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Chapter 16
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16.1 Indications 166
The Anteromedial
Corridor via the
Expanded Endonasal
Approach: The “Front
Door to Meckel’s Cave”
16.2 Anatomic Considerations 166
16.3 Surgical Steps 166
16.4 Case Example 177
16.5 Complications 177
16.6 Tips and Tricks 179
The Anteromedial Corridor via the Expanded Endonasal Approach: The “Front Door to Meckel’s Cave”
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16 The Anteromedial Corridor via the Expanded
Endonasal Approach: The “Front Door to Meckel’s Cave”
Sammy Khalili, Srikant S. Chakravarthi, Juanita M. Celix, Nishit Shah, Martin Corsten, Melanie Fukui, Richard Rovin, Amin Kassam
Introduction
Meckel’s diverticulum, or Meckel’s cave, as the name suggests, represents a hidden pyramidally shaped den that
is situated deep in the skull base, harboring a carefully
guarded anatomic treasure of vascular and neural structures. The cave is no larger than the size of a thumbnail,
vulnerable to pathologic entities that can infiltrate from
within, namely schwannomas, or other lesions that can
intrude along the perimeter and eventually invade the
protective dural walls. To best preserve the highly prized
treasures contained within, it is imperative to understand
the intricacies of the intrinsic and adjacent anatomic
structures, such as the gasserian ganglion and its pre- and
postbranches, the abducens nerve and internal carotid
artery (ICA), and the protective osseous and soft-tissue
frameworks.
Over the past two decades, we have come to the realization that the most common primary long-term
morbidity with skull base surgery is associated with
cranial nerves. Therefore, every effort should be taken
to minimize their manipulation. To better understand
this crowded space, we will review, in significant detail,
the anatomic boundaries of Meckel’s diverticulum and
its treasures contained within. This represents the essential truth by which a strategy of modular approaches
can be designed and executed to minimize impairment.
The goal of this chapter is to describe a step-by-step approach to the endoscopic endonasal anteromedial corridor—“the front door to Meckel’s cave.” The reader must
not forget, however, that this represents all but one corridor for surgical access. The role of the traditional transcranial antero- and posterolateral corridors, and their
variants, while beyond the scope of this chapter, must
be a part of the surgeon’s armamentarium. Our guiding
principle in selecting the specific corridor has been to
let the truth of the anatomy, rather than the agenda of
the surgeon, guide the selection of corridor. Explicitly stated, when possible, avoid crossing the plane of a
cranial nerve.
16.2 Anatomic Considerations
Meckel’s cave represents a potential space in the middle
cranial fossa where the two layers of dura mater (periosteal and meningeal) split, forming a diverticulum
fore, we prefer to refer to it as Meckel’s diverticulum. At
this point, the trigeminal nerve travels from the brainstem to the Gasserian ganglion.
divides into its three primary divisions that exit through
their respective foramina in the middle cranial fossa.
More precisely, the boundaries of the trigeminal cave are
formed superolaterally by the meningeal layer of the dura
mater that covers the middle cranial fossa. Inferomedially, Meckel’s diverticulum is bounded by the periosteal
layer of the temporal fossa and petrous carotid canal.
In 2009, we described the key anatomic boundaries of
Meckel’s diverticulum as a quadrangle (parallel oblique
4
The quadrangular space is defined medially by the
lines).
ascending paraclival ICA, inferiorly by the petrous ICA,
laterally by V3, the mandibular division of CN V, and superiorly by the abducens nerve or, by surrogacy, V2, the
maxillary division of the trigeminal nerve.
Four approaches have been described to access this corridor that can generally be categorized into the respective
trajectories: (1) anteromedial, (2) anterolateral, (3) lateral,
and (4) posterolateral. We have previously reported that
all four are valuable trajectories in avoiding crossing the
plane of the nerve, to better guide the operator. The location and nature of the pathology will, respectively, displace
the cranial nerves within and juxtaposed around Meckel’s
diverticulum. Specifically, the appropriate corridor should
ideally be selected to avoid crossing the path of the nerve,
to allow direct access to the lesion, and to leave the primary nerves along the perimeter. Given the ventral nature of
many of the pathologies that afflict this region, such as meningiomas, the nerves are often displaced posterolaterally.
This situation lends itself ideally to an anteromedial approach to the diverticulum. In this chapter, we describe, in
stepwise detail, accessing Meckel’s diverticulum through
the anteromedial corridor via the expanded endonasal
approach.
5
From there, the nerve
4
; there-
6–9
16.1 Indications
Every surgeon requires a complete understanding of
the anatomy, the anatomic landmarks, and the surrounding structures, to surgically address a region
appropriately. Meckel’s cave, or the trigeminal cave,
is often described as a challenging area of the skull
base to access, involving complex anatomy and requiring technical finesse. Various abnormalities can
affect Meckel’s cave, including epidermoid cysts,
chondrosarcomas, chordomas, and sinonasal malignancies, which often experience perineural invasion
and spread. The most common lesions in this area are
meningiomas and schwannomas originating from the
trigeminal nerve.
166
16.3 Surgical Steps
16.3.1 Preparation
1
1. Each patient obtains a preoperative computed tomog-
raphy angiography to precisely (CTA) locate the ICA (petrous and paraclival segment), defining critical inferior
and medial boundaries of the quadrangular space, and
to be used for image-guidance during the procedure.
2. Ideally, the patient should have a high-resolution
magnetic resonance imaging (MRI) such as a FIESTA
sequence to provide a general perspective of the lo-
2,3
cation of the juxtaposed cranial nerves defining the
superior and lateral quadrangular boundaries.
The Anteromedial Corridor via the Expanded Endonasal Approach: The “Front Door to Meckel’s Cave”
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3. Once the images have been set up in the room, the
patient is placed under general anesthetic and orotracheally intubated.
4. The head is fixed in a three-pin head holder positioned with the neck extended slightly and the head
turned slightly to the right, extended and rotated to
allow for the nares to be in an ergonomic position for
the operating surgeon. We prefer fixed pining positions to allow for drilling without the risk of moving.
5. The nose is decongested with 0.05% topicalxylometazoline or oxymetazoline using ½" x3" cottonoid pledgets.
6. Povidone solution is then applied perinasally. It is also
applied to the periumbilical areas as well in preparation for the possibility of using a fat graph during the
reconstructive phase of the procedure. The right thigh
can also be prepared in preparation for possibly using a tensor fascia lata graft as part of the reconstruction. Once the solution has been placed, the patient
is draped, exposing the nose and eyes in one field
and keeping the lower abdomen and leg completelyseparate.
16.3.2 Nasal Cavity Approach
After the patient is appropriately positioned, prepped,
and draped, and the image-guidance system has been
accurately registered, we can begin with our endonasal
exposure. Our preferred instrumentation is a 0-degree
rod lens endoscope for direct visualization, with an
irrigation system for lens cleaning—either the Medtronic
Endo-Scrub (Medtronic Corporation, Minneapolis, MN)
or Infiniti syringe irrigation (Nico Corporation, Indianapolis, IN). We recommend a four-handed technique for
these approaches, and we find the Infiniti is best with the
team approach. This helps maintain our visualization. We
then begin with our exposure.
We have espoused the concept of a “cavity and a half”
to allow for adequate visualization. We separate one-half
of one nasal cavity for endoscope insertion and the other
half as a working cavity for the bimanual binasal dissec-
tion. In the case of the front door exposure to Meckel’s
cave, this consists of creating a vertical rectangle that extends from the posterior ethmoid through the nasopharynx and laterally, incorporating wide bilateral sphenoid/
ethmoidectomies (lamina papyracea to lamina papyracea) with extension to the ipsilateral maxilla. This process
is described in the following.
Phase I: Rostrocaudal Binasal Rectangular Midline Nasal Exposure
1. Ipsilateral nasal cavity preparation: The inferior turbinate is out-fractured and lateralized to maximizevisualization. This is done using either a Goldman
freer or caudal elevator, in conjunction with decongesting the nose with oxy- or xylometazoline
(Figs. 16.1 and 16.2).
a. The middle turbinate is then injected in the axilla
with 1% lidocaine and epinephrine, and allowed
to set for 3 minutes.
2. Ipsilateral nasal cavity preparation (continued): On
the ipsilateral side of the lesion, the lower third of
the middle turbinate is resected, leaving a stump.
One can use either endoscopic scissors or a Colorado needle tip monopolar cautery to make the initial
incision of the middle turbinate. Hemostasis of the
residual middle turbinate stump is achieved with either an endoscopic bipolar or a suction cautery to
control the middle turbinate branch of the sphenopalatine artery (SPA) (Fig. 16.3a, b). Lateralization of
the inferior turbinate and partial middle turbinate
creates a wide endonasal working corridor (Fig.
16.4; the inferior turbinate is lateralized and still in
place in this figure).
3. Contralateral nasal cavity preparation: On the contralateral side of the lesion, the middle turbinate is
in-fractured and medialized (Fig. 16.5). This allows
for both a binasal approach to the sphenoid sinus and
greater exposure to raise the nasoseptal mucosal flap
(Fig. 16.9). With our lateralization, we are able to visualize the natural sphenoid ostium (Fig. 16.6).
Fig. 16.1 In-fracturing of the ipsilateral inferior turbinate.
Fig. 16.2 Out-fracturing (lateralization) of the ipsilateral
inferior turbinate.
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ab
Fig. 16.3 (a) Removal of the anterior portion of the middle turbinate. (b) Removal of posterior portion of the middle turbinate.
Fig. 16.4 Panoramic view of the ipsilateral nasal corridor
after lateralization of the inferior turbinate and transection of
the middle turbinate.
4. Contralateral nasoseptal flap harvest: A nasoseptal
flap (NSF) is harvested on the contralateral side. This
is based on the need to expose the paraclival and genu
segments of the ICA (boundaries of the quadrangular
space) which would put the base of the NSF at risk
(Figs. 16.7–16.10). We raise the flap by making a superior incision inferior to the olfactory epithelium
(this is identified as thicker and with a more yellowish hue in comparison to the normal nasal mucosa) on
the septum and extending it anteriorly to the limen
nasi (we use a Covidien Bovie with an arthroscopic
needle tip; Fig. 16.7). The inferior cut extends posteriorly from the inferior aspect of the nasal choana
on the nasal floor. One can create an extended width
168
Fig. 16.5 In-fracturing (medialization) of the contralateral
middle turbinate.
of the NSF by making the inferior cut lateral and inferior to the inferior turbinate (Fig. 16.8). However,
to decrease the risk of postoperative dental hypoesthesia, we recommend decreasing the power on the
cautery needle or to make the incisions with an extended-length beaver blade. We then raise the flap in
a subperichondrial plane using a suction Cottle elevator (Fig. 16.9). Once fully elevated, we then place
the NSF in the nasopharynx to keep it out of the way
during the remainder of the exposure (Fig. 16.10).
Alternatively, one can create a contralateral maxillary
antrostomy as a storage point for the NSF. A posterior
septectomy is then performed to allow for our binasal
approach to the posterior nasal corridor (Fig. 16.11).
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Fig. 16.6 Exposure of the contralateral natural sphenoid
ostium.
Fig. 16.8 Inferolateral cut of the contralateral nasoseptal fl ap
extending beyond the inferior turbinate to allow for greater
width of the fl ap given the wide exposure needed.
Fig. 16.7 Superior cut of the contralateral nasoseptal fl ap.
Fig. 16.9 Raising the anterior mucoperichondrial dissection
of the nasoseptal fl ap.
5. Upper rectangular corridor: Posterior and, when
needed, anterior ethmoidectomies are performed,
including an ipsilateral uncinectomy. The uncinectomy is completed using a back-biting rongeur and
a microdebrider, Stammberger downbiter, and/or a
through-cutting Blakesley (Fig. 16.12).
6. The sphenoid sinus ostium on the ipsilateral side of
the lesion is identified posteroinferior to the superior
turbinate. The posteroinferior aspect of the superior
turbinate is resected to allow for sufficient exposure.
Using a high-speed drill, the sphenoid sinus face is
resected and opened superiorly to the skull base and
inferiorly to the sphenoid sinus floor. Once the ipsilateral side is completed, the same process is repeated on
the contralateral side, providing the critically needed
wide bilateral exposure through the lateral recess of
the sphenoid sinus (Fig. 16.12).
7. At this stage, posterior septectomy and wide bilateral
sphenoidotomies have been completed, creating the
superior and the initial lateral working corridor. The
lateral wall can be widened via an ipsilateral maxillectomy later. Next, the floor of the sphenoid sinus is
drilled to the level of the clival recess to allow the inferior boundary to be extended (Fig. 16.13).
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Fig. 16.10 Mobilization of the nasoseptal fl ap and storage in
the nasopharynx.
Fig. 16.12 Posterior ethmoidectomy and sphenoid
sinusotomy to create a rectangular cavity. Note in this image
there is still tissue anterior to the left ethmoid that will be
removed to create a truly rectangular cavity. Also note that the
posterior septectomy has been completed.
Fig. 16.11 Posterior septectomy to create a binasal
approach. This is the beginning of the posterior septectomy.
LOCR
ON
LP
Fig. 16.13 The wide bilateral sphenoidotomies must extend
from lamina papyracea to lamina papyracea. The ipsilateral
posterolateral boundary must include the transition of the
optic canal and lateral opticocarotid recess into the periorbital
region bounded by the lamina papyracea. LOCR, lateral
opticocarotid recess; LP, lamina papyracea; MT, middle
turbinate; ON, optic nerve.
ICA
ON
LP
MT
Phase II: Lateral Paramedian Expansion
toward Meckel’s Diverticulum
The corridor is expanded laterally by adding a transpterygoid approach ipsilateral to the targeted Meckel’s
diverticulum. The expansion of the corridor follows a systematic pattern to sequentially expose the boundaries of
the quadrangular space described earlier.
170
Lateral Maxillary Window: Working
Corridor “Cavity and a Half”
1. Exposing the medial pterygoid plate: On the ipsilateral
side of the lesion, the maxillary ostium is identified and
a wide maxillary antrostomy is performed. The maxillary window is extended posteriorly to expose the
posterior wall of the maxilla (Fig. 16.14). It is critical to
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create a large ipsilateral maxillary antrostomy to allow
adequate working space. The inferior boundary is the
inferior turbinate (if not resected previously), the superior boundary the orbit, and the posterior boundary the
posterior maxillary wall. The sphenopalatine foramen
is opened and widened, and the descending and greater
palatine arteries are exposed, ligated, and transected to
provide a broad exposure. The medial pterygoid plate is
exposed and resected to provide a transpterygoid approach. Thus, the resection is extended posteriorly until the medial maxillary wall is removed, leaving only
the orbit superiorly and the inferior turbinate inferiorly.
With this, we can begin the next phase of the exposure.
2. Deepening the maxillary corridor: The lateral maxillary
framework requires a pan exposure consisting of the
bilateral wide sphenoid osteotomies exposing the medial orbital wall (lamina papyracea) and the posterior
wall of the maxilla. Once this outer frame is created, the
deeper exposure to access Meckel’s diverticulum can
begin. The opening of the sphenopalatine foramen is
extended laterally to provide access to the main trunk
of the internal maxillary artery (IMAX) in the pterygopalatine fossa. One can further resect the posterior wall
of the maxillary sinus, anterior to the IMAX. This can
be done with either a down-biting Kerrison rongeur or
a high-speed drill placed into the sphenopalatine foramen to thin the bone. Once the bone is sufficiently thin,
it can be removed with a Cottle or a J-curette.
3. Exposing the posterior wall of the maxillary sinus: The
terminal branches of the IMAX, specifically the SPA
and posterior nasal arteries, are dissected and identified at the level of the sphenopalatine foramen, which
is located posterior to the superior third of the posterior wall of the antrum. The crista ethmoidalis is the
common landmark that is often described in identifying the sphenopalatine foramen. By definition, it is
the ridge of palatine bone that attaches to the middle
turbinate. The vessels are isolated by removing the
posterior wall of the maxillary sinus. The posterior
wall of the antrum is removed with a 1- to 2-mm
Kerrison rongeur, to expose the pterygopalatine fossa and follow the arteries. The posterior wall of the
maxillary sinus is removed just lateral to the infraorbital nerve and fissure. It is important to note that
the infraorbital fissure is continuous with the pterygomaxillary fissure superoposteriorly, forming a large
C-shaped fissure in continuity. It also demarcates the
boundary between the pterygopalatine fossa and the
infratemporal fossa, and its exposure gives access to
the entire base of the pterygoid plates (Fig. 16.15).
With the lateral framework and extension deepened, the
specific elements of the quadrangular space can be systematically exposed (Fig. 16.16).
Inferior (Petrous Carotid) and Medial
(Paraclival Carotid) Boundaries
4. Exposing the medial pterygoid wedge: With the medial
maxillary antrostomy completed and the soft tissue
overlying the medial pterygoid mobilized, the superomedial peak of bone at the base of the medial pterygoid
plate as it articulates with the floor of the sphenoid is
exposed. We have previously described and referred to
this as the “medial pterygoid wedge,” and we identified
it as a critical landmark in the localization of the ICA.
The medial pterygoid wedge is carefully isolated, and
the critical foramina located along an oblique line in the
adjacent region are sequentially identified (Fig. 16.17):
Foramen rotundum (FR): superolateral.
Vidian or pterygoid canal (VC): inferomedial to the FR
and superolateral to the palatovaginal canal (PVC).
PVC: inferomedial to the VC.
10
pwMS
Fig. 16.14 Lateral extension via a generous maxillary
antrostomy and exposure of the posterior maxillary sinus wall.
CE, crista ethmoidalis; ON, optic nerve; psSPA, posterior septal
branch of the sphenopalatine artery; pwMS, posterior wall of
maxillary sinus.
CE
psSPA
ON
SPF
VN
MPP
Fig. 16.15 Deeper exposure of the lateral extension following
a wide maxillary antrostomy (Fig. 16.14) and removal of the
posterior wall of the maxillary antrum. A large cavity and
a half has been created by the bilateral ethmoidectomies
and sphenoidotomies and the ipsilateral maxillectomy.
Note the medial pterygoid plate (MPP) is exposed and
the sphenopalatine foramen (SPF) opened, exposing the
sphenopalatine artery. The back wall of the sphenoid is exposed
and the optic canal is clearly visualized. VN, vidian nerve.
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5. Isolation of the vidian canal: The vidian canal is a
critically important landmark for localizing the
ICA (Figs. 16.18 and 16.19). The vidian nerve is the
confluence of the greater superficial petrosal nerve
(GSPN) and the deep petrosal nerve. The GSPN originates from the nervus intermedius, travels along the
facial nerve, bypasses the geniculate ganglion, courses
along the middle cranial fossa floor, and extends out
of the greater superficial foramina and lies beneath
the foramen ovale. From there, it leaves the skull base
and travels within the pterygoid canal, where it joins
with the deeper petrosal nerve and comes directly
ON
O
LOCR
MOCR
anteriorly toward the surgeon, like an eye looking out.
Once identified distally, and understanding its central
location along the oblique line of the three foramina
described in step 4 (Fig. 16.17), the vidian nerve can
be followed proximally, and provides an excellent
landmark to locate the genu of the ICA and, thereby,
the quadrangular boundary. Specifically, the vidian
nerve inserts just below the genu of the carotid canal.
6. Isolation of the vidian canal (continued): Another land-
mark that is effective in identifying the vidian canal is
the “H-sign” that we have previously described.
4
The
lateral ascending limb of the H represents the lateral
Fig. 16.16 A simultaneous endoscopic and image-guided view of the upper portion of the deep exposure demonstrating critical
landmarks in the posterolateral framework. The critical landmarks seen include the orbit (O), the optic nerve (ON), the lateral
opticocarotid recess (LOCR) with its relationship to the optic strut, the lamina papyracea laterally, and the suction in the superior
orbital fi ssure with the navigation pointer in the medial opticocarotid recess (MOCR).
FR
VN
MPP
PVC
Fig. 16.17 The exposure of the descending portion of the
medial pterygoid plate (MPP), the IMAX and its branches, and
the critical oblique foramina. The scissors are on the foramen
rotundum (FR), the vidian nerve (VN), and the palatovaginal
canal (PVC) are seen inferomedial in an oblique line. Note the
branches of the greater palatine artery.
Fig. 16.18 Isolation and circumferential drilling of the vidian
canal (VC) to expose the genu of the ICA, locating the inferior
and medial boundaries of the quadrangular space.
I
C
A
VC
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I
C
A
VN
VC
Fig. 16.19 The vidian canal (VC) and nerve are exposed after
circumferential drilling has been completed and the plane
deepened to the point where the vidian nerve (VN) inserts
inferior to the genu of the ICA, marking the transition from the
petrous to the paraclival ICA.
wall of the sphenoid sinus containing the canal of the
paraclival ascending ICA. The lateral descending limb
represents the medial pterygoid plate and the lateral
wall of the choanae. The horizontal bar represents the
floor of the sphenoid sinus. The vidian canal is identified at the intersection of the horizontal bar and the
lateral vertical limb (Fig. 16.20).
7. Exposing the vidian canal: Once the SPA is divided, the
vidian canal and its contents are exposed (Figs. 16.21
and 16.22). The sphenopalatine ganglia are located
just posterior to the SPA at the junction of the SPA
and descending/greater palatine foramina. There is a
small autonomic branch attaching the vidian nerve to
the sphenopalatine ganglia at this level that is transected. Upon doing so, the vidian artery and nerve are
completely mobilized.
PCICA
SPF
VN
MPP
Fig. 16.20 Same image as Fig. 16.16, with the “H-sign”
superimposed to locate the vidian nerve (see step 6 in text).
MPP, medial pterygoid plate; PC-ICA, paraclival ICA; SPF,
sphenopalatine foramen; SS, sphenoid sinus; VN, vidian
nerve.
VN
PVC
Supralateral Quadrangular Boundary
Having located the genu of the ICA and established the
inferomedial boundary of the quadrangular space, the
superolateral boundary, which consists of the mandibular division (V3) of the trigeminal nerve (lateral) and the
abducens nerve, and, by surrogacy, the maxillary division
(V2) of the trigeminal nerve, can now be identified.
1. Combining this with the previous exposure of the
pterygopalatine fossa (Fig. 16.15), one can identify
another very important landmark and relationship
that becomes critical to the dissection—the PVC and
oblique foramen line described earlier. The PVC is
located inferomedially, while the FR is the mostsuperolateral. With the PVC and the VC exposed,
these foramina create a line that connects with the
FR above and lateral, providing a focused direction to
the lateral boundary of the quadrangle. This provides
Fig. 16.21 Mobilization of the vidian nerve (VN) and artery
complex after transection from the attachment to the
sphenopalatine ganglia and release from the vidian canal (VC).
Note the relative relationship of the palatovaginal canal (PVC)
located inferomedial.
a direct trajectory for drilling and bone removal along
V2 and V3 (Figs. 16.19 and 16.20).
2. Isolation of the ICA genu: The vidian nerve is followed
directly posteriorly to locate the anterior genu of the
ICA, recalling that it inserts below the ICA. We have
previously described this as drilling along a clock face
with the vidian nerve at the center. The distal nerve
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ON
O
I
C
FR
Fig. 16.22 Simultaneous endoscopic and image guidance view of the trajectory (T) to Meckel’s diverticulum. The orbit (O) can be
seen above and oblique relationship between the foramen rotundum (FR), the vidian nerve (VN), and the palatovaginal canal (PVC) is
seen. The medial boundary of the paraclival ICA transitioning to the cavernous segment can be seen. The relationship of the ICA to the
optic nerve (ON) can also be seen above.
is followed around the clock face from 3 to 9 (i.e., below the insertion of the ICA). As one deepens in the
orthogonal plane (i.e., the plane perpendicular to the
VC) and confirms the ICA is deeper, then the drilling
along the VC continues from 9 to 3. This is repeated
until the foramen lacerum is reached and the transition between the petrous horizontal ICA segment
and the ascending vertical paraclival ICA segment is
identified. These represent the inferior and medial
boundaries of the quadrangular space, respectively.
3. The genu of the ICA and foramen lacerum is further triangulated by identifying the Eustachian tube (ET) below
and tracing this rostrally. The aponeurosis of the basopharyngeal fascia and ET join to form the cartilaginous
ring of the foramen lacerum, which encircles the ICA
genu. This triangulation consists of:
Following V2 from a superolateral position,
understanding that it converges to a narrow
region distally.
The vidian canal as it travels from distal superfi-
cial position medially to a deep lateral position.
Eustachian tube cartilage from below.
The confluence of these structures represents the ICA
(Fig. 16.23).
4. With the base of the skull along the pterygoid plates
exposed, the dissection is continued in a subperiosteal
plane, limiting bleeding. This allows for identification
of the FR, along with the above-mentioned landmarks. Accurate image guidance can aid in helping
to identify the landmark and confirming the vidian
canal’s location as well as the trajectory. Eventually,
this deeper plane will now expose the boundary of
the quadrangular space and Meckel’s diverticulum.
16.3.3 Final Deeper Plane
Dissections
At this point, with the osseous framework completely removed, there are a series of key bony bridges or tubercles
between each of these critical neurovascular landmarks
A
T
ICA
MS
V2
VN
FL
ET
Fig. 16.23 Confl uence of V2, vidian nerve (VN), and the
Eustachian tube (ET) at the level of foramen lacerum and ICA.
Note as one triangulates on these three structures and traces
them posteriorly, they converge on Meckel’s cave. FL, foramen
lacerum; ICA, internal carotid artery; MS, maxillary strut; V2,
maxillary division of CN V.
that now need to be carefully removed to essentially connect the dots.
1. There is an important relationship between the FR,
the optic nerve, the optic strut, the lateral opticocarotid recess, the maxillary strut, and the carotid
(Figs. 16.15, 16.24, and 16.25). The optic strut is the
medial tubercle between the carotid and the optic
nerve. The maxillary strut is the tubercle between the
superior orbital fissure (SOF) and V2. Finally, there is
a key tubercle between V2 and paraclival ICA known
as the lingular process (Figs. 16.16, 16.24, and 16.25).
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