A common finding in patients with hip impingement, or FAI, is a labral tear. Where there is a labral tear, there is frequently a paralabral cyst. In fact, cysts are seen on MRIs between 50-70% of patients with labral tears, but only 5% in the normal population (Shin et al., 2017). The association is so strong that the presence of a paralabral cyst can indirectly be used as a sign of a labral tear (Magee & Hinson, 2000). Many times these cysts do not cause pain, but for an unlucky few, it can press on neurovascular bundles and cause pain and paresthesia into the leg. It is not well understood, but it appears to be all about location. 

The cause of these cysts is unknown, but is commonly seen where there is injury. One line of thought is that a torn labrum allows for synovial fluid to “leak” causing a collection and a fluid filled sack. 

A symptomatic cyst will have the same pattern of pain as a labral tear. Pain with flexion, adduction, and internal rotation. Because of this position, hockey players are susceptible as well as anyone who is in a sustained flexed position. 

There is limited studies on paralabral cysts, and most are in the form of case reports. One case report described a patient that had a labral tear and a cyst about half the size of a penny on the back side of the joint. The patient was experiencing pain, and tingling down the leg, a.k.a. sciatica. All other pathologies were ruled out, and the patient had the cyst removed and the labrum repaired. It was considered a success and the patient was pain free following the surgery (Salunke & Panchal, 2014).

The good news is that most cysts of the hip occur towards the front of the hip and only 17% occur on the back side, near the sciatic nerve (El-Feky & Batta, 2021). So most of the time, they do not cause problems, but for the unlucky few, surgery or aspiration may be recommended. 

References:

Batta, N., & El-Feky, M. (n.d.). Paralabral cyst of the hip: Radiology Reference Article. Retrieved January 19, 2021, from https://radiopaedia.org/articles/paralabral-cyst-of-the-hip-1

Magee, T., & Hinson, G. (2000). Association of Paralabral Cysts with Acetabular Disorders. American Journal of Roentgenology, 174(5), 1381-1384. doi:10.2214/ajr.174.5.1741381

Salunke, A., & Panchal. (2014, July 21). A Paralabral Cyst of the Hip Joint Causing Sciatica: Case Report and Review of Literature. Retrieved January 19, 2021, from http://europepmc.org/articles/PMC4418116

Shin, K., Park, S., & Lee, W. (2017). Paralabral Cyst of the Hip Compressing Common Femoral Vein Treated with Sono-guided Cyst Aspiration Followed by Arthroscopic Labral Debridement: A Case Report. Hip & Pelvis, 29(3), 194. doi:10.5371/hp.2017.29.3.194