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Lateral cutaneous nerve of forearm

The lateral cutaneous nerve of the forearm is the terminal sensory branch of the musculocutaneous nerve. It emerges lateral to the biceps tendon near the elbow and descends along the anterolateral aspect of the forearm, supplying the skin of the lateral forearm as far as the wrist.

It provides pure sensory innervation to the lateral surface of the forearm and is a key structure in evaluating sensory loss after musculocutaneous nerve injury or postoperative forearm numbness following elbow surgeries. Its superficial position near the cephalic vein makes it vulnerable to iatrogenic injury or entrapment.

Synonyms

  • Lateral antebrachial cutaneous nerve

  • External cutaneous nerve of the forearm

Origin, Course, and Termination

  • Origin: Terminal branch of the musculocutaneous nerve (C5–C7), after it emerges between the biceps brachii and brachialis muscles.

  • Course:

    • Appears lateral to the biceps tendon just above the elbow.

    • Pierces the deep fascia lateral to the biceps tendon and divides into two main branches — anterior and posterior.

    • The anterior branch descends along the anterolateral forearm, superficial to the brachioradialis.

    • The posterior branch passes behind the lateral border of the forearm, supplying the dorsolateral skin.

  • Termination:

    • Ends near the wrist, supplying the skin over the lateral aspect of the forearm up to the thenar eminence.

Relations

  • Superiorly: Lies lateral to the biceps tendon in the cubital fossa.

  • Deep: Brachialis and brachioradialis muscles.

  • Superficial: Deep fascia of forearm and superficial veins (notably the cephalic vein).

  • Lateral: Brachioradialis tendon at distal forearm.

  • Medial: Adjacent to radial recurrent vessels near the elbow.

Branches

  • Anterior branch: Supplies the skin on the anterior and lateral surface of the forearm down to the wrist.

  • Posterior branch: Innervates the skin on the posterior-lateral surface of the forearm to the mid-level.

  • Communicating branches: May connect with the superficial branch of the radial nerve near the wrist.

Function

  • Sensory innervation: Provides cutaneous sensation to the anterolateral and posterolateral surfaces of the forearm.

  • Clinical landmark: Used for assessing musculocutaneous nerve integrity.

  • Protective role: Detects tactile, pain, and temperature stimuli on the lateral forearm.

Clinical Significance

  • Injury: Commonly injured in venipuncture, IV cannulation, or surgical procedures near the cephalic vein or biceps tendon.

  • Entrapment: May occur as it pierces the deep fascia, causing burning pain or paresthesia over the lateral forearm.

  • Sensory loss: Seen in musculocutaneous nerve lesions or compression neuropathies.

  • Postoperative numbness: Common after elbow arthroscopy or lateral forearm incisions.

  • Diagnostic role: Useful in nerve conduction studies for localizing upper limb sensory neuropathies.

MRI Appearance

T1-weighted images:

  • Nerve appears as a thin, low-to-intermediate signal linear structure along the lateral forearm.

  • Surrounded by bright subcutaneous fat for clear contrast.

  • In entrapment or trauma, focal thickening or intermediate hyperintensity may be seen.

T2-weighted images:

  • Normal nerve: intermediate signal 

  • Neuropathy or inflammation: marked hyperintensity and enlargement of the nerve.

  • Surrounding soft-tissue edema may also be evident.

STIR:

  • Normal: intermediate-to-dark signal (flow void appearance).

  • Pathology: bright hyperintensity indicating neuritis, edema, or post-traumatic change.

Proton Density Fat-Saturated (PD FS):

  • Normal: intermediate-to-dark, homogeneous linear signal.

  • Entrapment or injury: focal bright signal with loss of fascicular pattern.

  • Excellent for depicting small nerve lesions and perineural inflammation.

T1 Fat-Sat Post-Contrast:

  • Normal nerve: minimal or no enhancement.

  • Neuritis or scar entrapment: mild to moderate enhancement.

  • Neuroma or traumatic lesion: nodular or fusiform enhancement with surrounding soft-tissue enhancement.

CT Appearance

Non-Contrast CT:

  • Nerve itself poorly visualized due to small caliber and soft-tissue density.

  • Indirect signs: adjacent soft-tissue swelling or fibrosis near the cephalic vein.

Post-Contrast CT (standard):

  • Nerve shows minimal or no enhancement in normal conditions.

  • Inflammation or traumatic neuroma: may show mild perineural enhancement.

  • Surrounding fascial thickening or scarring occasionally delineated in chronic entrapments.

MRI image

Lateral cutaneous nerve of forearm axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

MRI image

Lateral cutaneous nerve of forearm axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00001

MRI image

Lateral cutaneous nerve of forearm axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00002

MRI image

Lateral cutaneous nerve of forearm axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00003

MRI image

Lateral cutaneous nerve of forearm axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00004