Foraminal Narrowing

Foraminal narrowing is a frequent finding on spine imaging studies. It refers to the narrowing of nerve exit pathways between vertebrae. This article explains the radiological appearance of foraminal narrowing across different imaging modalities, its common causes, and clinical significance.

What Is Foraminal Narrowing?

Foraminal narrowing, also called foraminal stenosis, refers to the narrowing of the small openings (foramina) between your vertebrae. These openings are passageways where nerves exit your spinal cord to travel to other parts of your body. When these spaces become narrower than normal, they can potentially put pressure on the nerves passing through them.  This finding often indicates some degree of degenerative change in the spine, which is extremely common as we age. 

How Foraminal Narrowing Appears on Different Imaging Tests

MRI Findings of Foraminal Narrowing

Magnetic Resonance Imaging (MRI) is best for visualizing foraminal narrowing. On MRI scans, radiologists can clearly see:

• Open spaces between vertebrae where nerves exit have become compressed
• The nerve roots themselves and whether they appear pinched
• Surrounding soft tissues like discs and ligaments that might be contributing to the narrowing

MRIs are particularly valuable because they show excellent contrast between different tissues, allowing doctors to see if the narrowed foramen is affecting nerves.

CT Scan Appearance of Foraminal Stenosis

Computed Tomography (CT) scans use X-rays to create detailed cross-sectional images. On CT scans, foraminal narrowing appears as:

• Reduced space in the bony openings where nerves exit between vertebrae
• Bone spurs (osteophytes) that may be growing into the foramen
• Changes in the facet joints that might contribute to narrowing

CT scans excel at showing bone detail, making them ideal for identifying when bony changes are the primary cause of foraminal narrowing.

X-Ray Signs of Foraminal Narrowing

While less detailed than MRI or CT, X-rays can show:

• Decreased space where nerves exit between vertebrae
• Bone spurs forming around the edges of vertebrae
• Changes in spine alignment that might affect the foramina

X-rays are often the first imaging test ordered because they’re quick and inexpensive, but they provide less information about soft tissues and neural structures than advanced imaging methods.

Common Causes of Foraminal Narrowing Visible on Imaging

Several conditions can lead to foraminal narrowing, all of which have distinctive appearances on imaging:

Degenerative Disc Disease

When discs between vertebrae lose height and hydration, they appear darker and flatter on MRI. This disc collapse can directly reduce the size of the foramina on both sides of the vertebrae. Radiologists typically note this when they see the disc space narrowing along with corresponding foraminal narrowing.

Herniated Discs

A herniated or bulging disc can protrude into the foramen, reducing the available space. On MRI, this appears as disc material extending beyond its normal boundaries and potentially encroaching on the nerve root.

Bone Spurs (Osteophytes)

As joints experience stress over time, bone spurs can form and grow into the foramen. These appear as irregular bony projections on X-rays, CT scans, and MRIs, and are a common finding in older adults.

Spondylolisthesis

This condition occurs when one vertebra slips forward over the one below it. Imaging clearly shows the misalignment, and the resulting abnormal position can significantly narrow the foramina.

Severity Levels of Foraminal Narrowing on Imaging Reports

Radiologists typically describe foraminal narrowing using specific terminology:

Mild Foraminal Narrowing

Imaging shows slight reduction in the foramen size, but there remains adequate space around the nerve root. The report might mention “minimal” or “mild” narrowing.

Moderate Foraminal Narrowing

There is noticeable reduction in the foramen size with possible contact with the nerve root, but no definite compression. The nerve may appear to be touching surrounding structures but maintains its normal shape.

Severe Foraminal Narrowing

Imaging reveals significant reduction in foramen size with clear compression or distortion of the nerve root. The nerve often appears flattened or displaced from its normal position.

Common Locations for Foraminal Narrowing on Spine Imaging

Cervical Foraminal Narrowing

The neck region commonly shows foraminal narrowing, especially at C5-C6 and C6-C7 levels. On imaging, this appears as compression of the nerve roots that travel to the shoulders, arms, and hands.

Lumbar Foraminal Narrowing

The lower back, particularly L4-L5 and L5-S1 levels, frequently develops foraminal narrowing. Imaging shows compression affecting nerve roots that supply the legs and feet.

Thoracic Foraminal Narrowing

While less common, foraminal narrowing can occur in the mid-back. Imaging in this region may be more challenging to interpret due to the ribs and orientation of the foramina.

How Radiologists Evaluate Foraminal Narrowing

Radiologists look at several key factors when assessing foraminal narrowing:

• The size of the foramen compared to normal expectations for a patient’s age
• Whether there’s contact with or compression of the nerve root
• If there are associated findings like disc herniation or bone spurs
• Whether the narrowing appears on one side (unilateral) or both sides (bilateral)

Radiologists typically note foraminal narrowing when it’s significant enough to potentially explain a patient’s symptoms or when it might influence treatment decisions.

When Foraminal Narrowing on Imaging May Explain Symptoms

Not all foraminal narrowing causes symptoms. However, imaging findings are more likely to be clinically significant when:

• The narrowing corresponds to the exact location of the patient’s pain
• There is clear compression of a nerve root visible on imaging
• The affected nerve supplies the area where the patient experiences symptoms
• The narrowing is severe or present at multiple levels

It’s important to remember that imaging findings must always be correlated with clinical symptoms – many people have foraminal narrowing on imaging without experiencing any problems.

Conclusion

Foraminal narrowing is a common finding on spine imaging that refers to the narrowing of spaces where nerves exit the spine. While it can sometimes cause pain or neurological symptoms, many people with this finding on imaging tests have no symptoms at all. Understanding how this condition appears on different imaging modalities helps both patients and doctors interpret radiology reports more effectively.   This helps them make appropriate treatment decisions based on both imaging findings and clinical symptoms.

References:

1. https://www.healthline.com/health/neural-foraminal-stenosis
2. https://www.ajronline.org/doi/10.2214/AJR.09.2772
3. https://www.healthline.com/health/foraminal-stenosis#symptoms