Narrow Spinal Canal

► [Decreased sagittal and/or transverse diameter of the spinal canal]

Stenosis of the spinal canal can be congenital or acquired. Symptoms are related to compression of the thecal sac and/or nerve roots, and vary according to the level of spine involvement. When narrowing is in the cervical region symptoms are experienced in the arms and hands, whereas with narrowing of the lumbar spine symptoms occur in the legs and feet. Pain and numbness in the extremities are common presenting symptoms. Headache and neck pain are also frequent complaints. With lumbar spine stenosis, pain in the back and legs is aggravated by standing and walking and relieved by sitting or forward bending. In fact, in the bent-over and sitting positions the capacity of the lumbar spinal canal is maximized. Neurological deficits, including weakness, sensory loss, and sphincter or sexual dysfunction can develop in the advanced stages (cauda equina syndrome), requiring surgical decompression.

The most common cause of spinal stenosis in adults is degenerative disease of the spine. Changes usually involve the cervical and lumbar spine, and they include formation of bony spurs, thickening of the posterior longitudinal ligament and ligamenta flava, facet joint hypertrophy, enlarged laminae, and prolapse of disc material. Osteophytes can arise from the intervertebral discs and the apophyseal articulations, encroaching on the spinal canal and the neural foramina, respectively. Though much less commonly, cases of thoracic myelopathy associated with thoracic canal stenosis are encountered, in the absence of a generalized rheumatological, metabolic, or or thopedic disorder (Barnett et al. 1987). Spinal stenosis may also be secondary to disorders of traumatic, infectious, neoplastic, and metabolic origin. Spondylolisthesis, meaning anterior dislocation of a vertebra over the body of the adjacent vertebra located below, can be responsible for narrowing of the intervertebral foramina,resulting in compression of the exiting nerve roots. Spondylolisthesis can be secondary to spondylolysis, degenerative disease, or trauma. Spondylolysis is the term applied to a corticated cleft in the pars interarticularis at the lumbar level, or between the superior and inferior articular facets of the articular pillar, the equivalent of the pars inter-articularis in the cervical spine. Controversy persists over whether this lesion is congenital (faulty ossification within the ossification center for the articular mass) or acquired (repetitive microtrauma or post-traumatic nonunion) (Forsberg et al. 1990; Charlton et al. 1978). Instances of autosomal dominant transmission with about 75 % penetrance have been docu-mented,probably as a result of a dysplastic pedicle or pars interarticularis (Haukipuro et al. 1978). The lesion is more common in the lumbar than in the cervical spine and is most frequently located at L-5. In the cervical spine, C-6 is the most common location, followed in frequency by C-4 (Schwartz 2001). Symptoms range from none to mild neck pain, neck stiffness, and radiculopathy. Unilateral lesions are far more common than bilateral ones. Arthritides and enthesopathies, such as rheumatoid arthritis, anky-losing spondylitis, synovial cysts of the facet joint, calcium pyrophosphate dihydrate crystal deposition disease, and ossification of the posterior longitudinal ligament or ligamentum flavum from any cause, can result in narrowing of the spinal canal. Primary or secondary spinal tumors and tumor-like lesions, such as hemangioma, aneurysmal bone cysts, osteochon-droma, and osteoblastoma can also cause spinal canal stenosis. Paget disease may also compromise the spinal cord (Munday et al. 1994). In pseudohypoparathyroidism (OMIM 103580) and pseudo-pseudohypoparathyroidism (OMIM 300800) spinal stenosis is not uncommon, occurring because of the presence of vertebral anomalies or as a result of ectopic calcifications involving the ligaments of the vertebral canal. Cheirolumbar dysostosis is characterized by brachydactyly (brachymetacarpia/brachy-phalangia) and stenosis of the vertebral canal (lumbar or, less frequently, cervical) (Fig. 3.62). Whether it represents a distinct entity or a phenotype of pseudohypoparathyroidism is debated (Halloran et al. 1983). Individuals with X-linked hypophospha-temia (vitamin D-resistant rickets, X-linked, OMIM

Hypophosphatemia
Fig. 3.62. Cheirolumbar dysostosis. Note relative proximity of the lumbar pedicles, with lack of normal craniocaudal increase in the interpediculate distance

307800), a disorder characterized by hypophosphatemia secondary to phosphate loss at the renal tubuli with normal serum levels of calcium (gene locus maps to Xp22.2-p22.1), typically show ricketslike changes at the growth plates in childhood and increased bone density and ligament calcifications in adulthood. Progressive ankylosis of the spine and major joints, simulating ankylosing spondylitis, is common in adult males. New bone formation in the ligamentum flavum and laminar thickening may be responsible for stenosis of the spinal canal and compression of the spinal cord (Adams and Davies 1986).

A narrow spinal canal may be present at birth as an isolated anomaly, in association with congenital vertebral anomalies, or as part of more complex

Fig. 3.63. Isolated spinal canal stenosis. Note marked reduction of the interpediculate distance in the lumbar spine, with severe shortening of the laminae and 'dysplastic' joint facets. Right-sided mild scoliosis is also evident malformation syndromes and skeletal dysplasias. Hemivertebrae, wedged vertebrae, and fused vertebrae can cause spinal stenosis by compromising the spinal alignment, inducing vertebral instability or precocious degenerative spine disease (Lee and Weiss 1981).

Isolated, constitutional narrowing of the spinal canal has long been recognized (Fig. 3.63). Several antenatal factors, including small gestational age, small placental weight, relatively advanced maternal age, and low birth weight, can permanently stunt the growth of the spinal canal, giving rise to constitutional spinal stenosis (Papp et al. 1997). Only rarely does a constitutionally narrowed spinal canal produce clinical symptoms in childhood (Dauser and

Fig. 3.64. Hypochondropla-sia.Note reduced interpedicu-late spaces from L-1 to L-5, indicating narrowing of the spinal canal. (From Prinster et al. 2001)

Narrowing The Spine

Fig. 3.64. Hypochondropla-sia.Note reduced interpedicu-late spaces from L-1 to L-5, indicating narrowing of the spinal canal. (From Prinster et al. 2001)

Chandler 1982). With aging, acquired disease processes and degenerative abnormalities may further compromise a congenitally narrowed spinal canal, leading to severe spinal cord compression and more obvious clinical symptoms. Familial instances of lumbar stenosis (OMIM 152550) have been reported (Verbiest 1973; Varughese and Quartey 1979; Post-acchini et al. 1985).

Spinal stenosis is extremely common in achon-droplasia (OMIM 100800), both at the lumbar and at the cervical level. Spinal stenosis and resultant compression of the spinal cord and nerve roots usually develops in adulthood and may be further exacerbated by thoracolumbar gibbus, osteophyte formation, or disc herniation (Wynne-Davies et al. 1981). Cervical cord compression and hydrocephalus may develop owing to tightness of the foramen magnum (Rimoin 1995). Hypochondroplasia (OMIM 146000) (Lamy and Maroteaux 1961), which often cannot be reliably diagnosed by clinical and radiologic examination, resembles true achondroplasia in many respects, but especially in the appearance of the spinal canal, with its caudad narrowing of the interpedicu-late distance and anteroposterior shortening of the pedicles (Wynne-Davies et al. 1981). This is indeed a constant radiographic finding in hypochondroplasia (Fig. 3.64). The skeletal abnormalities in these two allelic disorders are qualitatively similar but quantitatively different, with strikingly milder features in the pelvis and skull in hypochondroplasia. Moreover, in hypochondroplasia no tibial bowing is found and the trident appearance of the hands is also lacking. Brachyolmia, which literally means short trunk, encompasses a heterogeneous group of conditions characterized by gross spinal involvement while limb involvement ranges from none (Shohat et al. 1989) to minimal (Kozlowski et al. 1982). The vertebral bodies are small, squared-off (Hobaek type, OMIM 271539; and Toledo type, OMIM 271630) or anteriorly rounded (Maroteaux type, OMIM 271530) and radiolucent, with marked end-plate indentations and irregularities, especially in the cervical spine. Severe scoliosis and platyspondyly are also features (Shohat et al. 1989; Gardner and Beighton 1994). Spinal stenosis throughout the entire length of the spine and precocious calcification of costal cartilages are striking features in Hobaek type (Hobaek 1961) (Fig. 3.65). Changes in the spine resembling those of brachy-olmia, including platyspondyly with short pedicles and narrow intervertebral and interpedicular distances, are found in the condition referred to as platyspondyly with amelogenesis imperfecta (OMIM 601216). A distinctive finding in this probably autosomal recessive condition is absence of the enamel cap of the teeth (Verloes et al. 1996). The spinal canal is usually only mildly narrowed in diastrophic dys-plasia (OMIM 222600), although significant spinal cord and cauda equina compression may occur owing to severe cervical kyphosis, thoracolumbar kyphoscoliosis, and exaggerated lumbar lordosis (Remes et al. 2001). In multiple hereditary exostoses (OMIM 133700) bony outgrowths encroaching on the spinal canal may cause spinal cord or nerve root compression (Johnston and Sklar 1988). Coffin-Lowry syndrome (OMIM 303600) is characterized by mental retardation, short stature, thick hands with tapered fingers, and a coarse face, consisting of square forehead, pugilistic nose, prominent lips, and

Brachyolmia Type Toledo Type
Fig. 3.65. Brachyolmia. The vertebral bodies are flat and project laterally beyond the pedicles.The interpedicular distance is markedly decreased

large ears. Spinal abnormalities include thoracic kyphosis, lumbar gibbus, and calcification of the lig-amenta flava, resulting in marked spinal canal stenosis (Ishida et al. 1992; Miyazaki et al. 1990). Stenosis of the cervical spinal canal has been found in 25 % of patients with Klippel-Feil syndrome (OMIM 148900) (Ritterbusch et al. 1991). An association of cervical stenosis, brachydactyly, syndactyly, and hyperopia has been described in several members in the same family (Iida et al. 1989). A multiple malformation syndrome has been described in a girl who presented with müllerian dysgenesis, conductive hearing loss, facial hypoplasia and asymmetry, bowed forearm, brachydactyly, spinal canal stenosis, and thoracolumbar kyphoscoliosis (Kumar and Masel 1997).

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