MRI of the canine lumbosacral spine for degenerative lumbosacral stenosis

Why lumbosacral MRI needs careful reading

Degenerative lumbosacral stenosis (DLSS) is the most common disorder of the caudal lumbar spine in dogs (Meij and Bergknut, Veterinary Clinics of North America: Small Animal Practice, 2010). Affected dogs are typically “neuro-orthopaedic” patients, and the most consistent sign is lumbosacral pain. CT and MRI show intervertebral disc degeneration, compression of the cauda equina and entrapment of nerve roots, which allows treatment to be tailored to the dog.

The difficulty is that definitive criteria for a reliable diagnosis remain elusive (Jeffery et al., The Veterinary Journal, 2014), whether from examination, imaging or electrodiagnostics. MRI is the most commonly used advanced imaging test for DLSS, but stenosis of the central canal and foramina does not reliably correlate with clinical signs (Siauciunaite et al., The Veterinary Journal, 2026).

Degeneration is common in dogs without signs

• Young German Shepherd Dogs. In 110 clinically sound German Shepherd Dogs and 47 healthy dogs of other large breeds (Amort et al., Veterinary Radiology & Ultrasound, 2012), most younger than 18 months, the lumbosacral disc of German Shepherd Dogs showed significantly higher grades of degeneration.
• Healthy large breed dogs. In 22 healthy large breed dogs imaged in different positions (Lampe et al., Veterinary Radiology & Ultrasound, 2020), subclinical compression was seen in 45% in neutral position and 85% in extension. Disc protrusion was seen in 55% and 73% respectively.

Compression at the lumbosacral junction is therefore common in dogs without signs. On its own it does not prove that DLSS causes the signs.

Findings that relate to clinical signs

In the studies below, foraminal and nerve root findings were the ones associated with clinical signs.

MRI finding	What the studies found
Foraminal stenosis	Present in 66% of 50 dogs with DLSS and in 1 of 17 controls. Unilateral clinical signs were associated with ipsilateral foraminal stenosis (Siauciunaite et al.).
Lumbar nerve root changes	Present in 60% of dogs with DLSS and 2 of 17 controls. Ipsilateral thickening of the L7 nerve root was associated with unilateral nerve root dysfunction (Siauciunaite et al.).
Loss of foraminal fat signal	In 240 dogs, 480 L7 foramina, on low-field MRI (Lichtenhahn et al., Veterinary Surgery, 2020), 364 foramina had loss of fat signal, and 87.9% of those also had nerve root changes.
Unilateral imaging findings	Clinical signs were in the ipsilateral pelvic limb in 85% of dogs with unilateral findings (Lichtenhahn et al.).
Nerve root sedimentation sign	Did not differ significantly between dogs with DLSS and controls (Siauciunaite et al.).
Redundant nerve roots	Small to moderate association with DLSS (Siauciunaite et al.).

Position changes the picture

The lumbosacral junction moves, and MRI measurements change with it.

• In the healthy dogs, most measurements were larger in flexion and smaller in extension than in neutral position.
• In 24 clinically affected dogs (Baldo Clemot et al., Veterinary Surgery), disc protrusion, foraminal stenosis and ventral bulging of the ligamentum flavum were significantly reduced in flexion. No dog had persistent cauda equina compression or completely occluded foramina in flexion.

Lumbosacral MRI protocol at a glance

The main protocol choice at the lumbosacral junction is position, because measurements change between neutral, flexed and extended positions. Whether a flexed or extended series is added is usually agreed with the surgeon in advance. For the L7 nerve roots, the low-field foraminal study relied on dorsal oblique and transverse images.

What the radiologist looks at

• The foramina and the side of the signs. Foraminal stenosis and nerve root changes are matched to the side of the clinical signs, because unilateral signs were associated with ipsilateral findings.
• Signs of L7 radiculopathy. On low-field MRI, these included nerve root enlargement and hyperintensity, and changes in nerve root shape, size or position.
• Compression in context. Disc protrusion and compression are common in healthy dogs, so they are weighed against the examination, not read as proof of DLSS.
• Signs that do not discriminate. The nerve root sedimentation sign did not separate dogs with DLSS from controls. In the healthy dogs, agreement between observers was poor for loss of foraminal fat signal and for evidence of compression.

What your report will include

Every Veheri case is read by a radiologist or neurologist, and when you order you can choose Diplomate-only reporting or the full specialist panel. Neurology reporting covers CT and MRI. You can chat directly with the specialist assigned to your case, and a simplified pet owner report helps you explain the findings to the owner.

When you take the report forward:

• Imaging and surgery do not always agree. In 35 dogs (Suwankong et al., Journal of the American Veterinary Medical Association, 2006), CT and MRI agreed closely with each other, for example on the degree of disc protrusion (kappa 0.88). Agreement between either modality and the surgical findings was only moderate for disc protrusion (kappa 0.44 to 0.56) and nerve root swelling (kappa 0.40 and 0.50).
• Extrusion or protrusion. In 117 dogs with surgically confirmed lumbosacral disc herniation (Shing et al., Frontiers in Veterinary Science, 2023), low-field MRI separated extrusion from protrusion with an overall accuracy of 68.8% and fair agreement between radiologists. Accuracy rose to 85.3% for diagnoses made with confidence.
• Surgical technique. The authors of the flexion study suggest that, when distraction-stabilisation is used, the need for added decompression should be questioned, and call for surgical case-control studies.
• Talking to the owner: because definitive diagnostic criteria remain elusive, MRI findings are interpreted together with the examination. Explain that a scan can show changes that are not the cause of the signs.

What to include when you request a lumbosacral MRI report

• signalment: age, breed and sex
• the dog’s activity or working use
• the main sign, such as lumbosacral pain or pelvic limb lameness, and any tail or continence signs
• which side is affected, since unilateral signs can be matched to foraminal and nerve root findings
• orthopaedic findings, because these dogs are often neuro-orthopaedic patients and joint disease may coexist
• whether surgery is planned and which technique, so the radiologist knows whether flexed or extended imaging is useful

How Veheri can help

Veheri works with veterinary radiologists and neurologists and reports spinal MRI studies remotely for clinics. For disc disease further forward, see MRI of the canine thoracolumbar spine, and read when veterinary MRI is the right move.