Common Peroneal Neuropathy



  • Synonyms: Common peroneal nerve (CPN) palsy, CPN entrapment

  • CPN entrapment at fibular head


  • CPN swelling, abnormal T2 hyperintensity

    • Fascicular architecture preserved in milder cases (neuropraxic injury)

    • Loss of internal fascicular architecture in more severe cases (axonotmetic, neurotmetic)

Top Differential Diagnoses

  • Ganglion cyst

  • Viral neuritis

  • Nerve sheath tumor

  • Direct acute CPN trauma


  • Usual etiology is entrapment or sequelae of continued pressure on CPN at fibular head level

  • Edematous/indurated CPN ± thickened “fibular tunnel” at surgery

Clinical Issues

  • Foot drop, sensory abnormality along anterolateral leg

  • Prognosis variable; frequently good recovery following conservative management

  • Surgical decompression reserved for recalcitrant cases

Diagnostic Checklist

  • Focal CPN enlargement, abnormal T2 hyperintensity at fibular head suggests CPN neuropathy

  • MR imaging more sensitive for detecting acute than chronic nerve injuries

  • Electrodiagnostics (EMG/NCS) can help localize and detect chronicity

Coronal graphic depicts the normal course of the common peroneal neuropathy (CPN). The sciatic nerve
branches into the tibial nerve
(shown behind the femur) and the CPN
, which courses around fibular head.

Axial T1WI MR demonstrates atrophy and fatty infiltration of the right anterolateral compartment muscles
innervated by the CPN. Mild fascicular enlargement within the right CPN
is not as conspicuous on T1WI as it is on T2WI FS MR or STIR MR.

Axial T2WI FS MR (same patient) reveals abnormal T2 hyperintensity in some anterolateral compartment muscles
, confirming ongoing denervation superimposed on chronic denervation. The right CPN
is mildly enlarged, with swollen, hyperintense fascicles.

Axial STIR MR confirms abnormal T2 hyperintensity in some anterolateral compartment muscles
. The CPN
shows mild enlargement and abnormal signal intensity with preservation of intrinsic fascicular architecture.



  • Common peroneal nerve (CPN) palsy, CPN entrapment


  • Common peroneal nerve entrapment at fibular head


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