What Is Your Diagnosis?

Alejandro Alvarez Sanchez Section of Veterinary Clinical Sciences, University College Dublin, Belfield, Dublin 4, Ireland.

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Ronan A. Mullins Section of Veterinary Clinical Sciences, University College Dublin, Belfield, Dublin 4, Ireland.

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Seamus Hoey Section of Veterinary Clinical Sciences, University College Dublin, Belfield, Dublin 4, Ireland.

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Barbara M. Kirby Section of Veterinary Clinical Sciences, University College Dublin, Belfield, Dublin 4, Ireland.

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History

A 10-year-old 5.3-kg (11.68-lb) neutered male Bichon Frise was evaluated because of a sudden onset of hind limb paralysis and signs of pain in the thoracolumbar vertebral area. The dog briefly had similar signs of pain 4 days prior to hospital admission, which resolved without intervention. No trauma or previous neurologic deficits were reported.

On physical examination, vital parameters were within reference intervals. Findings on orthopedic examination were unremarkable. The dog was nonambulatory paraplegic, with kyphosis of the thoracolumbar vertebral column. The dog had normal cranial nerve reflexes and forelimb function. Hind limb myotatic and flexor withdrawal reflexes were normal. The perineal reflex was intact. Hopping reactions in the hind limbs and extensor postural thrust were absent. The panniculus reflex was absent caudal to the level of the midlumbar portion of the vertebral column. On palpation, signs of pain were repeatable in the region of L2. The superficial pain response was absent in the hind limbs; however, the deep pain response was intact.

Findings on hematologic evaluation were unremarkable. Serum biochemical analysis revealed mild increases in the activities of alkaline phosphatase (96 U/L; reference interval, 0 to 82 U/L), alanine aminotransferase (83 U/L; reference interval, 0 to 36 U/L), aspartate aminotransferase (44 U/L; reference interval, 0 to 37 U/L), and creatine kinase (422 U/L; reference interval, 0 to 122 U/L). The dog was anesthetized, and MRI of the vertebral column was performed at the level of T3 through L3 (Figure 1).

Figure 1—
Figure 1—

Midsagittal T2-weighted (A), transverse T2-weighted (B), transverse T1-weighted (C), and transverse T2-weighted fluid attenuation inversion recovery (FLAIR; D) MRI images of the thoracolumbar vertebral column of a 10-year-old 5.3-kg (11.68-lb) neutered male Bichon Frise that was evaluated because of a sudden onset of hind limb paralysis and signs of pain in the thoracolumbar vertebral area. Panel A—Cranial is to the left of the image. The 13th thoracic vertebra is represented as T13. Panels B, C, and D—Images were obtained at the level of the L1–2 disk space (see inserts). The left side of the dog is to the right of the images.

Citation: Journal of the American Veterinary Medical Association 251, 9; 10.2460/javma.251.9.1007

Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page

Diagnostic Imaging Finding and Interpretation

At the level of the L1–2 disk space, there is dorsal deviation and deformation (dorsoventral flattening) of the spinal cord by a ventrally located, extradural, ovoid lesion. The lesion is centered on midline and extends from the midbody of L1 to the midbody of L2. The lesion is hypointense on the T1-weighted image, hyperintense on the T2-weighted image, and suppressed on the T2-weighted fluid attenuation inversion recovery (FLAIR) image (Figure 2). There is minimal to mild reduction in signal intensity of the L1–2 disk on the T2-weighted image, compared with that of the adjacent disks, with no loss of volume within the L1–2 disk. There is moderate hypointensity on the T2-weighted image of the T13-L1 disk, with narrowing of the disk space, and minimal focal compression of the ventral aspect of the spinal cord. The CSF and epidural fat are attenuated ventrally but are maintained dorsally. There is moderate reduction in signal intensity of the L2–3 disk on the T2-weighted image, with narrowing of the disk space and mild focal compression of the CSF and epidural fat ventrally. Dorsally, the CSF and epidural fat are intact but mildly compressed. There is mild hypointensity of the T9–10 and L4–5 disks on the T2-weighted image. On the basis of the MRI findings, a ventrally located intraspinal cystic lesion was considered most likely.

Figure 2—
Figure 2—

Same MRI images as in Figure 1. A (midsagittal T2-weighted image)—There is a hyperintense (relative to the spinal cord) lesion (asterisk) that extends from the midbody of L1 to the midbody of L2 and crosses the subjacent disk in a cap-like fashion. There is minimal to mild reduction in signal intensity of the L1–2 disk. B (transverse T2-weighted image)—The spinal cord (asterisk) is dorsoventrally flattened and compressed from a hyperintense ovoid extradural lesion that is ventral to the spinal cord. C (transverse T1-weighted image)—The compressive ovoid extradural lesion is hypointense relative to the dorsally located spinal cord (asterisk). D (transverse T2-weighted FLAIR image)—There is signal dropout of the compressive lesion (asterisk). The lesion is hypointense, compared with the nucleus pulposus within the L1–2 disk.

Citation: Journal of the American Veterinary Medical Association 251, 9; 10.2460/javma.251.9.1007

Treatment and Outcome

A left-sided T13 through L2 double hemilaminectomy was performed. The spinal cord appeared mildly contused at the level of the L1–2 disk space. A small, focal, fluid-filled bulge, which tapered cranially and caudally, was adherent to the ventral aspect of the dura mater at this location. No obvious connection with the dorsal longitudinal ligament or dorsal annulus fibrosus of the subjacent disk was identified. Following gentle probing with a right-angled ball probe, clear serous fluid emanated from the bulge, leaving no discernible tissue to biopsy. No nucleus pulposus was identified within the vertebral canal. No defect was identified in the dorsal annulus of the L1–2 disk. Recovery from anesthesia and surgery was uneventful.

Six weeks following surgery, the dog was brought back to the hospital for a neurologic assessment. The dog was ambulatory; however, bilateral hind limb proprioceptive ataxia remained. Follow-up conversation with the owner at 6 months after surgery revealed that the dog had regained complete neurologic function.

Comments

Magnetic resonance imaging findings of the dog of the present report were consistent with a ventrally located intraspinal fluid-filled structure. An extradural, compressive lesion with signal intensities analogous to those of pure fluid were identified on MRI images. The nature and pathogenesis of similar lesions have been debated in recent literature1–4; the authors of 2 studies1,2 proposed classification of these lesions as diskal cysts on the basis of their ventral extradural location, close association with the intervertebral disk, and MRI signal intensities. Compared with CSF, diskal cysts are typically isointense on short T1 inversion recovery and T2-weighted images; isointense to slightly hyperintense on T1-weighted images; and hypointense to hyperintense on T2-weighted FLAIR images—MRI findings that are similar to those of the dog of the present report.1,2 Acute compressive hydrated nucleus pulposus extrusion and partially degenerate disk extrusion in dogs have recently been found to also have MRI findings suggestive of cystic lesions.3,4

Findings on MRI proved instrumental in obtaining a preoperative diagnosis of a ventrally located intraspinal cystic lesion in the dog of the present report, and helped preclude the existence of extruded nucleus pulposus from the subjacent disk. T2-weighted sagittal images suggested no loss of nuclear volume within the L1–2 disk. On the T2-weighted FLAIR image, signal dropout of the hyperintense lesion allowed characterization of the lesion as pure fluid. Also on the transverse T2-weighted FLAIR image, the lesion was hypointense to the nucleus pulposus within the L1–2 disk, which suggested lack of involvement of the contents of the disk.

In humans, diskal cysts are well-defined homogeneous lesions located in the ventrolateral aspect of the extradural space, adjacent to an intervertebral disk. They occur almost exclusively in the lumbar vertebral column, causing chronic painful lumbar radiculopathy.5,6 On MRI, diskal cysts in humans are hyperintense on T2-weighted images and hypointense on T1-weighted images, and isointense relative to CSF; these lesions have been confirmed by CT diskography to communicate with the subjacent intervertebral disk.5 To our knowledge, CT features of these types of cystic lesions have not been reported in dogs in the veterinary literature. In a clinical report7 of a dog with a chronic history of thoracolumbar vertebral pain and inability to stand, a histologically confirmed intraspinal cyst associated with the annulus fibrosus of the subjacent intervertebral disk was found. In that dog, MRI revealed a centrally and ventrally located, extradural, compressive lesion that was hypointense on T1-weighted images, hyperintense on T2-weighted images, and isointense to CSF on all sequences.7 The acute onset of neurologic signs in the dog of the present report is difficult to explain, as a cyst would be expected to result in slowly progressive spinal cord compression and a more protracted history of neurologic dysfunction.7 The dog of the present report had a brief episode of apparent vertebral pain 4 days prior to hospital admission, which resolved without intervention; however, no previous neurologic deficits were described. A similar acute onset of neurologic signs has been described in 2 separate reports1,2 of dogs with suspected ventrally located intraspinal or diskal cysts, although the nature of these lesions has recently been questioned.3,4 In the dog of the present report, rupture of the fluid-filled structure occurred intraoperatively with careful probing, leaving behind no identifiable tissue to biopsy, and precluded establishment of a definitive diagnosis of an intraspinal cyst.1,2

Several other spinal cystic lesions were initially considered as differential diagnoses in the dog of the present report, most of which were eliminated on the basis of their typical dorsal or dorsolateral location within the vertebral canal. An intraspinal cyst associated with the dorsal longitudinal ligament, analogous to posterior longi- tudinal ganglion cysts in people, has not been previously reported in dogs.8 The possibility of the existence of this lesion could not be excluded on the basis of findings on preoperative MRI; however, no obvious connection between the fluid-filled lesion and the dorsal longitudinal ligament could be identified intraoperatively. Perineurial cysts (also known as Tarlov cysts) are extradural cysts involving the spinal nerve roots. They are hyperintense on T2-weighted images and hypointense on T1-weighted images and are located dorsolateral to the spinal cord or at the level of the intervertebral foramen.8,9 Arachnoid diverticula are intradural fluid-filled dilations of the subarachnoid space. They are almost exclusively located dorsal or dorsolateral to the spinal cord. Computed tomographic features include teardrop-shaped extensions of the subarachnoid space. They are hyperintense on T2-weighted images, hypointense to isointense on T1-weighted images, and hypointense on T2-weighted FLAIR images.8,9 Synovial cysts arise from the synovium of the articular facet joints and communicate directly with the joint. Findings on CT and MRI include a dorsolaterally located, well-circumscribed, extradural lesion in close association with a degenerative facet joint. They are hyperintense on T2-weighted images and variably hypointense on T1-weighted images. So called ganglion cysts do not possess an epithelial lining and are believed to arise from the periarticular joint tissue; they are hyperintense and isointense to CSF on T1-weighted images and T2-weighted images, respectively.8,9

In the present report, we describe a presumed intraspinal cyst that was ventrally located and adherent to the ventral aspect of the dura mater of the thoracolumbar spinal cord, which resulted in clinical signs similar to acute disk herniation. The dog achieved full neurologic recovery following hemilaminectomy and spinal cord decompression.

References

  • 1. Konar M, Lang J, Flühmann G, et al. Intraspinal cysts associated with the intervertebral disc: magnetic resonance imaging observations in seven dogs. Vet Surg 2008; 37:94101.

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  • 2. Kang BJ, Jung Y, Park S, et al. Discal cysts of the cervical spine in two dogs. J Vet Sci 2015; 16:543545.

  • 3. Beltran E, Dennis R, Doyle V, et al. Clinical and magnetic resonance imaging features of canine compressive cervical myelopathy with suspected hydrated nucleus pulposus extrusion. J Small Anim Pract 2012; 53:101107.

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    • Search Google Scholar
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  • 4. Falzone C. Canine acute cervical myelopathy: hydrated nucleus pulposus extrusion or intraspinal discal cysts? Vet Surg 2017; 46:376380.

  • 5. Kono K, Nakamura H, Inoue Y, et al. Intraspinal extradural cysts communicating with adjacent herniated disks: imaging characteristics and possible pathogenesis. Am J Neuroradiol 1999; 20:13731377.

    • Search Google Scholar
    • Export Citation
  • 6. Chiba K, Toyama Y, Matsumoto M, et al. Intraspinal cyst communicating with the intervertebral disc in the lumbar spine: discal cyst. Spine (Phila Pa 1976) 2001:21122118.

    • Search Google Scholar
    • Export Citation
  • 7. Penning V, Benigni L, Steeves E, et al. Imaging diagnosis—degenerative intraspinal cyst associated with the intervertebral disc. Vet Radiol Ultrasound 2007; 48:424427.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8. Lowrie M, Platt S, Garosi L. Extramedullary spinal cysts in dogs. Vet Surg 2014; 43:659662.

  • 9. Da Costa RC, Cook L. Cystic abnormalities of the spinal cord and vertebral column. Vet Clin North Am Small Anim Pract 2016; 46:277293.

  • Figure 1—

    Midsagittal T2-weighted (A), transverse T2-weighted (B), transverse T1-weighted (C), and transverse T2-weighted fluid attenuation inversion recovery (FLAIR; D) MRI images of the thoracolumbar vertebral column of a 10-year-old 5.3-kg (11.68-lb) neutered male Bichon Frise that was evaluated because of a sudden onset of hind limb paralysis and signs of pain in the thoracolumbar vertebral area. Panel A—Cranial is to the left of the image. The 13th thoracic vertebra is represented as T13. Panels B, C, and D—Images were obtained at the level of the L1–2 disk space (see inserts). The left side of the dog is to the right of the images.

  • Figure 2—

    Same MRI images as in Figure 1. A (midsagittal T2-weighted image)—There is a hyperintense (relative to the spinal cord) lesion (asterisk) that extends from the midbody of L1 to the midbody of L2 and crosses the subjacent disk in a cap-like fashion. There is minimal to mild reduction in signal intensity of the L1–2 disk. B (transverse T2-weighted image)—The spinal cord (asterisk) is dorsoventrally flattened and compressed from a hyperintense ovoid extradural lesion that is ventral to the spinal cord. C (transverse T1-weighted image)—The compressive ovoid extradural lesion is hypointense relative to the dorsally located spinal cord (asterisk). D (transverse T2-weighted FLAIR image)—There is signal dropout of the compressive lesion (asterisk). The lesion is hypointense, compared with the nucleus pulposus within the L1–2 disk.

  • 1. Konar M, Lang J, Flühmann G, et al. Intraspinal cysts associated with the intervertebral disc: magnetic resonance imaging observations in seven dogs. Vet Surg 2008; 37:94101.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2. Kang BJ, Jung Y, Park S, et al. Discal cysts of the cervical spine in two dogs. J Vet Sci 2015; 16:543545.

  • 3. Beltran E, Dennis R, Doyle V, et al. Clinical and magnetic resonance imaging features of canine compressive cervical myelopathy with suspected hydrated nucleus pulposus extrusion. J Small Anim Pract 2012; 53:101107.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Falzone C. Canine acute cervical myelopathy: hydrated nucleus pulposus extrusion or intraspinal discal cysts? Vet Surg 2017; 46:376380.

  • 5. Kono K, Nakamura H, Inoue Y, et al. Intraspinal extradural cysts communicating with adjacent herniated disks: imaging characteristics and possible pathogenesis. Am J Neuroradiol 1999; 20:13731377.

    • Search Google Scholar
    • Export Citation
  • 6. Chiba K, Toyama Y, Matsumoto M, et al. Intraspinal cyst communicating with the intervertebral disc in the lumbar spine: discal cyst. Spine (Phila Pa 1976) 2001:21122118.

    • Search Google Scholar
    • Export Citation
  • 7. Penning V, Benigni L, Steeves E, et al. Imaging diagnosis—degenerative intraspinal cyst associated with the intervertebral disc. Vet Radiol Ultrasound 2007; 48:424427.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8. Lowrie M, Platt S, Garosi L. Extramedullary spinal cysts in dogs. Vet Surg 2014; 43:659662.

  • 9. Da Costa RC, Cook L. Cystic abnormalities of the spinal cord and vertebral column. Vet Clin North Am Small Anim Pract 2016; 46:277293.

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