Introduction

71-year old male patient with PMH of knee OA and lower back pain with remote history of left sided

sciatica in the past who presented with acute right sided lower extremity pain from knee to shin/ankle

with associated right ankle dorsiflexion weakness. Initial visit diagnosed peroneal nerve cyst with

ultrasound guidance and treated with aspiration in two different visits with 90% resolution in 3 weeks.

Our case proves the importance of utilizing point of care ultrasound exam for diagnosis and treatment

of peripheral nerve pathologies such as ganglion cyst in timely manner with full recovery of the nerve

damage resulting pain relief and motor recovery.

Materials and Methods

As the case report is devoid of patient identifiable information, it is exempt from IRB review requirements as per Faith

Regional Health Services policy.

Results/Case Report

71-year-old male patient with PMH of knee OA and lower back pain with remote history of left sided sciatica in the past

who presented with acute right sided lower extremity pain from knee to shin and ankle with associated right ankle

dorsiflexion weakness started about four weeks ago. Patient denies any history of trauma to the right lower extremity.

MRI of the knee a year ago demonstrated advanced tricompartmental OA with large baker's cyst in Jan, 2024. Patient

was referred to our clinic for an evaluation and treatment of acute right lower extremity pain to rule out RLE

radiculopathy. Patient tried anti-inflammatories, heat & ice and physical therapy with minimal relief. Physical

examination demonstrated right knee varus deformity, tinel's sign was positive over peroneal nerve at the dorsal

fibular head, right ankle dorsiflexion strength was 3/5, straight leg raises or seated slump tests were negative

bilaterally with functional lumbar spine ROM; gait demonstrated steppage gait on the right side. Point of care limited

ultrasound exam was performed and large ganglion cyst encompassing the peroneal nerve sized at 3 x 4 cm at the

knee level was detected. Superficial peroneal nerve cyst was aspirated under ultrasound guidance and 3 cc straw

colored dense aspirate was obtained. Patient was scheduled follow up visit in two weeks. Eleven days later, patient

showed significant improvement in strength with ongoing slight numbness and electric-type pain at the right shin.

Repeat USG exam demonstrated 1 x 1 cm cyst noted around the peroneal nerve at the knee level and aspiration

under USG guidance was performed which obtained 1 cc straw colored dense aspirate. Patient called the clinic a

week later with 90% resolution of his symptoms.

Discussion

Our case demonstrates the importance of diagnosing a peroneal nerve ganglion cyst and treating it in

timely manner with almost full recovery in three weeks. Patient could have been ordered knee and

lumbosacral MRIs to rule out radiculopathy vs peroneal nerve pathologies with subsequent nerve

conduction studies/EMGs which could have taken many weeks while patient is losing further muscle

strength and advanced nerve damage that would have prolonged the recovery dramatically even

treatment was performed at a later time.

Utilizing MSK ultrasound in pain clinics is very important and useful to help patients and treat

pathologies right away to provide instant relief and prevent further complications. It is also cost effective

compared to MRI, NCS/EMG and further referrals such as orthopedic surgery. Our case proves the

importance of utilizing USG in pain medicine practice to offer patients accurate and faster diagnosis and

treatment plan.

References

1-Ultrasound-guided treatment of common peroneal neuropathy caused by Baker's cyst: a clinical note -

A case report; Hana Cho, Dong-Rim Kim, Je Jin Lee, Seung Young Lee, Yong Bum Park, Hee Sung Kim,

Hwa-Yong Shin.

2-Compression neuropathy of common peroneal nerve caused by a popliteal cyst: A case report

Xiaobin Zeng, Lifeng Xie, Zhiqiang Qiu, Kuo Sun.

3-Ultrasound-guided aspiration and injection of an intraneural ganglion cyst of the common peroneal

nerve Teresa Liang, Anukul Panu, Sean Crowther, Gavin Low, Robert Lambert.