Ganglion cysts within the knee cavity are rare and usually originate from the cruciate ligaments, the menisci, the alar folds that cover the patellar fat pad , and the popliteus tendon and from osteochondral fractures or subchondral bone cysts . The reported prevalences of intra-articular ganglia in the knee are from 0.2% to 1% on knee MRI and 0.6% on knee arthroscopy . Many cases of ganglia, ranging in size from 1.8 to 4.5 cm, have been reported , and occasionally they are bilateral. Most of them are incidental findings and of little clinical significance.
The first intra-articular knee ganglion was described by Caan  in 1924, and there have been several references to ganglia around the knee since then. Brown and Dandy  reported 38 intra-articular ganglia in 6500 knee arthroscopies and half of the patients had no other abnormality.
The differential diagnosis of knee cystic lesions must include ganglia, lipoma, synovial myxoma, meniscal or parameniscal cyst, synovial cysts, pigmented villonodular synovitis, synovial hemangioma, aneurysm, synovial sarcoma, and synovial chondromatosis . Symptomatic ganglia usually present with a history of or signs of mimicking an internal derangement of the knee. The differential diagnosis should include meniscal injury, loose body, chondral flaps, osteoarthritis, cyst of menisci, or discoid meniscus [4, 10].
Ganglion cysts do not have a fixed set of common symptoms, and their symptoms may correlate with size and the location within the knee joint . Knee pain, clicks, stiffness, incomplete extension of the knee, and pain at the extremes of motion are common symptoms. Occasional findings include a palpable mass and bone erosion.
Imaging studies include plain X-rays to exclude pathologies such as a loose body or other bone abnormalities. Ultrasound (U/S), computed tomography (CT) scan, and arthrography are not very helpful examinations, and MRI is the most sensitive, specific, accurate, and noninvasive method for depicting cystic masses, including their size and location. In addition, MRI helps to exclude neoplastic lesions and to detect other intra-articular pathologies . The characteristic findings of a ganglion cyst include a fluid-filled lesion with low T1-weighted and high T2-weighted signal intensities in MRI . In histological sections, ganglia show a dense connective-tissue capsule with a thick jelly-like content. Microscopy shows a pseudocystic space with small multifocal areas of mucoid degeneration.
A variety of treatment modalities have been employed to treat intra-articular ganglion cysts of the knee. Spontaneous size reduction has been reported . Excellent results with percutaneous aspiration using U/S and CT guidance have also been obtained . Recently, the trend is for arthroscopic excision of intrarticular cysts [12, 13]. However, the recurrence of ganglia after arthroscopic treatment has been reported with cyst reformation . In such cases, the recurrence risk is high; therefore, patients should be followed up more carefully .
We believe that puncturing the lesion in an attempt to reduce its content reduces its volume but does not alter its margins. On the contrary, when the lesion collapses, it is very difficult to pinpoint the margins of the pseudocapsule extension, especially when an arthroscopy is performed for a lesion within the fat pad. Therefore, we believe that puncturing the lesion poses a high potential risk of recurrence. Of course, open excision of an infrapatellar fat pad ganglionic cyst does not nullify the recurrence risk, but given the literature data mentioned above, arthroscopic treatment of such lesions has high recurrence rates .
On the other hand, when an open procedure for a large ganglionic cyst of the knee has been decided upon, the preservation of an intact synovium should be the main consideration of the surgeon. Unfortunately, in our patient, the preservation of an intact synovium was inevitable because of the lesion's firm attachment to the capsule (Figure 5C). Our decision to carry on with an open excision of the ganglion lesion was based more on our pursuit for a complete resection of the lesion in order to diminish the recurrent rates and less on avoiding synovium invasion. The substantial defect of the synovium that was left after the complete resection of the ganglion was repaired by approximating the defect margins with interrupted sutures. The latter would be quite difficult with an arthroscopic procedure that primarily invades the synovium in order to excise such lesions.