Surgical management of vertebral synovial cysts in a rabbit (Oryctolagus cuniculus)

• Localización: JAVMA: Journal of the American Veterinary Medical Association, ISSN-e 0003-1488, Vol. 244, Nº. 7, 2014, págs. 830-834
• Idioma: inglés
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• Resumen

  • Case Description�An approximately 8-month-old female Miniature Lop rabbit (Oryctolagus cuniculus) was evaluated because of an acute onset of progressive paraparesis.

    Clinical Findings�The rabbit was ambulatory paraparetic, and results of neurologic examination were consistent with a myelopathy localizing to the T3-L3 spinal cord segments. Evaluation with CT myelography revealed focal extradural spinal cord compression bilaterally at the level of the articular process joints of T12-L1.

    Treatment and Outcome�A Funkquist type A dorsal laminectomy was performed at T12-L1, and the vertebral column was stabilized with pins and polymethylmethacrylate-based cement. Multiple vertebral synovial cysts were confirmed on histologic evaluation of the surgically excised tissues. The rabbit was nonambulatory with severe paraparesis postoperatively and was ambulatory paraparetic at a recheck examination 7 weeks after surgery. Fourteen weeks after surgery, the rabbit appeared stronger; it walked and hopped slowly but still fell and dragged its hindquarters when moving faster. Thirty-seven weeks after surgery, the neurologic status was unchanged.

    Clinical Relevance�Although thoracolumbar myelopathy in rabbits is commonly secondary to vertebral fracture, vertebral synovial cysts should be considered a differential diagnosis for rabbits with slowly progressive paraparesis. Decompressive surgery and stabilization can result in a good outcome for rabbits with this condition.

    An approximately 8-month-old sexually intact female Miniature Lop rabbit (Oryctolagus cuniculus) was evaluated because of a 3-day history of progressive paraparesis. The rabbit was acquired as a stray 3 months prior and subsequently housed with 1 other domestic rabbit. The rabbit was allowed to roam freely in the house during the day and was crated overnight. The diet consisted of adult rabbit food,a Timothy hay,b and a variety of vegetables. The only known previous medical history was an episode of poor appetite 2 months prior that had resolved within 24 hours with supportive care. There was no known history of trauma. Three days prior to the veterinary visit, the rabbit seemed weak and was observed to drag a pelvic limb during locomotion. In retrospect, the client thought that the rabbit may have missed some jumps onto low furniture and had seemed clumsy when it turned corners for an unspecified length of time. The client also noted that the rabbit would walk around corners, so that one pes was always in contact with the floor, rather than hopping. For the last few days, the rabbit had been scattering fecal pellets as it ran. The day prior to the examination, ataxia had seemed to progress. The rabbit was eating normally and did not have obvious signs of pain.

    On initial evaluation, the rabbit was alert and responsive. Heart rate, respiratory rate, and body temperature were within the respective reference ranges, and body weight was 2.2 kg (4.84 lb). Dry fecal material was found adhered to the perineum, but the remainder of the physical examination findings were considered normal. On neurologic examination, the rabbit was ambulatory with moderate paraparesis and general proprioceptive ataxia. Postural reactions (paw replacement test and hopping) were normal in the thoracic limbs and absent in the pelvic limbs. The patellar and withdrawal reflexes were normal in the pelvic limbs. The cutaneous trunci reflex was absent caudal to L2. Thoracic limb reflexes were not assessed. The neuroanatomic localization was within the T3-L3 spinal cord segments. Differential diagnoses included intervertebral disk herniation, congenital malformation (synovial cyst, subarachnoid diverticulum, and hemivertebrae), vertebral fracture, infectious disease (eg, diskospondylitis or encephalitozoonosis), mild traumatic injury with degenerative changes and spinal cord compression, or metabolic bone disease.

    The rabbit was administered meloxicamc (0.3 mg/kg [0.14 mg/lb], PO, q 12 h) and fenbendazoled (20.0 mg/kg [9.10 mg/lb], PO, q 24 h). Results of serologic testing of a blood sample for Encephalitozoon cuniculi were negative, and fenbendazole administration was discontinued after 5 doses. Packed cell volume, total solids concentration, and results of routine serum biochemical analysis were within reference intervals.e The rabbit was anesthetized for CT myelography. Following premedication with oxymorphone hydrochloridef (0.11 mg/kg [0.05 mg/lb]), ketamine hydrochlorideg (11.0 mg/kg [5.0 mg/lb]), and midazolam hydrochlorideh (1.1 mg/kg [0.5 mg/lb]) by IM injection, a 24-gauge right auricular IV catheter was placed, and anesthesia was induced with isoflurane delivered via face mask. Inhalation anesthesia was maintained with isofluranei in oxygen for the duration of the procedure (2.5 hours). A balanced electrolyte solutionj (10 mL/kg/h [4.5 mL/lb/h], IV) was administered throughout the procedure.

    A 22-gauge, 1.5-inch spinal needle was placed through the L6�7 interarcuate space with fluoroscopic guidance, and iohexolk (0.18 mL/kg; 54 mg I/kg [0.08 mL/lb; 24.5 mg I/lb]) was injected into the subarachnoid space. Immediately after the injection, the rabbit was placed in dorsal recumbency, and transverse-plane multi�detector row CT imagesl collimated to 1.25 mm and 50% overlap were obtained for the thoracolumbar region of the spinal column from the level of T6�7 through the L7-S1 vertebral articulation. Dorsal and sagittal plane reconstructions were made with a 64bit Digital Imaging and Communications in Medicine (DICOM) viewer and software.m Focally, at the T12-L1 articulation, the spinal cord was severely compressed from the dorsal left aspect and moderately compressed from the dorsal right aspect, with complete attenuation of the contrast column; the spinal cord had a triangular shape in the transverse plane in this region (Figures 1 and 2). At the level of maximal compression, width of the dorsal aspect of the spinal cord was approximately one-third that of the ventral aspect of the spinal cord. The left caudal articular process of T12 was displaced dorsally by approximately 0.1 cm, compared with the right caudal articular process of the same vertebra. Also, the T12-L1 articular facet joints were abnormally widened by fluid-attenuating material, more severely on the left than on the right side. The diagnostic interpretation was severe focal extradural spinal cord compression from the dorsal left (major) and dorsal right (moderate) aspects at the level of the T12-L1 articular facet joints. The primary differential diagnosis was bilateral articular facet joint synovial cysts. Other differential diagnoses included compression resulting from fibrosis secondary to previous spinal column trauma.

    View larger version(90K) Figure 1� Sagittal (A) and dorsal (B) plane reconstructed CT myelographic images of the vertebral column of an approximately 8-month-old Miniature Lop rabbit (Oryctolagus cuniculus) evaluated because of progressive paraparesis. The subarachnoid contrast column is focally attenuated and displaced from the left and right dorsal aspects at the level of T12-L1 (arrowheads). L = Left. R = Right.

    View larger version(52K) Figure 2� Transverse plane CT myelographic image obtained at the level of the T12-L1 articular process joints in the same rabbit as in Figure 1. Severe and mild extradural spinal cord compression from the left and right dorsal regions, respectively (white arrowheads), widened the articular process joints (black arrowheads), and dorsal displacement of the left T12 caudal articular process are evident. L = Left. R = Right.

    One day after CT myelography, the rabbit was nonambulatory paraparetic with urinary and fecal incontinence. Two days later, the patient's motor function had improved but it was still nonambulatory. The rabbit was anesthetized for surgery with the previously described anesthetic protocol, and a 2.5-mm endotracheal tube was placed with endoscopic guidance. Cefazolin sodiumn (22.7 mg/kg [10.3 mg/lb], IV, q 2 h), oxymorphone (0.11 mg/kg, IV, q 2 h), a bolus of hetastarch solutiono (2 mL/kg [0.9 mL/lb]), and a balanced electrolyte solution (10 mL/kg/h [4.5 mL/lb/h]) were administered during surgery.

    The rabbit was placed in sternal recumbency with the pelvic limbs in an extended position. A midline skin incision was made, and a Funkquist type A dorsal laminectomy was performed at T12-L1. The left T12-L1 articular facet joint was cauterized for identification as a landmark for histologic evaluation. The lamina and left and right articular facet joints were removed en bloc. Four 0.9 × 1.1-mm mini-interface pinsp were placed in the T12 and L1 vertebral bodies at the level of the transverse process, directed ventromedially parallel to the disk space, and stabilized with a polymethylmethacrylate-based cement.q A thin piece of gel foamr was placed over the exposed region of the spinal cord. Closure was routine. Postoperative radiographs showed that the pins purchased bone and had appropriate trajectory (Figure 3). The rabbit was administered meloxicam (0.3 mg/kg, SC, once, followed by the same dose PO, q 12 h for 9 days) and buprenorphine hydrochlorides (0.03 mg/kg [0.014 mg/lb], SC, q 8 h for 5 doses). Following recovery from anesthesia, the rabbit received syringe feedings and remained nonambulatory paraparetic while hospitalized. The rabbit was discharged 24 hours after surgery with orders for strict cage rest and continued nursing care. The rabbit was seen several times a week by a licensed veterinary physical therapist who developed a home exercise program for rehabilitation.

    View larger version(115K) Figure 3� Right lateral (A) and ventrodorsal (B) postoperative radiographic views of the same rabbit as in Figure 1. The dorsal laminae of T12 and L1 and the T12-L1 articular processes have been removed. All pins purchase bone, have appropriate trajectory, and are covered by polymethylmethacrylate-based cement (black arrowheads).

    The excised articular facet joints of T12 and L1 were submitted to the facility's pathology service for histologic evaluation. Two clear-fluid�filled, thin-walled cysts, measuring 0.15 to 0.25 cm in diameter, protruded from the ventral aspect of the en bloc section of the T12-L1 vertebral dorsal lamina and articular facets. On histologic examination, the cysts extended from the ventral surface of the interarcuate ligament, and each was composed of a thin fibrous wall lined by synoviocytes. The larger cyst was on the left side. The smaller cyst on the right side was continuous with the synovium (Figure 4). Within both facet joints, there was widening of the joint space, villous to nodular proliferation of the synovium, joint capsule fibrosis, mild osseous resorption, and periosseous new bone proliferation on both articular processes and the spinous process of L1. Findings were compatible with the diagnosis of vertebral synovial cysts with chronic osteoarthrosis.

    View larger version(65K) Figure 4� Photomicrograph of a histologic section of the excised articular process joints and lamina at T12-L1 from the rabbit in Figure 1. Multiple synovial cysts extend from the ventral surface of the vertebral arch of T12-L1. The smaller synovial cyst is continuous with the synovial lining of the right articular process joint through a breach in the interarcuate ligament (white arrowhead). Villonodular synovial hyperplasia (black arrowheads) and joint space widening are present in both the right and left articular process joints, and there is mild bony remodeling of the caudal articular process of T12 and cranial articular process of L1 (asterisks). H&E stain; bar = 500 µm.

    Seven weeks after surgery, the rabbit was weakly ambulatory with severe paraparesis and proprioceptive ataxia. The rabbit often became laterally recumbent in the pelvic region and hind limbs, instead of holding itself upright. Paw replacement tests were normal in the thoracic limbs and absent in the pelvic limbs. The patellar and withdrawal reflexes were normal in the pelvic limbs, and the cutaneous trunci reflex was normal. Thoracic limb reflexes were not assessed. Radiography of the lumbar region revealed static pin positioning.

    Fourteen weeks after surgery, the rabbit was weakly ambulatory with moderate paraparesis and pelvic limb ataxia. The pelvic limb muscle atrophy was less severe than at the 7-week recheck examination. The rabbit was stronger and able to raise its pelvis by pushing with its pelvic limbs. When ambulating slowly, the rabbit walked and hopped, but when moving faster, it fell and dragged the pelvic limbs. Results for the remainder of the neurologic examination were unchanged from the previous visit. The rabbit had regained urinary and fecal continence. The client was satisfied with the outcome and reported that the rabbit had continued improvement without signs of pain. Thirty-seven weeks after surgery, the neurologic status remained unchanged. The owner had constructed a device that, when used to support the abdomen, allowed the rabbit to jump with normal movements without falling.