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2. Access to Paramedian Corridor (Coronal
Plane)
The most critical and dening structure is
ICA in this plane. The paramedian skull base
may be divided into anterior (corresponding
to the orbit and anterior cranial cavity), middle (corresponding to the middle cranial, pterygopalatine and infratemporal fossae) and
posterior (includes the craniovertebral junction lateral to the occipital condyles and the
jugular foramen) segments.
(A) Anterior Coronal Plane
It is further divided into the supraorbital
and transorbital approaches [9–11].
Supraorbital approach provides access to
anterior cranium lesion extending laterally over orbit. Transorbital is designed to
reach both extraconal and intraconal
lesions. The indications for the extraconal approach are the sinonasal lesions
that displace, erode or invade the medial
wall of the orbit and for orbital/optic
nerve decompression in Graves’ disease
or trauma. The intraconal approach is
indicated to address intraorbital benign
space- occupying lesions, such as schwannomas, haemangiomas and meningiomas. The steps include complete
ethmoidectomy and exposure of lamina
papyracea in full extend. The next step is
the removal of lamina. For supraorbital
lesions, periorbita is lifted off from the
cranium base with cauterization of ethmoid vessels. Binostril approach can be
performed by superior septectomy. For
intraconal compartment access, periorbita is incised to expose the medial and
inferior rectus muscles. The gap between
these two muscles represents the window
for intraconal access (Fig.7.7). As ophthalmic arteries and the optic nerves cannot be mobilized, they constitute the
lateral limits of the approach.
(B) Middle Coronal Plane
It is further divided into ve different
zones, according to their relationship
with specic segments of the ICA.Zone 1
is the boundary to approach the lesions
211
Fig. 7.7 Right transorbital intraconal approach.
(Courtesy Dr. M. Arulalan, Senior Resident, NeuroOtology, Department of Neurosurgery, SGPGIMS,
Lucknow)
found medial to petrous apex, zone 2 is
corridor for infrapterous access, zone 3 is
passage for suprapetrous access, zone 4 is
for lateral cavernous sinus access and
zone 5 is for middle fossa and infratemporal fossa. Except for zone 1, all zones
start with a transpterygoid approach using
the maxillary sinus as the working corri-
12–15]. These approaches provide
dor [
access to skull base lesions posterior to
the maxillary sinus (e.g. middle cranial,
pterygopalatine and infratemporal fossae,
lateral sphenoid recess, petrous apex, cavernous sinus). Common pathologies
include schwannomas, juvenile nasopharyngeal angiobromas, sinonasal malignancy and meningoencephaloceles.
(i) Transpterygoid Approach
The pterygopalatine fossa (PPF) is
bound by the pterygoid process
posteriorly, the palatine bone
anteromedially and the maxilla
anterolaterally. The ITF is an anatomic space located under the oor
of the middle cranial fossa and posterior to the maxilla. It communicates medially with the
pterygopalatine fossa through the
pterygomaxillary ssure, anteriorly
ITF is continuous with the inferior
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orbital ssure. Pneumatization of
the sphenoid sinus extending into
the greater sphenoid wing bears a
lateral sphenoid recess (i.e. pterygoid recess), which projects under
the middle fossa. The paired pterygoid processes comprise medial
and lateral plates, fused at their
anterior cephalic aspect, the pterygoid base. Three important foram-
Ethmoid
sinus
Maxillary
sinus
posterior
wall
choana
ina located from superolateral to
infero-medial: foramen rotundum,
vidian canal and palatovaginal
canal.
The surgery begins with uncinectomy, anterior ethmoidectomy and
wide middle meatus antrostomy
(Fig. 7.8). The sphenopalatine and
posterior nasal arteries are then
identied at the sphenopalatine
Angiofibroma
c
Infratemporal
fossa
Fig. 7.8 Right middle coronal plane. (a) Complete expo-
sure of posterior and part of the lateral wall of right maxillary sinus, (b) complete removal of posterior wall, (c)
ligation of terminal branches of maxillary artery, (d) complete removal of pterygopalatine fossa content and dis-
d
Sphenoid
sinus
Lateral
recess
Pterygoid
plates
placement of tissue laterally after ligation of vessels, (e)
line diagram is showing surgical eld after removal of
posterior maxillary sinus wall (Courtesy Dr. M.Arulalan,
Senior Resident, Neurootology, Department of
Neurosurgery, SGPGIMS, Lucknow)
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Fig. 7.8 (continued)
foreman. The posterior wall of the
antrum is removed, revealing the
contents of the PPF covered with
periosteum. The sphenopalatine and
posterior nasal arteries can be
divided and mobilized laterally
which exposes the vidian canal. The
location of the vidian canal is usually at the insertion of the medial
pterygoid plate on the pterygoid
process of the sphenoid bone. The
vidian nerve and artery inside the
canal can be coagulated and divided,
allowing for the subsequent lateralization of the contents of the pterygopalatine fossa and identication
of the pterygoid base as well as the
foramen rotundum. The base of the
pterygoid plate is drilled, and the
lateral sphenoid recess is opened.
The infratemporal approach is discussed in the next section. The
objective behind reconstruction is to
restore the natural isolation of the
intracranial structures from the sinonasal cavity, avoiding a CSF leak
213
and secondary complications, such
as infection or meningitis. A vascularized reconstruction (e.g. nasoseptal ap) is favoured. The
reconstruction options are mentioned in the last section.
Trans-cavernous Approach [13]
(ii)
It allows access lateral to cavernous
carotid. Pituitary macroadenomas
extending posterior to cavernous
carotid is the only indication for the
trans-cavernous approach. It allows
lateral displacement of the carotid
artery.
(iii)
Petrous Apex Approach [10, 12]
Petrous apex lesions extending
towards the sphenoid sinus can be
accessed by this approach.
Extended sphenoidotomy and drilling of bone over the petrous apex
allows access.
(iv) Suprapetrous Approach
It starts with complete exposure of
the course of internal carotid artery.
Lesion extending into trigeminal
nerve and Meckel’s cave are managed by suprapetrous approach.
Infra-petrous, trans-condylar
and parapharyngeal are the posterior coronal approaches. The surgical exposure in posterior coronal
approaches is improved by
Denker’s approach, septal window
and by wide maxillectomy. Zone 5
is discussed in the next section.
7.1.1 Contraindications ofEEAs
Contraindications to an endoscopic approach to
the skull base include tumour extending lateral
to the midline of orbital roof, or lateral to optic
nerve, cases where an oncological resection
mandates a total maxillectomy, orbital exenteration or resection of facial skin, and most importantly lack of progressive experience in surgical
team [16].
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7.1.2 Limits ofEEAs
Certain limitations to EEAs are signicant posterior fossa extension with the tumour located
behind the ICA, institutional limitations (lack
of transnasal Doppler, stereotactic neuronavigation, specialized endo-bipolars and
extraocular EMG monitoring) and tumours that
circumferentially encase the carotid, so the
endoscopic endonasal approach cannot achieve
a gross total resection [16, 17].
7.2 Part B: Anatomy andSurgical
Approaches
toPterygopalatine Fossa,
Pterygomaxillary Fissure
andInfratemporal Fossa
The pterygopalatine fossa (PPF), pterygomaxillary ssure (PMF) and infratemporal fossa (ITF)
are continuous compartments that lie lateral to
the sphenopalatine foramen with a greater wing
of sphenoid forming their roof. Pterygomaxillary
ssure (PMF) is a communication between the
pterygopalatine fossa medially (which in turn
communicate with the nasal cavity via the
sphenopalatine foramen) and infratemporal fossa
(ITF) laterally. It is formed by a narrow gap
between the lateral pterygoid plate and the infratemporal surface of maxilla. The contents of
PMF are third part of the maxillary artery and
posterior superior alveolar nerve, artery and
veins.
Infratemporal fossa is a three-dimensional
space lies below the middle cranial fossa base
which comprises of greater wing of the sphenoid and squamous temporal bone. It is bounded
laterally by ramus of mandible, zygomatic arch
and medially by lateral pterygoid plate which
has pterygomaxillary ssure connecting it to the
pterygopalatine fossa. Anteriorly, it is bounded
by posterior-lateral wall of maxilla with inferior
orbital ssure and posteriorly with carotid
sheath and styloid apparatus. Inferiorly, it communicates with the neck (Figs.
Infratemporal fossa contents lie in three planes
from supercial-to-deep in the axial plane. The
rst layer immediately posterior to periosteum
of posterior wall of maxillary sinus consists of
branches of maxillary artery. Second layer
formed by various branches and anastomosis of
V2 and V3 and third layer is consist of muscles
of ITF.This surgical anatomy is important while
dealing with the pathology of PPF and ITF
(Fig.7.11) [18–21].
7.9 and 7.10).
Fig. 7.9 Infratemporal fossa—bony outlines. (a) Lateral view and (b) posterior view
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ab
Fig. 7.10 Computed tomography Axial sections (a) showing tumour (asterisk) involving sphenopalatine foramen and
pterygomaxillary ssure and (b) involving infratemporal fossa
The surgical approach to PPF and ITF can be
either an endoscopic approach or an open
approach. The endoscopic approach is mainly
the anterior approach to ITF and suited for SPF,
PPF and medial ITF which can combined with
endoscopic Denker’s approach or anterior maxillotomy for lateral ITF pathology. Open
approaches can be either anterolateral like maxillary swing and midfacial degloving or lateral
like Fisch’s ITF approach C and infratemporal
fossa approach D (preauricular transzygomatic
approach).
7.2.1 Surgical Approach toPPF
andITF
Surgery of PPF and ITF can be done by either an
endoscopic approach or by an open approach.
The endoscopic approach is mainly an anterior
approach to ITF and suited for SPF, PPF and
Medial ITF which if combined with endoscopic
Denker’s approach or maxillotomy can be used
for lateral ITF pathology. Open approaches can
be either anterolateral like maxillary swing and
midfacial degloving or lateral like Fisch’s ITF
approach C and D. Surgical approach to PPF
and ITF are decided mainly by the type of
lesion, its extension and experience of the surgical team.
1. Endoscopic Approach to SPA, PPF and
ITF
It is indicated for sphenopalatine artery ligation, maxillary artery ligation, vidian neurectomy, juvenile nasopharyngeal angiobroma
(Fisch Stage I, II and III JNA). Schwannomas
of PPF and ITF are commonly arising from
the maxillary nerve and mandibular nerve,
paranasal sinus tumours (non-squamous) with
extension into the SPA, PPF or ITF.Temporal
lobe meningo-encephalocele is extending into
the infratemporal fossa. Lesions of the middle
cranial skull base, which are lying (intradural/
extradural) lateral to cavernous sinus.
Contraindications of Endoscopic Approach:
Tumours are extending to the masseteric
space and gingivobuccal sulcus. Large juvenile nasopharyngeal angiobroma is receiving signicant feeders from the internal
carotid artery and other tumours encasing
ICA. Tumours extending to the cavernous
sinus, in around optic nerve and orbital apex,
middle fossa and para-sellar extension are the
relative contraindications.
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Fig. 7.11 Contents of infratemporal fossa in three planes.
(1) Vascular layer (with branches of internal maxillary
artery), (2) neural layer (with branches of maxillary and
mandibular nerves) and (3) muscular layer. Right side
(asterisk) is the tumour arising from the sphenopalatine
foramen involving the nasopharynx and entering infratemporal fossa causing splaying of the vascular and neural
layers
P. Mittal et al.
Surgical Steps (Fig. 7.12):
Endoscopic large meatal antrostomy is the
rst step of the endoscopic approach as this
exposes the posterior-medial wall of the maxillary sinus, which lies anterior to SPF, PPF
and ITF. Wider access can be gained by a
medial maxillectomy. Removal of the lower
part of middle turbinate creates more space
for instrumentation. This is followed by an
anterior and posterior ethmoidectomy.
Pathologies in the SPA, PPF and medial ITF
can be accessed after removal of posterior
wall of maxilla with a Kerrison’s rongeurs or
drill starting from the anterior lip of SPA taking care to prevent injury to the periosteum of
posterior wall of maxillary sinus, as maxillary
artery and its branches lie directly posterior to
it. The sphenopalatine artery can be identied
just posterior to cristae on the posterior part of
medial wall of maxilla and maxillary artery
b
e
Fig. 7.12 Endoscopic excision of the infratemporal fossa
tumour. (a) Axial CT showing hypodense lesion in left
ITF, (b) zoomed image, (c) coronal section for the same
lesion, (d) endoscopic exposure after removal of posterior
wall of maxillary sinus, (e) tumour dissection from surrounding tissue, (f) postoperative cavity
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Fig. 7.13 Endoscopic view of right internal maxillary
artery in the infratemporal fossa. (1) Internal maxillary
artery, (2) sphenopalatine artery, (3) descending palatine
artery, (4) infraorbital artery, (5) infraorbital nerve, (6)
infratemporal fossa fat, (7) lateral wall of the maxillary
sinus, (8) medial wall of the maxillary sinus
and its branches by careful dissection of periosteum of posterior wall of maxilla to expose
contents of PPF, PMF and ITF (Fig.7.13).
The maxillary artery dissection and the
control is important as it is the major vascular
supply to the tumours arising or located in this
area. Preoperative embolization can reduce
the vascularity in vascular tumours like JNA
and hemangiopericytoma.
Lateral exposure of ITF by endoscope is
limited by Piriform aperture, which can be
removed by modied Denker’s approach or
by wide anterior wall maxillotomy to gain
access to the lateral compartment of
ITF.Single surgeon endoscopic approach can
be converted into a two surgeon 4 handed
technique after making a septal window anytime during surgery for better visualization,
dexterity, dissection, for controlling the vessels and for tumour removal. For pathology
located in the middle fossa and surrounding
skull base, a greater wing of sphenoid and
pterygoids can be drilled to access the middle
fossa above, the petrous carotid from cavernous sinus to lateral part of temporal bone after
either displacing the maxillary artery and its
branches downward and clipping it [14, 15].
Complications
Bleeding can occur intraoperatively due to
injury to the maxillary artery or its branches
and rarely from feeders of ICA.Injury to the
nasolacrimal duct is evident after surgery with
complaints of epiphora. Injury to V2, sphenopalatine ganglia can lead to dry eye and numbness of the face. Orbital injury can occur
during dissection of tumours, dissection
around orbital ssure and optic nerve can lead
to visual deterioration, if the optic nerve is
injured and extraocular muscle injury can lead
to diplopia. CSF leak can occur from the middle cranial fossa after tumour removal and
repair of encephaloceles. Intracranial bleeding
can also occur during tumour removal from
the intradural compartment. Complications
can happen due to removal of normal structures like piriform aperture leading to numbness of the vestibular area, nasal obstruction
from crusting in nasal cavity and septal perforation. Postoperative epistaxis can occur leading to blood loss or aspirations [
19, 22]. So,
each and every step of the procedure has to be
meticulously performed and the possible complication has to be anticipated and avoided.
2. Open Approach to PPF and ITF
Indications
It is indicated for the tumours of ITF with
extensions to masticator space, buccinators
space and Zygomatic space. Malignant lesions
of the maxillary sinus with ITF involvement
are managed by open anterior approach. It is
also advised for gross extension of lesion to
middle cranial fossa through foramen rotundum or ovale. Parotid gland, mandible and
zygomatic bone can be involved by lateral
extension of ITF lesions. Inferior extension of
ITF lesions into parapharyngeal space is also
managed by an open approach. Jugular foramen lesion with ITF extension is also handled
by open approaches [23, 24]. Approaches for
malignant lesions of the nose and PNS are
mentioned in Part D (Sect. 7.4).
Contraindications
There is no absolute contraindication to the
open approach to ITF as this approach can be
extended or combined with other open or
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endoscopic approaches for tumour removal.
Being a lateral vector, this approach is not
suited for lesion crossing midline to other
sides like contralateral sphenoid sinus and
nasopharynx. Extensive malignant tumour
like squamous cell carcinoma and tumour
having extensive involvement of ICA or vertebral artery are deemed inoperable.
Surgical Steps
Open approaches to PPF and ITF are many.
Most commonly performed open approaches
are transmaxillary like midface degloving and
maxillary swing approach which works in an
anterior vector (Fig. 7.14), while commonly
performed lateral approaches are preauricular
transzygomatic (Fig.7.15) approach for ITF
lesions and a preauricular fronto-temporal
orbitozygomatic for ITF lesions having major
intracranial extension.
For a preauricular transzygomatic approach,
a curvilinear incision is made in the preauricular region staying above the lower attachment
of tragus coursing superiorly and then anteriorly in the frontal scalp to end superior to the
supraorbital notch near the midline. Scalp incision is elevated by giving incision in the supercial layer of deep temporal fascia to prevent
injury to the frontal branch of facial nerve.
Temporal muscle is incised to gain exposure of
zygomatic arch and lateral orbital rim in
Fig. 7.14 Midfacial degloving for left ITF lesion
Fig. 7.15 Preauricular transzygomatic approach. (a)
MRI is showing dumbbell tumour with ITF involvement
of right side, (b) preauricular incision is marked with tem-
poral extension, (c) aps elevated, (d) temporal craniotomy bone, (e) postoperative CT scan and (f) healed wound
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selected cases where zygomatic arch needs
removed and in more advanced case orbitozygomatic osteotomy is required. Combining this
with pterional craniotomy, middle cranial fossa
can be approached. The middle fossa skull base
is drilled to expose the V2, V3 and Middle
meningeal artery which can be mobilized or
sacriced combining ITF and middle fossa.
This approach can provide access for tumour
removal medially from sphenoid sinus to cavernous sinus, superiorly from middle cranial
fossa, laterally up to skin mandible and parotids, inferiorly till parapharyngeal space and
lower neck if skin incision is extended below.
Control of great vessels in the neck can be
taken for lesions involving the petrous ICA.
Complications
Mandibular nerve needs to be sacrificed
sometimes leading to hypoesthesia.
Temporomandibular joint dysfunction can
occur due to drilling, leading to varying
degrees of trismus. Injury to ICA can occur
if vertical petrous carotid is involved by
lesion, as this approach does not give
access to gain control over it. Injury to
facial nerve and branches can lead to facial
nerve palsy [25].
Conclusion
PPF and ITF have a complex anatomy and
contain many neurovascular structures and a
clear understating of this anatomy is important for surgery in this area. Medial and
medium-size lesions are better suited by
endoscopic approach while laterally based
extensive tumours are better suited by open
approach. Both approaches can be combined
in selected cases for complete resection of
lesions (Fig.
7.16).
Fig. 7.16 Endoscopic and midfacial degloving approach is used to excise the lesion (pre- and postoperative
radiology)
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7.3 Part C: Pituitary Tumours
andSurgical Management
Pituitary adenoma is the most common tumour
of the sellar region (90–95%). The adenomas
constitute 10–15% of all intracranial tumours
[26]. The preoperative assessment, indication
of surgery, selection of approach and postoperative care are jointly done by neurosurgeon,
otolaryngologist, neuro-radiologist, endocrinologist and neuro-anaesthetist for a better
patient outcome [27]. The presenting symptoms are based on the type of adenoma. Except
prolactinoma, surgery remains the treatment of
choice. The endoscopic transnasal trans-sphenoidal approach is the gold standard due to the
panoramic view, preservation of normal function and reduced hospital stay. The use of
newer technologies like plasma ablation provides a relatively bloodless eld. An expertise
in endoscopic techniques and the ability to use
angled endoscopes is required. Detailed anatomical knowledge is the prerequisite as the
margin of error is very less. During postoperative monitoring in ICU, one should look out for
diabetes insipidus, CSF leak, meningitis and
visual disturbance among other complications.
The endoscopic endonasal approach is the
standard surgical approach for pituitary tumours;
hence, it will be discussed in detail in this chapter. Transcranial approaches are mentioned in
Part E (Sect.
7.5).
7.3.1 Anatomy
The pituitary gland is projected from inferior part
of the hypothalamus and it maintains the functional connections via the infundibulum (pituitary
stalk). The gland has an anterior lobe called adenohypophysis derived from the ectoderm of Rathke's
pouch and a posterior lobe called neurohypophysis
derived from neuroectoderm prosencephalon. The
intermediate lobe is rudimentary in humans and
degenerates after birth. The gland resides in the
sella turcica and is covered by diaphragmatic sella
(dural fold). Laterally it is bound by cavernous
sinus and its contents (ICA, CN III, IV, V1,V2 VI)
and anterior and inferiorly by the sphenoid sinus
(Fig.7.17).
Fig. 7.17 Anatomical
location and relations of
pituitary gland (1)
pituitary gland, (2) ICA
(cavernous part), (3)
cavernous sinus, (4)
oculomotor nerve (III),
(5) trochlear nerve (IV),
(6) ophthalmic nerve
(V
), (7) abducent nerve
1
(VI), (8) maxillary nerve
(V
), (9) optic chiasm,
2
(10) sphenoid sinus, (11)
ICA (clinoidal part),
(12) posterior
communicating artery
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