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

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

What are these paired enhancing structures

Internal jugular veins

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?

P

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

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?

cerebellum

cerebrum

Tentorium cerebelli

Identify the superior sagittal sinus and the transverse sinuses

Superior sagittal sinus

Hint, blood in these sinuses is white after contrast as there is slow flowing blood

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

P

Pons

Medulla

M

Mastoid air cells

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

C2

Odontoid process

This is an important image for your understanding of the relationships between the cavernous sinus and the pituitary gland.

Identify the internal carotid arteries in the cavernous sinuses

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?

Where is the optic chiasm? What is its relationship to the pituitary?

Do you see how a big pituitary tumor could come up and press on the chiasm?

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

3. Airway (nasopharynx and oropharynx)

4. Cervical vertebral bodies

5. Spinal cord

6. Cerebrum

7. Cerebellum

tongue

Turbinates and mucosaAirway

np

opCervical vertebral bodies

spinal cord

cerebrum

cerebellum

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

S

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

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

NT

S