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The Anteromedial Corridor via the Expanded Endonasal Approach: The “Front Door to Meckel’s Cave”
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MS
L
V2
Fig. 16.24 Simultaneous endoscopic and image-guided view demonstrating the critical landmarks: maxillary division of trigeminal
nerve (V2), paraclival ICA (PC-ICA), vidian nerve (VN), and foramen lacerum (FL). Two key bony landmarks or tubercles are noted;
specifi cally, the maxillary strut (MS) separating the superior orbital fi ssure from V2 and the lingular process (L) separating V2 from the
PC-ICA.
MS
V2
L
V3
Fig. 16.25 The endoscopic view of Fig. 16.24 but with the
mandibular division (V3) shown and the practical boundaries
of the quadrangular space superimposed to demonstrate
the trajectory. FL, foramen lacerum; L, lingular process; MS,
maxillary strut; V2, maxillary division of CN V; V3, mandibular
division of CN V.
Knowing these bony landmarks can help with the
overall exposure and entering into Meckel’s cave.
2. At this stage, removing the maxillary strut is animportant step. In general, it is important to remove
these tubercles encompassing neurovascular structures as it allows the mobilization of these structures
in an unencumbered fashion without impedance.
3. V2 is subsequently identified and followed back toward
its insertion into Meckel’s cave. The drilling starts along
the inferior medial aspect of the vidian canal. This occurs
PCICA
VN FL
PCICA
FL
in an inferior hemicircumference around the vidian as
the ICA is the superior margin, as previously described.
The FR is then identified either directly or when following the infraorbital nerve proximally. The key tubercle at
this point is the lingular process that separates V2 from
the paraclival ICA. This must be removed with care to allow for entrance into Meckel’s diverticulum (Figs. 16.24
and 16.25). With the FR identified, the bone around V2
is removed until the nerve is seen to pierce the dura mater of the middle cranial fossa.
4. Once this portion of the genu of the ICA is located
approximately just superior to the foramen lacerum
(Figs. 16.25 and 16.26), the bone of the petrous horizontal segment is removed laterally. Paraclival bone
is also drilled to obtain more proximal and distal control of the ICA to allow for mobilization and ability
to dissect within Meckel’s diverticulum. However,
this is not required in every case, depending on the
involvement of the carotid with each lesion. We have
typically noted three instances where skeletonization of the petrous carotid is of benefit for proximal–
distal control: (1) carotid encroachment involving
bony erosion, (2) carotid encasement, and (3) carotid
displacement or mobilization to reach the posterior
aspect of the ICA.
5. Once the ICA is skeletonized, one can then beginexposure of the quadrangular space—which is bounded by the ICA medially, V2 laterally, and the horizontal petrous ICA inferiorly. The superior boundary is
the abducens nerve which runs obliquely and under
V1, and is essentially tucked under it as if V1 were a
blanket covering it as it runs through the cavernous
sinus into the SOF. The key to avoiding the abducens
nerve is not to cross the superior margin of V2; therefore, functionally and by surrogacy, V2 serves as the
superior margin of the quadrangle (Fig. 16.27).
At this point, further dissection along the trigeminal
often is influenced by the type of lesion involved (e.g.,
benign or malignant disease). At this time, if malignancy is involved, such as an adenoid cystic carcinoma,
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ON
PCR
V2
V1
CS
AN
GG
VN
V2
ON
O
MS
LOCR
SOF
Cavernous
ICA
Paraclival
ICA
OS
Paraclinoidal
ICA
V3
Sella
Fig. 16.26 View of the critical relationship of the great
tubercles: optic strut (OS) between the optic nerve and
paraclinoidal ICA; lateral OCR (LOCR) between optic nerve (ON)
and the superior orbital fi ssure (SOF); and the maxillary strut
(MS) between the SOF and V2. MS is being removed to gain
access to Meckel’s diverticulum by allowing an unencumbered
superior mobilization of V2. V2, maxillary division of CN V.
ON
PCR
V1
V2
Fig. 16.27 View following removal of the key bony tubercles
(maxillary strut and lingular process). This now provides a
direct view of Meckel’s diverticulum. Note the relationship of
V2 superolateral and the paraclival ICA medial with the genu
(inferomedial) border of the quadrangle being marked by the
vidian nerve (VN). AN, abducens nerve; CS, cavernous sinus;
GG, gasserian ganglion; ON, optic nerve; PCR, proximal carotid
ring; VN, vidian nerve; V1, ophthalmic division of CN V; V2,
maxillary division of CN V; V3, mandibular division of CN V.
AN
GGV3
VN
Fig. 16.28 Intradural exposure of Meckel’s diverticulum: ICA
can be seen as it travels superiorly from the foramen lacerum,
through the paraclival segment and into the cavernous sinus
(CS) where it is retracted and then rises to enter into the
carotid cave (note the relationship of the proximal carotid
ring (PCR), ICA, and optic nerve (ON) as ICA transitions into
the paraclinoidal segment. The abducens nerve (AN), as it
free fl oats, marks a good transition to form the inferior medial
boundary of the CS rising and hiding under ophthalmic division
(V1) using it as a blanket to travel within the CS as the two
enter the superior orbital fi ssure (SOF). Inferior and lateral
to the potential space between the periosteal layer of the
ICA and the bony tubercles that have been removed and the
meningeal layer of the temporal dura contains the gasserian
ganglion (GG), i.e., Meckel’s cave or more accurately Meckel’s
diverticulum. The GG now trifurcates into its three divisions:
ophthalmic (V1), maxillary (V2), and mandibular (V3). The
maxillary division functionally serves as the superolateral extent
of the quadrangle to protect the abducens nerve as it travels
and can be seen exiting from the Dorello’s canal through
the cavernous sinus on its way to the SOF. Also note the rich
blood supply provided by the meningohypophyseal trunk
and branches of the ICA. Also, note the critical relationship
of the vidian nerve (VN) as it emerges from the greater
sphenopalatine foramen in the middle cranial fossa below V3,
the foramen ovale, and travels along the petrosal ICA.
which is often known to be neurophilic, the trigeminal
nerve can be sacrificed in an effort to achieve adequate
margins. With benign lesions such as schwannomas that occupy the medial compartment of Meckel’s
cave, however, the trigeminal is preserved with minimal manipulation, typically displacing it superiorly
into the middle fossa. As discussed, the removal of the
maxillary strut greatly facilitates this (Fig. 16.27).
6. To reach the lateral compartment of Meckel’s cave in
the rare situations of benign lesions, we can selectively use the anteromedial corridor between V1 and
V2 or the anterolateral corridor between V2 and V3.
These nerves are used as landmarks; the meningeal
dural layer is opened to expose the anterior temporal
fossa and the arachnoid space (Figs. 16.28–16.30).
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The Anteromedial Corridor via the Expanded Endonasal Approach: The “Front Door to Meckel’s Cave”
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ON
PCR
V1
CS
V2
V3
Fig. 16.29 The anatomic landmarks of Fig. 16.28 but with
the superimposed quadrangular space demarcating the
functional working space of the Meckel’s diverticulum.
AN
GG
VN
16.4 Case Example
To demonstrate the clinical applicability of our anatomic approach to Meckel’s diverticulum, we here describe a
case of a 31-year-old woman who presented to the clinic
with hypoesthesia in the right trigeminal nerve distribution. Imaging showed a large lesion in the infratemporal
fossa extending to the dura. There was some invasion into
the cavernous sinus and Meckel’s diverticulum, as well
as the ipsilateral carotid artery. As such, a decision was
made to biopsy the lesion (suspected at the time to be a
schwannoma) via an expanded endonasal approach.
Intraoperatively, an NSF, as previously described, was
first prepared for future reconstruction. A wide sphenoidotomy and bilateral posterior ethmoidectomies were
completed to fully expose the sphenoid sinus. The vomer
and the PVCs were drilled down to the level of the clival
recess. A medial maxillectomy was then undertaken by
first locating the uncinate, opening the inferior turbinate
and then entering the maxilla. The front and back walls of
the maxilla were identified and opened. The sphenopalatine arteries were then identified. The pterygomaxillary
fissure was then identified and opened to allow access to
the infratemporal fossa. Next, the greater palatine artery
and the vidian nerve were identified. The vidian nerve, in
particular, was separated up to the genu of the carotid artery using a drill. Using a transpterygoid approach, both
medially and laterally, circumferential exposure and access
of the lesion were undertaken. Final pathology revealed an
unusual, poorly differentiated sarcomatoid carcinoma that
was not fully characterizable. Figs. 16.31–16.36 show the
key surgical steps in the resection of this lesion.
AN
Fig. 16.30 Magnifi ed view of Fig. 16.29 demonstrating the
free-fl oating course of the abducens nerve (CN VI).
16.5 Complications
The main complications with this approach have been
well described. In the largest case series by Kassam et al,
in which 40 patients were operated on via the expanded endonasal approach, the main complications noted
were injury to one of the three branches of the trigeminal
nerve, transient sixth nerve palsy, postoperative hemorrhage, and visual dysfunction. In addition, other potential complications include those associated with general
anesthetic, bleeding, and infection of all types, which are
known complications to any surgical procedure. However, it is also important to note that in the same case series
many cranial deficits improved with surgery and removal
of the lesion. Overall, in the case series described, only
5% of patients suffered any permanent deficits (2 patients
out of 40). The remaining six patients who suffered transient deficits recovered their nervous deficits by the time
of their 6-month follow-ups.
Based on the anatomic considerations, this approach
is well suited for ventral skull base pathology wherein the critical nerves in Figs. 16.28–16.29 are located
along the superolateral perimeter. It is the experience
of our group that recovery time postsurgery, compared
with open approaches, is generally shorter, given the
tissue preserving nature of the approach. Overall, patients feel improved after 2 weeks, particularly after
the packing is removed. Patient’s experience decreased
nasal crusting after the second week and a significant improvement by after the third week. Overall,
postoperative recovery for patients is generally very
well tolerated.
4
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The Anteromedial Corridor via the Expanded Endonasal Approach: The “Front Door to Meckel’s Cave”
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PreOp
a
PostOp
b
Fig. 16.31 Preoperative and
postoperative T1-weighted,
enhanced, axial and coronal MRI
images. Preoperative images (a) show
a large, heterogeneously enhancing
mass that replaces the clivus, extends
anteriorly into sphenoid sinus and
nasopharynx, and invades and
enlarges the left cavernous sinus
and Meckel’s diverticulum. There
is encasement of internal carotid
arteries, greater on the left. The optic
chiasm is deformed and displaced
superiorly. Postoperative images (b)
show substantial resection. There is
fat fi lling the operative defect in the
clivus and sphenoid sinus and there
is peripheral enhancement within
resection cavity with minimal residual
disease.
SS
pwMS
SPF
Fig. 16.32 Removal of bone of the posterior wall of the
maxillary sinus to reveal the sphenopalatine foramen and the
pterygomaxillary fossa and its contents, including the internal
maxillary artery (IMAX). pwMS, posterior wall of the maxillary
sinus; SPF, sphenopalatine foramen; SS, sphenoid sinus.
Greater Pal.
M
Fig. 16.33 Dissecting the greater palatine nerve bundle
(Greater pal.) and subsequently ligating it. M, Maxilla.
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ON
I
C
A
SS
VC
VN
MPP
Fig. 16.34 Drilling away the vidian canal toward the genu of
the petrous carotid artery. ICA, internal carotid artery; MPP,
medial pterygoid plate; ON, optic nerve; SS, sphenoid sinus;
VC, vidian canal; VN, vidian nerve.
Fig. 16.36 Placement of nasoseptal fl ap over the surgical
cavity.
16.6 Tips and Tricks
However, we caution the reader that this represents a
critical tool in the armamentarium of a skull base surgeon, but, like any tool, it is subject to the experience of
the user and should be applied with judgment and based
on three key factors:
1. Operator experience.
2. Relative juxtaposed anatomy.
SS
PM
Ca
C
Fig. 16.35 Partially resected tumor within Meckel’s
diverticulum. Imaging shows remaining normal anatomy. C,
choana; Ca, Cavity; PM, pterygoid muscle; SS, sphenoid sinus.
3. We should always carry with us the guiding principle
of avoiding crossing the plane of a nerve, as much as
possible.
References
1. Ginsberg LE, DeMonte F. Imaging of perineural tumor spread from
palatal carcinoma. AJNR Am J Neuroradiol 1998;19(8):1417–1422
2. Kouyialis AT, Stranjalis G, Papadogiorgakis N, et al. Giant
dumbbell-shaped middle cranial fossa trigeminal schwannoma
with extension to the infratemporal and posterior fossae. Acta
Neurochir (Wien) 2007;149(9):959–963, discussion 964
3. Yuh WT, Wright DC, Barloon TJ, Schultz DH, Sato Y, Cervantes CA.
MR imaging of primary tumors of trigeminal nerve and Meckel’s
cave. AJR Am J Roentgenol 1988;151(3):577–582
4. Kassam AB, Vescan AD, Carrau RL, et al. Expanded endonasal approach: vidian canal as a landmark to the petrous internal carotid
artery. J Neurosurg 2008;108(1):177–183
5. Morrison AW, King TT. Experiences with a translabyrinthinetranstentorial approach to the cerebellopontine angle. Technical
note. J Neurosurg 1973;38(3):382–390
6. Inoue T, Rhoton AL Jr, Theele D, Barry ME. Surgical approaches
to the cavernous sinus: a microsurgical study. Neurosurgery
1990;26(6):903–932
7. Seoane E, Rhoton AL Jr. Suprameatal extension of the retrosigmoid
approach: microsurgical anatomy. Neurosurgery 1999;44(3):
553–560
8. Yasuda A, Campero A, Martins C, Rhoton AL Jr, de Oliveira E, Ribas
GC. Microsurgical anatomy and approaches to the cavernous
sinus. Neurosurgery 2005; 56(1, Suppl):4–27, discussion 4–27
9. Yasuda A, Campero A, Martins C, Rhoton AL Jr, Ribas GC. The medial
wall of the cavernous sinus: microsurgical anatomy. Neurosurgery
2004;55(1):179–189, discussion 189–190
10. Labib MA, Prevedello DM, Carrau R, et al. A road map to the internal
carotid artery in expanded endoscopic endonasal approaches
to the ventral cranial base. Neurosurgery 2014;10(Suppl 3):
448–471, discussion 471
179
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Chapter 17
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17.1 Anatomic Background 182
Endoscopic Endonasal
Approach to
Intrapetrous Carotid
Artery
17.2 Indications 182
17.3 Surgical Steps 183
17.4 Case Examples 187
17.5 Complications 187
Endoscopic Endonasal Approach to Intrapetrous Carotid Artery
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17 Endoscopic Endonasal Approach to Intrapetrous
Carotid Artery
Paolo Castelnuovo, Paolo Battaglia, Mario Turri-Zanoni
Introduction
The petrous portion of the internal carotid artery (ICA)
is a critical structure when managing skull base lesions
placed in areas such as the petrous apex, the Meckel’s
cave, and the superior aspect of the infratemporal fossa
(ITF). The continued advancements of endoscopic surgical techniques and instrumentation have progressively
expanded the indications for transnasal approaches over
the past decade. As interest in these approaches grows, so
do the risks. Injuring the ICA during skull base procedures
is a devastating complication and has been reported by
multiple authors.
of the relationships between the petrous ICA and nearby
anatomic landmarks, as well as a rigorous training method in approaching this region, is an imperative issue.
1–4
Therefore, a thorough understanding
17.1 Anatomic Background
The petrous portion of the ICA is extradural and intraosseous. It extends from the carotid foramen to the superior
margin of the petrolingual ligament (PLL). The carotid foramen is anteromedial to the styloid process and posteromedial to the temporomandibular joint.
between the sphenoidal lingula and the petrous apex,
represents the posteromedial border of the cavernous sinus (CS). Once it enters in the petrous bone, the ICA presents a short vertical course, and then it turns in front of
the cochlea, forming the posterior genu (Fig. 17.1). From
here, it runs horizontally within the temporal bone in an
FO
SpL
Fig. 17.1 Relationship between the petrous portion of the
internal carotid artery and the cochlea (vision from above).
ASC, anterior semicircular canal; Co, cochlea; EAC, external
auditory canal; FO, foramen ovale; FS, foramen spinosum; IAC,
internal auditory canal; LSC, lateral semicircular canal; pICA,
petrous segment of the internal carotid artery; PSC, posterior
semicircular canal; SpL, lingula of the sphenoid. Black circles,
groove for the greater petrosal nerve.
FS
plCA
IAC
1
The PLL, placed
Co
ASC
PSC
EAC
LSC
anteromedial direction, posterior to the tensor tympanic
muscle, eustachian tube (ET), and the foramina spinosum
and ovale. Within the carotid canal, the horizontal portion of the petrous ICA is surrounded by a venous plexus
in direct continuity with the CS.
curves upward above the foramen lacerum (FL), thus giving the anterior genu and therefore becoming vertical
(paraclival segment of the ICA). At this level, the vidian
canal is always lateral to the vertical segment (Fig. 17.2).
1
The petrous ICA then
17.2 Indications
Pathology will dictate the necessary exposure of the
petrous ICA. A thorough understanding of the relationships
of relevant landmarks is paramount to remove the lesion
successfully with the most minimal bone and soft-tissue
resection. Therefore, the surgical approaches related to
the petrous ICA can be divided between the ones directed
only to its medial aspect (anterior genu) and the ones
requiring a complete exposure of the vessel from the
anterior genu back to the posterior genu.
The surgical approaches directed to the medial portion
of the petrous ICA are as follows:
• The petrous apex approach (upper petroclival fissure)
is directed medial to the paraclival ICA and posterosuperior to the petrous ICA. The guiding principle here
is to identify the anterior genu between the paraclival
and petrous ICA segments and unroof its canal completely from proximally to distally to avoid injury to the
petrous segment of the sixth cranial nerve as it ascends
behind the paraclival ICA to reach the uppermost edge
of the petrous apex where it enters the sphenopetroclival gulf.
• The inferior petroclival approach is directed medial
to the petrous ICA in the interval rostral to the jugular foramen along the inferior (horizontal) segment of
the petroclival fissure. The venous structures related to
this approach are the inferior petrosal sinus and the inferior petroclival vein. The inferior petroclival approach
allows access to the posterior cranial fossa at the level
of cranial nerves VII and VIII.
• The petrous ICA constitutes the inferomedial bound-
ary of the front door to Meckel’s cave approach. This
approach is directed lateral to the paraclival ICA and
below the V2 nerve, which can be followed posteriorly
toward the gasserian ganglion.
• The inferior CS approach is performed laterally to
the paraclival ICA and superiorly to the petrous ICA.
Although practically very similar to the front door to
Meckel’s cave approach, the target lesion for this approach is more medial and superior and by definition
localized in the CS. Hence, special care must be taken
while opening the dura and resecting the tumor to protect the abducens nerve.
The surgical approaches requiring a complete exposure
of the petrous ICA are generally directed below the vessel
and extended laterally as far as the parapharyngeal ICA.
The petrous ICA lies at the superomedial margin of these
2
3
3
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TM
a
Fig. 17.2 (a) Relationship between the carotid canal and the eustachian tube. (b) Anatomic representation of the course of the
ICA. BA, basilar artery; Cl, clivus; Co, cochlea; CP, coronoid process; ET, eustachian tube; IAN, inferior alveolar nerve; ICAh, horizontal
portion of the internal carotid artery (petrous ICA); IJV, internal jugular vein; LN, lingual nerve; LPM, lateral pterygoid muscle; MA,
maxillary artery; ME, middle ear; MPM, medial pterygoid muscle; P, pons; SS, sphenoid sinus; TM, temporal muscle; TVPM, tensor veli
palatini muscle; VN, vidian nerve; V3, third branch of the trigeminal nerve.
approaches. For this reason, the inferior aspect of the petrous ICA is completely skeletonized, from the anterior
genu back to the posterior one, to safely identify the carotid
foramen and therefore the parapharyngeal tract of the ICA.
The main surgical procedures entailing such an expo-
sure of the petrous ICA are as follows:
CP
ME
LPM
Co
ICAh
MPM
TVPM
BA
ICAh
V3
LPM
IAN
MA
LN
IJV
MPM
IJV
b
P
VN
ET
• Computer-assisted magnetic neuronavigation system
ith CT–MR fusion images) can help intraoperatively
(w
to identify prominent vascular and neural structures
associated with the skull base.
• An acoustic Doppler ultrasound probe is mandatory for
such surgery, helping in identification of carotid artery.
SS
• Endonasal nasopharyngectomy extended laterally to
include the ET (type III nasopharyngeal endoscopic resection).
• Endoscopic approaches to the ITF and upper parapha-
ryngeal spaces (UPPS).
4
5
17.3.2 Approach to the Medial
Aspect of the Petrous ICA
• The dissection begins with a partial middle turbinec-
tomy and total ethmoidectomy. An ipsilateral sphe-
17.3 Surgical Steps
noidotomy with enlargement of the natural ostium is
performed. The mucosa overlying the inferior margin
17.3.1 Instrumentation
• Preoperative computed tomography angiography (CTA)
scan is recommended to study the course of the ICA
and to exclude atypical (particularly medial) kinking of
the vessel.
• Preoperative CT and magnetic resonance (MR) analysis
with a program such as OsiriX, to examine anatomic
relationships between important structures. The opensource DICOM viewer provides the possibilities of analyzing any chosen CT collection both as normal scans
and with 3D reconstruction or virtual dissection.
• For this surgical approach, 0- and 45-degree rigid en-
doscopes (4 mm in diameter) are essential.
• Straight high-speed diamond burr drills are useful to
approach the bony skull base and skeletonize the petrous portion of the ICA.
• Straight, curved, and malleable dissectors are neces-
sary for ITF and UPPS surgery.
• Straight and curved bipolar cautery forceps facilitate
optimum visualization and access during surgery, to
control intracranial bleeding.
of the sphenoidotomy is elevated to preserve the vascular pedicle of the ipsilateral nasoseptal flap (so-called
“rescue flap”). Generally, bilateral sphenoidotomies are
performed to provide more space for instrumentation
and allow a four-hand surgery by a team consisting of
an otolaryngologist and a neurosurgeon. For the same
reason, the posterior one-third of the nasal septum is
disarticulated from the rostrum and removed. A bilateral exposure allows improving the angle for visualization and instrumentation from the side opposite to the
lesion. Anatomic landmarks within the sphenoid sinus
are identified: planum sphenoidale, sella, clival recess,
optic canal, medial and lateral opticocarotid recesses,
and the carotid canal (Fig. 17.3). Septations within the
sphenoid sinus are removed. Aggressive instrumentation is avoided during removal of these septations to
avoid injury to the ICA, and thus drilling is preferred.
• The floor of the sphenoid is drilled out. Vidian canal
and foramen rotundum are identified along the face of
the pterygoids base. The vidian canal provides a good
depth gauge for the position of the ICA as it transitions
from the petrous to the paraclival segment at the level
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ON
OCR
psICA
Sf
C
V2
Fig. 17.3 Endoscopic endonasal approach to the medial
portion of the petrous ICA. The fi rst step is represented by a
wide sphenoidotomy with identifi cation of intrasphenoidal
landmarks. C, clival recess; cICA, paraclival portion of the
ICA; OCR, opticocarotid recess; ON, optic nerve; psICA,
parasellar segment of the ICA; sbSPA, septal branches of the
sphenopalatine artery representing the vascular pedicle for the
nasoseptal recue fl ap; Sf, sellar fl oor; V2, second branch of the
trigeminal nerve; VC, vidian canal.
cICA
VC
sbSPA
of the FL (Fig. 17.4a). In light of this, the vidian nerve
(VN) and vidian artery are cauterized and cut, and the
medial aspect of the pterygoids base is addressed as the
vidian canal is completely drilled out. This provides exposure of the anterior genu of the ICA at the level of FL.
The fibrocartilago basalis is removed as far as the superior aspect of the cartilaginous ET is encountered. The
paraclival and petrous tracts of the ICA are skeletonized
using a drill with diamond burr (Fig. 17.4b).
• Once the vertical (paraclival) and horizontal (petrous)
segments of the ICA are visualized, the drilling may
proceed inferiorly and posteriorly to the petrous carotid into the petrous apex (Fig. 17.5) or it may be carried
on above the petrous carotid toward the Meckel’s cave
and the inferior portion of the CS.
3
17.3.3 Complete Exposure of the
Petrous ICA
• Once the anterior genu of the ICA is visualized and the
medial portion of the petrous ICA is exposed, the dissection has to be extended laterally as far as the carotid foramen (posterior genu of the ICA). To this purpose, an endoscopic endonasal Denker’s approach with removal of the
medial wall of the maxillary sinus together with the inferior turbinate and the drilling of the pyriform aperture
is able to provide an increased lateral access (Fig. 17.6).
• A transmaxillary window is created by removing the
posterior wall of the maxillary sinus. Vidian artery and
VN together with palatovaginal artery and descending
5
1
SS
cICA
VN
NP
a
Fig. 17.4 (a) The vidian canal is identifi ed at the pterygoid wedge where the medial pterygoid plate meets the fl oor of the sphenoid
sinus. Sequential drilling of the vidian canal beginning at the inferomedial border. (b) By drilling out the vidian canal in a medial to
lateral direction it is possible to identify the anterior edge of the carotid canal and petrous ICA (below the level of the lingular process
of the sphenoid bone). To note, the posterior opening of the vidian canal is always fi lled with fi brocartilaginous tissue (pointed out by
the dissectors), which fused with similar tissue overlying the foramen lacerum, medially, and the ET, inferiorly. cICA, paraclival portion
of the ICA; ET, eustachian tube; NP, nasopharynx; pICA, petrous portion of the ICA; SS, sphenoid sinus; VN, vidian nerve.
b
VN
cICA
pICA
ET
184
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