The prevalence and characteristics of a subcortical cystic lesion at the subspinous region of the knee.

Background Although we observed that subcortical cysts near the attachment of the meniscus or cruciate ligaments are frequently seen with a tear or degeneration of the adjacent meniscus and/or cruciate ligament, there is no large study describing the prevalence, distribution, and associated findings of these cysts. Purpose To evaluate the prevalence and distribution of subcortical cysts near the attachments of the meniscus or cruciate ligaments and evaluate pathologies of the meniscus or cruciate ligaments using magnetic resonance imaging (MRI). Material and Methods We reviewed 1009 knee MRIs for the presence of subcortical cysts near the meniscus or cruciate ligament attachments and evaluated their size, location, edema of the adjacent bone marrow, and integrities of the medial and lateral meniscus and anterior and posterior cruciate ligaments. Results The 110 cysts were found in either the middle (n = 56), posterior (n = 52), or anterior (n = 2) subspinous regions. Sixty-two were at meniscal root insertion, including seven at the lateral meniscus anterior horn, five at the lateral meniscus posterior horn, 48 at the medial meniscus posterior horn, and two at the medial meniscus anterior horn. All were associated with an adjacent meniscal pathology. Of the 34 cysts at the anterior cruciate ligament (ACL) insertion, 28 had ACL pathology. Nine cysts had surrounding edema in the adjacent bone marrow. Conclusion Subcortical cysts at the subspinous region of the knee were seen in 9.6% of knee MRI examinations. Most were in close proximity to the meniscal or cruciate ligaments with associated pathologies, suggesting that abnormal stress on the bone induces cyst formation.