Are cranial nerves normal in patients with paraplegia?

Cranial Nerves in Paraplegia

Cranial nerves remain normal and intact in patients with paraplegia, as paraplegia affects the spinal cord and spinal nerves but not the cranial nerves which originate from the brain and brainstem. 1

Anatomical Basis for Normal Cranial Nerve Function in Paraplegia

• Cranial nerves (CN I-XII) emerge from the rostral portion of the embryologically developing neural tube, forming the brain and brainstem, while paraplegia involves injury to the spinal cord below the level of the brain and brainstem. 2, 1
• The 12 pairs of cranial nerves provide specialized sensory and motor innervation specifically to the head and neck region, with their nuclei located in the brain and brainstem, anatomically separate from the spinal cord segments affected in paraplegia. 2
• Paraplegia typically results from spinal cord injuries or lesions at thoracic, lumbar, or sacral levels, leaving the cranial nerve nuclei and pathways in the brain and brainstem unaffected. 3

Clinical Considerations

• In paraplegia, neurological deficits manifest as motor and sensory impairments below the level of spinal cord injury, while cranial nerve functions (including smell, vision, eye movements, facial sensation, facial movement, hearing, swallowing, and tongue movement) remain preserved. 1
• The American College of Radiology notes that cranial neuropathy results from pathologies affecting nerve fibers at any point from the CN nucleus to the end organ, which are anatomical regions not typically involved in the pathophysiology of paraplegia. 2
• In rare cases where both cranial nerve palsies and paraplegia occur simultaneously, this represents either two separate pathological processes or a single extensive disease process (such as metastatic cancer) affecting both the brain/brainstem and spinal cord, rather than paraplegia causing cranial nerve dysfunction. 4

Diagnostic Considerations

• When evaluating patients with paraplegia, neurological examination should demonstrate normal cranial nerve functions, and any abnormalities would suggest a separate pathological process requiring specific investigation. 1
• MRI is the standard modality for imaging cranial nerves when dysfunction is suspected, with 3.0T preferred over 1.5T for better signal-to-noise ratio and spatial resolution. 2
• In the unusual circumstance of a patient with paraplegia presenting with cranial nerve dysfunction, a complete evaluation should include imaging of the entire course of the affected nerve from brainstem nuclei to end organs, as this represents a separate clinical entity from the paraplegia. 2

Exceptions and Special Considerations

• Certain extensive pathological processes can affect both cranial nerves and cause paraplegia, such as metastatic tumors with both cranial and spinal involvement, but these represent two separate sites of involvement rather than paraplegia affecting cranial nerves. 4, 5
• Iatrogenic causes such as pneumocephalus following spinal procedures can rarely lead to temporary cranial nerve palsies in patients who may also have paraplegia, but this represents a procedural complication rather than a direct relationship between paraplegia and cranial nerve function. 6
• Recovery patterns of cranial nerve palsies (when they do occur) depend on the underlying cause, with those due to vascular disease showing better recovery rates (71%) compared to those caused by trauma, aneurysm, or neoplasm. 7