The position of ischial bursa

[Xue Heng]

Hi, Steve!
The question confused me for some time.
According to textbooks, ischial bursa is located between gluteus maximus and ischial tuberosity.
But in clinical practice, I came across some cystic lesions in subcutaneous layer of posterior hip.
In other word, they are more superfical than the ischial bursa should be.
Are they ischial bursitis?
Thank you for your kind and patient answering everytime.

[Stephen Bird]

Hi Xue,

I will start my answer by declaring myself as an ischial bursa sceptic.

The ischial bursa is supposed to be exactly where you describe (between glut max and the ischial tuberosity), however the conjoint hamstring tendon and the sacrotuberous ligament are on the ischial tuberosity so the bursa is actually between the g-max and these structures.
Rather than a bursa I just think of this as a plane of minor friction and when we inject it we are simply injecting the surface of the hamstring origin. I do sometimes see Doppler signal in this area suggesting localised inflammation. The reason I am a “bursa” sceptic is when we do ultrasound guided injections into this plane the fluid simply flows away and ends up sitting between G-max and quadrates femoris in the same potential plane as the sciatic nerve. In other words it acts as a plane rather than a bursa with defined margins. Despite this these injections do seem to provide good relief.

If your cystic lesions are in the subcutaneous space superficial to the G-max this is certainly not the correct location for the bursa,

In this space I would consider fat necrosis, injection site injury, sebaceous cyst, Morel lavallee lesion.

Do you have any images?

Steve

[Xue Heng]

Hi, Steve. Thank you for your patient and detailed answer.
Here are the images.
The diagnosis from our doctors was ischial bursitis.

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[Stephen Bird]

Nice images Xue,

As always!

I am sticking to my prior comments,

This is a subcutaneous fat lesion rather than a sub G-Max lesion.

Hence I respectfully disagree this is a ischial bursitis and believe it is a subcutaneous fat lesion.

Hence I agree with you that it is in the wrong anatomical plane to be ischial bursitis,

The exact pathology differential diagnosis remains wide but ultimately benign.

I would still consider fat necrosis, injection site, perhaps an insect bite.

Looks like a localised subcutaneous fat abnormality,

Is there any history of trauma, injection, insect bite etc?

Steve

[Xue Heng]

Got it, Steve.
Thank you for solving the problem that confused me for a long time.
You are always kind and patient answering the questions. Thank you!
I might ask more questions, please don’t loathe me.

[Stephen Bird]

Ask as many as you like Xue,

I love it,

So nice to see your excellent work from Beijing,

I miss you guys,

We need to go out for a hot pot after the pandemic.

Steve

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