ACL Ganglion Cyst, Meniscal Cyst, Baker Cyst - Everything You Need to Know
Written by Ali Mahmoud with Dr. Nabil Ebraheim
There are many cysts that can occur in and around the knee joint. These types of cysts include an anterior cruciate ligament (ACL) ganglion cyst, meniscal cyst, and baker’s cyst.
Ganglion cysts contain yellow viscous fluid surrounded by a thin capsule, and are considered rare when associated with the ACL (1). Theorized pathogenesis of an ACL ganglion cyst includes synovial tissue herniation, post-traumatic mucoid degeneration mediated by local release of hyaluronic acid, ectopic synovial tissue theory, and displacement of synovial fluid during embryogenesis. These cysts are often discovered during knee MRI or knee arthroscopy while evaluating symptoms of knee pain or limited knee motion. There are no defining symptoms of ACL ganglion cysts, but they should be suspected in patients with knee pain or limited range of motion in their knees. MRI’s are the gold standard for diagnosing ACL ganglion cysts, with the diagnostic criteria being a fluid signal in the substance of the ligament with two of the following three criteria: 1) mass effect on ACL fibers, 2) lobulated margins, and 3) ACL fluid disproportionate to the joint. The treatment of choice for an ACL ganglion cyst is an arthroscopic decompression with debridement of the cyst for instant relief of pain, range of motion improvement, and return to physical activities. In cases where arthroscopic decompression is not available, aspiration under CT or ultrasound have shown excellent results in treating these cysts. These cysts do not recur after resection (2).
Meniscal cysts are believed to occur when the meniscal fibrocartilage tears, allowing synovial fluid to extrude through the meniscal tear and become encysted. Meniscal cysts can be classified into 3 subtypes: parameniscal, intrameniscal, and synovial. Parameniscal cysts appear on MRI as a loculated fluid-intensity lesion with a clear connection to the adjacent meniscus (4). Intrameniscal cysts appear as an abnormally increasing signal within an enlarged meniscus. Synovial meniscal cysts are cystic outpouchings of the joint capsule that are not associated with trauma. They are frequently asymptomatic, and are found incidentally on MRIs performed to assess for other knee pathologies. Symptomatic meniscal cysts can be treated with arthroscopic resection and repair of the causative meniscal tear (3).
Baker’s cyst (popliteal cyst) is the most common cyst in the knee (3). These are fluid-filled lesions arising in the popliteal fossa as an enlargement of the gastrocnemio-semimembranosus bursa. These cysts can expand into the spaces between muscle and knee capsule. Rarely, they can extend into nearby muscles such as the vastus medialis muscle and the head of the gastrocnemius muscle (6). Complications of a Baker’s cyst include rupture, hemorrhage and infection. Most Baker’s cysts are asymptomatic, but larger ones may cause nerve entrapment, compress nearby veins, or limit knee range of motion (3). Cysts that rupture can cause symptoms similar to phlebitis (5). They can be visualized on MRI along with any associated pathology that is causing the cyst, such as arthritis or meniscal tear. They can be treated conservatively with rest, ice, and anti-inflammatory medications. They can also be treated with aspirations, steroid injections or surgical excisions. If an intra-articular pathology is present that is causing the cyst, then treatment with arthroscopy and debridement of the pathology is recommended to prevent recurrence of the Baker’s cyst.
Citations
1. Plotkin B, Agarwal VK, Varma R. Ganglion Cyst of the Anterior Cruciate Ligament. Radiology Case Reports. 2009;4(3):1-4.
2. Vaishya R, Esin Issa A, Agarwal AK, Vijay V. Anterior Cruciate Ligament Ganglion Cyst and Mucoid Degeneration: A Review. Cureus. 2017 Sep 13;9(9):e1682. doi: 10.7759/cureus.1682. PMID: 29152439; PMCID: PMC5679775.
3. Telischak NA, Wu JS, Eisenberg RL. Cysts and cystic-appearing lesions of the knee: A pictorial essay. Indian J Radiol Imaging. 2014 Apr;24(2):182-91. doi: 10.4103/0971-3026.134413. PMID: 25024531; PMCID: PMC4094974.
4. Crowell MS, Westrick RB, Fogarty BT. Cysts of the lateral meniscus. Int J Sports Phys Ther. 2013 Jun;8(3):340-8. PMID: 23772349; PMCID: PMC3679639.
5. Handy JR. Popliteal cysts in adults: a review. Semin Arthritis Rheum. 2001 Oct;31(2):108-18. doi: 10.1053/sarh.2001.27659. PMID: 11590580.
6. Li TY. The Sonographic Spectrum of Baker Cysts. Journal of Diagnostic Medical Sonography. 2017 Sep 9;34(1):38-48. doi: 10.1177/8756479317733750.
