ACL Ganglion: Definition and Etiology
An ACL ganglion is a cystic swelling that arises from or adjacent to the anterior cruciate ligament, typically filled with gelatinous fluid, and small ones are generally benign findings that rarely require intervention unless symptomatic. 1, 2
What is an ACL Ganglion?
ACL ganglia are cystic formations that develop close to or within the substance of the anterior cruciate ligament, representing rare intra-articular lesions of the knee 1, 2
These cysts contain gelatinous or mucinous fluid and have a synovial-like lining on histological examination 2
Intra-articular ganglia of the knee are uncommon, with the anterior cruciate ligament being the most frequent location when they do occur 1, 2
The cysts can be intraligamentous (within the substance of the ACL) or extraligamentous (adjacent to the ACL), with intraligamentous variants being extremely rare 3
Causes of Small ACL Ganglia
Trauma-Related Factors
Some patients report a history of knee trauma, though this is not universally present and the exact causal relationship remains unclear 1
The mechanism may involve microtrauma or degeneration of the ligament tissue leading to mucoid degeneration and cyst formation 2
Non-Traumatic Etiology
Many cases occur without any history of trauma, suggesting that repetitive stress or degenerative processes may play a role 4, 3
The exact pathogenesis remains uncertain, but theories include mucoid degeneration of connective tissue, synovial herniation, or developmental variants 2
Clinical Significance of Small ACL Ganglia
When Small Ganglia Are Not Concerning
Asymptomatic ganglia discovered incidentally on MRI do not require surgical treatment 2
Small cysts that cause no pain, mechanical symptoms, or range of motion limitations can be observed conservatively 2
When to Be Concerned
Symptomatic ganglia warrant intervention, particularly when causing pain, movement restrictions, clicks, locking, or limitation of knee extension or flexion 2, 4
Larger cysts (>1.5 cm) are more likely to cause symptoms due to mechanical impingement, though even large cysts can be asymptomatic 4
Extension anteriorly can impinge on the intercondylar notch roof during knee extension, restricting extension, while posterior extension can restrict flexion 4
Diagnostic Approach
MRI is the investigation of choice for diagnosis, showing fluid-filled cysts with low T1-weighted signal intensity and high T2-weighted signal intensity 5, 3
Physical examination findings are non-specific, with pain and range of motion limitations being the most common presentations when symptomatic 2, 3
Arthroscopy confirms the diagnosis and allows for simultaneous treatment if indicated 2, 3
Management of Small ACL Ganglia
Observation is appropriate for asymptomatic small ganglia discovered incidentally on imaging 2
Arthroscopic excision and debridement is the treatment of choice for symptomatic ganglia, with good to excellent results in the vast majority of cases 1, 2
Complete excision of the cyst provides the best outcomes, with patients typically resuming normal activities within 3-5 months 2, 4