Possible location for tenosynovial giant cell tumor

[Xue Heng]

Hi, Steve.
We know that tenosynovial giant cell tumor is also called giant cell tumor of the tendon sheath.
Does it indicate the tumor is originated from the tendon sheath?
Therefore, the tumor cannot be located in places where the tendons sheath is absent, such as the extensor tendon at the MCP joints?
Thank you for your kind and meticulous answers.

[Stephen Bird]

Hi Xue,

For a GCT to develop you don’t necessarily need a tendon sheath.

All you need is synovium.

This means it can occur within a joint capsule like PVNS of the knee, or be associated with a bursa.

Given that synovium is so prolific in the human body the potential to gave a GCT in almost any location seems possible.

Obviously tendon sheaths are the most common location but anywhere synovium exists is a potential site.

Hence an extensor tendon at a MCP joint seems a reasonable location for synvium to exist and hence potentially a GCT.

Steve

Steve

[Xue Heng]

Hi, Steve.
As I know, the inner layer of joint capsule, bursa, and tendon sheath have synovium.
But since extensor tendon do not have tendon sheath and consequently, they do not have synovium,
how can they have the potential to develope a GCT?
Thank you, Steve.

[Stephen Bird]

I agree there needs to be synovium and there is no formal synovial sheath in this location.

I wonder if it is possible to have small amounts of synovium in these locations regardless of there not being a formal tendon sheath.

Some people refer to it as a “synovial rest” where there are small traces of synovium around a tendon for example that does not have a formal sheath.

I asked my radiologist I am working with today and they have seen GCT in these unusual locations. It is not common, but it is possible.

I would include it on my differential list.

Steve

[Xue Heng]

Thank you and the radiologist you are working with.
This is my first time hearing the term “synovial rest”, and that well explained why GCT could develope in some seemingly impossible locations.
Thank you, Steve.

[Xue Heng]

Hi, Steve. Here is a new case related to this topic.
The patient was a 76-year-old male, with palpable mass on the palmar side of left hand.
A hypoechoic nodule was observed superficial to the flexor tendon, with increased blood flow.
When the patient flexed his finger, we saw the tendon sliding beneth mass, while the mass kept stationary.
Can we conclude the mass is outside the tendon sheath, and it was not a GCT?
Thank you, Steve.

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[Stephen Bird]

Hi Xue,

This is a miscellaneous finding with a variety of possible differentials.

It still could be a GCT.

The GCT would arise from the tendon sheath itself rather than from the tendons within the sheath .

The tendons slide within a stationary sheath so if it was a GCT of the sheath I would expect to remain stationary just as this one does.

So it is behaving like something arising from the sheath.

It could also be arising from the palmar aponeurosis like a dupuytrens lesion.

It could also me a post traumatic lesion.

Many possibilities I think !

Let me know if you ever get a final diagnosis.

Steve

[Xue Heng]

Thank you, Steve.
I would follow up the patient and tell you the final diagnosis if he removed the tumor.

[Stephen Bird]

Thanks Xue.

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