1) The skull base surgery approaches discussed allow surgeons to access different regions of the skull base to treat lesions while avoiding harm to intact structures. 2) Key approaches described include the pterional, frontolateral, transsphenoidal, suboccipital lateral, and various transpetrous approaches. 3) Endoscopic skull base surgery has advanced to allow minimally invasive access to regions from the cribriform plate to the foramen magnum and laterally to the infratemporal fossa.

1. Surgical approaches to skull base
Dr Ajay kumar
Mch PDT Dept of neurosurgery BIN
Kolkata

2. The skull base surgery is one of the most
demanding surgeries. There are different
structures that can be injured easily, by
operating in the skull base. It is very important
for the neurosurgeon to choose the right
approach in order to reach the lesion without
harming the other intact structures.

3. • Due to the pioneer work of Cushing, Hirsch,
Yasargil, Krause, Dandy and other dedicated
neurosurgeons, it is possible to address the
tumor and other lesions in the anterior, the
mid-line and the posterior cranial base. With
the transsphenoidal, the frontolateral, the
pterional and the lateral suboccipital approach
nearly every region of the skull base is
exposable.

4. Approaches
1) pterional approach
2) frontolateral approach
3) transsphenoidal approach
4) suboccipital lateral approach
These approaches can be extended and
combined with each other

5. Pterional approach
Historical overview
In the 1970 s Yasargil laid to the foundation of
the pterional approach.The pterional approach
allows the surgeon to address the circle of Willis
and also pathological changes in cavernosinus
area.
The pterional approach is the standard surgical
treatment for aneurysms in the anterior circle of
Willis. During the Cushing era the term "nole mi
tangere" ("don't touch me") was a rule for
neurological surgeons, which considered treating
intracranial aneurysms.

6. Surgical technique
There are many variants for the pterional
approach. Mainly it is a trepanation which
permits access to the frontal and to the
temporal lobe as well as the Sylvian fissure .
.

7. • Positioning - the patient should be placed
supine, with the shoulder at the edge of the
surgical table in a neutral position, and head
and neck remain suspended after removal of
the head support
• The head should be secured by a three-pin
skull fixation devise (Mayfield or Sugita model)
and must be maintained above the level of the
right atrium to facilitate venous return.

9. • There is a sequence of five movements for the
positioning of the head: traction, lifting,
deflection, rotation and torsion.
• Skin marking starts at the superior rim of the
zygomatic arch anterior to the tragus, and
extend up to the midline of the skull in the
frontal region, respecting the hairline
whenever possible

10. • the interfacial dissection of the temporalis
muscle, as originally described by Yasargil, is
specifically intended to preserve the
frontotemporal branch of the facial nerve and
reduce postoperative cosmetic changes
resulting from the surgical wound.

11. The pterional craniotomy should be performed starting
from three points of trepanation
• The first trepanation must be set between the
superior temporal line and the frontozygomatic
suture of the external orbital process;
• the second trepanation is performed on the most
posterior extension of the superior temporal line;
• third one should be made on the inferior portion
of the squamous part of the temporal bone

12. • In cases of prominent sphenoid wing, the
osteotomy of that segment should be
complemented with the use of drilling,
• After the trepanations, the dura must be
properly detached from the internal bone
surface with the aid of dissectors suitable for
this purpose.

13. • Basal drilling - the purpose of the drilling of
the lesser wing of the sphenoid bone is to
achieve bone flattening to facilitate the basal
access with minimal brain retraction, which
will be further optimized with cisternal
opening and the aspiration of cerebrospinal
fluid

15. • Intraoperative view,
left pterional approach.
The tumor bulges
behind the internal
carotid artery. In front
of the tumor the left
optic nerve can be seen.
Behind the tumor the
oculomotor nerve is
demonstrated

16. Image of the pituitary
stalk. The pituitary stalk
is demonstrated with
the suction tip behind
the chiasm.

17. Fronto lateral approach
Historical overview
• The frontolateral or unilateral subfrontal
approach provides exposure of the anterior
cranial base.
• It allows addressing olfactory groove
meningiomas (OGMs) by a minimally invasive
procedure.

18. Surgical technique
• This approach allows different skin incisions
• The trepanation above the pterion and above
the temporal muscle follows a curved skin
incision or an eyebrow skin incision
• The trepanation of an approximately 3 × 4-cm
frontolateral craniotomy allows the entry to the
anterior fossa. It is essential to include
radiological data of the patient in order to
prepare a performance of a sophisticated
approach such as the frontolateral approach.

20. • A common iatrogenic injury is the injury of
superficial structures. The super ciliary skin
incision allows the surgeon to protect superficial
structures like the frontal branches of the facial
nerve and the superficial temporal artery.
• Perneczky led to the development of
endoscopical approaches using the supraorbital
"key-hole" approach . Via endoscopic techniques
it is possible to provide relatively great exposure,
while offering less brain retraction

21. • Intraoperative view
from the right side. The
cystic lesion (Rathke's
cleft cyst) can be
detected behind the
optic nerves

22. Trans-sphenoidal approach
• Historical overview
• The transsphenoidal route was first used by the
Egyptians in order to remove the brain.
• The pioneer work of Harvey Cushing and Oskar Hirsch
led to one of the most efficient ways to operate in the
sellar region.
• Cushing advocated the approach sublabially and Hirsch
accessed the sellar region endonasally
• Sir Victor Horsley was the first to operate on the
pituitary gland.

23. Surgical technique
• The classic technique begins with the patient
in supine position. An x-ray machine is
positioned laterally to control each step of
intervention.
• In microsurgery the surgeon stands at the tip
of the head whereas in pure endoscopic
pituitary surgery the neurosurgeon stands at
the shoulder of the patient.

24. • After incising the septal mucosa and revealing
the anterior wall of the sphenoid sinus, the
anterior wall of the sphenoid sinus will be
removed with punch forceps . Then excise the
sinus mucosa. After opening the dura , the
tumor must be indentified in order to
extirpate it with a curette by using lateral
extensions.

25. • Incision inside the nasal ostium

26. • Partial resection of bony septum

27. • Opening of the sellar floor

28. • The dura is exposed and opened

29. • The tumor is resected with a curette

30. suboccipital lateral approach
/retrosigmoid approach (RSA)
Historical overview
• The posterior cranial base can be explored
through the lateral suboccipital route.
• Processes in the posterior fossa such as
acoustic neuroma surgery can be carried out
through the lateral suboccipital approach.
• The unilateral suboccipital approach was
popularized by Woolsey (1903) and with great
contributions by Krause (1905)

31. • After several refinements and modifications
through different dedicated neurosurgeons (Fish ,
House and Seiffert , Dandy's suboccipital
approach (1917) with an ipsilateral suboccipital
flap evolved to what we call retrosigmoid
transmeatal approach.
• Cushing (1917) on the other hand described a
bilateral suboccipital access and stated the
unilateral suboccipital approach as
disadvantageous.

32. • Surgical techniqu
• semi-sitting position/ lateral position for the
suboccipital lateral route .
• After local shaving of the hair behind the pinna
and disinfection of the surgical field,
• A slightly curved skin incision 2–2.5cm medial to
the mastoid process is performed and the
underlying muscles are incised in line with the
skin .
• If the foramen magnum area has to be
approached, however, the caudal end of the
incision has to be extended further towards
midline.

33. • The question as to whether to perform a
craniectomy or craniotomy is a matter of
individual preference and institutional
tradition,the one-piece craniotomy is a more
dangerous procedure in regard to the safety of
venous sinuses and the risk of a dural tear. After
the initial burr hole is made, the craniectomy
done.
• Now the sigmoid sinus and parts of the
transverse sinus are exposed with the drill.

34. • Patient in the semi-sitting position. The hair is shaved
and the later skin incision is marked

35. • Attention should be paid to the variable
emissary veins, which lead to the sigmoid
sinus. First the dura should be opened under
microscopic magnification in a triangular
shape to gain cerebrospinal fluid and in order
to relax the cerebellum.
• Then the dura has to be opened near the
sinus via a curved skin incision that connects
with the previous dural opening

36. C2 Rhizotomy
• This surgical approach is used primarily to
treat medically refractory occipital neuralgia.
• The surgical target is to perform a posterior
cervical C1 hemilaminectomy to access the C2
dorsal nerve roots for selective rhizotomy. This
can provide relief for neuropathic pain
localized to the occiput.

37. • The patient placed prone on the operating room table. The
head is kept in the midline position and maximally flexed as
the patient’s anatomy will allow. This widens the exposure
above and below the lamina of C1.
• A midline posterior cervical incision is used. Once the
unilateral exposure is completed, removal of the ipsilateral
C1 lamina is performed. This allows access to the cervical
dura at the level of the C2 nerve roots.
• The dura is opened in the middle of the exposure to expose
the lateral spinal cord and dorsal exiting roots. The C2
dorsal nerve roots are carefully selected and ligated.
• The dura is then sutured watertight to prevent a spinal
fluid leak.

38. Trans-petrous approaches
• Translabyrinthine approach
The gate of this approach is the mastoid (a
retroauricular-transmastoid approach), and the
target is the internal auditory canal and CPA .
• The approach removes the bone lying between
the petrous dura-sigmoid sinus posteriorly and
the mastoid fallopius anteriorly.
• The facial nerve, cochlea, tympanic cavity and
outer ear canal are left in place
.

40. • The occipital bone in the retrosigmoid area is
partially drilled to expose the retrosigmoid dura
and allow retraction of the sigmoid sinus. The
dura of the temporal lobe, in the retro- and pre-
sigmoid area, is exposed.
• Once the approach is finished, the jugular bulb is
the inferior limit. The temporal dura, superior
petrosal sinus and tentorium are the superior
limits of the approach. The presigmoid dura is
transected and the CPA is entered

41. Translabyrinthine-transapical approach
This an extension of the translabyrinthine
approach to the petrous apex .
• In the translabyrinthine approach, the
anterior wall of the canal may represent an
obstacle to the anterior CPA. Removing all of
the petrous apex around the canal brings
about the concept of surgical unity of the
petrous bone and CPA. This allows early and
wider exposure of the anterior CPA,

42. Translabyrinthine-transapical
approach

43. • Transcochlear approach
• The transcochlear approach is an extension of the
translabyrinthine approach, with three main
additional steps: removal of outer ear canal and
tympanum and entire petrous bone up to the
clivus, posterior transposition of the facial nerve,
drilling of the cochlea and closure of the external
auditory canal
• The approach gives wide access to the CPA and is
suitable for large lesions with anterior extension
into the prepontine cistern. The cavity is filled
with fat. The approach is the widest
surgical corridor in the lateral skull base.

44. • The complete petrous bone is removed
including the external ear and middle ear
• The approach allows good exposure of the
complete CPA, with the surgical corridor
extending from the anterior wall of the
external ear canal to the clivus, making a
surgical cavity of the entire petrous bone

46. • Pre-sigmoid-retrolabyrinthine approach
(conservative petrosectomy), transtentorial and
subtemporal
• This surgical corridor extends between the
sigmoid sinus, which lies posteriorly and the
labyrinth, which is the anterior boundary.
• The facial nerve is skeletonized but left in place.
This is a classical retro-auricular-trans-mastoid
approach, otherwise termed "conservative
petrosectomy".
• It is a narrow corridor. It allows access to the
area of dura from sigmoid to labyrinth, and to the
adjacent portion of the posterior CPA

48. • Infratemporal approaches
• Approach that exposes the inferior aspect of
the temporal bone, with the jugular foramen
and the adjacent area of the parapharyngeal
space including the jugulo-carotid vessels .

49. • A large retroauricular and upper neck incision
opens the entry area. The dissection of the upper
neck exposes the jugular vein and carotid artery.
Removal of the outer ear canal and anterior
transposition of the VII cranial nerve allow drill
out removal of the infralabyrinthine petrous bone
up to the entire jugular foramen, to the occipital
condyle and low clivus.
• This typical skull base approach allows removal
of lesions from the CPA to the jugular foramen
and parapharyngeal space.

51. Endoscopic Skull Base Surgery
• Endoscopic skull base surgery has undergone
rapid advancement in the past decade moving
from pituitary surgery to suprasellar lesions
and now to a lesions extending from the
cribriform plate to C2 and laterally out to the
infratemporal fossa and petrous apex.

52. • The history of endoscopic skull base surgery is de
facto the history of pituitary surgery.
The first pituitary operation was likely performed by
Sir Victor Horsley in 1889 via a transfrontal
approach
Schloffer who is widely regarded as the father of
modern pituitary surgery.

53. • There are several distinct anatomic regions of the skull
base that are accessible via a transnasal endoscopic
approach:
• cribriform,
• parasellar,
• clivus,
• spinomedullary junction
• petrous apex,
• pterygopalatine and infratemporal fossa

54. Standard Endoscopic Approach
In the standard endoscopic approach to the sellar region
• the endoscope is introduced through the right nostril,
close to the floor of the nasal cavity.
• The first structures to be identified are the inferior
turbinate, the middle turbinate, and the nasal septum.
• The head of the middle turbinate is dislocated laterally
to widen further the space between the middle
turbinate and the nasal septum and to create an
adequate surgical pathway in the posterior nasal cavity

55. • As the endoscope advances into the nasal cavity,
it reaches the choana, which represents the
main, inferior landmark of the approach.
• Its medial margin is the vomer, which confirms
the “midline” of the approach, whereas its roof is
shaped by the inferior wall of the sphenoidal
sinus. Lateral to the choana is the tail of the
inferior turbinate.
• The endoscope is then angled rostrally until it
reaches the sphenoid ostium, which is usually
located approximately 1.5 cm above the roof of
the choana .

56. • Sometimes, especially in a well-pneumatized
sphenoidal sinus, the ostium cannot be visualized
because it is covered by the superior turbinate. In
these cases, the superior turbinate can be gently
lateralized or removed to expose the ostium and gain
access to the sphenoidal sinus through its
enlargement.
• After identification of the sphenoid cavity, the nasal
septum is separated from the sphenoid rostrum.
• The whole anterior wall of the sphenoidal sinus is
enlarged circumferentially, taking care not to enlarge
the sphenoidotomy too much in the inferolateral
direction, where the sphenopalatine artery and its
major branches lie

57. • After removal of the sphenoid septa, the
posterior and lateral walls of the sphenoidal sinus
are visible, with the sellar floor at the center
• Lateral to the sellar floor, the osseous
prominences of the ICA and the optic nerve can
be seen, and between them is the opticocarotid
recess, molded by the pneumatization of the
optic strut of the anterior clinoid process

58. • The sella can be opened in many different ways. If
the tumour has eroded part of the bone then it is
quite easy to use the smallest Kerrison punch to
remove loose bone to expose the dura.
• If the bone is firm and does not break easily with
the pressure of the punch, then an osteotome
may be used to make a window in the sella which
can then be enlarged using punches
• The another option is to use a drill to thin the
bone prior to opening it

59. • The dura is incised using 15 number knife in a
cruciate fashion. Occasionally there may be
bleeding from the cut ends of the dura which
needs to be cauterized with bipolar forceps.
• Once the dura is incised, soft tumour usually
pops out .Further tumour removal is done
using ring curettes

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