Baker’s Cyst on Ultrasound

What is a Baker’s cyst?

This is a cyst that is located on the back of the knee. This cyst lies between the gastrocnemius muscle and the tendon of the semimembranosis tendon.  A Baker’s cyst communicates with the knee joint.

Baker’s cyst symptoms

This can be an asymptomatic finding or one that causes pain. Additionally, these cysts can sometimes leak or rupture and produce pain.

How is a Baker’s cyst diagnosed?

This is very common finding on ultrasound done to look for deep vein thrombosis or clot of the leg. The technologists usually look at the back of the knee to look for these cysts as they can mimic the symptoms you would have with clot.

What does a Baker’s cyst look like on the ultrasound?

On ultrasound, the cyst will be filled with fluid and have the typical appearance of a cyst. At times, these cysts will have debris or other complex internal appearances. There is usually no internal blood flow with cysts, which the technologist will look for.

Popliteal cyst ultrasound

This is another way of referring to Baker’s cysts.  Popliteal cysts have the same appearance on ultrasound as Baker’s cysts.

Ruptured Baker’s cyst ultrasound

In the cases of leak or rupture, we will see fluid going down the leg, sometimes all the way to the calf.

Infected baker’s cyst ultrasound

Infected cysts are rare and can be associated with an infected knee joint.  The cyst will usually contain pus.   Imaging can not diagnose an infected cyst. Fluid sampling is needed for diagnosis.

Complex baker’s cyst ultrasound

It is important to confirm  the cystic nature of a baker’s cyst.  Rare tumors can have a similar appearance in the back of the knee. In cases that are not clear, an MRI of the knee may be ordered.

Who gets baker’s cysts?

Baker’s cysts can be associated with arthritis.   They can occur after trauma.  Baker’s cysts are associated with tears of the knee menisci.  The cysts are more common in older adults.

Baker’s cyst treatment

I often see these cysts left alone and not treated when asymptomatic.

In some cases, a specially trained radiologist will remove the fluid from the cyst when it is causing pain. This is done under ultrasound guidance so that the needle is placed directly into the cyst.

When cysts are especially large, a surgery may be done to remove it.

In some cases, the cyst can compress the blood vessels and nerves around it.

Baker’s cyst on ultrasound: summary

Baker’s cyst on ultrasound is a common finding that is found behind the knee.  Baker’s cysts are often asymptomatic but can cause pain.   Baker’s cysts can rupture and rarely become infected.  Further imaging evaluation of a Baker’s cyst can be done with an MRI of the knee.