Spina bifida

From Dog
Clinical appearance of a dog with spina bifida[1]
Microscopic view of C5 region of a Dalmatian with spina bifida[2]

Spina bifida is a rare neurological disease of dogs characterized by the presence of a midline cleft in the vertebral arch of a single or several vertebrae.[3].

Spina bifida is a developmental anomaly where a cleft forms due to failure of fusion of the halves of the dorsal spinous processes in utero, and may involve most of the vertebral arch or only the dorsal spinous process. This anomaly may be accompanied by protrusion of the spinal cord or its membranes.

While spina bifida has been reported in a wide variety of dogs, there is a high incidence of this condition in young English Bulldogs with sacrocaudal dysgenesis[4].

The disease has also been reported in the German Shepherd[5], Weimeraner[6], Pekingese[7], Dalmatian[2], Chinese Crested and Swedish Vallhund[8].

Spina bifida may occur anywhere along the spinal column but is most common in the lumbar region. In some instances, the defect can be extensive, involving most of the thoracic, lumbar, and caudal vertebrae[9] and dermoid sinus may be an accompanying complication[10].

Spina bifida manifesta, cystica and operta are synonymous subclassifications indicating presence of meningocele cyst (protrusion of the spinal cord membranes through a defect in the spinal column), myelocele (protrusion of the spinal cord) or meningomyelocele (protrusion of the spinal cord and its membranes through a defect in the spinal column)[11].

Rarely, diastematomyelia (dysraphism; split cord syndrome)[12], rachischisis (embryonic failure of fusion of the vertebral arches and neural tube) and myeloschisis (cleft spinal cord resulting from failure of the neural folds to close normally in the formation of the neural tube) are reported together[13].

Spina bifida occulta is characterized by a bony defect without visible protrusion of enclosed vertebral canal structures and is usually associated with smaller defects in the lamina. Most meningoceles and meningomyeloceles occur in the lumbosacral area and mainly involve nerve roots and spinal nerves of the cauda equina rather than spinal cord itself[14]. In such conditions, the meninges and their associated subarachnoid space extend through the vertebral defect to attach to the overlying skin from which CSF may leak. Subdermal or epaxial accumulation of CSF may also be found.

As a consequence of the meningeal attachment in the meningomyelocele, abnormal tension may be exerted on the spinal cord. This has been termed tethered cord syndrome[15]. The degree of spinal cord dysfunction in tethered cord syndrome appears to be related to both the force and duration of traction. Other anomalies, such as hydrocephalus, multiple thoracic and/or sacral hemivertebrae, may also be present in affected dogs[16].

Myelodysplasia, especially in sacrocaudal and lower lumbar segments, consisting of gliosis, hydromyelia (dilation of the central canal), syringomyelia (cavitations within the spinal cord), myeloschisis, or abnormal position of the central gray matter and anomalies of dorsal and ventral horns, may occur with spina bifida.

In some instances of myelodysplasia, necrosis of dorsal horns and dorsal white columns has been observed, creating a spongiform appearance to the parenchyma. Astrocytosis may be seen in affected white matter[17]. The embryonic pathogenesis of this anomaly is controversial: it may represent overgrowth of cells of the dorsal neural tube that, in turn, interferes with fusion of the neural tube and vertebral arches; or the vertebral arches may fail to fuse as a result of a neuroschistic bleb.

Clinical signs in animals with spina bifida usually indicate an associated myelodysplasia or protrusion of the meninges, spinal cord or cauda equina and are usually noticed when affected animals begin to ambulate.

Signs may include pelvic limb ataxia and paresis, fecal and urinary incontinence, perineal analgesia, and flaccid anal sphincter[18]. The analgesia may extend to the most proximal part of the posterior surface of the thighs, to the level of the scrotum and prepuce anteriorly, in male dogs, and to the tail caudally. The site of the bony defect may be marked by dimpling of the overlying skin, streaming of hair coat, and palpable cavitation in the dorsal spinous process.

Meningocele alone can be present without neurological deficits[19].

Diagnosis is based on presenting clinical signs, obsvious deformation and radiography which usually demonstrates abnormalities ranging from non-fusion of dorsal laminae to a cleft spinous process; however, myelography or advanced imaging techniques (e.g., ultrasonography, CT, or MRI) may demonstrate protrusion of spinal cord, nerve roots, and/or meninges through the sacral defect to the skin or subcutaneous spaces.

A differential diagnosis would include dermoid sinus and spinal arachnoid pseudocysts (mainly Rottweilers)[20].

Treatment of mild cases is usually unnecessary as it is often a subclinical condition and an incidental radiographic finding. Severe cases associated with myelodysplasia usually require euthanasia.

In some dogs with a fistulated meningocele/meningomyelocele, surgical ligation of the meningocutaneous tract can correct problems associated with loss of CSF and surgical untethering may reverse some of the neurological dysfunction caused by the tethered cord syndrome and prevent further deterioration of the motor, sensory and urinary functions[21].

References

  1. Atlas Garden
  2. 2.0 2.1 Neufeld JL & Little PB (1974) Spinal dysraphism in a Dalmatian dog. Can Vet J 15(11):335-336
  3. Vite, Ch (2004) Developmental disorders. In: Braund's Clinical Neurology in Small Animals: Localization, Diagnosis and Treatment. IVIS, Ithaca, New York, USA
  4. Fingeroth JM et al (1989) Neuroradiographic diagnosis and surgical repair of tethered cord syndrome in an English bulldog with spina bifida and myeloschisis. J Am Vet Med Assoc 194(9):1300-1302
  5. Clayton HM & Boyd JS (1993) Spina bifida in a German shepherd puppy. Vet Rec 112(1):13-15
  6. Engel HN & Draper DD (1982) Comparative prenatal development of the spinal cord in normal and dysraphic dogs: embryonic stage. Am J Vet Res 43(10):1729-1734
  7. Ruberte J et al (1995) Malformations of the vertebral bodies and the ribs associated to spinal dysraphism without spina bifida in a Pekingese dog. Zentralbl Veterinarmed A 42(5):307-313
  8. Kiviranta AM et al (2011) Dermoid sinus and spina bifida in three dogs and a cat. J Small Anim Pract 52(6):319-324
  9. Clayton HM, Boyd JS. (1983) Spina bifida in a German shepherd puppy. Vet Rec 112:13-15
  10. Motta L et al (2012) Dermoid sinus type IV associated with spina bifida in a young Victorian bulldog. Vet Rec 170(5):127
  11. Wilson JW, Kurtz HJ, Leipold HW, et al (1979) Spina bifida in the dog. Vet Pathol 16:165-179
  12. Allett B et al (2012) MRI of a split cord malformation in a German shepherd dog. J Am Anim Hosp Assoc 48(5):344-51
  13. Camon J, Sabate D, Franch J, et al (1990) Associated multiple congenital malformations in domestic animals. Contribution of four cases. Zentralbl Veterinarmed A 37:659-668
  14. Summers B, Cummings J, de Lahunta A. (1995) Veterinary Neuropathology. St Louis: Mosby, pp:68-94
  15. Yamada S, Iacono RP, Andrade T, et al (1995) Pathophysiology of tethered cord syndrome. Neurosurg Clin N Am 6:311-323
  16. Wilson JW, Kurtz HJ, Leipold HW, et al (1979) Spina bifida in the dog. Vet Pathol 16:165-179
  17. Wilson JW. (1982) Spina bifida in the dog and cat. Compend Contin Educ Pract Vet 4:626-636
  18. Brunetti A, Fatone G, Cuomo A, et al (1993) Meningomyelocele and hydrocephalus in a Bulldog. Prog Vet Neurol 4:54-59
  19. Furneaux RW, Doige CE, Kaye MM. (1973) Syringomyelia and spina bifida occulta in a Samoyed dog. Can Vet J 14:317-321
  20. Jurina K & Grevel V (2004) Spinal arachnoid pseudocysts in 10 rottweilers. J Small Anim Pract 45(1):9-15
  21. Shamir M, Rochkind S, Johnston D. (2001) Surgical treatment of tethered spinal cord syndrome in a dog with myelomeningocele. Vet Rec 148:755-756