Recurrent pain in the right knee.
The patient, who was active in sport as an adult, presented with recurrent pain in his right knee.
Plain films showed non-specific changes of degenerative arthritis. MR was performed for further evaulation.
MR imaging revealed, in addition to joint effusion, a fluid intensity lesion in the region of the posterior cruciate ligament, which itself had a split in its fibres. The cyst extended both cranially and caudally. A diagnosis of a posterior cruciate ligament (PCL) cyst was made.
PCL cysts arise from the tibial insertion site of the PCL. The PCL is a primary stabiliser of the knee, resisting posterior translation of the tibia. The origin of the PCL is fan-shaped in a fossa in the posterolateral surface of the medial femoral condyle. The attachment is in a depression in the posterior tibia about 1cm below the articular surface. It is an intracapsular but extrasynovial structure. The ligament is posteriorly convex. There is a larger anterolateral band and a smaller posteriomedial band. PCL injuries are less common than those of the anterior cruciate ligament (ACL). The PCL ganglion cyst is a potential pitfall in the diagnosis of PCL injuries.
Intra-articular ganglion cysts of the knee are uncommon lesions, with a prevalence of 0.2-1.9%. They are usually associated with cruciate ligaments. They may be associated with the infrapatellar fat pad, but these are rarer. The aetiology of the cysts is unknown, although various causes have been postulated including herniation of the synovium and degeneration of connective tissue after trauma. Clinically, symptoms include localised pain (most common), joint tenderness, a palpable mass, clicking sensation and limitation of range of movement. Clinical significance depends on the size and location.
Plain radiography may show pressure erosion of the femoral condyles and is best seen on tunnel views. On CT an intercondylar soft tissue mass is seen in close proximity of the ligament. Ultrasound shows a hypoechoic cystic lesion. MR is the imaging modality of choice. Globular, well-defined, multiloculated (sometimes uniloculated) cysts are demonstrated on MR imaging, either located within the ligament or adjacent to it and with distortion from mass effect. The lesions exhibit homogeneously high signal intensity in relation to muscle on T2-weighted spin echo and STIR sequences. On T1-weighted images the cysts are hypo-iso intense to muscle. Cysts are posterior to the ligament, and can also extend anteriorly. The cysts may demonstrate a peripheral thin rim of enhancement, which is helpful in differentiating the cysts from other lesions. Contrast studies are indicated only to differentiate from other lesions.
Differential diagnosis includes pigmented villonodular synovitis, synovial chondromatosis, meniscal cyst, synovial haemangioma, and synovial sarcoma. Except for meniscal cysts all other entities have a characteristic appearance on MR imaging. Mensical cysts (pericruciate cysts) are in close contact with horizontal tears of the underlying meniscus, and a communicating channel is seen between the cyst and the meniscus. PCL cysts rarely communicate with the joint. Meniscal cysts begin posterioinferior and extend upward (mainly posterior to the location of PCL cysts) and may surround the ligament. PCL cysts are more often located at the insertion of the PCL. ACL cysts are more fusiform in shape.
If the cyst requires treatment, it is often performed arthroscopically. Percutaneous aspiration has also been successful.
Posterior Cruciate Ligament Ganglion Cyst
The MRI of the patient's right knee shows a well-defined, relatively homogeneous cystic lesion near the posterior cruciate ligament (PCL) and its attachment point. On T2-weighted and STIR sequences, it appears as a high-intensity lesion, while on T1-weighted images it is slightly low or isointense to muscle. The lesion often appears lobulated or septated, located near the posterior cruciate ligament, and may mildly compress surrounding soft tissues. Currently, there is no clear evidence of ligament fiber disruption or bony destruction on imaging. A thin ring enhancement may be visible around the lesion (if contrast enhancement is performed), suggesting mild enhancement of the cyst wall. Overall, these imaging characteristics are consistent with a cystic lesion within the knee joint.
Considering the patient is a 55-year-old male with recurrent right knee pain, and the MRI shows a localized cystic lesion at the posterior cruciate ligament attachment with signal characteristics of an intra-articular cystic lesion, the most likely diagnosis is a PCL cyst. If further exclusion of less common synovial pathologies is necessary, clinical correlation and possible arthroscopic evaluation or additional enhanced imaging could be considered.
The rehabilitation process should be tailored to the individual’s joint function and condition to avoid reinjury and facilitate functional recovery. The FITT-VP principle (Frequency, Intensity, Time, Type, Volume, Progression) is recommended.
Throughout rehabilitation, adjust for individual factors (such as bone health, cardiovascular capacity, previous joint injuries, etc.), and monitor knee pain, swelling, and function. If notable discomfort or joint effusion increases, reduce exercise frequency or modify exercise types.
Disclaimer: This report is based on available imaging and clinical information and is intended for reference only. It does not replace an in-person consultation or the diagnosis and treatment recommendations of a qualified medical professional. If you have any questions or changes in your condition, please seek medical advice promptly.
Posterior Cruciate Ligament Ganglion Cyst
