3D Ischioanal (Ischiorectal) Fossa
Channel: About Medicine
Date: 2018-07-28

View this model here: https://www.aboutmedicine.com.au/models/ischioanal-fossae


The ischioanal (formerly known as ischiorectal) fossae are hard to get your head around in 2D, but it's a breeze in 3D. 

Learn the relations to the pelvic floor, the pelvic organs, and the raison d'être of the fossae themselves.

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In order to appreciate better the 
space that is the ischioanal fossa,
let's first get our bearings.

Here we have the pelvis, which I'm going
to make a sagittal cut through.

This reveals the 3 organs of the female 
pelvis - bladder, uterus, and rectum,
which becomes the anal canal. 

The muscles of the pelvic floor support
these organs like a hammock. The ischio-
anal fossae is directly lateral to levator
ani here. It contains mostly fat, and 
thus acts as a kind of cushion, 
surrounding the hammock.

In this model, we've scraped out
all of the fat which fills it.

So this opening here, is the IAF. 

And it's one of those areas of anatomy 
that is quintessentially hard to grasp in 
2D. In 3D it becomes much easier.

The space is shaped like a wedge,
Like this.

I'll bring in the pubic bone for 
orientation.

I hope that geometry makes sense to you.

Let's bring in the medial wall, which
is levator ani.

Now we see that the space exists 
between the bowl-shaped
pelvic floor and the bony pelvis. 

As I mentioned, it is filled with fat.
The cushioning allows the anal canal to
expand during defecation.

As always in anatomy, the form reflects
function.

Let's round out the boundaries now,

The lateral wall is a bit of bone, 
obturator internus

Floor is deep perineal fascia

Post wall sacrotuberous ligament, 
and some part of gluteus maximus.

Now - this view may look more familiar 
to you. This is the version we tend
to see in med school, and if you imagesearch
ischioanal fossae this is what appears.
I hope now that the dimensions of the 
space make sense to you.

If you'd like to navigate around this
model yourself, hit the link in the video
description below.

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