Compression Neuropathy of Common Peroneal Nerve Caused By a Popliteal Cyst: A Case Report
Xiaobin Zeng, MD, Lifeng Xie, MD, Zhiqiang Qiu, MD, Kuo Sun, MD, PhD
Medicine (Baltimore). 2018 Apr; 97(16): e9922.
JACO Editorial Reviewer: Joseph F. Ferstl, DC, FACO
Published: September 2018
Journal of the Academy of Chiropractic Orthopedists
September 2018, Volume 15, Issue 3
The original article copyright belongs to the original publisher. This review is available from: http://www.dcorthoacademy.com ©2018 Ferstl and the Academy of Chiropractic Orthopedists. This is an Open Access article which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Approximately 37 years ago the first report regarding the synovial cysts was written by Bamzai relating the cyst to chronic rheumatoid arthritis and later Baker called the synovial cyst in the leg a Bakers cyst.
The astute physician needs to understand the difference between a simple Bakers cyst or popliteal cyst in the posterior popliteal fossa versus a Bakers cyst or popliteal cyst that also encompasses the common peroneal nerve and causes compression at the lateral aspect of the head of the fibula. It is rare that a popliteal cyst will cause extra neural compression of the common peroneal nerve and cause serious complications. Compression neuropathy of the common peroneal nerve caused by a popliteal cyst is very rare. The paper goes on to state that a consultation with a patient which whom experienced lower leg numbness sensation especially over the lateral aspect of the left calf and the dorsum of the foot with no apparent weakness and pain noted. The patient denied any apparent history of trauma to the left calf. A positive Tinel sign was incited with tapping of the mass. There was no apparent muscle atrophy of the lower extremities on either side and neurological examination showed hypoesthesia over the dorsum of the left foot and the lateral aspect of the left calf with normal knee joint motion. It was determined a surgical procedure was required to remove the popliteal cyst and it was found encased in about 6 cm of the left common peroneal nerve at the level of the fibula.
Conclusions: A popliteal cyst can compress various anatomical structures which would include synovial, meniscal, and ganglion cysts. The most frequent synovial popliteal cyst is generally considered to be a distension of the bursa.
Discussion or Conclusions: It is necessary to rule out a typical popliteal cyst from an extra neural popliteal cyst which is rarely encountered. This type of cyst is often related to a history of knee trauma and can cause entrapment of the peroneal nerve, part of the sciatica nerve.
Diagnosis: Standard plain film radiographs are of little use in demonstrating soft tissue lesions. Ultrasound may be useful in showing the cystic nature of the mass, but MRI can show in much better detail their size and internal contents as well as their relation with surrounding anatomical structures. The final diagnosis is established through aspiration of the popliteal mass which is much easier when the swelling is large. Generally surgical excision should be reserved only for those cases where more conservative interventions have failed and where there is significant functional impairment that can be ascribed to the cysts.
JACO Editorial Summary:
The purpose of this study was to demonstrate that a common peroneal nerve compression is rarely caused by an extra neural popliteal cyst, but astute physicians should keep in mind the difference between a true sciatica arising out of the lumbar spine versus nerve entrapment extra neural popliteal cyst.