To our knowledge, there have been only two reported cases of large acetabular paralabral cysts causing sciatica1,2 and none reported in the English-language orthopaedic surgical literature.
Sciatica is defined as pain experienced along the sciatic nerve distribution. It is most commonly caused by a herniated disc or spinal stenosis3. Extraspinal pathology associated with symptoms and signs of sciatica is infrequent.
Synovial cystic lesions are commonly found in large joints, such as the shoulder, knee, and hip. Such lesions, when occurring in the hip and shoulder joints, are often associated with labral tears and are known as labral or paralabral cysts according to their anatomical relationship with the joint1,4.
In the hip, tears of the labrum can cause loss of congruity between the femoral head and the acetabulum, thus leading to increased intra-articular pressure. This elevated pressure can force synovial fluid into the acetabulum or the surrounding soft tissues, causing a paralabral cyst. These cysts can produce joint instability and pain5,6.
There have been many reports of juxta-articular cysts causing compression of adjacent neurovascular structures. Glenoid paralabral cysts of the shoulder have been reported to be associated with compression of the axillary and suprascapular nerves7, elbow or wrist ganglia have been associated with radial nerve compression8 or ulnar nerve compression in the cubital tunnel9, and large paralabral cysts, which are much less common than other cysts and occur around the hip joint, have been associated with compression of the vascular and neurological structures, such as the femoral vein and artery10,11 and the sciatic nerve1.
In this case report, we present a patient who had a paralabral cyst and associated symptoms and signs of sciatic nerve compression. The patient was informed that data concerning the case would be submitted for publication, and he consented, and approval from the institutional review board was obtained.
A thirty-eight-year-old man presented to our spinal unit with a four-year history of gradually worsening pain in the lower back, radiation of the pain down both lower limbs, and intermittent paresthesias. These symptoms began following an automobile accident. He was otherwise in good health. After having undergone several years of conservative treatment that included anti-inflammatory medication and physiotherapy, the patient was referred to the spinal team at our institution.
A clinical diagnosis of sciatica was made, and a magnetic resonance imaging scan of the lumbar and sacral spine was acquired. The magnetic resonance imaging scan of the lumbar spine showed a posterior-central prolapse of the disc between L4 and L5, with narrowing of the thecal sac on the left side. The sacroiliac joints and the disc between L3 and L4 as well as the disc between L5 and S1 were normal.
The patient was given an epidural injection of steroid medication, which temporarily relieved the pain in the back and left lower limb but did not relieve the pain that radiated down the right lower limb. A repeat magnetic resonance imaging scan of the lumbar spine and sacroiliac joints was acquired twelve months later. Although the newer scan showed no further changes in the spine, it did reveal a large cystic lesion just posterior to the right acetabulum. This lesion could not be evaluated in detail because it was at the edge of the field of view.
The patient was then referred for evaluation of the hip. He had deep gluteal pain that radiated down the right lower limb, which made walking very painful. On physical examination, the patient had a positive result (starting at 25° to 30°) on the straight-leg-raising test, no pain on abduction, and normal motor, sensory, and reflex function in the lower limb.
A more detailed magnetic resonance imaging scan of the pelvis was acquired, which confirmed the presence of a 5.8 × 2.2 × 3.8-cm multilobulated mass deep to the right gluteus maximus muscle and inferior to the piriformis muscle. The mass had internal lobularity and septations, with the tail proceeding anteriorly to the region of the posterior aspect of the right labrum (Fig. 1). The sciatic nerve was seen to cross the anterior aspect of the lesion. We concluded that this multilobulated, cystic structure was most likely a posterior paralabral cyst and the cause of the sciatica. No obvious damage to the labrum was seen on the scan. We recommended to the patient that he undergo excision of the cyst.
A posterior approach to the hip was used, but the insertions of the short external rotators were preserved. The large cystic lesion was found and was noted to be compressing the right sciatic nerve. The lesion was aspirated, and 15 mL of straw-colored fluid was removed. The sciatic nerve was identified proximally and distally, and the cyst was carefully dissected from it (Fig. 2). A benign, fibrous-walled cyst, largely devoid of lining epithelium, was identified on histological examination of the specimen (Fig. 3).
Postoperatively, the patient noted improvement in pain almost immediately. By one week after the operation, there was little pain at the surgical site, no symptoms or signs of sciatica, a full range of hip movement, and no neurological deficit. At the six-week follow-up, the patient's symptoms had completely resolved.