Text in Italics is general (instructional) information
The straight X ray above shows expansion of the space between the proxima tibia and fibula, with gradual bowing of the fibula away from the tibia. The knee joint appears osteoarthritic. MRI show a large cystic lesion in the region of the interosseous membrane region proximally. The lesion extends anteriorly as well as into the posterior compartment. An intramedullary bone infarct is noted in the proximal tibial metaphysis. The differential diagnosis includes Myxoma, ganglion cyst and nerve tumours such as neuroma. A biopsy and partial excision of this cyst was done. The cyst contained the typical jelly like contents of a ganglion.
This is an example of a poplitelal or Baker's cyst which, in this case, has become very large. It is usually found in the popliteal fossa in this case it has tracked to the anterior compartment via the interosseous membrane.
It is really a symptom of other problems inside the knee which are causing excessive joint fluid to form. The knee appears osteoarthritic and chronic increase of synovial fluid pressure has led to this cyst appearing. Once the joint fluid is sufficient to cause pressure, the fluid pushes out at the back of the knee where the capsule is thinnest.
Treatment of a Baker's cyst must include treatment of the underlying condition, when the cyst will often spontaneously resolve. A very large cyst may be problematic in its own right, causing pain and pressing on structures in the back of the knee. In this case the cyst may be cut out, but attention still needs to be paid to the underlying condition which precipitated cyst formation.
A very tense Baker's cyst may rupture, and cause symptoms resembling deep venous thrombosis.