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Transbasal/Subfrontal-Transcribriform Approach to Anterior Skull Base
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FS
PEA
Or
ON ON
ICA ICA
a
Fig. 27.6 (a) Endoscopic endonasal exposure of the anterior skull base. (b) The planum sphenoidale is usually the posterior limit of
the resection. The close relationship between the optic nerve and the posterior ethmoidal artery is outlined. FS, frontal sinus; ICA,
internal carotid artery, ON, optic nerve; Or, orbit; PEA, posterior ethmoidal artery; SF, sellar fl oor.
ethmoidal arteries are exposed, cauterized with bipolar
electric forceps and cut. The posterior limit of this surgical approach is usually represented by the planum sphenoidale (Fig. 27.6).
Or
b
FS
ON
SF
ON
ICAICA
FS
27.2.7 Crista Galli Removal
Once the bony anterior skull base is removed (at least
at the level of the cribriform plate) and the dural layer is exposed, the crista galli is carefully detached from
the dura of the falx cerebri and removed with blunted
instruments, trying to avoid dural iatrogenic lesions.
In case of wide crista galli, an internal debulking with
a diamond burr can be advisable. In approximately 10%
of cases, the crista galli is pneumatized. This step can be
performed either transnsally or transcranially, according
to the preference and experience of the surgical team
(Fig. 27.7).
ACFd
CG
Fig. 27.7 Removal of the crista galli. ACFd, dura of the
anterior cranial fossa; CG, crista galli; FS, frontal sinus.
27.2.8 Complete Dural Exposure
and Epidural Dissection
Once the cranial base bone is completely removed, according to the surgical necessities, the dura mater of the
anterior skull base is exposed. Craniotomy can be extended from orbit to orbit and from the frontal sinuses back to
the planum sphenoidale.
The key point for subsequently performing an optimal skull base reconstruction is to properly dissect
the dura from the orbital roofs (laterally), the planum
sphenoidale (posteriorly), and the posterior wall of the
frontal sinus (anteriorly). This should be done before
starting the resection of the dura itself. With this epidural dissection, the dura of the anterior cranial fossa is
completely detached from the residual bony skull base,
obtaining an epidural pocket between these two layers
Given the combined transcranial phase, this step might
not be necessary (Fig. 27.8).
27.2.9 Critical Points in Anterior
Falx Cerebri Resection
The falx cerebri is in close relationship with several vascular structures such as the anterior falcine artery and
some sagittal sinus venous emissaries. For this reason,
specific attention has to be paid during its resection. It
is advisable to clip the anterior portion of the falx cerebri
or, at least, to cauterize it with curved bipolar forceps
before its resection, to avoid annoying bleeding. This
surgical trick is particularly critical when approaching
the anterior skull base through an exclusive endoscopic
endonasal approach, but it is useful also for such
combined transcribriform–transbasal approach. The
foramen cecum lies between the frontal and ethmoidal
bones, and it is open rarely in adults (≅1%; Fig. 27.9).
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FS
FC
*
*
*
*
ACFd
PS
Fig. 27.8 Adequate exposure of the anterior cranial fossa
dura and careful dissection of the epidural space of the
anterior skull base. To better detach the dura mater from
the bony edges of the anterior skull base, the anterior and
posterior ethmoidal arteries are cauterized and dissected.
ACFd, dura of the anterior cranial fossa; FC, falx cerebri; FS,
frontal sinus; PS-planum sphenoidale; black asterisks point out
the olfactory fi bers.
27.2.10 Anterior Cranial Fossa
Dural Resection
The dura is then incised and circumferentially cut with
dedicated instrumentations, starting from the lateral
margins of anterior skull base to reduce the risk of damage of intracranial vessels. It is advisable to pull gently
the dura inferiorly before cutting. Whenever possible, the
arachnoid plane is then dissected and separated from the
brain parenchyma. Generally, the anterior skull base dural layer is removed in an anteroposterior direction. The
dural layer can be removed together with one or both of
the olfactory bulbs. In a combined transcranial–endonasal procedure, this step can be performed through the
transcranial window (Fig. 27.10).
27.2.11 Complete Dural Resection
The dura mater of the anterior skull base is completely
removed from orbit to orbit and from the posterior wall
of the frontal sinus back to the planum sphenoidale. The
falx cerebri is cut and removed as much as possible from
the transnasal approach. The olfactory bulbs can be resected or not, in relation to the lesion to treat. As a matter
of fact, in combined procedures, the intracranial steps are
normally performed through the transcranial window
(Fig. 27.11).
27.2.12 Coronal Incision
The head can be fixed with the face up on a Mayfield apparatus in the supine position, and the vertex is usually
slightly raised. The incision of the scalp is begun just anterior to the tragus and lies behind the hairline. The galeal-skin flap (including skin, subcutaneous fat, and galea)
is elevated forward, preserving the underlying periosteal
layer possibly with the loose areolar connective tissue.
Laterally, the superficial layer of the temporalis fascia and
the superficial fat pad are raised with the scalp flap to
preserve the frontal and zygomatic branches of the facial
nerve (Fig. 27.12).
a
Fig. 27.9 Anterior cranial fossa vision from above on a color-injected dry skull. (a) The anterior artery of the falx (black arrow) is the
largest intracranial branch of the anterior ethmoidal artery and is involved in the supply of the falx and frontal pole dura. (b) Venous
emissaries of the sagittal sinus (black arrowhead) in close relationship with the falx cerebri and foramen cecum. CG, crista galli.
286
CG
CG
b
ON
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Transbasal/Subfrontal-Transcribriform Approach to Anterior Skull Base
GR
GR
OB
GR GR
OB
ACFd
Fig. 27.10 The dura mater of the anterior skull base is incised
and removed. Posteriorly, the olfactory bulbs come into view
and they are resected together with the dural layer. ACFd, dura
of the anterior cranial fossa; GR, gyrus rectus of the frontal
lobe; OB, olfactory bulb; ON, optic nerve.
27.2.13 Pericranial Flap Harvesting
The pericranium is incised at the posterior limit of
exposure and along the superior temporal line bilaterally. The pericranial flap is elevated anteriorly toward the supraorbital rims as far as the nasofrontal
suture. The exit points of the supraorbital nerves from
the supraorbital notches/foramina should be visualized bilaterally. When the nerves are included in a
supraorbital notch, dissection proceeds easily. In the
presence of supraorbital foramen, the nerves can be
preserved by resecting a small wedge of the bone of
this foramen using an osteotome or a drill. It is very
important to maintain the thickness of the pericranial flap by leaving the loose areolar tissue attached to
the pericranium. Sometimes, in the presence of a thin
pericranium, the galea can be harvested together with
the pericranium (Fig. 27.13).
27.2.14 Subfrontal/Transbasal
Craniotomy
In standard transbasal approaches, the temporalis muscles can be left in place.
proaches, the temporalis muscle should be dissected
off and the greater wing of the sphenoid exposed. Two
or more burr holes are performed, usually close to the
pterion. Through the keyholes, the dura is dissected off
from the inner aspect of the frontal bone. Especially in
older patients, multiple holes are necessary to safely elevate the bone flap avoiding dural laceration. The inferior cut of the frontal craniotomy can be performed a
few millimeters above the orbital rim to obtain an approach to the anterior skull base as broad and tangential
as possible. This is an effective maneuver that allows to
5
In the case of extended ap-
PS
OB
ON
OB
ON
Fig. 27.11 Appearance of the brain parenchyma and
intradural structures of the anterior skull base after the
endoscopic endonasal bilateral craniectomy. GR, gyrus rectus
of the frontal lobe; OB, olfactory bulb; ON, optic nerve; PS,
planum sphenoidale.
reduce to the minimum the brain retraction and to avoid
excessive kinking of the pericranial flap during the anterior skull base reconstruction. Some authors prefer a
subfrontal approach. Furthermore, the craniotomy can
be performed even in more than one piece. As a matter of fact, the transbasal approach consists in a frontal
craniotomy, the size and shape of which depend on the
surgical requirements and the preference of the surgeon
(Fig. 27.14).
27.2.15 Frontal Bone Flap Removal
for the Transcranial Approach
The cranial bony flap is detached from the dural layer.
The posterior wall of the frontal sinus is removed usually
with the high-speed drill and all the mucosal lining of
the frontal sinuses is removed. The ostium of the frontal
sinus communicating with the ethmoidal air cells (frontal
recess) can be seen bilaterally. Normally, in surgery for
anterior cranial base malignancies, the dura behind the
frontal bones is cut and the procedure proceeds since first
steps intradurally. On the contrary, in typical neurosurgical transbasal approaches, the dural layers are usually
spared during first steps.
If not done transnasally, the falx cerebri is then
detached from the crista galli (if still present) and divided. The frontal lobes are gently retracted, exposing
therefore the anterior skull base dura (if not previously removed). The dura, if still present, can be elevated
from the floor of the anterior cranial fossa using a periosteal elevator until reaching posteriorly the planum
sphenoidale. Normally, when dealing with anterior
cranial base malignancies, the procedure calls for an
intradural work and this should be done according to
the need of the patient. If not performed transnasally,
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Fig. 27.12 (a) Coronal incision of the scalp. (b) The galeal-skin fl ap is elevated forward, paying attention to preserve the underneath
pericranial layer (it is better to leave the loose areolar tissue attached to the pericranium). GSF, galeal-skin fl ap; P, pericranium.
GSF
PF
STF
PF
a
Fig. 27.13 (a) The pericranium is incised and elevated, preserving the main branches of the superfi cial temporal artery (black
arrowheads). (b) The pericranial fl ap is elevated until the supraorbital bundles (black arrows) become visible. GSF, galeal-skin fl ap; PF,
pericranial fl ap; STF, superfi cial temporal fascia.
b
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GSF
PF
BF
Fig. 27.14 A bony fl ap usually including the anterior wall
of the frontal sinus is harvested. The exit points of the
supraorbital nerves from the supraorbital notches are seen
bilaterally (black arrows). BF, bony fl ap; GSF, galeal-skin fl ap;
PF, pericranial fl ap.
27.2.16 Skull Base Reconstruction
Watertight dural closure is obtained by suturing the remaining dura mater with fascial layers (fascia lata, fascia
temporalis, etc.). The anterior skull base bony defect is then
repaired using the pericranial flap, supplied by the supraorbital and supratrochlear vessels, that is placed into the
resection cavity reaching the margins of the bone defect.
The pericranial flap can be fixed by means of button sutures to the remaining sphenoidal borders and to the orbital process of the frontal bone (medial edge). In this way, the
flap provides an effective closure of the skull base defect
and an adequate barrier against infection. Fibrin adhesive
glue can be particularly useful in this repair. Autologous
fat (harvested from the anterior abdominal wall or the leg)
can then be packed between the pericranial flap and dura
as a sandwich basal reconstruction (fat, fibrin glue, vascularized pericranial flap, fibrin glue, fat) to occlude the dead
spaces. The pericranial flap position is finally checked endoscopically through the transnasal approach. Moreover,
the endoscopic endonasal approach can be useful also to
cover the entire exposed skull base with an extracranial
layer of fascia lata or temporal fascia. In case of lesions sparing the nasal septum, for the extracranial layer of the skull
base reconstruction, it is also possible to use a pedicled
flap harvested from the nasal septum (Hadad–Bassagaisteguy flap or other variations) placed overlay to resurface the
anterior skull base defect. Its use facilitates rapid healing of
the sinonasal cavities, especially in patients who require
adjuvant irradiation (Fig. 27.16).
the dura is incised around the cribriform plate on both
sides and the olfactory nerves are divided. The procedure proceeds in a combined fashion, and part of the
work is performed from above and part from below. At
this point, if not yet managed transnasally, the bony
floor of the anterior cranial fossa, including the fovea
ethmoidalis, is completely removed. The lateral bony
margins of the typical skull base defect are given by the
medial orbital walls, while the posterior border is given
by the planum sphenoidale (Fig. 27.15).
PF
*
a
FC
*
FL
27.2.17 Cranioplasty
At the end of the procedure, the bony flap is put back into
place and fixed with titanium plaques and screws (it can
be even fixed with stiches; Fig 27.17). It is important not
to devitalize the pericranial flap by compressing it between the bone segments. The galeal-skin flap is then relocated and fixed with a button suture. One or two drains
are usually placed.
PF
FR
FR
PO
ACFd
FL
b
PO
Fig. 27.15 (a) Standard transbasal approach involving a standard bifrontal craniotomy extended up to the nasofrontal suture
line. After removing the bony fl ap and the underlying dural layer, the frontal lobes are evident. The white arrow indicates the crista
galli, where the falx cerebri attaches to the skull base. The black asterisks indicate the fl oor (lateral aspect) of the frontal sinuses.
(b) Extended transbasal approach with complete removal of the supraorbital bar. The orbits are exposed bilaterally. Remarkably, the
falx cerebri is removed and the frontal lobes gently retracted, allowing the exposure of the dura mater of the anterior skull base. ACFd,
dura of the anterior cranial fossa; FC, falx cerebri; FL, frontal lobes; FR, frontal recess; PF, pericranial fl ap; PO, periorbita.
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GSF
PF
FL
b
PF
a
Fig. 27.16 The pericranial fl ap is placed into the resection cavity, reaching the margins of the bony skull base defect. (a) Anatomic
representation in sagittal view. The yellow line represents the pericranial fl ap that is rotated down to close the skull base defect.
(b) Cadaveric dissection model where the pericranial fl ap is rotated to seal the anterior skull base. (c) Endoscopic endonasal view of
the pericranial fl ap fi xed in the surgical cavity. FL, frontal lobes; GSF, galeal-skin fl ap; PF, pericranial fl ap.
c
27.3 Case Example
27.3.1 Combined Transnasal
Endoscopic and Transbasal
Approach for Extensive
Esthesioneuroblastoma
A 39-year-old patient comes to our attention for unilateral nasal obstruction and epistaxis. The contrast enhanced
computed tomography scan and magnetic resonance scan
revealed a right monolateral mass involving the anterior
skull base. A preoperative biopsy was compatible with olfactory neuroblastoma, Hyams grade II. Preoperative total
body positron emission tomography scan demonstrated
regional metastasis (right parotid) but not systemic dissemination of disease. Given the intracranial extension of
the lesion, extended also over the orbital roof, the tumor
was surgically removed by combing the endoscopic endonasal transcribriform approach with the transcranial
subfrontal approach. After the surgery, the patient underwent adjuvant chemo-irradiation on the surgical field
(60 Gy) and retropharyngeal/neck nodes (54 Gy). The patient is alive without evidence of disease 3 years after the
treatment (Fig. 27.18).
Fig. 27.17 The bony fl ap is placed for the cranioplasty. BF,
bony fl ap; PF, pericranial fl ap.
PF
BF
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a b
Fig. 27.18 (a) Preoperative magnetic resonance (MR) scan in sagittal view showing an extensive sinonasal lesion involving the
anterior skull base and abutting in the anterior cranial fossa (white arrow). (b) Subfrontal approach with elevation of the pericranial fl ap.
27.4 Complications
• CSF leak (the most common).
• Pneumocephalus.
• Vascular damages of:
– Internal carotid artery (very rare in typical anterior
cranial base surgery).
– Basal cerebral arteries (frontopolar, fronto-orbital ar-
t
eries, and their branches).
– Nasal vessels—ethmoidal and sphenopalatine arter-
ies (epistaxis—even some weeks after surgery).
– Other arteries (superficial temporal arteries, supra-
orbital arteries).
– Superior sagittal sinus.
• Neural damages of (as a consequence of vascular dam-
age or direct injury):
– Optic nerve (visual impairment or even amaurosis).
– Olfactory nerve (it should be considered a conse-
quence and not a complication).
– Brain parenchyma (edema, hematoma, etc.).
– Supraorbital nerves (anesthesia).
– Upper branches of the facial nerves.
• Orbital and lacrimal system damage.
– Hematoma.
– Pneumo-orbit.
– Epiphora.
• Local infection.
– Meningitis, encephalitis.
– Brain abscess.
1
27.5 Instruments Required
The combined cranio-endoscopic approach (transbasal/
subfrontal-transnasal) benefits from endoscopic assistance and therefore 0- and 45-degree rigid endoscopes
(4 mm in diameter) are both essential for these surgical
techniques. Straight and curved diamond burr drills are
useful to approach the bony skull base, especially for the
transnasal procedures. Dedicated instrumentations for
external craniotomy are necessary for the transbasal/
subfrontal phase. Moreover, several rigid and flexible dissectors are recommended to free the dura immediately
around the burr hole and subsequently along the whole
length of the proposed cutting line of the craniotomy.
Straight and curved bipolar cautery forceps facilitate
optimum visualization and access during surgery, to
control intracranial bleeding. Typical endoscopic instruments for advanced procedures are strongly advisable.
With regard to the topic of skull base reconstruction, it
is important to have double curved forceps and angled
positioners to help the placement of the grafts. Angled
instruments with spatula tips are really useful in performing the extradural pockets.
Moreover, skull base lesions benefit from computerassisted magnetic neuronavigation system, particularly
when planning a critical approach. This technology can
help to identify critical vascular and neural structures
within the skull base.
27.6 Tips and Tricks
Identification, coagulations, and transection of the ethmoidal arteries have to be performed before working on
the dura mater; otherwise, the dura cannot be dissected
adequately from the skull base. This is a critical step to
perform a satisfactory skull base reconstruction.
bined procedures, these steps could be less important
given the transcranial phase.
The pericranial flap should be elevated anteriorly
toward the supraorbital rims as far as the nasofrontal
suture. In the presence of supraorbital foramen, the
supraorbital nerves should be freed from the foramen
by removing the most inferior part of the foramen itself.
Make the flap as long as possible.
4
In com-
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In particular cases, the flap used for reconstruction can
also include the galea. In any case, the loose areolar tissue
should always been left attached to the pericranium.
Perform the frontal bone flap as low as possible. This
trick reduces the risk to create tension to the pericranial
flap used for reconstruction.
1,3
Buttress the reconstruction with pericranial flap using
fascia lata of fat, especially in the most anterior part.
References
1. Nicolai P, Yakirevitch A, Bolzoni Villaret A, Battaglia P, Locatelli D,
Castelnuovo P. Combined Cranioendoscopic Approach. In: Stamm
AC, ed. Transnasal Endoscopic Skull Base and Brain Surgery: Tips
and Pearls. New York, NY: Thieme; 2011:350–354
2. Castelnuovo P, Battaglia P, Turri-Zanoni M, et al. Endoscopic endonasal surgery for malignancies of the anterior cranial base. World
Neurosurg 2014; 82(6, Suppl):S22–S31
3. Castelnuovo PG, Belli E, Bignami M, Battaglia P, Sberze F, Tomei G.
Endoscopic nasal and anterior craniotomy resection for malignant
nasoethmoid tumors involving the anterior skull base. Skull Base
2006;16(1):15–18
4. Castelnuovo P, Battaglia P, Locatelli D, Delù G, Sberze F, Bignami M. Endonasal micro-endoscopic treatment of malignant
tumours of paranasal sinuses and anterior skull base. Operative Techniques in Otolaryngology-Head and Neck Surgery
2006;17(3):152–167
5. Kurtsoy A, Menku A, Tucer B, Suat Oktem I, Akdemir H, Kemal Koc
R. Transbasal approaches: surgical details, pitfalls and avoidances.
Neurosurg Rev 2004;27(4):267–273
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Chapter 28
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28.1 Indications 294
Retrosigmoid–
Transclival Approach
28.2 Surgical Steps 294
28.3 Conclusion 302
Retrosigmoid–Transclival Approach
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28 Retrosigmoid–Transclival Approach
Diego Mazzatenta, Matteo Zoli, Ernesto Pasquini, Giorgio Frank
Introduction
Different approaches have been proposed to access
tumors located in the posterior fossa. They can be classified into posterior routes, such as the presigmoid
transpetrosal, the retrolabyrinthine, the retrosigmoidal retropetrosal, and the far lateral, lateral routes, such
as the subtemporal transpetrosal and the subtemporal
preauricular, anterolateral approach, such as the frontotemporal transcavernous, and, finally, anterior routes,
such as the anterior endonasal approach.
decades, the retrosigmoidal retropetrosal approach has
gained a prominent role among the nonanterior approaches for its versatility, directness, and simplicity.
Meanwhile, the endoscopic endonasal approach has
expanded its indications, allowing to approach different tumors in the posterior fossa.
analysis of the indications, limits, advantages, and complications of these two approaches is proposed.
6,7,10
1–10
In the last
1–10
In this chapter, an
28.1 Indications
The retrosigmoid approach is one of the more commonly adopted approaches for posterior fossa surgery. It gives an optimal exposure of the cerebellum-pontine angle (CPA), the foramen magnum, and
the tentorium incisura. Conversely, the endoscopic
endonasal transclival approach is an innovative ventral route to expose the posterior fossa in all its extension on the sagittal plane and to reach paramedian anatomic regions such as the CPA. The endoscopic
endonasal approach allows the surgeon to reach the
posterior fossa through a direct and straightforward
route, facing frontally the lesion and passing throughout the nasal and paranasal sinuses, differently than the
retrosigmoid approach which could require cerebellum
retraction.
endonasal approach was considered suitable for midline
extradural tumors, eroding the bone structures of the
spheno- occipital region, like selected chordomas and
chondrosarcomas, or other more uncommon histotypes
such as osteomas, osteosarcomas, hemangiomas, isolated
fibrous tumor, plasmocytoma, and bone metastases.
The improvement of the anatomical knowledge of area,
technological advancement, and spreading of this surgical experience have allowed extending this approach
intradurally and to paramedian regions.
this approach has been recently adopted for dura-derived tumors as well, such as petro-clival and foramen
magnum meningiomas,
brainstem, such as pons cavernomas
arterial circulation, e.g., posterior inferior cerebellar artery aneurysms
This chapter is focused on the role these two approaches can play in the treatment of a posterior fossa
tumor, highlighting their advantages, limitations, and
complications.
5–10
When it was proposed, the endoscopic
6,7,10,11,12,13
9
and for lesions of the ventral
16
or vertebral artery aneurysms.
14,15
or of posterior
17
8,9
Thus,
28.2 Surgical Steps
28.2.1 Endoscopic Endonasal
Transclival Approach
The front door to approach the posterior fossa through
an endoscopic endonasal route is represented by the
clivus. For surgical purposes, it can be schematically
divided into three portions: upper, middle, and lower
(Fig. 28.1). The upper third of the clivus is usually approached through the sphenoid sinus. It is composed by
the posterior clinoids and the dorsum sellae, medially
to the parasellar segment of the carotid artery (Fig. 28.2a).
The main landmarks of the route to the upper clivus
are the same as those routinely adopted for a midline
endoscopic transsphenoidal approach, i.e., the tail of the
superior turbinate to identify the sphenoethmoid recess
and the opening of the sphenoid sinus, the sellar bulge,
and the two optic–carotid recesses, which are formed
by the optic nerves and parasellar carotid artery protuberances, to localize the course of the carotid artery (Fig.
28.2b). The intradural space corresponding to the upper
clivus is represented by the interpeduncular cistern, occupied by the tip of basilar artery, posterior communicating artery, superior cerebellar artery, and the third
cranial nerve (CN III) in its cisternal portion (Fig. 28.2c).
To expose the middle clivus it is necessary to extend the
previous route, drilling off the floor of the sphenoid sinus
in the space comprised by the two internal carotid arteries (ICA) (Fig. 28.3b). An useful landmark for these vessels
Fig. 28.1 Sagittal computed tomography scan. The clivus is
divided in three portions: upper, middle, and lower. The upper
portion is represented by posterior clinoid processes and the
dorsum sellae. The middle portion is comprised between the
sellar and sphenoidal sinus fl oor. The inferior third lies below
the fl oor of the sphenoidal sinus.
294
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