Lumbar canal stenosis

Lumbar canal stenosis is a general term that refers to the pathological narrowing of the spinal canal, nerve root canals and/or the intervertebral foramina in the lumbar spine ^1-4,6,7,9,10.

Epidemiology

Lumbar canal stenosis is common, especially among individuals over 60 years old, and its prevalence increases with age. 5-10% of individuals over 50 years and up to 40% of individuals over 60 years may have lumbar canal stenosis. Onset typically occurs between 50 and 60 years, but it can also occur in younger individuals with congenital or developmental spinal abnormalities. Gender distribution is equal, affecting both males and females ^3,4,6,7,9.

Clinical presentation

Patients with lumbar canal stenosis may be asymptomatic or exhibit a variety of neurological symptoms including ^3,4,6,7,9:

• neurogenic claudication

  • exacerbated by downhill walking

  • symptom relief by uphill walking

• low back pain (lumbago)

• lower limb changes to sensation (e.g. paresthesia and/or tingling)

• lower limb weakness, fatigue, or heaviness

• priapism

• neurogenic bladder symptoms

• fecal incontinence

• nocturnal leg cramps

Pathology

Etiology

Degenerated discs are the predominant cause of lumbar canal stenosis. Lumbar central canal stenosis can arise due to the narrowing of the anteroposterior, transversal, or combined diameter, which may occur as a consequence of disc height reduction, intervertebral disc bulging, and hypertrophy of both facet joints and the ligamentum flavum.

Lateral recess stenosis can also occur as a result of similar processes, such as reduced disc height, hypertrophy of facet joints (with or without spondylolisthesis), and/or the presence of osteophytes on vertebral endplates.

Foraminal stenosis can manifest as either anteroposterior narrowing, which occurs due to a combination of disc space reduction and excessive growth of structures anterior to the facet joint capsule, or vertical narrowing, which arises from the protrusion of posterolateral osteophytes from the vertebral endplates into the foramen. In addition, a laterally bulging annulus fibrosus or herniated disc can compress the nerve root against the superior pedicle. Most commonly, foraminal stenosis predominantly affects the L5 nerve root, as the L5-S1 foramen exhibits a smaller foramen-to-root area ratio ^2,5,9.

The causes of lumbar canal stenosis can be divided into acquired or congenital etiologies ⁶:

• acquired

  • degenerative

    • juxtafacet cyst

    • posterior longitudinal ligament ossification

    • ligamentum flavum ossification

    • spondylosis

    • spondylolisthesis

    • abnormal alignment, e.g. scoliosis, kyphosis (can also be due to trauma)

  • postoperative

    • fusion

    • laminectomy

    • fibrosis

  • trauma

    • burst fracture

  • metabolic/endocrine

    • acromegaly

    • epidural lipomatosis (Cushing syndrome)

    • hypoparathyroidism

    • osteoporosis

    • pseudogout (calcium pyrophosphate dihydrate deposition)

    • renal osteodystrophy

  • skeletal

    • ankylosing spondylitis

    • diffuse idiopathic skeletal hyperostosis

    • rheumatoid arthritis

    • Paget disease

• congenital

  • achondroplasia

  • idiopathic

  • spondyloepiphyseal dysplasia

  • Morquio syndrome

  • spinal dysraphism (lipoma, myelomeningocele)

Classification

Lumbar canal stenosis can be further classified according to location and severity ^3,5,6.

Location

The location of stenosis is generally referred to using intervertebral disc disease nomenclature into:

• central

• lateral (subarticular)

• foraminal

Severity

Describing severity is more complicated and although the terms mild, moderate and severe are used ubiquitously in clinical reports, they are often not defined.

Probably most widely used, and endorsed by the "Lumbar disc nomenclature: version 2.0" - from The American Society of Spine Radiology, The American Society of Neuroradiology and The American Spine Society ¹¹, is a classification system first described by Laurie et al ⁴:

• mild: decrease of <1/3 of space available for neural elements ^2,4

• moderate: decrease of 1/3 to 2/3 of space available for neural elements ^2,4

• severe: decrease of >1/3 of space available for neural elements ^2,4

Although simple this does not take into account the great variability in normal canal diameter between individuals. As a result of this a number of additional lumbar spinal stenosis grading systems have been described.

Ideally, reports would explicitly indicate which grading system is being used, or describe the stenosis in such a way as the degree of stenosis can be determined independent of the classification system preferred.

Radiographic features

CT

CT is effective in visualizing various bony abnormalities associated with lumbar canal stenosis, such as spondylolysis, spondylolisthesis, end plate irregularities, sclerosis, facet joint osteoarthritis, articular process hypertrophy, vacuum phenomenon of discs and joints, as well as subchondral and synovial cysts ^7,8. CT can accurately demonstrate extrathecal nerve root compression in the lateral recesses and intervertebral foramina by identifying effacement of epidural fat or compression of the root, while also effectively distinguishing compression caused by disc, ligament, and bone. However, CT has limitations in detecting intrathecal nerve root compression due to the inability to differentiate it from the surrounding CSF ⁷.

CT myelogram

The myelographic findings observed in cases of central lumbar canal stenosis involve either complete or partial obstruction of the contrast column, presenting with hourglass appearance. Lateral lumbar canal stenosis may be represented by indentation of the thecal sac and/or insufficient filling of the nerve root sheath ⁷.

MRI

The characteristic findings of central lumbar canal stenosis is observed on sagittal images, such as a smoothly marginated waist or hourglass shape, and on axial images, such as a trefoil-shaped or circumferentially narrowed neural canal. Lateral lumbar canal stenosis is demonstrated as loss of fat signal and bone intrusion ⁶.

• T1

  • loss of fat high T1 signal

  • hypertrophic bone: dark region of low T1 signal

• T2: resembling a myelogram of thecal sac