Paralabral cyst of the hip

Paralabral cysts of the hip joint are a location specific subtype of paralabral cysts. They are predominantly small, sometimes septate, well-defined multiloculated fluid intensity lesions seen closely associated with acetabular labral tears. Their presence requires a thorough search for a labral tear which may be missed as non-arthrographic MRI imaging may look deceivingly normal.

Some authors have divided these as cysts that directly communicate with the synovial fluid of hip joint (true paralabral cysts) and those that do not (perilabral cyst). They may be confused with small bursal fluid collections around the hip joint, however, 90% of cystic lesions lateral to the iliopsoas are paralabral cysts.

Epidemiology

Usually seen in 1-4% of the asymptomatic population and in 50-70% of patients with labral tears. They are more common in males.

Clinical presentation

• anterior hip pain
• restriction of rotatory movements
• painful flexion at the hip
• snapping sensation

Pathology

Paralabral cysts are seen at multiple joints, commonly at hip and shoulder, and less commonly at knee and wrist.

Commonly seen with labral tears which occur due to:

• developmentally dysplastic hips
• trauma which includes overuse ie, sports injuries
• degenerative arthrosis of the hip.

It is thought that incongruity of the femoral head with acetabulum causes increased intraarticular pressure especially during flexion and rotatory movements of the hip joint, which forces the synovial fluid through the pathological labrum into the periarticular soft tissues.

Size

Their usual size range is around 3-30mm.

Location

Most are located anterosuperiorly: ~ 56% ⁴, other locations include:

• anteriorly: ~ 22%
• posterosuperiorly: ~ 17%
• anteroinferiorly: ~ 6%

Radiographic features

Plain radiograph

Plain radiographs have limited value but may detect other associated bony pathologies.

Ultrasound

Ultrasound is helpful in cysts larger than 1.5 cm but gives little information about the labrum.

MRI

MRI with MRI arthrography is the modality of choice to detect paralabral cysts and delineate labral tears, hip dysplasia, signs of trauma and degenerative changes.

The vast majority are seen as multilocular cysts and fill with intra-articular contrast medium.

• T2 / STIR - high signal

Treatment and prognosis

Cysts may be aspirated but recur commonly. The definitive treatment is to surgically excise the cyst with arthroscopic labral repair.  Arthroscopic cyst decompression and debridement of the degenerative labral tissues were performed using an arthroscopic thermal probe and a shaver is an effective surgical method of management.