Knee Ganglion Cysts

[Diane]

Hi Steve!
Scanned this female the other day for a posterior knee lump.
Saw a cystic area which I thought was a ganglion cyst coming from the posterior knee joint. Are the images typical of one?
Also saw a complex lobulated cystic area in the semimembranosus tendon, does this look like an intratendinous ganglion cyst to you?

Thanks!

• This topic was modified 3 years, 5 months ago by Diane.

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[Diane]

Hi Steve, just got another case. This female came in with chronic right anterolateral shin pain. She had an US done which was query intramuscular haematoma. When I scanned her, it was looking more cystic so I was querying ?ganglion cyst as it looked like it was coming from the knee joint.
She had a MRI after which said ” Further evaluation with ultrasound would be of value to confirm the cystic nature of the lesion and its origin from the proximal tibiofibular joint.”

Is the proximal tibiofibular joint something that we can see easily/assess for on ultrasound?

Thanks!

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[Stephen Bird]

I think this is a common site for a knee joint ganglion.
In fact I was just looking at some scanning being done in London and our patient had almost identical lesions in both knees.
I think they are often asymptomatic incidental findings and I suspect MRI sees them all the time.
They are not bakers cysts but arise from the poster-medial joint capsule and often sit right against the semimemb tendon and are often multiloculated and non compressible.
Mostly I see them displacing the semimemb tendon but it is possible for them to become intratendinous and remember at this level the semimemb is breaking up into several insertion slips so it might simply be between the slips.

This one would be too small and deep for it to be a clinical lump I think.

Steve

[Diane]

Thanks! So do you reckon its just 1 cyst that has come from the posteromedial joint and appears as that small anechoic cystic structure and has somehow also seeped its way through the SM tendon as well? Or do you reckon they’re 2 separate cysts?

Thanks!

[Stephen Bird]

This is an interesting one,

Yes indeed you can see the proximal tibia-fibular joint with ultrasound,

It is fairly simple as you can easily palpate the head of the fibula and then simply line this up with the tibia.
The joint can get OA and synovitis and the joint capsule ligaments can be damaged by trauma or degenerative change.
This is what I suspect has happened in your patient and like other joints this leads to a ganglion arising from the joint through the capsule.
It is possible for a ganglion to become “intra-muscular” and this occurs where there is a small defect in the muscle fascia and this might be anatomical where a vein / artery or nerve is entering or exiting the fascia or it may be a congenital deficiency in the fascia. Either way it is a possible entry site for a ganglion looking for a path of least resistance to grow along.
You can see the same thing with a bakers cyst which ends up intra-muscular inside medial gastrocnemius, and I saw one recently that became intramuscular inside soleus.

So I think this is an intra-muscular extension of a proximal tibia-fibular joint ganglion and it looks like it is inside peroneus longus.

Remember also the proximal tibia-fibular joint ganglions have another trick up their sleeve and they can find a path of least resistance along the intra-articular branch of the common peroneal nerve. They can track along this and become an intramural ganglion of the common peroneal nerve.

Sneaky eh!!

Steve

[Stephen Bird]

I think it is impossible to tell for sure,

It is more likely that it is one ganglion cyst that is in very close proximity to the semimemb tendon and is either making its way inside the tendon or is it between the distal insertion slips.

An MRI could settle the argument.

Mostly when I see this appearance it is incidental and not a direct source of pain.

I have attached a couple of images from an excellent article which explains the anatomy of the semimemb insertion.

It is not as simple as you think!

I will email you the full article as well.

Steve

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