A Giant Atypical Baker’s Cyst Causing Compressive Neuropathy of Combined Peroneal and Tibial Nerves - A Case Report

INTRODUCTION: Popliteal cysts (Baker cysts) causing compressive neuropathy of combined tibial and common peroneal nerves is an exceptional entity. Especially, an isolated multi-septate unruptured cyst (usually posteromedially) dissecting posterolaterally, thereby causing compression of multiple components of the popliteal neurovascular bundle as seen in this case report is unique in clinical field and in the literature. Awareness and early diagnosis of such cases along with a prudent technique will preclude permanent impairment. CASE REPORT: A 60-year-old man with a 5-year history of a symptomless popliteal mass in his right knee was hospitalized with aberrant gait and walking difficulty that had deteriorated during a 2-month period. The patient reported hypoesthesia across the sensory innervations of tibial and common peroneal nerves. Clinical examination indicated a prominent painless and unfixed cystic, fluctuant swelling extending around 10 × 7 cm in the popliteal fossa encroaching into the thigh. Motor examination showed decrease in the power of ankle dorsiflexion, plantar flexion as well as inversion and eversion of the foot resulted in progressive difficulty in walking with high stepping gait. The action potential amplitudes of the right peroneal and tibial compound muscles were dramatically decreased with a drop in motor conduction velocities and a prolonging of the F-response latencies, according to nerve conduction studies. Magnetic resonance imaging of the knee showed a multi septate popliteal cyst measuring 13.8*6.5*6.8 cm along the medial head of gastrocnemius, and the T2-weighted sagittal and axial sections revealed the cyst connecting with the right knee. He was planned and undergone open cyst excision with decompression of the peroneal and tibial nerves. CONCLUSION: This exceptional case establishes that Baker’s cyst very rarely can cause compressive neuropathy vandalizing both the common peroneal and tibial nerves. Excision of the cyst by open technique along with neurolysis may be a more judicious and successful strategy for resolving symptoms quickly as well as to prevent permanent impairment.