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C 2012 The American Laryngological,
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Rhinological and Otological Society, Inc.
Endonasal Endoscopic Exposure of the Internal Carotid Artery:
An Anatomical Study
Felipe S. G. Fortes, MD, PhD; Carlos D. Pinheiro-Neto, MD, PhD; Ricardo L. Carrau, MD;
Rubens V. Brito, MD, PhD; Daniel M. Prevedello, MD; Luiz U. Sennes, MD, PhD
Objectives/Hypothesis: The aim of this work was to define the anatomical landmarks, limitations, and difficulties of
obtaining internal carotid artery (ICA) exposure via endonasal endoscopic approaches (EEA).
Study Design: Cadaveric descriptive study.
Methods: The ICA was dissected via EEA in 10 cadaveric specimens (20 sides) prepared with intravascular injections of
colored silicone. We carried the ICA dissection from the cavernous to the distal parapharyngeal segments through a transpterygoid corridor.
Results: The transpterygoid approach provided adequate exposure of the lacerum and horizontal petrous ICA. Additional exposure of the ICA and the infrapetrous area required resection of the eustachian tube (ET) and the fibrocartilaginous
tissue of the foramen lacerum after a medial maxillectomy and resection of the pterygoid plates. The main anatomical landmarks to the corresponding ICA segment include: the vidian nerve that points to the lacerum and horizontal segments, the
mandibular nerve (V3) that heralds the petrous segment, the foramen ovale and the ET that signal toward the carotid canal,
and the posterior trunk of the mandibular nerve (V3) and the ET that mark the parapharyngeal segment.
Conclusions: EEAs provide access to the ICA from its cavernous to the distal parapharyngeal segments. A stepwise
approach is critical to its exposure and control. Surgeons must be aware of its frequently tortuous three-dimensional course
and the intimate relation of the vessel to the carotid canal and the cartilage of the foramen lacerum.
Key Words: Endoscopy, skull base surgery, internal carotid artery, anatomy, infratemporal fossa, eustachian tube,
transpterygoid approach.
Level of Evidence: 2b.
Laryngoscope, 122:445–451, 2012
INTRODUCTION
Advances in endoscopic endonasal techniques, customization of endonasal instruments, and improved
image-guided systems, coupled with the increased familiarity of surgeons with the skull base anatomy from the
endoscopic perspective1,2 and the recent development of
various vascularized flaps for skull base reconstruction,3–6 have propelled the use of expanded endonasal
approaches (EEAs) for the management of select skull
base lesions.7–13 EEAs can be classified in anatomical
modules that access specific areas of the skull base as
defined by the sagittal7,8 and coronal planes.14 Coronal
plane EEAs allow access to the middle cranial and posterior fossae and their respective skull base.14,15 These
include approaches to the petrous apex, suprapetrous
From the Department of Otolaryngology (F.S.G.F., C.D.P.-N., R.V.B.,
University of São Paulo, São Paulo, Brazil; and the Department of
Otolaryngology–Head and Neck Surgery (R.L.C.), and Department of
Neurological Surgery (D.M.P.), The Ohio State University, Columbus,
Ohio, U.S.A.
Editor’s Note: This Manuscript was accepted for publication
August 2, 2011.
This work was supported by FAPESP (Fundação de Amparo a Pesquisa do Estado de São Paulo). The authors have no other funding, financial relationships, or conflicts of interest to disclose.
Send correspondence to Felipe S. G. Fortes, MD, PhD, Departamento de Otorrinolaringologia, Universidade de São Paulo, Rua Prudente Meireles de Morais 847, 12243-750 SJC, São Paulo, Brazil.
E-mail: [email protected]
L.U.S.),
DOI: 10.1002/lary.22395
Laryngoscope 122: February 2012
area (i.e., above the petrous internal carotid artery
[ICA]), infrapetrous area (i.e., below the petrous ICA),
and infratemporal fossa. In addition, the posterior coronal approach includes the area extending from the
foramen magnum, across the occipital condyle and hypoglossal canal, to the jugular foramen.14 Control of the
ICA is the keystone of all the coronal anatomical
modules.
A fundamental difference in exposing the ICA during an EEA, as opposed to a conventional open
approach, is the dimensions of the surgical corridor. An
EEA, although providing superior visualization, involves
working through a narrow surgical corridor that imposes
limitations on the movements of the dissecting instruments. In properly selected cases the risk of a major
vascular or cranial nerve injury may be less than that
associated with open approaches. However, the management of catastrophic bleeding through the EEA requires
a two-team approach, and the instrumentation may be
more complex. A comprehensive transpterygoid approach
involves the identification and exposure of the cavernous, paraclival, horizontal segments of the ICA (lacerum
and petrous).16 However, when performing a infrapetrous approach or a posterior coronal approach, a
more proximal control of the ICA at the carotid canal
and its distal parapharyngeal segment may be necessary.14,17,18 Surgical exposure of these segments—the
parapharyngeal ICA, the carotid canal, and the petrous
Fortes et al.: Endoscopic Exposure of the ICA
445
Fig. 1. Endoscopic exposure of the left pterygopalatine fossa (PPF) after medial maxillectomy. The fat content of the PPF have been
removed. (A) The third portion of the maxillary artery with the terminal branches can be identified anteriorly to the neural content of the
PPF. (B) Neural compartment of the PPF after lateral displacement of the vascular structures. At the level of the foramen rotundum, V2 continues as the infraorbital nerve. The pterygopalatine ganglion lies anteriorly to the vidian canal. Cav. ¼ cavernous; Post. ¼ posterior; A. ¼
artery; Seg. ¼ segment; Sphenopal. ¼ sphenopalatine; Max. ¼ maxillary; Desc. ¼ descending; Pteryg. ¼ pterygoid; Proc. ¼ process; Palat.
¼ ???; N. ¼ nerve; Gr. ¼ greater; Eust. ¼ eustachian; For. ¼ foramen; Infraorb. ¼ infraorbital; Pal. ¼ palatine; Les. ¼ lesser.
portion of the ICA—represents a significant surgical
challenge imposed by their deep and protected location
in the skull base.19–21
In previous studies, we described surgical models
and provided detailed descriptions of the anatomy
related to endoscopic transpterygoid and infratemporal
fossa approaches.16,17 The objectives of this study were
to better define the anatomical landmarks, the limitations, and the difficulties of obtaining exposure of the
ICA via EEAs using a previously developed anatomical
model.
MATERIALS AND METHODS
This study, approved by our local institutional research
committee, was completed at the Otolaryngology Surgical Skills
Lab of the University of São Paulo Medical School. Ten fresh
cadaveric specimens (20 sides) were prepared with intravascular injection of colored silicone using a previously described
technique.22 The surgical dissection was performed using paranasal sinus and skull base/neurosurgical endoscopic
instruments (Karl Storz, Tuttlingen, Germany), and a highspeed drill with angled handpiece and diamond cutting burrs
(Karl Storz). All dissections were performed via a pure endonasal endoscopic approach with a two-surgeon/four-hand
technique and using a 0 , 30 , and 45 rod-lens endoscope
coupled to a high-definition camera and monitor (Karl Storz
Endoscopy–America, El Segundo, CA). Photographs were taken
during the endonasal endoscopic dissections with a digital single-lens reflex Nikon D70 with a resolution of 6.5 MP (Nikon,
Tokyo, Japan), coupled to the rod-lens endoscopes.
Dissection Technique
Unilateral anterior and posterior ethmoidectomies, wide
maxillary antrostomy, and sphenoidotomy were the initial steps
of the dissection. After isolating the sphenopalatine and posterior septal arteries, we completed a medial maxillectomy
(inferior turbinectomy and removal of the lateral nasal wall
down to the level of the nasal floor). Next, we removed the
posterior maxillary sinus wall and the orbital process of the
palatine bone. After removing the periosteum of the posterior
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446
maxillary sinus wall and fat from the pterygopalatine fossa, we
identified the third and most distal segment of the maxillary
artery and its major terminal branches: descending palatine
artery, sphenopalatine artery, posterior septal artery, vidian
artery, pharyngeal artery, and superior alveolar artery. This
was best accomplished via retrograde dissection of the sphenopalatine artery (Fig. 1A). After displacing the vascular
compartment of the pterygopalatine fossa laterally, we exposed
the neural structures of the pterygopalatine fossa including the
pterygopalatine ganglion, vidian nerve, greater palatine nerve,
lesser palatine nerve, infraorbital nerve, and maxillary nerve
(V2) at the foramen rotundum and its anastomotic branch to
the pterygopalatine ganglion (Fig. 1B). A posterior septectomy
and bilateral sphenoidectomies, removing the intrasinus septa
and part of the floor of the sphenoid sinuses, facilitated a fourhand dissection. We then proceeded with the transpterygoid
approach, drilling the base of the pterygoid process around the
vidian canal in an anterior to posterior direction to expose the
anterior genu and lacerum segment of the ICA (Fig. 2A). At
this point we could access the medial aspect of the infratemporal fossa and identify the foramen rotundum, the infraorbital
artery and infraorbital nerve entering the infraorbital canal,
the inferior orbital fissure, the medial insertion of the upper
and inferior heads of the lateral pterygoid muscle inserting on
the lateral pterygoid plate, the deep aspect of the temporalis
muscle (sphenomandibular muscle), and the temporal branches
of the maxillary artery (Fig. 3). Removal of the bone around the
foramen ovale facilitated the visualization of the horizontal
petrous segment of the ICA just posterior to the foramen. On
completion of the transpterygoid approach we had exposed V2,
V3, the Gasserian ganglion, the dura mater of the middle cranial fossa, the cavernous sinus, and the ICA extending from the
paraclival segment to the horizontal aspect of the petrous segment (Fig. 2B). Next, we removed the inferior remnants of the
pterygoid plates to expose the eustachian tube. Muscles related
to the eustachian tube, namely the tensor veli palatini and the
levator veli palatini muscles, could be visualized at this point
(Fig. 4A). Transection of the tensor veli palatini improves the
visualization of the levator veli palatini muscle, the cartilaginous portion of the eustachian tube, and the fibrocartilaginous
tissue of the foramen lacerum (Fig. 4B). Next, we removed the
cartilaginous eustachian tube, exposing its proximal bony canal
and the carotid canal, which lies just posterior. Drilling of the
Fortes et al.: Endoscopic Exposure of the ICA
Fig. 2. Endoscopic exposure after the transpterygoid approach. (A) The vidian nerve leads to the anterolateral aspect of the lacerum segment and the anterior genu of the internal carotid artery (ICA). V2 lies in a lateral and superior position to the vidian nerve and runs over the
dura mater of the middle cranial fossa. A sympathetic bundle nerve on the cavernous sinus and a muscular branch of V3 are also visualized. (B) The bone of the floor of the middle cranial fossa, between V2 and V3, together with the anterior wall of the ovale foramen, has
been removed. The cavernous, anterior genu, lacerum, and part of the horizontal petrous segment of the ICA are visualized. One can see
the Gasserian ganglion, the branches of the V cranial nerve, and the VI cranial nerve in the cavernous sinus and their relation to the suprapetrous area. Cav. ¼ cavernous; Paracl. ¼ paraclival; Seg. ¼ segment; Sympat. ¼ sympathetic. Bund. ¼ bundle; Ant. ¼ anterior; MCF ¼
middle cranial fossa; For. ¼ foramen; N. ¼ nerve; M. ¼ muscular; Max. ¼ maxillary; A. ¼ artery; Pteryg. ¼ pterygoid; Proc. ¼ process; Lat.
¼ lateral., Opht. ¼ ophthalmic; G. ¼ ganglion; Fibr. ¼ fibro; Lac. ¼ lacerum.
bony eustachian tube and the anteromedial carotid canal helped
to expose the most proximal aspect of the petrous segment and
the distal parapharyngeal ICA. Finally, we opened the carotid
sheath exposing the parapharyngeal carotid artery down to the
level of the nasal floor (Figs. 5 and 6).
RESULTS
We were able to expose the ICA, from the parapharyngeal to the cavernous sinus space, in all specimens
Fig. 3. Endoscopic view of the medial infratemporal fossa. The infraorbital nerve arises from V2 and passes through the inferior orbital fissure before reaching the orbit. The infraorbital arterial
branch of the maxillary artery can be seen entering the fissure.
The temporal muscle and temporal arterial branches of the muscular division of the maxillary artery running and the lateral pterygoid muscle medial insertion are demonstrated. Infraorb. ¼
infraorbital; A. ¼ artery; MCF ¼ middle cranial fossa; N. ¼ nerve;
ICA ¼ internal carotid artery; Temp. ¼ temporal; Pteryg. ¼ pterygoid; P. ¼ process; M. ¼ muscle; Lat. ¼ lateral; Max. ¼ maxillary;
M = middle.
Laryngoscope 122: February 2012
(Fig. 5). Access to the cavernous segment of the ICA was
possible after widely opening the sphenoid sinus and
removing the bone from its lateral and superior walls.
The difficulty of this step was proportional to the degree
of sphenoid sinus pneumatization. Access to the more
proximal paraclival segment was facilitated by a prior
exposure of the anterior genu. This step was followed by
a superior (distal) dissection, thinning, and removing
the bony canal around the paraclival ICA.
A transpterygoid approach allowed us to expose the
lacerum segment (including the anterior genu) and part
of the horizontal petrous segment. The pterygoid canal
and nerve (i.e., vidian canal and nerve) were constant
landmarks to help identify the ICA anterior genu and
lacerum segment, as the nerve runs on the anterolateral
aspect of the ICA (Fig. 2). We found that drilling inferior
and medial to the vidian nerve provided the safest
access to the anterior genu of the ICA. After completing
the transpterygoid approach, we also exposed the foramen rotundum and V2 (following the infraorbital nerve
posteriorly) at a level that was superior and lateral to
the vidian nerve (Fig. 3). Drilling and removing the bone
inferior to V2 exposed the foramen ovale and V3. In
turn, following V2 and V3 proximally exposed the Gasserian ganglion (Meckel’s cave) and the floor of the
middle cranial fossa. The foramen ovale and the short
segment of V3 proximal to the foramen are always anterior and superior to the petrous ICA. Therefore, they are
reliable landmarks that help to control the petrous ICA
(horizontal segment) (Fig. 2B). From the endoscopic
standpoint, V3 partially blocks the view of the proximal
petrous segment of the ICA (Fig. 5).
A transpterygoid route provided a corridor that
allowed access to the suprapetrous area (mid-coronal
plane), which is bounded by the paraclival and lacerum
segments of the ICA (Fig. 6). The medial infratemporal
Fortes et al.: Endoscopic Exposure of the ICA
447
Fig. 4. The entire pterygoid process has been removed to expose the eustachian tube. (A) The tensor veli palatini runs in a vertical orientation laterally to the levator veli palatini muscles. The relation between lateral pterygoid muscle, V3, and tensor veli palatini is demonstrated.
(B) The tensor veli palatini has been removed to expose the levator veli palatini muscles and the eustachian tube. The posterior opening of
the vidian canal in the lacerum foramen can be seen as well as the relation of the vidian nerve to the horizontal internal carotid artery. Mid.
¼ middle; Cr. ¼ cranial; F. ¼ fossa; Paracl. ¼ paraclival; Seg. ¼ segment; N.¼ nerve; Ant. ¼ anterior; P. ¼ posterior; Max. ¼ maxillary; A. ¼
artery; Lat., lateral; M., muscle; Pteryg. ¼ pterygoid; Lev. ¼ levator; V. ¼ veli; Pal.¼ palatine; Tens. ¼ tensor; G. ¼ ganglion; Horiz. ¼ horizontal; For. ¼ foramen; Lac. ¼ lacerum; Fibrocart. ¼ fibrocartilaginous.
fossa was adequately exposed, and the second portion of
the maxillary artery was identified between the heads of
the lateral pterygoid muscle. Temporal branches of the
maxillary artery, running in the anterior surface of the
temporalis muscle, were also well visualized (Fig. 3).
At this point, the eustachian tube and the fibrocartilaginous tissue of the foramen lacerum represented the
boundaries of the infrapetrous approach. To proceed
with the proximal dissection of the ICA we found that it
is important to expose the entire height of the pterygoid
plate. In turn, this required partial removal of the lat-
Fig. 5. Endoscopic access to the internal carotid artery (ICA) after
resection of the eustachian tube and the foramen lacerum fibrous
tissue. The relation of the V cranial nerve and the ICA is demonstrated: V1 and cavernous segment, Gasserian ganglion and
suprapetrous area, foramen ovale and the posterior genu, V3 and
the carotid canal, the posterior trunk of V3 and the cervical segment. Note the tortuous course of the horizontal ICA. Seg. ¼ segment; Mid. ¼ middle; Cr.¼ cranial; F. ¼ fossa; For. ¼ foramen;
Ant. ¼ anterior; Post. ¼ posterior; N. ¼ nerve; P. ¼ posterior;
Rosenm. ¼ Rosenmüller; Fos. ¼ fosseta.
Laryngoscope 122: February 2012
448
eral nasal wall. After dissecting off the insertion of the
lateral pterygoid muscle and elevating the mucosa of the
lateral nasal wall anterior to the eustachian tube, we
were able to remove the pterygoid plates and identify
the muscles related to eustachian tube in all cases (Fig.
4A). The fibers of the tensor veli palatini are lateral to
the eustachian tube and can be identified arising from
its origin at the skull base (superiorly). The tensor veli
palatini loops around the pterygoid hamulus to insert in
the soft palate. Its insertion, however, is at a level that
is inferior to the nasal floor; therefore, it was not visualized. Fibers from the levator veli palatini muscles are
medial and follow the eustachian tube orientation to
insert at the soft palate. Thus, they could be visualized
after transecting the tensor veli palatini (Fig. 4B). The
Fig. 6. The middle coronal plane modules areas and their relation
to the internal carotid artery (ICA) are demonstrated. The neural
landmarks (vidian nerve, Gasserian ganglion, ovale foramen, V3)
and their relationship to the different segments of the ICA can be
seen. Cav. ¼ cavernous; Seg. ¼ segment. MF. ¼ middle fossa.
Fortes et al.: Endoscopic Exposure of the ICA
TABLE I.
Anatomically Based Classification of the Internal Carotid Artery*.
Segment
Proximal Limit
Distal Limit
Cervical (C1)
Carotid artery bifurcation
Carotid canal
Petrous (C2)
Carotid canal
Posterior edge of the foramen lacerum
Lacerum (C3)
Cavernous (C4)
Posterior edge of the Foramen lacerum
Superior border of the petrolingual ligament
Superior border of the petrolingual ligament
Proximal dural ring
Clinoid (C5)
Proximal dural ring
Distal dural ring
Ophthalmic (C6)
Communicating (C7)
Distal dural ring
Posterior communicating artery
Posterior communicating artery
ICA bifurcation
*Proposed by Bhoutillier et al.23
ICA ¼ internal carotid artery.
eustachian tube is anterior and medial to the ICA
(carotid canal and parapharyngeal segments). Thus, we
had to resect the eustachian tube to fully expose the ICA
in these areas (Fig. 5).
Anteriorly, we followed the cartilaginous eustachian
tube to the level of its isthmus and bony canal. We were
able to disarticulate the cartilaginous from the bony
component of the eustachian tube, which was then carefully removed to expose the ICA foramen and petrous
segment. We found that grasping the eustachian tube
with angled forceps stabilized the cartilaginous canal to
subsequently disarticulate it from its bony component. A
posterior cut followed a medial to lateral diagonal orientation and was limited posteriorly by the mucosa of the
fossa of Rosenmüller, which provided a safe plane for
dissection. Exposure of the petrous ICA was relatively
difficult to accomplish, as the vessel is firmly adherent
to the bone canal and the lateral petrous bone. In the carotid canal, V3 lies anterior to the petrous ICA and
lateral to its anterior genu and paraclival segments
(Figs. 4B and 5). To have a better visualization of the
posterior genu of the ICA during an EEA, V3 should be
retracted laterally. Removing the eustachian tube and
the fibrocartilaginous tissue of the foramen lacerum
improved the working corridor of the infrapetrous EEA
(Fig. 6).
Complete exposure of the parapharyngeal ICA
down to the level of the nasal fossa floor was accomplished in all specimens after opening the carotid
sheath. The posterior trunk of V3 also serves as a landmark to this segment of the ICA, located laterally and
anteriorly to the ICA as it runs in a course, which is relatively parallel to the parapharyngeal ICA (Fig. 5).
DISCUSSION
Multiple clinical situations may require exposure
and control of the ICA, including the management of
advanced sinonasal or nasopharyngeal malignancies,
paragangliomas, and other skull base lesions originating
in the middle or posterior cranial fossa, such as meningiomas, schwannomas, chordomas, and chondrosarcomas.
In addition, primary lesions from the pterygopalatine
fossa and infratemporal fossa can extend around the
ICA. Traditionally, surgical approaches to this region
Laryngoscope 122: February 2012
include a lateral corridor via an infratemporal approach
(Fisch B and C), subtemporal-preauricular with orbitozygomatic osteotomies or Fisch D, and/or an anterior
approach, such as the degloving technique or the Lefort
I osteotomy. These approaches, although providing
adequate exposure, may require retraction or resection
of the glenoid fossa, mandibular condyle, facial nerve
manipulation, and/or a craniotomy.19–21
Regardless of the approach, exposure of the ICA is
a surgical challenge. This is more evident when dissecting the petrous, lacerum, and distal parapharyngeal
segments. Thus, a detailed knowledge of the ICA is
mandatory.19–21 The anatomy of the ICA from the perspective of the open skull base approaches is well
established. However, despite recent advances in EEAs,
the understanding of the endoscopic anatomy of the ICA
remains insufficient.
Various anatomical classifications of the ICA exist
in the literature. Bouthillier et al.23 proposed a classification that seems most useful from our standpoint, as it
is based on structures that are exposed during an EEA
(Table I). In this article, we refer to the vertical segment
of the cavernous segment as the paraclival segment and
the distal cervical segment as parapharyngeal.
During an endoscopic transpterygoid approach,
which is a common step in the exposure of the suprapetrous and infrapetrous areas, one should recognize
critical anatomical landmarks to the different segments
of the ICA. The vidian canal and nerve are reliable landmarks to determine the height (vertical axis position) of
the anterior genu and lacerum segment of the ICA as it
emerges from the petrous bone (Fig. 2). In fact, the
vidian canal connects the pterygopalatine fossa to the foramen lacerum. It is important to note that the canal
has a slight posterolateral orientation, with the posterior
opening located inferolateral to the anterior end of the
carotid petrous canal and anterior genu of the ICA. Its
anterior opening is at the upper medial surface of the
pterygoid process of the sphenoid bone and can only be
identified after exposing the medial pterygopalatine
fossa. The union of the greater superficial and deep
petrosal nerves forms the vidian nerve. It travels
through the vidian canal to end in the pterygopalatine
ganglion, which is positioned in front of the anterior
opening of the canal (Fig. 1B).24–26 When present, a
Fortes et al.: Endoscopic Exposure of the ICA
449
vidian artery runs in the vidian canal along with the
vidian nerve. In the pterygopalatine fossa, the artery
will be anterior to the nerve and ganglion. Therefore, it
needs to be mobilized laterally to better expose the neural structures (Fig. 1A). Thus, the vidian nerve should
be used as a landmark to determine the vertical position
of the petrous ICA and lacerum foramen and not to
injure the most medial aspect of the ICA as it turns into
the paraclival ICA.
After exposing the anterior genu, we can safely
follow the ICA distally to the paraclival segment by
removing its bony canal at the lateral wall of the sphenoid sinus. This exposure allows access to the petrous
apex, located between the clival recess (mid-clivus) and
paraclival ICA (Figs. 2 and 6).
Constant landmarks to the ICA during the suprapetrous transpterygoid approach include the Gasserian
ganglion and V3, both located lateral to the paraclival
segment and superior to the lacerum segment of the ICA
(Figs. 2B and 4B). An infrapetrous approach implies a
working corridor inferior to the petrous and lacerum
segments of the ICA (Fig. 6).15–17 The foramen lacerum
is located at the confluence of the petrous portion of the
temporal bone, basi-occipital, and basi-sphenoid bones,
and in vivo is filled with fibrocartilage. The ICA courses
across the endocranial surface of the foramen lacerum,
and climbs upward at its rostral end to enter the posterior cavernous sinus (Fig. 4B).27 Inferior retraction of
this fibrocartilage and the cartilage of the eustachian
tube provides only limited access to the inferior aspect of
horizontal petrous carotid. Therefore, to approach the
proximal petrous carotid, carotid canal, and distal parapharyngeal segment it is necessary to remove the medial
eustachian tube and fibrocartilaginous tissue of the foramen lacerum.
The bony canal of the eustachian tube begins at the
superior aspect of the anterior wall of the tympanic
cavity and narrows progressively until it ends at the
isthmus. The isthmus is located immediately anterior
and superior to the bend of the petrous segment. The
cartilaginous eustachian tube, which forms its inferior
and medial aspect, is shaped as a concave gutter.3 The
posterior wall of the cartilaginous eustachian tube interdigitates with the bony canal at the level of the isthmus.
The eustachian tube guards the ICA, as it is medial and
anterior to the parapharyngeal segment and lateral and
anterior to its petrous segment. At this level, V3 is
located anterolateral to the eustachian tube (Fig. 4).
When resecting the eustachian tube, it is safe to develop
a posterior plane of dissection between the eustachian
tube and the mucosa of the nasopharynx, as this mucosa
extends posteriorly and laterally into the Rosenmüller
fossa.
The petrous segment can be divided in a vertical, a
bend (posterior loop), and a horizontal portion. The transition of the petrous segment of the ICA to the lacerum
segment is inferomedial to the Gasserian ganglion
within Meckel’s cave (Fig. 5). In this segment, the ICA
runs within the periosteum of the carotid canal and is
surrounded by areolar tissue, a venous plexus extension
from the cavernous sinus and postganglionic sympaLaryngoscope 122: February 2012
450
thetic nerves. Endoscopic endonasal exposure of the
horizontal petrous ICA is compounded by its orientation,
as it runs in an anterior, inferior, and medial orientation
(Fig. 2B).11 The cochlea lies posterior to the bend of the
petrous carotid. The eustachian tube lies lateral and
anterior to this horizontal portion. The petrous bone
bounds the horizontal ICA (petrous segment) anteriorly,
medially, and posteriorly. Therefore, after removing the
cartilaginous eustachian tube, we have to drill petrous
bone to expose the ICA.23,24,27 After drilling the petrous
bone around the foramen ovale, the posterior bend of
the petrous ICA can be visualized just posterior to V3
(Figs. 5 and 6).
At the level of the carotid canal, the carotid sheath
divides into two layers; the inner layer continues as the
periosteum of the carotid canal and the outer layer continues as periosteum of the extracranial surface of the
skull base.23 Removal of the anterior wall of the carotid
canal requires utmost care, because the artery lies in
intimate relation to the bone. Immediately posterior to
the carotid canal lies the jugular fossa.28,29
The cervical segment of the ICA begins at the level
of the carotid bifurcation usually at the level of C4.21
This segment runs inside the carotid sheath with the internal jugular vein laterally and the vagus nerve
posterolaterally. Inside the carotid sheath, as in the
carotid canal, the artery is surrounded by areolar tissue
containing fat, a venous plexus, and postganglionic sympathetic nerves.23 However, in this segment, opening of
the sheath is relatively easier and safer than in the
carotid canal. We could approach this segment through
an EEA only to the level of the nasal floor. In our dissections, we observed that this cervical segment usually
makes a slight posterior and lateral curvature as it
enters the carotid canal vertically before bending anteriorly toward the lacerum segment. We strongly advocate
a stepwise approach identifying the lacerum and petrous
segments of the ICA. V3 (posterior trunk) is a useful endoscopic anatomic landmark to the parapharyngeal
segment, as it is located anterior and lateral and with a
relative parallel orientation (Fig. 5).
In this anatomical study, an EEA provided
adequate exposure of ICA, from the cavernous to the
parapharyngeal segments. It should be noted, however,
that this surgical exposure is complex and requires
ample experience and training before it is applied
clinically, where injury to the vessel may produce catastrophic complications. In addition, we strongly advocate
the use of an image-guided system (preferably using
computed tomography angiography) and intraoperative
acoustic Doppler sonography to further aid the identification of the ICA. Institutional intensive care support
and the availability of an interventional angiographer
are also important safeguards.
CONCLUSION
Endoscopic endonasal approaches provide access
that extends from the cavernous to the parapharyngeal
segments of the ICA. A stepwise approach is critical to
the endonasal endoscopic exposure and control of the
Fortes et al.: Endoscopic Exposure of the ICA
ICA. The vidian nerve is an important landmark to the
lacerum segment of the ICA in the transpterygoid
approach. Our study suggests that resection of the fibrocartilaginous tissue of the foramen lacerum and
the eustachian tube is critical to access the petrous and
parapharyngeal segments of the ICA during the infrapetrous and posterior coronal approaches. V3 and its
foramen (foramen ovale) are other useful landmarks to
identify and control these segments of the ICA. When
approaching the petrous and parapharyngeal segments
the surgeon must be aware of the tortuous three-dimensional course of the ICA and the intimate relation of the
ICA to the carotid canal.
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