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Ki Hong Won1*†, Na Na Lim1, Geun Su Lee1, Sung Hoon Lee1, Youn Kyung Cho1, Hyun Kyung Lee1*†, Eun Young Kang1, Jin Sun Kang1, Young Ryul Jung1 |
Introduction
Popliteal synovial cysts (Baker's cysts) usually develops in the posteromedial popliteal fossa, therefore spares neurovascular bundles, but occasionally migrate posterolaterally cause compression of one or more components of neurovascular bundles, resulting thrombophlebitis, arterial compression, tibial or sciatic neuropathy, and rarely common peroneal neuropathy.
We report a case of Baker's cyst compressing of the common peroneal nerve(CPN) sparing tibial nerve.
Case
A 46-year-old man was hospitalized with Rt. foot drop for 1 month. He complained that he went near to fall down due to foot drop and decreased sensation & tingling on lateral aspect of leg and dorsum of the foot in Rt. side. Manual muscle testing revealed 1/5 in extension of ankle and toes.
Ultrasound examination demonstrated hypoechoic and edematous CPN compressed by a cystic lesion measuring 2x1cm in posterolateral side of knee. For decompression of the nerve, 2cc of gelatinous materials was aspirated from the cyst under guidance of ultrasound.
figure 1. ultrasonography of Right common peroneal nerve
Electrodiagnostic study revealed incomplete common peroneal nerve lesion.
Electrical stimulation and strengthening exercise of muscles innervated by CPN were applied and a posterior leaf spring ankle foot orthosis was prescribed to compensate weak dorsiflexion of ankle.
After rehabilitation for 4wks, the strength of Extensors of ankle and toe had improved to grade 3+/5 in manual muscle testing. However, The follow-up ultrasound examination revealed the cystic lesion growed back and was about to compress CPN again.
Magnetic resonance imaging was undergone and showed compression of the CPN by the cyst mass with narrow and long stalk which stretched out posteolaterally from middle popliteal fossa. figure 2. MRI views(sagittal,coronal, and axial) of the knee rvealing a hyperintense fluid collection near common peroneal nerve
He was referred to a orthopedic surgeon for resection of the cyst to prevent recurrence of compression of CPN. The cyst compressing CPN with long stalk measuring 4cm was detected through posterior approach and removed completely, which was confirmed as synovial cyst pathologically. figure 3. synovial cyst is seen at near common perneal nerve and cross-section of resected synovial cyst.
At 4 weeks after operation, the strength of muscles innervated by CPN improved to grade 4/5 and he could walk safely without PLS AFO.
Conclusion
Acute compressive neuropathy of the CPN can be caused by various causes such as intraoperative injury, trauma, stretch, and extrinsic or intrinsic masses, but rarely by a Baker's cyst. In spite of improvement of neurologic symptoms after aspiration of cystic content, operative resection might be needed to prevent neurologic deterioration ,considering tendency of recurrence caused by anatomical characteristics of Baker's cyst connecting with synovial joint.
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