Ultrasound Case of the Day- Ganglion Cyst

Today's case focuses on a ganglion cyst of the wrist.

This is the class bump to the back of the wrist that can form as a "wear and tear" injury.  In the olden days, these were typically treated by smacking the cyst with a Bible.  Bible smacking still works (sometimes), but we can also use ultrasound to help treat the cyst in a less brutal manner

I chose to show this image both because:1. It can help show patients the techniques Dr. Hyman and I use for treating different conditions in a more accurate and less painful way

2. It highlights an advanced technical point for other clinicians learning to use ultrasound

The ganglion cyst is the large black area highlight by the yellow area.  It appears large and black because the sound waves from the ultrasound machine penetrate easily through water, so it does not reflect back signal (as does the underlying bone)

The blue and red arrows are pointing to the extensor tendon of the ring finger.  This is the tendon that would help straighten out the ring finger if the finger was bent.  You can see a series of white parallel fibers that are extending from left to right across the screen.   One of the great strengths of ultrasound is that it is a MUCH higher resolution than an MRI.  On an MRI, then tendon would like like a simple black line, but using the ultrasound we can see the individual collagen fibers at a much higher level of detail.

The green arrow points at the underlying joints in the wrist (called a carpal joint).  This is an advantage of looking at the cyst under ultrasound - in this particular case, we can see that the cyst is very clearly NOT in continuity with the joint.  This has significance in terms of risk of infection or other complications

For this specific patient, we drained the cyst using ultrasound guidance.  In the past, we used to perform this procedure the way most doctors still do, which is feel around and just stick a needle into it.  The reason we use ultrasound guidance is to make sure we are not inadvertently injuring other structures (e.g., the carpal joint or the extensor tendon).  I can also do a detailed refinement called a fenestration, where I create multiple small holes in the cyst, which helps prevent the cyst from reforming.

Finally, a technical point for aspiring ultrasonographers- you may notice that the tendon immediately below cyst (the red arrow) is brighter than the tendon that is not beneath the cyst (the blue arrows).  This is an artifact called "through transmission."   What happens here is that the computer processor used by the ultrasound machine works under the assumption that the tissue density is uniform throughout the width of the ultrasound beam.  However, because the sound waves passing through the cyst have very little resistance, the computer processor will make everything deep to the cyst appear more bright (called hyperechoic) than it actually is.

One of the quirks with ultrasound is that because it shows so much detail, it is prone to artifacts that, in the wrong hands, can be misread as pathology in the patient.  This is why Dr. Hyman spend so much time travelling across the country working with other physicians to learn more about the nuances of ultrasound