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Neuroradiology Case of
the Week
Case 247
Jeremy Duda, BA,
Jerry Lee, MD,
and P-L Westesson, MD, PhD, DDS
Clinical
Presentation: A
43-year-old woman with previous chronic lower back pain presented to her PCP with acute worsening of symptoms, including 10+/10 dysesthesias and a burning sensation radiating down her right leg.
Imaging Findings:
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Figure 1: Axial T2 image shows a severe posterior paracentral L5-S1 extruded disc. |
The patient refused surgery and elected to pursue medical management.
Four month follow up:
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Figure 2: This axial T2 weighted image from four months later shows a significant decrease in the size of disc extrusion, with only mild narrowing of neural foramen right greater than left.
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Diagnosis: L5-S1 disc extrusion spontaneous disappearance without surgery
Discussion: Lifetime prevalence of low back pain is 60-90%, at an annual rate of 2-5% per year. The disease may be caused by injury to soft tissues such as muscles or ligaments, compression of nerves as seen in spondylolisthesis or disc herniation, bone disorders like osteoarthritis, and malignancy. However, an anatomic diagnosis is elusive 85% of the time and often nonspecific terminology such as “strain” is used. Ninety-seven percent of cases of low back pain have a mechanical cause, and 4% can be attributed to a disc herniation. Clinical workup is often directed at eliminating systemic causes and neurological emergencies.
Lumbar disc herniation occurs most commonly in patients 40-50 years old, with a 3:1 male to female ratio. Risk factors include heavy lifting, obesity, and long periods of sitting such as in driving. MRI studies of asymptomatic individuals found 22-40% had evidence of a herniated disc at any spinal level. Only 4-6% of herniated lumbar discs are symptomatic.
Intervertebral discs consist of the annulus fibrosus and the central nucleus pulposus either of which can herniate. Antecedent changes in biomechanics related to disc dehydration, excessive vertical loads, and deterioration of the annulus fibrosus lead to annular fissures and herniation. The nucleus preferentially exits the intervertebral space lateral to the posterior longitudinal ligament and posteriorly into the vertebral canal. Local pain results when nerve fibers in the outer annulus are irritated.
Clinical presentation involves “sciatica,” a group of symptoms including low back and leg pain that may be burning or stabbing, and parasthesias. Patients with urinary incontinence and dermatomal sensory loss in a saddle distribution is a neurological emergency representing compression of the cauda equina. On exam patients may exhibit increased symptoms when their leg is raised in a supine position.
MR allows visualization of soft tissues, and is the test of choice in diagnosis of disc disease. MR is sensitive and specific for annular tears, disc herniations, and nerve root swelling. T2 imaging may demonstrate the low signal of disc extending into the high signal CSF in the spinal canal. Annular tears may also be seen on T2 as a hyperintense focus along the posterior aspect of the annulus. T1 may show effacement of epidural fat by an isointense disc bulge. Contrast is not indicated in routine evaluation of disc herniation. CT myelogram is used as a secondary test and in surgical planning. Interventional procedures such as fluoroscopic nerve block, usually used for therapy, may also aid in diagnosis.
Because of the prevalence of asymptomatic herniation, clinical signs and symptoms should be carefully compared to radiologic findings. A clinical diagnosis is not always confirmed by imaging, and patients often improve within 4-6 weeks. Consequently, imaging is not indicated unless an ominous cause must be ruled out or symptoms have not resolved after that period. The prognosis of the lumbar disc herniation is very favorable – 46% of patients eventually experience a 75%-100% decrease in the size of the lesion.
Nonoperative management of acute disc herniation benefits most patients – 90% of patients with lumbar disc herniation in one study were found to have a “good” or “excellent” outcome. Therapy consists of initial rest, then muscle relaxants and narcotic analgesics for 1-2 weeks, followed by NSAIDs, oral or injectible corticosteroids, and lumbar stabilization exercises. However, 1-3% of patients with lumbar disc herniation go on to have surgery, either for persistent and intolerable pain refractory to medical management, or for emergent sequelae of the lesion.
This case demonstrates near resolution of the severe lumbar disc herniation over a four month period without surgery.
References:
- Smeal WL, Tyburski M, Alleva J, Prather H, Hunt D. Conservative management of low back pain, part I. Discogenic/radicular pain. Dis Mon. 2004 Dec;50(12):636-69. [Medline]
- Deyo RA, Weinstein JN. Low back pain. N Engl J Med. 2001 Feb 1;344(5):363-70. [Medline]
- Awad JN, Moskovich R. Lumbar disc herniations: surgical versus nonsurgical treatment. Clin Orthop Relat Res. 2006 Feb;443:183-97. [Medline]
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