Disclosures: Stephen K. Anderson, MD: No financial relationships or conflicts of interest

Case Description: Obturator Internus Synovial Cyst Presenting as Chronic Right Buttock Pain

Setting: Outpatient sports medicine clinic

Patient: A 76-year-old male presented with one year of progressive, atraumatic pain in his right buttock. Assessment/

Results: The patient presented with chief complaint of chronic, progressive right buttock pain without any pain in his back or groin. The pain was focal, did not radiate, and became worse with prolonged sitting. He had tried a previous ischial bursa corticosteroid injection without any relief. On examination, he had tenderness to deep palpation over the right buttock at the level of the obturator internus. Hamstring provocative maneuvers including resisted extension produced pain. Manual muscle testing, range of motion and neurovascular examination were normal. Radiographic imaging revealed low-grade degenerative changes in bilateral hips. Magnetic resonance imaging (MRI) demonstrated a polylobulated fluid collection with thin peripheral enhancement located within the obturator internus along the posterior and medial aspect of the acetabulum and extended posterior to the right ischium and adjacent to the superior gemellus . The fluid collection was irregular in shape and “saddle-bagged” the obturator internus tendon; there was no communication with the hip joint. The decision was made to perform an ultrasound-guided cyst aspiration and corticosteroid injection. The patient tolerated the procedure well with significant reduction of pain at follow-up.

Discussion: Synovial cysts are fluid-filled lesions due to herniation of the synovial membrane through the joint. Synovial cysts of the hip joint are uncommon, often asymptomatic and incidentally found on MRI. The diagnostic imaging gold-standard is MRI, but ultrasound can also be used.

Conclusion: This case identifies a rare cause of hip pain that is easily amenable to diagnostic and interventional US, a much less invasive option than surgical excision. Physiatrists practicing musculoskeletal medicine should be aware of these cysts, the pertinent sonographic anatomy when considering interventions, and the role of surgical consultation.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/obturator-internus-synovial-cyst-presenting-as-chronic-right-buttock-pain/