History

A 5-year-old 15-kg neutered male Beagle dog was evaluated for a 3-week history of low tail carriage. No previous trauma was reported by the owner. The dog had been prescribed a 10-day steroid anti-inflammatory treatment (prednisolone, 1 mg/kg, PO, q 24 h for 4 days, then 0.5 mg/kg, PO, q 24 h for 4 days) and strict rest, with initial mild improvement of the tail motricity. However, the dog’s status worsened 2 days prior to presentation at our institution, when the dog developed pain and vocalizations while defecating. General physical examination was unremarkable. A neurologic examination was performed.

View Full Size

• Download Figure
• Download figure as PowerPoint slide

Assessment

Diagnostic Test Findings

Results of the CBC and biochemical analysis were within normal limits. CT of the spine extending from the fourth lumbar vertebra (L4) to the seventh caudal vertebra (Cd7) was performed using a 16-slice CT unit (Revolution ACT; GE Healthcare) while the dog was under general anesthesia and positioned in dorsal recumbency. Selected scanning parameters were as follows: 120-kVp tube voltage, 80-mA tube current, 1-second tube rotation time, 16-cm display field of view, 0.625-mm slice thickness, 1:1 helical pitch, and 2 image reconstruction algorithms (medium [proprietary term bone] and low frequency [proprietary term soft tissue]). Spinal CT examination findings included 2 separate, well-delineated mineral density structures extending from the ventral region of the vertebral canal through the right Cd1-Cd2 and right Cd2-Cd3 intervertebral foramen with an almost complete obliteration of both foramen, a not displaced mineralized Cd3-Cd4 disk, mild ventral spondylosis deformans of the Cd2-Cd5 coccygeal segment, and mild L7-S1 disk protrusion with no evidence of nerve roots compression (Figures 1 and 2).

View Full Size

Transverse CT images at the level of 2 adjacent intervertebral disk spaces Cd1-Cd2 (A) and Cd2-Cd3 (B), showing 2 separate mineral density materials extending from the ventral region of the vertebral canal through the right Cd1-Cd2 and right Cd2-Cd3 intervertebral foramen (white arrows). Both Cd1-Cd2 and Cd2-Cd3 intervertebral disk spaces contain calcified disk material (red arrows).

Citation: Journal of the American Veterinary Medical Association 261, 2; 10.2460/javma.22.07.0276

• Download Figure
• Download figure as PowerPoint slide

View Full Size

Parasagittal CT reconstruction of the L5-Cd6 spinal segment showing 2 mineralized materials occupying most of the right Cd1-Cd2 and right Cd2-Cd3 intervertebral foramen (white arrows). The normal-appearing right Cd3-Cd4 foramen contains normal hypodense fat (green arrow). Notice the strongly mineralized Cd3-Cd4 disk (short blue arrow), mild ventral spondylosis deformans of the Cd2-Cd5 spinal segment (yellow arrowheads) and mild protrusion of the L7-S1 disk (red arrow) with no evidence of cauda equina nerve roots compression.

Citation: Journal of the American Veterinary Medical Association 261, 2; 10.2460/javma.22.07.0276

• Download Figure
• Download figure as PowerPoint slide

Comments

Coccygeal intervertebral disk herniation has been rarely reported in dogs.^1–5 Various treatment modalities have been described, including conservative management, surgical treatment, and epidural steroid and local anesthetic injections.^1–5 In the current case, conservative treatment consisting of strict rest and administration of prednisolone at an anti-inflammatory dose only resulted in a mild clinical improvement. Surgical decompression was therefore elected. A right-sided hemilaminectomy was performed at the level of Cd1-Cd2 and Cd2-Cd3 intervertebral spaces. Extruded disk material was removed on both sites until the nerve roots appeared completely free and mobile. A postsurgical CT scan confirmed complete removal of the extruded mineralized material, with preservation of the coccygeal vertebral alignment. Postoperative analgesia was initially provided using morphine (0.2 mg/kg, IV, q 4 h for 12 hours) and subsequently buprenorphine (0.01 mg/kg, IV, q 6 h for 24 hours). Additionally, the dog received prophylactic antibiotics (cefalexin, 15 mg/kg, PO, q 12 h for 4 days), prednisolone (1 mg/kg, PO, q 24 h for 3 days, then 0.5 mg/kg, PO, q 24 h for 7 days), and gabapentin (10 mg/kg, PO, q 12 h for 10 days). Recovery from the surgical procedure was uneventful. The day following surgery, the dog was wagging its tail and defecating without any obvious discomfort and was therefore discharged from hospital. Ten months after surgery, during a phone interview, the owners reported that the dog had completely recovered. Coccygeal intervertebral disk herniation appears to be a rare pathology in dogs, with only 9 cases reported in the literature.^1–5 Chondrodystrophic and nonchondrodystrophic breeds have been reported.^1–5 Dogs were essentially middle aged (mean, 7 years; range, 3.5 to 9 years). As in the current case, previously reported clinical signs of coccygeal disk herniation were mostly low tail carriage, difficulty defecating, and signs of pain when the tail was manipulated.^1–5 A progressive tail paresis was less commonly observed.^3,5

In all of the cases reported in the literature, coccygeal disk herniation involved the Cd1-Cd2 intervertebral disk.^1–5 Furthermore, even though in some cases the authors reported the presence of multiple, nondisplaced, degenerated disks, no case of multiple sites of coccygeal intervertebral disk extrusion has been reported.^1,4,5 Therefore, this was the first case reporting multiple coccygeal intervertebral disk extrusions in a dog with involvement of the Cd2-Cd3 intervertebral disk space along with the previously described Cd1-Cd2 intervertebral disk space. It has been postulated that the preferential involvement of the cranial coccygeal intervertebral disk spaces was due to an accelerated disk degeneration supported by an increased mobility of this region.³ Indeed, motion at the most proximal part of the canine tail when dogs wag their tails may contribute significantly to disk herniation in the cranial aspect of the caudal spine. Another hypothesis is that the dorsal longitudinal ligament, normally providing a strong support against disk herniation, may be thinner and tapers into the caudal vertebral region, predisposing for disk herniation in this region. To explain the very low prevalence of documented coccygeal disk herniation in dogs, despite the above-mentioned factors that theoretically put dogs at risk, it has been hypothesized that the disease may be underestimated due to lack of clinical signs.⁴ de Vicente et al⁴ postulated that the large width of the spinal canal of the first coccygeal vertebra and presence of only peripheral roots at this level, associated with the high resistance of the peripheral nerves to injury and their great regenerative response, may lead to the absence of clinical signs in cases of relatively small volumes of extruded disk material.

While radiographs may allow detection of mineralization in a caudal intervertebral disk space or vertebral canal, advanced imaging such as CT or MRI provides more information and is useful to evaluate location and extent of an extruded disk material and the compression of nerve roots.^2,4,5 MRI is generally more sensitive to detect soft tissue lesions and fibrous intervertebral disk material, whereas CT is very effective for the identification of bone lesions and mineralized intervertebral disk material, faster, and less expensive. In the event of surgical decompression, both of these modalities are also very helpful for surgical planning. In our case, the owner opted for CT due to financial issues. Furthermore, given the dog’s chondrodystrophic breed, we expected CT to be adequate to provide a diagnosis.

Various treatments of coccygeal intervertebral disk herniation have been described. Very few cases have been managed with a conservative treatment alone; however, detailed treatment and follow-up of these few cases were not reported. One case was managed successfully with epidural injection of dexamethasone and bupivacaine, without recurrence of signs during the 6-month follow-up.¹ As in the current case, most of the dogs reported in the literature presented partial or no improvement following medical treatment with steroids or nonsteroid anti-inflammatory drugs, antalgic drugs including opioids, and rest.^1,3 However, the small number of cases reported in the literature makes it possible that the efficacy of medical treatment is underestimated. Dogs with coccygeal intervertebral disk herniation may have responded to medical treatment alone either as an empirical therapy or after an imaging confirmation but without any report in the literature. Surgical treatment is indicated for dogs that do not respond to conservative management. Dorsal laminectomy, foraminotomy, and hemilaminectomy associated with a lateral corpectomy have all been described for the surgical treatment of a coccygeal intervertebral disk extrusion.^2–5 No biomechanics studies have been performed to compare the stability of the coccygeal spine after the different surgical procedures. The choice is usually guided by the location of the herniated disk material and the surgeons’ preferences. In the case reported here, we opted for a hemilaminectomy on both sites due to the large volume and ventrolateral location of the extruded disk material extending in both the spinal canal and intervertebral foramen. No sign of coccygeal instability secondary to burring of the vertebral laminae in this high-mobility segment of the vertebral column was ever reported.

As in the case reported here, prognosis of coccygeal intervertebral disk herniation seems to be excellent after surgical treatment, although in 1 case it took more than a month for the dog to be comfortable and pain free.^2–5 The case that received epidural injection of steroids and anesthetic drugs was also reported to have recovered without recurrence of signs at 6 months following the procedure.¹

In conclusion, coccygeal intervertebral disk herniation should be considered in dogs that are presented with caudal vertebral pain or pain upon tail manipulation or during defecation. Whatever the technique, decompressive surgery should be considered when clinical signs are unresponsive to medical treatment, with excellent prognosis.