A 57-year-old woman was referred to the Orthopedic department due to chronic pain on her right knee and difficulty with knee extension. Physical examination revealed mild joint effusion, and tests for ligament or meniscal injury were negative. A magnetic resonance imaging (MRI) examination was performed for diagnostic purposes.
MRI of the right knee was performed using proton density (PD), with and without fat suppression, and T1-weighted (T1W) sequences. The examination revealed a multilocular cystic lesion interspersed within the anterior cruciate ligament (ACL) fibres, mostly on its posterior aspect, compatible with a large ACL ganglion cyst. The ligament’s fibres were intact, although abnormally thickened due to mass effect from the embedded ganglion cyst, with also signs of mucoid degeneration. The ganglion cyst showed growth anteriorly into the ACL tibial insertion, forming a small exophytic ganglion cyst posterior to the transverse intermeniscal ligament. Adjacent to the tibial insertion of the ACL, another intra-osseous ganglion cyst was detected, along with a substantial area of tibial bone marrow oedema. A large enchondroma was depicted on the distal femur, as well as supra-patellar recess joint effusion. There were no signs of ACL tear, and the posterior cruciate ligament and the menisci were unremarkable.
Background
Ganglion cysts are myxoid cystic lesions with a pseudomembrane and mucin-rich gelatinous content, arising from joint capsules, muscles or tendon sheaths [1-6,8]. Unlike synovial cysts, ganglion cysts do not communicate with the joint space [4]. The incidence of intra-articular ganglion cysts of the knee is below 1%, and 62% of them are located in the ACL [1,2,7]. Its pathogenesis is unclear, with current theories citing post-traumatic mucinous degeneration and embryogenic synovial herniation as possible causes [1,2,7-9].
Clinical perspective
The mean age of ACL ganglion cysts (ACLGC) is 39 years of age, being more common in men [1,7]. Many cases are incidental findings on MRI performed for other reasons [2].
ACLGC can be asymptomatic or present non-specific symptoms, including chronic knee pain, mechanical locking and difficulty in extreme knee movement [1,2]. Symptoms correlate with the size and position of the cyst, with posterior cysts limiting flexion and anterior cysts limiting extension [2,7,8].
Physical examination may reveal joint effusion and limitation of motion, but ACL stability tests are usually negative since associated ACL tear is rare [1].
Imaging perspective
Conventional radiographs and computed tomography (CT) have little diagnostic value for intra-articular ganglion cysts [1].
MRI is the gold standard examination, with optimal assessment of synovial and tendinous tissue [1,7]. ACLGC present as cystic lesions, with hypointensity on T1W images and hyperintensity in T2-weighted (T2W) and proton density images [1,3,7]. Hyperintensity on T1W can occur due to high protein or hemorrhagic content [3,5,7]. They can have a rounded, fusiform or spindle shape surrounding the ACL, or be interspersed within its fibers [1,2]. The ACL is intact from tibial to femoral insertion in most cases [1,9]. Accompanying intra-osseous ganglia have also been described in the literature [9].
It is also important to differentiate AGLGC from mucoid degeneration of the ACL. AGLGC usually presents fluid signal within the ligament substance, mass effect of the cystic components on ligament fibres, lobulated margins and ACL fluid disproportionate to joint fluid. Mucoid degeneration, on the other hand, normally shows an abnormally thickened and bulky ACL, with ligament fibres poorly seen on T1W images, but well seen on T2W images, with overall increased signal of the ligament on T1W and T2W images, but no cystic areas within the fibres. Both entities show normal integrity and continuity of the ACL fibres [1,9].
Outcome
Symptomatic cases of ACLGC can be treated with excision or puncture and aspiration, usually with arthroscopic surgery, although CT and ultrasound-guided aspiration have also been reported as successful [1,2]. Treatment allows for pain relief, improvement in knee movement and return to normal physical activity [1,7]. Recurrence of ACLGC has not been reported in the literature [1].
Take Home Message / Teaching Points
Intra-articular ganglion cysts of the knee are rare, affecting more commonly the ACL.
MRI is the gold standard examination for accurate diagnosis of ACL ganglion cysts.
Symptomatic ACLGC can be excised or aspirated with arthroscopic surgery, with optimal clinical results and no recurrence.
Written informed patient consent for publication has been obtained.
Large anterior cruciate ligament ganglion cyst with anterior exophytic and intra-osseous components.
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
1. MRI sequences (primarily T1-weighted and T2-weighted images) show a round to lobulated cystic lesion in the region of the right knee anterior cruciate ligament (ACL). On T1-weighted images, it appears as low or slightly high signal intensity. On T2-weighted images, it is high signal intensity with well-defined margins. A small amount of joint effusion is noted around the lesion.
2. The lesion is closely adjacent to or partially envelops the ACL fibers, but the overall continuity of the ligament is preserved without obvious signs of fiber rupture.
3. No evident fracture or destructive change of the cartilage surfaces or adjacent bone structures; the menisci appear generally intact without a clear tear signal; no obvious loose body is seen in the joint space.
4. Mild edema or exudative changes in the surrounding soft tissues, possibly related to chronic irritation or mild synovitis.
Based on the imaging characteristics and the patient’s clinical presentation, the following diagnoses or differential diagnoses are considered:
1. ACL Ganglion Cyst (intra-articular tendon sheath cyst or ganglion cyst): Commonly located near the ACL, appearing as a cystic lesion with low signal intensity on T1 and high signal intensity on T2, without disrupting the continuity of the ligament.
2. Mucoid Degeneration of the ACL: Usually presents as a diffuse thickening and abnormal signal within the ligament fibers, rather than a distinct cystic lesion. High signal changes are often uniform, without a clearly defined separate cystic structure.
3. Parameniscal Cyst: Often seen around the meniscus periphery or nearby; if the location and imaging appearance do not match, the likelihood is lower.
4. Other Cystic Lesions in the Knee: Such as synovial cysts or capsular protrusions, which often have more obvious communication with the joint space.
Considering the patient’s age, symptoms (chronic knee pain and difficulty fully extending the joint), physical examination findings (negative ligament stability tests), and the typical cystic high-signal lesion located near the ACL on MRI, the most likely diagnosis is:
An anterior cruciate ligament ganglion cyst (ACL ganglion cyst).
If further confirmation is required, arthroscopic exploration and simultaneous cyst removal or aspiration biopsy could be performed to confirm the nature of the lesion.
1. Treatment Strategies:
2. Rehabilitation and Exercise Prescription (FITT-VP principle):
Disclaimer: This report is for medical reference only and does not substitute for in-person consultation or professional medical advice. In case of any questions or changes in condition, please consult a qualified healthcare professional in a timely manner.
Large anterior cruciate ligament ganglion cyst with anterior exophytic and intra-osseous components.
