Transcript Iac Pit Anatomy

Goals
• Be familiar with the extracranial take-off of CN
VIII and its relationship to the pons and
cerebellum
• Appreciate how the anatomic position of tumors
of CN VIII will dictate the surgical approach
• Understand the relationship of CN VIII to the
petrous portion of the temporal bone
• Be familiar with the axial and coronal MRI
anatomy of the cerebellar-pontine angle
Goals
• Be familiar with cavernous sinus anatomy and its
relationship to the pituitary gland and optic
chiasm
• Understand the mid sagittal anatomy and
relationships of the pituitary gland
• Appreciate how these relationships will make a
trans-sphenoidal approach to pituitary surgery
the least invasive
This is an axial fat-suppressed T1 weighted MRI in the upper neck.
Let’s review some neck anatomy.
Can you find (click for answer)
1. The parotid glands
2. Masseter muscles
3. Medial pterygoid muscles
The parotid glands
Masseter muscles
Medial pterygoid muscles
Can you find the internal carotid
arteries and the internal jugular veins?
ICA’s
Internal jugular veins
Can you find the lateral pterygoids? What do they attach to?
lateral pterygoids
What are these paired
enhancing structures
Internal jugular veins
Attach to the mandibular condyles,
Hard to see on these images
What part of the brain is this?
cerebellum
What are these enhancing
structures?
Nasal mucosa on the tubinates
Can you find the mastoid air-cells?
Hint, look at the maxillary sinuses and
notice that the are black (no signal)
because they are filled with air
Mastoid air cells (black)
What are these paired
enhancing structures?
Sigmoid sinuses, at the
junction with the transverse
sinuses
Now we are at the level of the cerebellar pontine angles (CPA’s)
Can you identify the pons?
What is the white dot,
immediately anterior to the
pons?
Basilar artery
What are the paired enhancing
structures in the CPA’s?
This is a difficult question,
as these are bilateral
tumors
Note how the one on the left is
entering the internal auditory
canal in the petrous portion of the
temporal bone. So, which cranial
nerve are these involving.
These are bilateral acoustic
schwanomas involving CN VIII
P
You can see that these are relatively large tumors and the one on the
right also extends into the internal acoustic canal in the petrous portion
of the temporal bone
Do you see the 4th ventricle?
Can you find the carotid arteries in the cavernous sinus at this level?
Hint the are black tubes because they have briskly flowing blood
Internal carotid arteries in
the cavernous sinuses
Do you see the pituitary?
Hard to see but you know that it
is between the cavernous
sinuses and just posterior to
the sphenoid sinuses
Sphenoid sinuses
Pituitary
This is a coronal T1 weighted post contrast image. Can you see the
cerebellum and the cerebrum. What is the diving structure?
Tentorium cerebelli
cerebrum
cerebellum
Identify the superior sagittal sinus and the transverse sinuses
Hint, blood in these sinuses is white after contrast as there is slow
flowing blood
Superior sagittal sinus
Transverse sinuses
Identify the lateral and 4th ventricles
Lateral ventricles
4th ventricle
What is the enhancing
material in the lateral
venticles?
Choroid plexus
Do you see where the
transverse sinuses drain into
the sigmoid sinuses
Follow these on the next image
We are starting to move into the region of the pons
Can you identify the
1. Pons
2. Medulla
3. Mastoid air cells
Pons
Medulla
Mastoid air cells
P
M
Now we are in the region of the cerebellar-pontine angles.
Do you see the paired enhancing lesions (acoustic
schwannomas) previously identified on the axial images
Note their relation ship to both the
pons and the internal auditory canal
(extending into the mastoids)
Just a few anatomic points for review on this image. Try and locate:
1. The parotid glands
2. The external auditory canals
3. The C2 vertebral body and the odontoid process of C2
Parotid glands
External auditory canals
Odontoid process
C2
This is an important image for your understanding of the relationships
between the cavernous sinus and the pituitary gland.
Where is the optic chiasm? What
is its relationship to the pituitary?
Identify the internal carotid arteries
Do you see how a big pituitary tumor could
in the cavernous sinuses
come up and press on the chiasm?
Hint, fast moving blood will look
like signal void (black),
occasionally the flow is slower
centrally (as in this case)
What is the bright signal
around the arteries?
This is slow flowing blood in
the cavernous sinuses
Do you see the pituitary gland?
Hint, what is its relationship to
the cavernous sinus?
These next 4 images are parasagittal and mid sagittal T1 weighted post-contrast
MRI images on a patient with a pituitary tumor.
Let get our bearings first and start
identifying some major
structures.
1. Tongue
2. Nasal turbinates and nasal
mucosa
cerebrum
3. Airway (nasopharynx and
oropharynx)
4. Cervical vertebral bodies
5. Spinal cord
cerebellum
6. Cerebrum
7. Cerebellum
Airway
Turbinates
and mucosa
np
Cervical vertebral bodies
tongue
spinal cord
op
This is a mid-sagittal image
Identify the pituitary gland
The tumor in this case does not
enhance as much as the normal
pituitary gland and looks like a
dark spot.
Find the sphenoid sinus
Appreciate the proximity of the
sphenoid sinus to the pituitary and
understand why going through this
sinus would be a less invasive
technique for resection then
through the cavernous sinus
S
This is a parasagittal image. Can you find the optic chiasm?
Again note the proximity of the pituitary gland to the optic chiasm
Note the relationship of the nasal
turbinates to the sphenoid sinus
S
NT