Epineurium
Outermost layer of a nerve
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Through Connective tissue, Nerve and Blood vessel
When the spinal nerve leaves the vertebral canal via an intervertebral foramen, two layers of the spinal meninges, the arachnoid and the dura invaginate the nerve to form a dural sleeve of connective tissue, which is the epineurium. The outer portion of this sleeve comprises the external epineurium which permits longitudinal nerve excursion and absorption of longitudinal stress. The layer of the epineurium that extends within the nerve to define the fascicles is termed the internal epineurium. Together, these two layers form the epineurium, which varies in thickness along the course of a nerve. The epineurium is usually most abundant around joints, as its function is to protect the nerves from stretching and subsequent injury. Epineurium is primarily made from collagen.
Clinical significance
A common surgical procedure to repair a torn nerve via the epineurium is termed an epineurial repair.
Schwannomas often remain completely encapsulated by the epineurium as they grow.
Epineurial barriers can be used to limit the formation of neuromas after neurotmesis. The epineurium is an effective barrier against axon growth.