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Sural nerve

The sural nerve is a superficial sensory nerve of the lower leg that provides cutaneous innervation to the posterolateral aspect of the distal leg, lateral heel, ankle, and foot. It is formed by the union of branches from the tibial nerve and common fibular (peroneal) nerve, making it an important sensory pathway for the lateral lower limb and foot.

Because of its superficial course behind the lateral malleolus, the sural nerve is prone to injury, entrapment, or iatrogenic trauma during Achilles tendon repair, ankle surgery, or external fixation procedures. It is frequently evaluated on imaging in cases of neuropathy, trauma, or nerve sheath tumors.

Synonyms

  • Short saphenous nerve

  • N. suralis

  • External saphenous nerve

Origin, Course, and Termination

  • Origin: Formed by the union of the medial sural cutaneous nerve (from the tibial nerve) and the sural communicating branch (from the common fibular nerve).

  • Course: Descends in the posterior compartment of the leg, lying superficially between the heads of the gastrocnemius muscle; continues along the lateral aspect of the Achilles tendon and passes posterior to the lateral malleolus.

  • Termination: Ends as the lateral dorsal cutaneous nerve, supplying the lateral side of the foot and the fifth toe.

Relations

  • Superiorly: Posterior aspect of the calf, between gastrocnemius and soleus muscles

  • Inferiorly: Superficial fascia near the Achilles tendon

  • Posteriorly: Skin of the posterior leg

  • Anteriorly: Deep fascia of the leg

  • At ankle: Lies posterior to lateral malleolus, accompanied by the small saphenous vein

Function

  • Sensory innervation: Supplies the skin over the lower posterolateral leg, lateral heel, ankle, and lateral border of the foot up to the fifth toe

  • Clinical sensory testing: Used to assess S1 dermatome integrity

  • Diagnostic importance: Commonly used site for nerve biopsy and nerve conduction studies

Clinical Significance

  • Entrapment neuropathy: Compression between the gastrocnemius heads or along the ankle course causes burning pain or paresthesia over the lateral foot

  • Trauma or surgery: Iatrogenic injury during Achilles tendon repair or ankle incision is common

  • Peripheral neuropathy: Affected in systemic diseases like diabetes and vasculitis

  • Sural nerve biopsy: Used to evaluate demyelinating or axonal neuropathies

  • Tumors: Schwannomas or neurofibromas may arise along its superficial course

  • Sensory loss: Leads to hypoesthesia or anesthesia in posterolateral foot region

MRI Appearance

  • T1-weighted images:

    • Normal sural nerve: low to intermediate signal intensity linear structure

    • Surrounded by bright subcutaneous fat, improving contrast

    • Nerve sheath tumors (schwannoma, neurofibroma): well-defined fusiform masses, isointense to muscle or slightly hyperintense

  • T2-weighted images:

    • Normal nerve: intermediate signal intensity, slightly darker than on T1

    • Pathology (neuritis, trauma, entrapment): bright hyperintense signal with possible thickening or irregularity

    • Nerve sheath tumors: heterogeneous or hyperintense signal with internal fascicular pattern

  • STIR:

    • Normal: low signal

    • Pathology: markedly hyperintense signal in neuritis, edema, or injury

  • Proton Density Fat-Saturated (PD FS):

    • Normal nerve: low-to-intermediate signal, sharply defined against suppressed fat

    • Neuropathy: diffuse or focal bright signal, sometimes with perineural edema

  • T1 Fat-Sat Post-Contrast:

    • Normal: minimal or no enhancement

    • Inflammatory neuritis: diffuse enhancement along nerve

    • Tumors: nodular or heterogeneous enhancement; schwannomas typically show strong, homogeneous contrast uptake

CT Appearance

Non-Contrast CT:

  • Sural nerve is not directly visualized due to its small size and low contrast with surrounding soft tissue

  • Indirect signs:

    • Adjacent soft tissue swelling or fat stranding (neuritis)

    • Calcified or ossified mass in nerve sheath tumor (rare)

  • Surrounding subcutaneous fat may highlight nerve course as a fine linear density

Post-Contrast CT (standard):

  • Normal sural nerve does not enhance

  • Pathology:

    • Enhancing perineural soft tissue in inflammatory or neoplastic lesions

    • Diffuse or nodular enhancement may suggest neuritis, tumor, or post-surgical scar

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Sural nerve coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

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Sural nerve coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

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Sural nerve axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

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Sural nerve axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

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Sural nerve axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002

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Sural nerve axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00003

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Sural nerve axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00004

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Sural nerve ct axial

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Sural nerve ct axial