Extensive Axis Laminectomy and Atlantoaxial Stabilization for an Axial Intraspinal Extradural Ganglion Cyst in a Dog

Abstract

We report the case of a 10-year-old male Pomeranian with an axial intraspinal extradural ganglion cyst who underwent extensive axis laminectomy, ganglion cyst excision, and atlantoaxial stabilization. The dog was examined due to acutely deteriorated tetraparesis. Upon neurological examination, the C1 to C5 segment was localized as the presumed impaired spinal cord. Magnetic resonance imaging (MRI) revealed a circumferential donut-like cystic lesion in the central axis of the epidural space. Axial hemilaminectomy was performed on the right side; however, the cyst was torn. A histopathological examination could not be performed. A significant initial improvement in clinical signs was followed by recurrence of the cystic lesions. During the second extensive laminectomy of the axis, partial ganglion cyst excision with atlantoaxial stabilization was performed. An intraspinal ganglion cyst was diagnosed based on MRI findings, the mucin-like cyst content, gross appearance, and histopathological examination results. The postoperative functional recovery was remarkable. At 25 months postoperatively, no neurological abnormalities were observed; absence of the ganglion cyst was confirmed on MRI. Surgical decompression involving extensive laminectomy, partial ganglion cyst excision, and atlantoaxial stabilization was successful in treating the extradural ganglion cyst. The clinical improvement was prompt; the long-term functional outcomes were satisfactory.

Keywords

intraspinal ganglion cyst - extensive laminectomy - atlantoaxial stabilization - dog

Introduction

In dogs, intradural or extradural spinal cysts that cause myelopathy and radiculopathy are relatively rare.[1] Extradural spinal cysts include epidural meningeal cysts,[2] facet joint cysts (synovial cysts and ganglions), synovial myxoma,[3] and developmental neurenteric cysts.[4] In dogs and cats, ganglion cysts can develop from the occipito-atlanto-axial joint,[5] [6] facet joint,[7] and dorsal longitudinal ligament.[8]

The term juxtafacet cysts was first proposed by Kao and colleagues in 1974.[9] Histologically, these cysts can be classified as synovial and ganglion cysts. Synovial cysts communicate with the facet joint, exhibit a synovial lining, and contain clear or xanthochromic fluid. In contrast, ganglion cysts do not communicate with the facet joint, exhibit a fibrous tissue wall without a synovial lining, and are filled with viscous/gelatinous material.[9] To the best of our knowledge, only four cases of intraspinal ganglion cysts have been reported, two in cats and two in dogs.[5] [6] [7] [8]

This study describes a case of a 10-year-old neutered male Pomeranian with intraspinal extradural ganglion cysts at the C2 level who was successfully treated via an extensive dorsal axis laminectomy combined with ventral atlantoaxial stabilization using pins and bone cement.

Case Description

A 10-year-old neutered male Pomeranian weighing 4.5 kg was referred for the neurological evaluation of an acutely deteriorated tetraparesis. The dog exhibited forelimb knuckling for 10 days. No history of trauma or illness was recorded. The dog appeared bright and alert and was tetraplegic upon neurological examination. Cranial nerve examination findings were unremarkable. The cervical area was not painful upon manipulation. Postural reactions were deficient in the thoracic and pelvic limbs, whereas the spinal reflexes were normal. The presumed spinal cord localization was at the level of the C1 to C5 segments. Cervical radiographs showed only degenerative intervertebral changes at the C5 to C7 segments. Radiographs of the thorax and the abdomen revealed unremarkable findings. The complete blood cell count and serum biomechanical panel were within normal reference limits. The dog underwent a magnetic resonance imaging (MRI) examination (Aperto, 0.4T; Hitachi Medical, Japan) of the cervical spine. A circumferential donut-like cystic lesion was identified at the midlevel of the C2 section in the epidural space, distant from the synovial joint of the C1 to C2 and facet joint of C2 to C3 segments. The lesion was well-delineated; the spinal cord parenchyma was hyperintense on T2-weighted (T2W) and hypointense on T1-weighted (T1W) images. Enhanced MRI showed ring enhancement in the cyst wall ([Fig. 1]). Although surgery was recommended, consent could not be obtained from the owner, and the dog underwent medical management with prednisolone (1 mg/kg orally, for 1 week; Shionogi Pharma, Japan).

Fig. 1 Sagittal (A), transverse T2-weighted (T2W) (B), transverse T1-weighted (T1W) (C), and postcontrast (D) magnetic resonance images of the cervical parts at initial presentation. A donut-like cystic lesion is visualized in the intraspinal extradural space of the central axis separating from the C1 to C2 synovial joint and the C2 to C3 facet joint, causing circumferential compression of the spinal cord. The lesion appears hyperintense on T2W images and hypointense on T1W images and demonstrates a ring enhancement of the cyst wall.

Two days later, the patient was able to stand on his own and walk; however, on the eighth day of the illness, the dog returned with tetraparesis. MRI confirmed severe spinal cord compression by the enlarging cystic structure. The dog was anaesthetized using a routine protocol involving endotracheal intubation and isoflurane (2.0–2.5%) in oxygen. A right hemilaminectomy of C2 was performed; a cyst resection was attempted. However, complete excision of the cystic structures was not possible due to limited surgical exposure. Briefly, a midline skin incision was made from the external occipital protuberance to the third cervical vertebra to expose the cervicalis, cervicoscutularis, and cervicoauricularis superficialis muscles. These muscles were incised along the medline fibrous raphe and retracted laterally. The biventer cervicis was identified superficially, along with the deeper rectus capitis attached to the axial vertebrae. The rectus capitis muscle was incised along the right lateral border of the axial spinous process and elevated from the axial vertebrae. The yellow ligament between the C1 and C2 sections on the right side and vertebral arch was identified; a hemilaminectomy was performed. Due to the unilateral approach to the spinal canal and limited exposure of the lesion, the cyst wall was inadvertently torn; complete excision could not be achieved. Moreover, tissue samples could not be obtained for histopathological examination. However, we noted that the cystic fluid was viscous and transparent.

Postoperative MRI confirmed sufficient spinal cord decompression; however, some cystic structures remained. Five days after surgery, the dog could stand on his own on four legs; 2 days later, the dog was able to walk and discharged from the hospital. Five months after surgery, the dog returned because of reluctance to walk and neck pain. No apparent abnormalities were found on neurological examination. MRI confirmed cyst recurrence. The owner declined further surgical treatment and decided on conservative management with prednisolone (1 mg/kg orally, for 1 week). After initial improvement, the dog developed tetraparesis again after 9 months, with some maintenance of voluntary motor functions. MRI confirmed the recurrence of the cystic lesion, which was again compressing the spinal cord, necessitating surgical treatment.

Revision Surgery Report

Premedication and general anaesthesia protocol were applied, similar to those of the first surgery. Ventral C1 to C2 stabilization was performed using positively threaded profile pins (Titanium Positive Hi Wire, Platon Japan, Japan) and polymethylmethacrylate (Simplex P Bone Cement; Stryker Corporation, Kalamazoo, Michigan, United States). No abnormal instability, joint capsule, or synovial fluid abnormalities were observed in the C1 to C2 joints.

Five days after ventral vertebral stabilization, the lesion was exposed and excised through an extensive axis laminectomy. Using a dorsal surgical approach,[10] as described above, the axial spinous process was exposed; the adhesions at the previous hemilaminectomy site were freed and resected. The majority of the axial spinous processes and lamina were resected using a rongeur, allowing sufficient exposure of the spinal cord and cystic lesion ([Fig. 2A, B]). The caudal region of the axial spinous process, origin of the nuchal ligament, was preserved to maintain the stability of the cervical region other than that in the C1 to C2 sections. After removing the contents of the cyst and collapsing it, we observed that, macroscopically, the cyst was located in a continuous position ventrally within the spinal canal, of which probing did not reveal any obvious dural defects. In addition, no contact or continuity of the cyst was found with either the C1 to C2 synovial joint or the C2 to C3 facet joint. Complete excision of the cystic structure was not possible. A histopathological examination of the resected cyst wall was performed. A 3–0 nylon thread suture (ETHILON, Johnson & Johnson, Japan) was placed in a figure of eight in the burr holes prepared at the level of the origin of the nuchal ligament in the axial spinous process and the remaining dorsal atlantoaxial ligament ([Fig. 2C]). Subcutaneous adipose tissue graft was placed on the exposed dura, and the wound was closed routinely.

Fig. 2 Intraoperative findings. (A) The axial spinous process is resected. (B) The image shows an enlargement of the circled section in a cyst (arrow) and the spinal cord (arrowhead). The cyst is continuous on the ventral side of the spinal canal. (C) The dorsal part at C1 to C2 is reinforced using Nylon between the remaining dorsal atlantoaxial ligament and the burr hole in the spinous process of the axis to recapitulate the dorsal stability of the C1 to C2 section.

Postoperative radiographs revealed a significant loss of the axial spinous processes ([Fig. 3A]). Postoperative MRI confirmed that cystic structure removal was incomplete; however, a sufficient decompression had been achieved ([Fig. 4A]). Histopathological examination of the resected cyst wall revealed dense and loose fibrous connective tissue surrounding pale basophilic mucinous substance, and no synovial lining was evident ([Fig. 5]). Based on the MRI and histopathological findings, cystic fluid properties, and intraoperative macroscopic findings, a diagnosis of intraspinal extradural ganglion was made. Judging from its anatomical position, the ganglion was most likely derived from the dorsal longitudinal ligament.

Fig. 3 Radiographs of the atlantoaxial parts after surgery. (A) Lateral (left) and ventrodorsal (right) computed radiographs of the atlantoaxial parts immediately after surgery. The axial spinous process remains largely resected. A remaining part of the bone fragment of the axial spinous process can be seen (arrow). (B) Twenty-five months after surgery. (Digital Radiographs) No implant failure is recorded, and partial bone fusion can be observed.

Fig. 4 Magnetic resonance imaging (MRI) of the cervical parts after surgery. (A) Sagittal (left) and transverse (right) T2-weighted (T2W) MRI of the cervical parts captured immediately after surgery. Sufficient decompression was confirmed. (B) Twenty-five months after surgery. No recurrence is observed. Most of the ganglion cyst has disappeared.

Fig. 5 Photomicrographs of the excised cyst. The wall (W) of the resected cyst is composed of loose and dense fibrous connective tissue admixed with some adipocytes and skeletal muscle, and pale basophilic mucinous substance (★) is noted along the cyst wall. No synovial lining is evident between the wall and substance. Haematoxylin and eosin stain in low (A) and medium (B) magnification.

Outcome

After surgery, due to concerns regarding neck instability, we decided to use a cervical corset for the dog (Toyo Sogu, Tokyo, Japan). The dog could walk 10 days after this revision surgery and was discharged the next day. No abnormalities were observed on radiographs or during the neurological examination after 2 months; the corset was removed.

After 25 months, a neurological examination showed no gait abnormalities. On radiographs, implants were intact and the atlantoaxial joint was partially ankylosed ([Fig. 3B]). MRI (Echelon Smart, 1.5T; Hitachi Medical, Japan) demonstrated the absence of any intraspinal lesion, confirming the ganglion cysts had not recurred ([Fig. 4B]).

Discussion

As known from reports in humans, ganglion cysts typically appear as hypointense lesions on T1W and hyperintense lesions on T2W in MRI. Under gadolinium contrast, peripheral enhancement of the cyst may be observed, possibly because of hyperplastic connective tissue in the wall.[11] [12] [13] Well-defined circumferential enhancement of variable intensity has been reported in dogs with synovial cysts.[14] [15] [16] [17] In our case, similar imaging findings were present. The cystic lesion was located in the central part of the axis. This location suggests that the cyst was neither contiguous with the joint capsules of the C1 to C2 nor with those of the C2 to C3 facet joints; this finding was confirmed intraoperatively. Moreover, we intraoperatively confirmed the cyst's continuity to the ventral side of the spinal canal. The dura mater seemed intact; the histopathological examination revealed that the cyst was not lined with a synovium, supporting the diagnosis of an “extradural ganglion cyst.”[1] Such ganglion cysts can develop from any connective tissue in the spinal canal.[18] Based on the intraoperative observation and the location of the lesion on the floor of the spinal canal,[19] it appeared that the ganglion may have originated from either the dorsal longitudinal ligament, the peridural membrane, or the meningovertebral ligament (Hofmann ligament). The dorsal longitudinal ligament extends from the dens of the axis to the end of the vertebral canal in the caudal region.[20] [21]

Dorsal longitudinal ligament ganglions have been reported in humans, more often in young men, and epidemiologically, they often occur just caudal to the L3 to S1 disc position.[18] [22] The peridural membrane is located ventral to the deep layer of the dorsal longitudinal ligament.[23] [24] To the best of our knowledge, no reports of peridural membrane ganglions in humans have been published. Kent and colleagues reported that the meningovertebral ligaments of the spine extended from the C3 to the sacrum, most prominently in the cervical spine, and the ligament attachment was stronger along the body of each vertebra than that over the intervertebral discs.[25] Considering the characteristics of these epidural connective tissues, intraoperative macroscopic observations, and MRI findings showing the dorsal longitudinal ligament bulging at the floor of the C2 spinal canal, it was reasonable to assume that the ganglion cyst originated from the ventral side of the dorsal longitudinal ligament or the peridural membrane.

Although spontaneous regression of extradural intravertebral cysts has been previously reported in humans and dogs,[12] [26] surgery is indicated in cases of pain or neurological signs that do not respond to medical management. In humans, percutaneous cyst aspiration has been performed; however, the recurrence and failure rates are high.[27] In the present case, surgery was considered the best treatment option because of progressive paresis of the extremities that did not respond in, the long run, to medical management. Hemilaminectomy did not provide a large enough surgical field for proper visualization or safe manipulation to completely excise the cyst. Hence, we were only able to decompress the cyst but could not prevent it from recurring. Therefore, revision surgery enhancing surgical exposure became necessary. Regarding the successful outcomes achieved by revision surgery without the recurrence of clinical symptoms or cyst during long-term follow-up, three considerations should be taken into account: extensive dorsal laminectomy, incomplete resection of the cyst, and immobilization from ventral fixation of C1 to C2. First, regarding extensive dorsal laminectomy, based on the experience from the first surgery, the revision included a total dorsal laminectomy achieved through extensive resection of the axial spinous process and pedicles, also ensuring sufficient enlargement of the spinal canal. This procedure not only provides good visualization but also proves effective in mitigating mass effects that compress the spinal cord if recurrence occurs. Second, about incomplete cystectomy, despite having a larger surgical field, complete resection of the cyst was not possible. Although complete resection is of course desirable to reduce the risk of recurrence of juxtafacet cysts,[28] a systematic review of human lumbar ganglion cysts stated that complete resection was only possible in 48.1% of cases.[29] In the four previous reported studies on dogs and cats[5] [6] [7] [8] diagnosed with ganglion cyst, only a 16-year-old cat with a lumbosacral ganglion could be subjected to complete resection;[8] only a 14-year-old Miniature Pinscher with a ganglion in the occipito-atlanto-axial joint showed recurrence during follow-up.[6] Despite limited case reports in animals, due to the recurrence in humans, resecting cysts as far as possible within a large operative field might be useful. Finally, fixation of the C1 to C2 sections resulted in three invasive procedures; two dorsal and one ventral. Recently, a method of fixing the C1 to C2 joint from the dorsal side with pins and bone cement has been reported,[30] which would allow the entire procedure to be carried out with a single technique from the dorsal side and be expected to greatly reduce the invasiveness of the procedure. A future biomechanical investigation is needed to assess the necessity for fixation of the C1 to C2 joint for extensive resection of the axial spinous process and lamina, including the dorsal atlantoaxial ligament.

Conclusion

The factors contributing to favourable long-term outcomes in such cases are unknown. However, we believe that we were successful in resecting as much of the cyst as possible within a wide field of view. Therefore, a hemilaminectomy should not be chosen, but a resection including the dorsal spinous process and vertebral arch of the axis should be performed. Extensive resection of the spinous process and vertebral arch of the axis would also be effective in mitigating mass effects compressing the spinal cord in the spinal canal again at the time of recurrence.

Conflict of Interest

None declared.

Acknowledgments

We thank the Animal Emergency Center staff for their cooperation and kind support throughout this study.

Note

This case report was presented in 2020 at the Japanese Society of Veterinary Anesthesia and Surgery conference in Osaka, Japan.

Author Contributions

K.T. performed the first surgery, F.O. performed the other surgery described in this case report. F.O. designed the case report, the main conceptual ideas, and proof outline. N.Y. collected the data. S.F. and M.T. aided in interpreting the results and worked on the manuscript. F.O. wrote the manuscript with support from S.F. All authors approved the submitted manuscript.

Animal Care

Informed consent was obtained from the client prior to their animals' participation in the study, and the study was conducted in accordance with best practices for veterinary care.

Ethical Approval

Ethical approval is not applicable. This case report did not use laboratory animals, as the subject is a domesticated dog.

• References

• 1 Lowrie ML, Platt SR, Garosi LS. Extramedullary spinal cysts in dogs. Vet Surg 2014; 43 (06) 650-662
• 2 de Nies KS, Edwards RA, Bergknut N, Beukers M, Meij BP. Caudal lumbar spinal cysts in two French Bulldogs. Acta Vet Scand 2018; 60 (01) 14
• 3 Neary CP, Bush WW, Tiches DM, Durham AC, Gavin PR. Synovial myxoma in the vertebral column of a dog: MRI description and surgical removal. J Am Anim Hosp Assoc 2014; 50 (03) 198-202
• 4 Gagliardo T, Corlazzoli D, Rosati M. et al. Spinal cord neurenteric cyst: clinical and diagnostic findings and long term follow-up in two dogs. Vet Q 2018; 38 (01) 106-111
• 5 Aikawa T, Sadahiro S, Nishimura M, Miyazaki Y, Shibata M. Ganglion cyst arising from the composite occipito-atlanto-axial joint cavity in a cat. Vet Comp Orthop Traumatol 2014; 27 (04) 319-323
• 6 Ji M, Kiupel M, Park H, Lee K, Yoon H. Magnetic resonance imaging features of bilateral multiloculated extraneural ganglion cysts of the occipito-atlanto-axial joint causing hypoglossal nerve paralysis in a dog. J Vet Intern Med 2024; 38 (05) 2675-2680
• 7 Webb AA, Pharr JW, Lew LJ, Tryon KA. MR imaging findings in a dog with lumbar ganglion cysts. Vet Radiol Ultrasound 2001; 42 (01) 9-13
• 8 de Strobel F, Taeymans O, Rosati M, Cherubini GB. Lumbosacral intraspinal extradural ganglion cyst in a cat. JFMS Open Rep 2015; 1 (02) 2055116915604875
• 9 Kao CC, Winkler SS, Turner JH. Synovial cyst of spinal facet. Case report. J Neurosurg 1974; 41 (03) 372-376
• 10 Fingeroth JM, Smeak DD. Laminotomy of the axis for surgical access to the cervical spinal cord. A case report. Vet Surg 1989; 18 (02) 123-129
• 11 Baba H, Furusawa N, Maezawa Y. et al. Ganglion cyst of the posterior longitudinal ligament causing lumbar radiculopathy: case report. Spinal Cord 1997; 35 (09) 632-635
• 12 Hsu KY, Zucherman JF, Shea WJ, Jeffrey RA. Lumbar intraspinal synovial and ganglion cysts (facet cysts). Ten-year experience in evaluation and treatment. Spine 1995; 20 (01) 80-89
• 13 Shiono T, Yoshikawa K, Aota Y. et al. Two cases of ganglion cysts in the lumbar spinal canal. Radiat Med 1994; 12 (03) 125-128
• 14 Forterre F, Kaiser S, Garner M. et al. Synovial cysts associated with cauda equina syndrome in two dogs. Vet Surg 2006; 35 (01) 30-33
• 15 Forterre F, Vizcaino Reves NV, Stahl C, Rupp S, Gendron K. Atlantoaxial synovial cyst associated with instability in a Chihuahua. Case Rep Vet Med 2012; 2012: 1-4
• 16 Levitski RE, Chauvet AE, Lipsitz D. Cervical myelopathy associated with extradural synovial cysts in 4 dogs. J Vet Intern Med 1999; 13 (03) 181-186
• 17 Penning VA, Benigni L, Steeves E, Cappello R. Imaging diagnosis–degenerative intraspinal cyst associated with an intervertebral disc. Vet Radiol Ultrasound 2007; 48 (05) 424-427
• 18 Roh SW, Rhim SC, Lee HK, Kang SK. Spinal ganglion cyst of lumbar posterior longitudinal ligament. J Korean Neurosurg Soc 2000; 29: 543-549
• 19 Ansari S, Heavner JE, McConnell DJ, Azari H, Bosscher HA. The peridural membrane of the spinal canal: a critical review. Pain Pract 2012; 12 (04) 315-325
• 20 Hermanson JW. Arthrology. In: Evans HE, de Lahunta A. eds. Miller's Anatomy of the Dog. 4th ed. St Louis, MO: Elsevier; 2012: 158-184
• 21 Hermanson JW, Evans HE, de Lahunta A. Arthrology. Miller's Anatomy of the Dog. 5th ed. Philadelphia, PA: Saunders; 2020: 176-206
• 22 Marshman LAG, Benjamin JC, David KM, King A, Chawda SJ. “Disc cysts” and “posterior longitudinal ligament ganglion cysts”: synonymous entities? Report of three cases and literature review. Neurosurgery 2005; 57 (04) E818
• 23 Wiltse LL. Anatomy of the extradural compartments of the lumbar spinal canal. Peridural membrane and circumneural sheath. Radiol Clin North Am 2000; 38 (06) 1177-1206
• 24 Wiltse LL, Fonseca AS, Amster J, Dimartino P, Ravessoud FA. Relationship of the dura, Hofmann's ligaments, Batson's plexus, and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament. An anatomical, radiologic, and clinical study. Spine 1993; 18 (08) 1030-1043
• 25 Kent M, Glass EN, Song RB, Warren JD, de Lahunta A. Anatomic description and clinical relevance of the meningovertebral ligament in dogs. J Am Vet Med Assoc 2019; 255 (06) 687-694
• 26 Bonelli MA, da Costa RC. Spontaneous regression of extradural intraspinal cysts in a dog: a case report. BMC Vet Res 2019; 15 (01) 396
• 27 Epstein NE, Baisden J. The diagnosis and management of synovial cysts: efficacy of surgery versus cyst aspiration. Surg Neurol Int 2012; 3 (Suppl. 03) S157-S166
• 28 Choudhri HF, Perling LH. Diagnosis and management of juxtafacet cysts. Neurosurg Focus 2006; 20 (03) E1
• 29 Rana S, Pradhan A, Casaos J. et al. Lumbar spinal ganglion cyst: a systematic review with case illustration. J Neurol Sci 2023; 445: 120539
• 30 Tabanez J, Gutierrez-Quintana R, Kaczmarska A. et al. Evaluation of a novel dorsal cemented technique for atlantoaxial stabilisation in 12 dogs. Life (Basel) 2021; 11 (10) 1039

Publication History

Received: 02 December 2024

Accepted: 18 March 2025

Article published online:
16 April 2025