Mechanical injury of peripheral nerves. Fine structure and dysfunction

Area of Science:

• Neuroscience
• Pathology
• Regenerative Medicine

Background:

• Peripheral nerve injuries encompass a spectrum from mild conduction blocks to severe structural disruptions.
• Understanding the histopathology and mechanisms of nerve injury is crucial for diagnosis and treatment.
• Neuralgia and sensorimotor deficits are common sequelae of both acute and chronic nerve lesions.

Purpose of the Study:

• To examine the morphology of normal peripheral nerves.
• To present types of mechanical nerve injury and associated histopathology.
• To discuss mechanisms responsible for pain, paresthesiae, and weakness in nerve lesions.

Main Methods:

• Morphological examination of normal peripheral nerves.
• Classification and description of mechanical nerve injury types.
• Review of histopathological findings in nerve lesions.
• Discussion of proposed mechanisms for associated symptoms.

Main Results:

• Neurapraxia involves myelin/axon intussusception at nodes of Ranvier, causing conduction block.
• Axonotmesis and neurotmesis represent severe nerve fiber disruptions with poor prognoses.
• Chronic entrapment lesions show myelin internode telescoping and sheath tapering.
• Both acute and chronic lesions primarily affect large myelinated fibers and can cause neuralgia.

Conclusions:

• Different types of mechanical nerve injuries exhibit distinct morphological and pathological features.
• The mechanisms of neuralgia in nerve injuries are not fully understood but may involve ectopic impulse generation and ephaptic transmission.
• Severe nerve disruptions (axonotmesis, neurotmesis) have limited potential for functional regenerative repair.