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Brain & Spine Disorders

Thoracic Spinal Stenosis

Background
Acute and chronic neck, mid back, and lower back pain represents a major health care problem in the United States. An estimated 75% of people will experience back pain at some time in their lives. Most patients who present with an acute episode of back pain recover without surgery, while 3-5% of patients presenting with back pain have a herniated disc and 1-2% have compression of a nerve root. Older patients present with more chronic or recurrent symptoms of degenerative spinal disease. Progressive narrowing of the spinal canal may occur alone or in combination with acute disc herniations. Congenital and acquired spinal stenoses place the patient at greater risk for acute neurologic injury.

The goal of spinal imaging is to localize the site and level of disease and to help differentiate between conditions in which patients require surgery and conditions in which patients recover following conservative treatment.

Pathophysiology
Spinal stenosis results from the progressive combined narrowing of the central spinal canal, the neurorecesses, and the neuroforaminal canals. The essential content of the spinal canal includes the spinal cord, the cerebral spinal fluid of the thecal sac, and the dural membranes that enclose the thecal sac. In the absence of prior surgery, tumor, or infection, the spinal canal may become narrowed by bulging or protrusion of the intervertebral disc annulus, herniation of the nucleus pulposis posteriorly, thickening of the posterior longitudinal ligament, hypertrophy of the facet joints, hypertrophy of the ligamentum flavum, epidural fat deposition, spondylosis of the intervertebral disc margins, uncovertebral joint hypertrophy in the neck, or a combination of two or more of the above factors.

The central canal and the neurorecess may be compromised by tumor infiltration, such as metastatic disease of the spine, and by infectious spondylitis. An abscess may directly compress the spinal cord if it is contained in the epidural space, while discitis and vertebral osteomyelitis may compress the canal following vertebral collapse. Paget disease results in spinal stenosis as result of enlargement of the vertebral body, while idiopathic ossification of the posterior longitudinal ligament directly narrows the central spinal canal most often in the cervical or thoracic regions.

Patients with spinal stenosis become symptomatic when pain, motor weakness, paresthesia, or other neurologic compromise causes distress. Spinal stenosis of the thoracic spine is more likely to directly affect the spinal cord due to the relatively narrow thoracic spinal canal. Compression of the thoracic spinal cord can result in myelopathy. Central compression of the cervical spinal cord also results in myelopathy, while paramedial and lateral disease causes radiculopathy and involvement of specific nerve root distributions.

Spinal stenosis of the cervical and thoracic regions may contribute to neurologic injury, such as development of a central spinal cord syndrome following spinal trauma. Spinal stenosis of the lumbar spine is associated most commonly with midline back pain and radiculopathy. In cases of severe lumbar stenosis, innervation of the urinary bladder and the rectum may be affected, but most often, lumbar stenosis results in back pain with lower extremity weakness and numbness along the distribution of nerve roots of the lumbar plexus.

Frequency
  • In the US: In the United States, as many as 35% of persons who are asymptomatic and aged 20-39 years demonstrate disc bulging. CT and MRI studies in patients who are asymptomatic and younger than 40 years demonstrate a 4-28% occurrence of spinal stenosis. In patients older than age 60 years, most manifest spinal stenosis to some degree. Since most patients with mild spinal stenosis are asymptomatic, the absolute frequency can only be estimated.
  • Internationally: The international occurrence of spinal stenosis is similar to the experience in the United States. Nations with large numbers of older citizens tend to have a higher occurrence of spinal stenosis.
Mortality/Morbidity
Spinal stenosis can result in significant morbidity. The primary symptoms are pain, numbness, and motor weakness. Severe disability and death may result from the association of cervical stenosis with even minor trauma resulting in the central cord syndrome. Upper (cervical), mid (thoracic), and lower (lumbar) spinal stenosis may result in motor weakness and chronic pain. Severe lumbar stenosis is associated with the cauda equina syndrome.
  • Central spinal stenosis of the cervical or thoracic regions may result in neurosensory changes at the level of the spinal stenosis or may further compress the spinal cord, resulting in myelopathy. In the patient with spinal canal stenosis, flexion or marked hyperextension may result in further compromise of the spinal canal in the absence of a fracture. Anterior compression of the cord may result in a central spinal cord syndrome. Dorsal compression of the spinal cord may result in a partial dorsal column syndrome. The effects of central spinal canal stenosis may result in lower extremity weakness and gait disturbance.
  • Lateral spinal stenosis generally results in symptoms that are directly related to compression of the nerve roots at the level of the stenosis. Both pain and muscular weakness may result from hypertrophy of the facet joints, spondylosis deformity, bulging of the disc annulus, or herniation of the nucleus pulposis. While large central disc herniations occur, most extruded disc fragments migrate laterally, while some disc fragments move to a position that is superior or inferior to the interspace.
  • Metastatic and infection processes that affect the spine may present with both regional pain and signs of central spinal canal narrowing. The regional pain may result from pathologic fractures or nerve root compression by the tumor or abscess. Long tract findings may result from bone fragments, hemorrhage, abscess, or tumor compressing the spinal cord.
Race
Cervical stenosis resulting from ossification of the posterior longitudinal ligament is more common among Asians.

Sex
Lumbar spinal stenosis occurs more commonly in males. This may be a combination of a congenitally narrow canal linked with occupational risk.

Age
Spinal stenosis can be seen in both children and adults. Primary (congenital) lumbar spinal stenosis is associated with achondroplastic dwarfism. The incidence of acquired spinal stenosis increases with age.

Anatomy
The anterior-posterior diameter of the normal adult male cervical canal has a mean value of 17-18 mm at vertebral levels C3-C5. The lower cervical canal measures 12-14 mm. Cervical stenosis is associated with an anteroposterior (AP) diameter of less than 10 mm, while diameters of 10-13 mm are relatively stenotic in the upper cervical region.

In the central cervical spinal region, hypertrophy of the ligamentum flavum, bony spondylitic hypertrophy, and bulging of the disc annulus contribute to development of central spinal stenosis. In each case, the relative significance of each structure contributing to the stenotic pattern is variable.

Movement of the cervical spine exacerbates congenital or acquired spinal stenosis. In hyperextension, the cervical cord increases in diameter. Within the canal, the anterior roots are pinched between the annulus margins and spondylitic bony bars. In the posterior canal, hypertrophic facet joints and thickened infolded ligamentum flavum compress the dorsal nerve roots. In hyperflexion, neural structures are tethered anteriorly against the bulging disc annulus and spondylitic bars. In the event of a vertebral collapse, the lordotic cervical loses its shape, resulting in chronic anterior cord compression.

Lateral cervical stenosis results from encroachment on the lateral recess and the neuroforamina of the cervical region, primarily as a result of hypertrophy of the uncovertebral joints, lateral disc annulus bulging, and facet hypertrophy. The thoracic spinal canal varies from 12-14 mm in diameter in the adult. Primary central thoracic spinal stenosis is rare. Occasionally, hypertrophy or ossification of the posterior longitudinal ligament results in central canal stenosis.

Lateral thoracic stenosis may result from hypertrophy of facet joints with occasional synovial cyst encroachment. The diameter of the normal lumbar spinal canal varies from 15-27 mm. Lumbar stenosis results from a diameter of less than 12 mm in some patients, while a diameter of 10 mm is definitely stenotic.

Clinical Details
The primary clinical manifestation of spinal stenosis is chronic pain. In patients with severe stenosis, weakness and regional anesthesia may result. Among the most serious complications of severe spinal stenosis is central cord syndrome. Central cord syndrome is the most common incomplete cord lesion. The presentation commonly is associated with an extension injury in a patient with an osteoarthritic spine. In hyperextension injury, the cord is injured within the central gray matter, which results in proportionally greater loss of motor function to upper extremities than to lower extremities with variable sensory sparing. Cauda equina syndrome presents with urinary retention, saddle anesthesia, loss of rectal tone, and loss of bulbocavernosus reflex with sacral sparing.

Preferred Examination
Older patients in whom spinal stenosis is suggested should be examined using conventional spinal radiology, including AP, lateral, oblique, and lower lumbar–centered views. Lateral views are most sensitive for central spinal stenosis, while oblique views of the cervical and lumbar areas better demonstrate lateral stenosis syndromes. Younger patients and all patients in whom conventional radiology findings are negative should be evaluated using either spinal CT scanning with reformatted images, spinal MRI, or single-photon emission computed tomography (SPECT) bone scintigraphy.

Spinal MRI is the most universally suitable technique for the diagnosis of spinal stenosis. The examination should be performed using thin sections (3 mm) and high resolution (256 X 192 matrix). Spinal MRI should include imaging sets obtained in the axial and sagittal planes using T1-weighted, proton-density, and T2-weighted techniques. The bony and osteophytic components of the spinal stenosis pattern are seen best using a T2-weighted gradient-echo technique.

CT of the cervical, thoracic, and/or lumbar spine may be useful in selected patients, often during the performance of CT myelography. Indications for CT myelography include contraindications for MRI, implanted metal devices in patients, and postoperative patients with suggested complications. CT of the spine should be followed by multiplanar reformatted images and 3-dimensional imaging techniques in selected patients.

Mid Back Pain & Disorders (Thoracic Spine)

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