Which side of the body is affected by foraminal stenosis?

Foraminal Stenosis Affects the Same Side of the Body as the Stenosis

Foraminal stenosis typically causes symptoms on the ipsilateral side (same side) of the body as the stenosis itself, resulting in radicular pain, sensory changes, and motor weakness in the affected limb. 1

Pathophysiology and Mechanism

Foraminal stenosis causes symptoms through compression of nerve roots as they exit the spinal canal through the neural foramina. This compression leads to:

• Radicular pain following the dermatome of the affected nerve
• Sensory changes (numbness, tingling, paresthesia) in the distribution of the compressed nerve
• Motor weakness in muscles innervated by the affected nerve root
• Reduced reflexes corresponding to the affected level

The transforaminal ligament may play a significant role in nerve root compression in foraminal stenosis, particularly when there is loss of intervertebral disc height causing the ligament to move downward and compress the nerve root 2.

Diagnostic Considerations

Imaging

• MRI of the spine without IV contrast is the first-line imaging modality for evaluating foraminal stenosis 3, 1
• CT may be used if MRI is contraindicated or to better visualize bony foraminal stenosis 1
• Selective radiculography with nerve root block can be particularly useful in diagnosing affected nerve roots, especially in cases where MRI findings are inconclusive 4

Clinical Patterns

• In lumbar foraminal stenosis with scoliosis:
  • L3 and L4 nerve roots are more commonly compressed by foraminal or extraforaminal stenosis on the concave side of the curve
  • L5 and S1 nerve roots are more commonly affected by lateral recess stenosis on the convex side 5

Important Differential Considerations

It's crucial to distinguish unilateral foraminal stenosis from other conditions that may present with similar symptoms:

• Central cord pathology can cause bilateral symptoms with asymmetric presentation 1
• Brainstem lesions affecting descending motor pathways may cause contralateral symptoms 1
• Vertebral artery pathology can cause brainstem ischemia affecting motor function 3, 1

Clinical Pitfalls to Avoid

1. Don't assume that symptoms on the right side of the body must be from right-sided foraminal stenosis - central cord pathology can cause contralateral symptoms
2. Don't miss bilateral foraminal stenosis which may present with asymmetric symptoms
3. Always consider vascular causes like vertebral artery dissection in patients with atypical presentations 3, 1
4. Remember that in patients with scoliosis, the pattern of nerve root compression varies based on the curve and the specific nerve root involved 5

By understanding that foraminal stenosis typically affects the ipsilateral side of the body, clinicians can more accurately diagnose and treat this common cause of radicular pain and neurological symptoms.