Diagnosing a herniated disc: from clinical examination to MRI

The clinical examination: the first step in diagnosis

Before any imaging, the doctor conducts an interview and a neurological examination to guide the diagnosis. This step is essential: it directs the choice of further tests and allows for an assessment of the severity of the nerve compression.

The interview focuses on the exact location of the pain, its type (radiating, sharp, dull), its duration, triggering factors, and medical history. The neurological examination then tests deep tendon reflexes, skin sensitivity, and muscle strength in the limbs; these are all markers used to identify which nerve is compressed and at what level.

For a lumbar hernia, the Lasègue sign is frequently checked: it involves lifting the straightened leg while lying on your back, which reproduces or worsens the radiating pain if a nerve root is indeed compressed. For a cervical hernia, neck mobility tests and axial compression provide information on nerve root involvement.

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MRI: understanding what the scan reveals about your hernia

MRI (magnetic resonance imaging) is the gold standard for diagnosing a herniated disc. It visualizes the intervertebral discs, nerve roots, spinal cord, and the extent of the compression with a level of precision that a CT scan cannot match for soft tissues.

What the MRI report actually describes

The terms used in radiology reports correspond to the stages of a herniated disc:

• Protrusion: the nucleus bulges locally without rupturing the fibrous ring. This is the most common and often the least severe form. ‍
• Extrusion: the nucleus passes through the fibrous ring but remains attached to the disc. Nerve compression is generally more pronounced. ‍
• Migration (or sequestration): a fragment of the nucleus detaches and moves into the spinal canal. This form often warrants a surgical evaluation.

The location of the hernia in the horizontal plane is also specified: median (in the center of the canal), foraminal (in the foramen where the nerve root exits), or paralateral. This location directly influences symptoms and treatment options.

Why an MRI is not prescribed immediately

In the first few weeks following the onset of symptoms, an MRI is not systematically indicated. In the absence of severe neurological signs, a period of observation with medical treatment is often recommended before resorting to imaging, as the vast majority of herniated discs heal spontaneously within a few weeks.

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When an MRI report does not match the clinical presentation or when a doctor is uncertain about the interpretation, having a spine specialist review the file can confirm or refine the diagnosis before starting treatment.

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CT scans and EMGs: when are these tests useful?

The CT scan (computed tomography)

A CT scan is less precise than an MRI for visualizing soft tissues like discs and nerves. It is useful for evaluating associated bone abnormalities—such as facet joint arthritis, spinal stenosis (narrowing of the spinal canal), or calcification of a herniated disc—or in situations where an MRI is contraindicated (e.g., presence of a pacemaker, severe claustrophobia). It is also used to plan certain surgical procedures.

Electromyography (EMG)

An EMG measures nerve conduction velocity and the electrical response of muscles. It is prescribed in specific situations: when nerve damage needs to be precisely quantified, when multiple nerve roots are potentially affected, or when the clinical presentation does not clearly establish the level of compression. It is not routinely performed in the assessment of a standard herniated disc.

X-rays

Standard X-rays do not show discs or herniations. However, they can provide information on bone structures (disc space narrowing, spinal arthritis, spinal alignment issues) and remain useful as an initial screening tool or for preoperative planning.

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