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Internal Medicine

Training Level

Resident PGY 1


Henry Ford Hospital


A 46 year old male with a past medical history of HTN and chronic pancreatitis presented to clinic with a chief complaint of right leg weakness and numbness/tingling that developed suddenly two months prior to presentation. He denied history of trauma or surgery to the right lower extremity. Physical exam revealed a right foot drop on ambulation with slight circumduction of right leg. Further neurological exam was remarkable for 2/5 muscle strength in right ankle dorsiflexion and eversion, with decreased sensation noted on right foot dorsal surface and lateral calf. EMG demonstrated a right common peroneal mononeuropathy at the knee with demyelinating and axonal features with active denervation. Ultrasound of the right knee showed enlargement of the right common peroneal nerve at the level of the fibular head with a1.1 x 0.5 x 1.6 cm hypoechoic collection in the region of the tibiofibular joint, possibly representing a ganglion cyst from the adjacent joint or an intraneural ganglion cyst. Follow-up MRI re-demonstrated a cystic lesion just medial to the common peroneal nerve and posterior to the proximal tibiofibular joint, which is suspected to arise from the articular branch of the common peroneal nerve. Patient had symptomatic improvement with physical therapy and use of a AFO boot for 2 months. The most common cause of foot drop is a compression peroneal neuropathy, often at the location of the neck of the fibula. In rare instances, the compression can occur due to a ganglion cyst, which is a benign tumor consisting of gelatinous material that is typically asymptomatic. Ganglion cysts compressing the peroneal nerve can be either intraneural or extraneural, with differentiation occurring via imaging. Intraneural ganglion cysts are non-neoplastic mucinous cysts located within the epineurium of a nerve. Although the exact pathogenesis of these cysts are unknown, it has been show in multiple case reports that as these cysts expand within the epineurium, they can cause compression of the adjacent nerve fascicles. Diagnosis is primarily via MRI; although an EMG study may assist in correlating clinical findings by distinguishing the extent of sensory and motor impairment. Treatment guidelines of peroneal intraneural ganglia are controversial. Current first line treatment recommendations endorse surgical removal of the ganglion cyst; however, it may be less invasive and beneficial to start with a conservative approach to minimize unwarranted procedures in patients. Ultimately, successful outcomes are based on early diagnosis and treatment.

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An Intraneural Ganglion Cyst causing Foot Drop: A Case Report