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Cervical spinal nerve 8 (C8)

The Cervical Spinal Nerve 8 (C8) is the eighth and final cervical spinal nerve, emerging from the spinal cord between the C7 and T1 vertebrae. Although there are only seven cervical vertebrae, there are eight cervical nerves, with C8 being unique as it exits below the C7 vertebra. This nerve is integral to motor and sensory innervation of the upper limb, especially the hand and fingers. Understanding its anatomy, function, and imaging characteristics is crucial for accurate diagnosis and management of cervical radiculopathies and other spinal pathologies.

Synonyms

  • C8 spinal nerve

  • Eighth cervical nerve

  • Nerveus cervicalis VIII

  • Cervical nerve root 8

  • C8 root

Anatomical Course and Function

  • Originates from the spinal cord, exiting the spinal canal below the C7 vertebra and above the T1 vertebra.

  • Contributes to the brachial plexus, specifically to the lower trunk.

  • Provides motor innervation to:

    • Intrinsic muscles of the hand (especially finger flexors and extensors)

    • Some forearm muscles (flexor digitorum profundus, flexor carpi ulnaris)

  • Provides sensory innervation to:

    • Medial aspect of the forearm and hand

    • Little finger and medial half of the ring finger

Clinical Function

  • Responsible for fine finger movements and grip strength.

  • Sensory distribution corresponds to the C8 dermatome, affecting the medial forearm and hand.

  • Lesions can result in weakness of hand muscles, loss of grip, and sensory changes (numbness, tingling) in the C8 dermatome.

MRI Appearance

  • T1-weighted Imaging:

    • Nerve roots appear as isointense to slightly hypointense relative to spinal cord and surrounding soft tissue.

    • Pathological changes (such as inflammation or tumor) may show as loss of normal signal or mass effect.

  • T2-weighted Imaging:

    • Normal C8 nerve root is of intermediate signal intensity.

    • Hyperintensity may indicate edema, inflammation, or nerve impingement.

    • Perineural or foraminal fluid may appear hyperintense if present.

  • STIR (Short Tau Inversion Recovery):

    • Highly sensitive for nerve pathology.

    • Abnormal C8 root will appear hyperintense (bright) in cases of neuritis, edema, or trauma.

    • Normal roots usually remain of low to intermediate signal unless pathology is present.

CT Appearance

  • Nerve roots are typically not directly visualized on standard CT due to limited soft tissue contrast.

MRI images

Cervical spinal nerve 8 (C2) MRI axial t2 image