Inferior Lateral Cutaneous Nerve of Arm: Anatomy, Course, Function, Imaging

Topic

Inferior lateral cutaneous nerve of arm

The inferior lateral cutaneous nerve of the arm is a sensory branch of the radial nerve, arising in the posterior compartment of the arm. It provides cutaneous innervation to the lower lateral aspect of the arm, just above the elbow. This nerve is important for sensory perception over the inferolateral deltoid region and lateral triceps area, and may be clinically involved in radial nerve injuries or surgical trauma to the posterior humerus.

It is smaller and more distal than the superior lateral cutaneous nerve of the arm (from the axillary nerve) and is sometimes referred to as the lower lateral cutaneous branch of the radial nerve.

Synonyms

Lower lateral cutaneous nerve of the arm
Inferior lateral brachial cutaneous nerve
Inferior lateral branch of the radial nerve

Origin, Course, and Distribution

Origin: Arises from the radial nerve in the radial (spiral) groove of the humerus, usually at or just distal to the origin of the posterior cutaneous nerve of the forearm.
Course:
- Descends obliquely through the lateral head of the triceps brachii.
- Pierces the lateral intermuscular septum to enter the subcutaneous tissue on the lateral aspect of the arm.
- Travels downward toward the lateral aspect of the elbow, supplying skin over the lower lateral arm.
Distribution: Provides sensory innervation to the skin over the inferolateral aspect of the arm and upper portion of the lateral forearm, often overlapping with the posterior cutaneous nerve of the forearm.

Relations

Proximally: Close to the radial nerve in the spiral groove of the humerus
Medially: Related to the lateral head of triceps brachii
Laterally: Pierces deep fascia near the insertion of the deltoid
Distally: Becomes superficial near the lateral epicondyle of the humerus, anterior to the triceps tendon
Overlying structures: Skin and superficial fascia of the lateral arm region

Function

Sensory: Supplies the skin over the inferolateral aspect of the arm, extending from the deltoid insertion to the lateral epicondyle.
Protective sensation: Provides cutaneous feedback during contact or pressure along the outer arm surface.
Clinical localization: Helps distinguish radial nerve lesions from axillary nerve injuries based on sensory loss distribution.

Clinical Significance

Radial nerve injury: Lesions in the radial groove (e.g., humeral shaft fractures) may affect this branch, causing sensory loss over the lower lateral arm.
Entrapment or compression: May occur near the lateral intermuscular septum or surgical incisions of the distal arm.
Iatrogenic injury: At risk during posterior arm approaches, triceps repair, or plate fixation of humeral fractures.
Sensory neuropathy: Presents as numbness, tingling, or burning over the inferolateral arm.
Electrodiagnostic importance: Helps in mapping sensory nerve conduction in radial neuropathy assessment.

MRI Appearance

T1-weighted images:
- Nerve appears as a thin, low-to-intermediate signal structure within the subcutaneous fat of the lateral arm.
- Surrounding fat: bright, providing clear contrast.
- In radial groove: seen adjacent to humeral cortex, deep to triceps.
- Thickening or discontinuity may indicate trauma or neuritis.
T2-weighted images:
- Normal nerve: intermediate signal intensity, darker than surrounding fat.
- Pathology: bright hyperintense signal in neuritis, entrapment, or contusion.
- Excellent for evaluating perineural edema or focal injury.
STIR:
- Normal: intermediate-to-dark signal due to uniform fascicular architecture.
- Pathologic: bright hyperintense changes indicating edema, traction injury, or inflammatory neuritis.
- Best for identifying subtle post-traumatic changes in nerve and adjacent soft tissues.
Proton Density Fat-Saturated (PD FS):
- Normal: intermediate-to-dark, smooth linear contour.
- Pathologic: focal bright signal indicating neuropathy or localized inflammation.
- Perineural fat stranding may suggest compression or postoperative scarring.
T1 Fat-Sat Post-Contrast:
- Normal nerve: minimal to no enhancement.
- Inflamed or injured nerve: demonstrates mild linear or nodular enhancement.
- Postoperative scar tissue: enhances more intensely than intact nerve, aiding differentiation from residual neuropathy.

CT Appearance

Non-Contrast CT:

Nerve not distinctly visualized; appears as fine soft-tissue density within subcutaneous fat lateral to the humerus.
Useful for identifying adjacent fractures or hardware impingement affecting the nerve’s course.
Chronic neuritis may show localized fat stranding or muscle atrophy in the triceps region.

MRI image

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