Age / Sex : 60 / M

Chief complaint :

Numbness in lateral aspect of left lower leg and foot dorsum + footdrop

Discussion

Answer:  

Intraneural ganglia

Findings:

Multilobulated cystic lesion adjacent to the proximal tibiofibular joint extending along the course of deep peroneal nerve articular branch and common peroneal nerve is seen.

Increased signal intensity of left tibialis anterior muscle represents denervation edema in the anterior compartment muscle.

Differential Diagnosis:

Extraneural ganglia

Cystic nerve sheath tumors

Discussion:

Intraneural ganglia are non-neoplastic cysts that are contained within the epineurium of peripheral nerves. Many nerves are affected by these cysts, but the common peroneal nerve at the fibular neck is by far the most frequent site. Numerous explanations have been proposed for the pathogenesis. According to the unifying articular theory, fluid from the synovial joints dissects intraepineurally from the joint via articular branches perforating the joint capsule along a path of least resistance.

 For intraneural ganglia of peroneal nerve, three signs on axial MRI have been described as follows;

• Transverse limb sign: cyst within the articular branch as it cross over the anterior surface of the fibular neck; and the “ signet ring ” sign,

• Signet ring sign: eccentric cyst within the outer epineurium of the common peroneal nerve

• Tail sign: a cystic connection between the articular branch of the common peroneal nerve and the joint.

For treatment of intraneural ganglia, decompression of the cyst through a limited epineurotomy along with disconnection of the articular branch (to eliminate intraneural recurrences) can be performed.

References:

Robert J. Spinner et al. Skeletal Radiol (2008) 37:1091 – 1099

Robert J. Spinner et al. J Neurosurg 2003; 99: 330 – 343