retraction.
Withdrawing 25 to 50 ml of CSF from the lumbar subarachnoid catheter,
lowering Pco2 through controlled hyperventilation, and occasionally
administering mannitol or steroids further reduce the need for mechanical
frontal lobe retraction.
The dura is then carefully dissected off the cristagalli and cribriform plate dividing the dural sleeves that extend along the olfactory nerves.
The intracranial portion of the tumor extension is then assessed. If it
involves the dura or in certain situations, frontal lobe this will have
to be resected, together with the tumor, If the
dura is intact, it is retracted back to the planum
sphenoidale.
Once the head and neck surgeon has completed the exposure
and mobilization of the tumor transfacially a
chisel or drill is used either from above or below to make the necessary
bone cuts to encompass the tumor and deliver the specimen.
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bicoronal
&lateral rhinotomy incision& its
extensions
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lateral rhinotomy
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defect after
tumor removal
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repair with
vascularized pericranial flap
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Facial Approach:
The facial approach depends on the extent of the tumor.
Often utilizes modifications of a lateral rhinotomy
incision which may or may not transect the upper lip. This depends on
whether a total maxillectomy is done in
conjunction with the resection.
The periosteum is elevated from the nasal bone as well as
from the medial and inferior surfaces of the orbit.
The nasolacrimal duct is identified and transected distally.
The anterior and posterior ethmoidal arteries are then identified and
cauterized or clipped.
In most cases it is necessary to perform a complete enbloc ethmoidectomy. For
this purpose a contra lateral lynch incision is made to elevate the
contra lateral periorbita, cauterize the
anterior and posterior ethmoidal vessels, and make the appropriate
osteotomies.
If preoperative imaging studies confirm the presence of
tumor in this, the soft tissues of the orbit, then orbital exenteration may be facilitated by extending the
incision laterally to include a portion of the eyelids.
RECONSTRUCTION:
The secret of avoidance of post operative
complications in anterior skull base surgery is the insurance of a water
tight dural closure. If a portion of the dura
has been excised, it is repaired with fascia lata.
The pericranium is used for
anterior cranial fossa reconstruction. It is usually pedicled
on the supraorbital and supratrochlear arteries. The pericranial
flap is placed across the defect in anterior cranial fossa. The distal
end is clamped between the cranial floor bone and the overlying dura. It
may be secured with sutures through the bone or anchored with fibrin
glue. Unless a large amount of anterior cranial fossa bone has been
resected and concern for brain herination
exists, it is usually not necessary to place a bone graft across the bony
defect. Also, it is usually not necessary to place a skin graft on the
under surface of pericranium(facing the nasal cavity), since this tissue has been
shown to "mucosalize" readily on its
nasal cavity.
Once the pericranial flap is in
place the spinal drain is clamped so that no further intraoperative CSF
decompression will take place. This will allow gradual reexpansion of the brain to make contact with the pericranial flap, obliterating any residual dead
space.
Since the pericranial flap
traverses the frontal sinus, it is necessary to obliterate the frontal
sinus with fat or free muscle after removing all the mucosa in the sinus.
If the sinus is quite large, it may be advisable to remove the posterior
wall of the sinus completely and allow the brain and dura to expand and
fill the space ( Cranialization of the frontal
sinus)
The bifrontal craniotomy bone flap
is then replaced and secured according to the surgeon's preference. This
may be done with wires, plates or sutures.
In all cases, an exclusive nasal pack is placed for at
least 5 days post operatively and a lumbar drain kept for the same
duration. In significantly larger defects, particularly if orbital exenteration and facial skin is excised, a bulky free
flap is considered.
Basal Sub frontal approach:
It is in many ways similar to the anterior craniofacial
resection operation except that the Transfacial
exposure is less extensive. Because the target area for this approach is
more posterior (Sphenoid and clivus) than in
the anterior cranio facial resection (ethmoid
and cribriform), the craniotomy bone flap is larger, and the orbital bone
cuts are broader. This approach also begins with a bicoronal
incision.
After exposing the orbital rims, periorbita
is elevated from beneath the orbital roofs and medial walls in
preparation for osteotomy. Bifrontal craniotomy
is then performed, and dura is elevated from above the orbital roofs and
cribriform areas. Using malleable retractors to protect the brain and
orbital contents, the reciprocating saw is used to create osteotomies
that result in temporary removal of both orbital roofs and the supra
orbital contents, the reciprocating saw is used to create osteotomies
that result in temporary removal of both orbital roofs and the supra
orbital bar.
The coronal osteotomies along the posterior orbital roof
should be made as far posteriorly as possible to simplify reconstruction,
by conserving orbital contour, and to prevent postoperative pulsatile
exophthalmoses.
The neurosurgeon completes the approach by drilling a small amount
of bone remaining posteriorly to unroof the
optic nerves, superior orbital fissures and sphenoid sinus. Extirpation
then proceeds as required by the tumor, followed by reconstruction which
is similar to that done for anterior craniofacial resection.
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