2007 Radiology Exam - Alternate Imaging Case 1

Information provided to candidate

  • Belgian Malinois
  • 4.5 years
  • Male
  • Bilateral hind limb lameness, and lower back pain. Unable to work X 3 months. Drug detection and sentry-trained military working dog.
  • Available images are sagittal and transverse MRI images of the lumbar spine

State the findings

  • Generate a prioritized differential diagnosis list.
  • Are other imaging studies indicated? Justify.
  • Do the imaging findings explain the clinical signs? Justify.

See images below. Click to enlarge.

Findings expected from candidate

  • Candidates were expected to describe decreased T2 signal intensity in the L7-S1 disc; T1 and T2 hypointense tissue in the ventral L7-S1 canal, with loss of ventral epidural fat and circumferential disc bulging; T1 and T2 hypointense tissue in both L7-S1 foramina with loss of caudoventral epidural fat; and a transitional S1 vertebra.

Differentials expected from candidate

  • L7-S1 type II disc degeneration, protruding disc or bone spurs in L7-S1 canal, protruding disc or bone spurs in both L7-S1 foramina.

Other imaging studies expected

  • Flexion/extension imaging (radiography, myelography) to assess instability.
  • Correlation between imaging findings and clinical signs
  • Imaging characteristics are consistent with degenerative/developmental lumbosacral disease and mild to moderate stenosis of the L7-S1 canal and foramina. Back pain could be due to physical compression of the cauda equina or local inflammation. Lameness could be due to entrapment of L7 nerve roots or intermittent venous congestion in the intervertebral foramina or lateral recesses. There is a poor correlation between severity of MRI compression and severity of clinical signs in working dogs.

Summary of overall candidate performance

  • Most candidates performed adequately on this case. None noticed the transitional vertebra. Many did not notice the foraminal encroachment. Many under-interpreted the foraminal and canal encroachment and did not think they were clinically significant. A few over-interpreted partial volume artifacts and diagnosed spinal neoplasia.


  • The dog had a decompressive laminectomy and discectomy at L7-S1. Protruding annulus and bone spurs were removed from the ventral canal and both lateral recesses. The dog improved post-operatively and was returned to active duty 6 months later.