0:01

Because of the well-confined nature of the posterior fossa,

0:07

deliminated by the tentorium and the foramen magnum.

0:12

Traumatic lesions of the posterior fossa are

0:15

considered separately by the neurosurgeons

0:18

for indications of surgery.

0:21

So it is said that patients who have mass effect on the

0:24

CT scan or neurologic dysfunction who deteriorate,

0:30

are surgical indications for the posterior fossa.

0:35

So mass effect on CT, by that,

0:37

they're referring to any type of compression or

0:40

distortion or rotation of the fourth

0:42

ventricle or the basal cisterns.

0:45

Or if that compression of the fourth ventricle,

0:48

or the cerebral aqueduct leads to obstructive hydrocephalus,

0:53

it would require surgical intervention.

0:56

This is an example of a patient who has a large posterior

1:00

fossa hematoma, in this case,

1:03

a parenchymal hematoma.

1:06

And there is mass effect, as you can see,

1:08

on the upper fourth ventricle,

1:10

it being displaced to the left side.

1:14

Not only that,

1:15

but the normal CSF around the basal cisterns have been

1:19

obliterated secondary to the mass effect of

1:22

the intraparenchymal hematoma.

1:24

Hence, this would be a surgical indication

1:28

for intervention for evacuation of the hematoma.

1:31

In some circumstances,

1:34

they may actually not perform the

1:37

evacuation of the hematoma,

1:39

but instead do what's called a suboccipital craniectomy.

1:42

With that,

1:43

they remove the posterior fossa bone

1:46

and therefore allow the brain to expand outward

1:50

through the defect that the absent bone has created,

1:54

and thereby take the pressure off

1:57

of the brainstem or the foramen magnum

2:01

where the tonsils may be herniating.

2:03

Remember, that need not be an intraparenchymal hematoma

2:07

that leads to compression of the basal cisterns

2:11

or the fourth ventricle.

2:12

This is an example of a patient

2:14

who has an epidural hematoma.

2:16

We will be talking about that shortly.

2:19

Due to an injury to the venous sinus,

2:23

in this case the transverse sinus.

2:26

This mass effect from this hematoma is causing some

2:30

effacement of the basal cisterns

2:32

around the perimesencephalic cistern.

2:35

This again,

2:35

would lead to an indication for surgical intervention.

2:39

Although we're not at the level of the fourth ventricle,

2:42

we can see that the midline structures are being

2:45

shifted from left to right in this individual.

2:49

When would they observe a patient who has hemorrhage in

2:53

the posterior fossa?

2:54

If the patient has no mass effect demonstrated on CT,

2:59

and is not demonstrating neurologic dysfunction,

3:01

referable to the posterior fossa,

3:04

then they would do serial scanning.

3:06

As I said, generally in our institution,

3:08

they will be scanning every 6 hours,

3:10

for about 24 hours,

3:12

and then on a 24-hour basis while in the hospital.