Tavola et al. Acta Veterinaria Scandinavica (2023) 65:37 Acta Veterinaria Scandinavica https://doi.org/10.1186/s13028-023-00700-2 CASE REPORT Open Access Lumbar vertebral canal stenosis due to marked bone overgrowth after routine hemilaminectomy in a dog Francesca Tavola1, Marco Ruggeri2, Ines Carrera3, Martí Pumarola4, Pablo Menendez Alegria2 and Anna Tauro2* Abstract Background Bone overgrowth after decompressive surgery for lumbar stenosis resulting in recurrence of neurological signs has not been reported in veterinary literature. However, there are few cases described in human medicine. Case presentation A 13-month-old entire female dog, a crossbreed between a Springer Spaniel and a Border Collie, weighing 24 kg, was referred with a 5-day history of progressive spastic paraplegia, indicative of a T3-L3 myelopathy. Magnetic resonance (MR) imaging revealed a right-sided L2-L3 compressive extradural lesion, compatible with epidural haemorrhage, which was confirmed by histopathology. The lesion was approached via right-sided L2-L3 hemilaminectomy and was successfully removed. One-year postoperatively the dog re-presented with pelvic limb ataxia. MR and computed tomography (CT) images demonstrated excessive vertebral bone formation affecting the right articular processes, ventral aspect of the spinous process of L2-L3, and contiguous vertebral laminae, causing spinal cord compression. Revision surgery was performed, and histopathology revealed normal or reactive osseous tissue with a possible chondroid metaplasia and endochondral ossification, failing to identify a definitive reason for the bone overgrowth. Nine-month postoperatively, imaging studies showed a similar vertebral overgrowth, resulting in minimal spinal cord compression. The patient remained stable with mild proprioceptive ataxia up until the last follow-up 18 months post-revision surgery. Conclusion This is the first report in the veterinary literature of bone overgrowth after lumbar hemilaminectomy which resulted in neurological deficits and required a revision decompressive surgery. Keywords Ataxia, Bone overgrowth, Inflammatory response, Laminectomy, Micromotion, Neurological deficits, Paralysis, Paraplegia, Spinal, Vasculopathy *Correspondence: Anna Tauro anna.tauro@yahoo.co.uk 1 Awake Djursjukhus, Hornsgatan 150A, Stockholm 117 28, Sweden 2 ChesterGates Veterinary Specialists, Units E & F, Telford Court, Gates Lane, Chester, Cheshire CH1 6LT, UK 3 Vet Oracle Teleneurology, CVS Limited, Owen Road, Diss, Norfolk IP22 4ER, UK 4 Mouse and Comparative Pathology Unit, Department of Animal Medicine and Surgery, Veterinary Faculty, Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Universitat Autònoma de Barcelona, Campus UAB, Bellaterra 08193, Barcelona, Spain © The Author(s) 2023. 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The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Tavola et al. Acta Veterinaria Scandinavica (2023) 65:37 Page 2 of 8 Background bone overgrowth following spinal surgery are not found Bone healing after injury is a complex process involving in veterinary literature. various biological and biomechanical factors. The three We present a case involving a young dog which experi- phases of bone healing are the inflammatory phase, the enced lumbar bone overgrowth after a routine hemilami- repair phase, and the remodelling phase [1, 2]. Bone nectomy surgery. To the authors’ knowledge, this is the healing depends on the initial inflammatory phase, both first report describing a severe bone overgrowth which local and systemic, in response to the injury. The repair required a revision decompressive hemilaminectomy. phase is characterised by the formation of a soft callus, consisting of fibroblasts, chondrocytes, and osteopro- Case presentation genitor cells. The new extracellular matrix produced by Clinical presentation and diagnostic findings these cells serve as a temporary scaffold for bone for- A 13-month-old entire female dog, a crossbreed between mation. This phase involves the recruitment and differ- a Springer Spaniel and a Border Collie, weighing 24 kg, entiation of mesenchymal stromal cells (MSCs), which was referred to ChesterGates Veterinary Specialists with have the potential to differentiate into osteoblasts, pro- a 5-day history of progressive paraplegia (Table 1). There moting bone regeneration and bridging the fracture site. was no history of trauma, however, the dog had been The remodelling phase is the final stage of bone healing, attending agility training prior to onset of neurological where the newly formed bone undergoes structural and signs. functional modifications, restoring the bone’s normal The dog was rescued from Romania at the age of 6 architecture [3]. months and had a history of intermittent lethargy, hypo- In human medicine, bone overgrowth is an uncom- rexia, and gastrointestinal signs. The patient had received mon but important cause of relapse of neurological signs regular vaccination and antiparasitic treatments. after decompressive surgery in elderly patients undergo- Physical examination was within normal limits. Neu- ing treatment for lumbar spinal stenosis, most performed rological examination revealed spastic paraplegia with at the L4-L5 level [4–10]. The exact osteopathological preserved nociception and normal mentation. Postural mechanism underlying post-operative bone overgrowth reactions (paw placement and hopping response) were remains unclear. However, factors such as segmental absent in the pelvic limbs, while myotatic reflexes were instability [8], micromotion [5, 6], and abnormalities unremarkable. Thoracic limbs and cranial nerve assess- in mechano-signalling have been hypothesised to con- ment were unremarkable. There was no pain elicited tribute to the excessive bone regrowth [5]. Conservative upon spinal palpation. Overall, the examination was con- management has been suggested as an initial approach sistent with T3-L3 myelopathy. to treating radicular pain caused by lumbar restenosis in Haematology and serum biochemistry profile revealed human patients [11]. However, in many cases, repeated mild neutrophilia (13.9 × 10^9/L, reference interval (RI) decompression surgeries are often required to address 3.5–12). Coagulation tests, including prothrombin time the bone overgrowth and alleviate clinical signs [5]. (PT; 9.6 s, RI 14–20), activated partial thromboplas- In the field of veterinary medicine, there is limited tin time (aPTT; 89.8 s, RI 94–123), and buccal muco- knowledge regarding vertebral bone regrowth after surgi- sal bleeding (BMBT; 4 min, RI < 4) were within normal cal interventions [12]. Furthermore, reports of vertebral limits. IDEXX AngioDetect™ test for Angiostrongylus Table 1 Timeline of the clinical findings, diagnosis, investigations, and surgical intervention. CRP = C-Reactive Protein; CSF = cerebrospinal fluid; n/a = not applicable; R = right; L = left TIMELINE Clinical signs Neurological signs Diagnosis Imaging CRP CSF Surgical (RI < 10) analysis procedures Day 0 Intermittent leth- Spastic paraplegia L2-L3 epidural MRI & CT CRP = 64 mg/L n/a L2-L3 right argy, hyporexia, with preserved haemorrhage sided hemi- GI signs nociception laminectomy 2 m after 1st surgery Pelvic limb ataxia n/a n/a n/a n/a 1 year after 1st surgery Intermittent Intermittent pelvic L2-L3 bone MRI & CT CRP = 104 mg/L n/a L2-L3 right lethargy and limb ataxia (R > L) overgrowth sided revi- vomiting sion surgery 3 m after revision surgery Occasional Pelvic limb ataxia n/a n/a n/a n/a vocalisation 9 m after revision surgery Pelvic limb ataxia L2-L3 bone MRI & CT CRP = 3 mg/L Normal n/a overgrowth 18 m after revision Pelvic limb ataxia surgery Tavola et al. Acta Veterinaria Scandinavica (2023) 65:37 Page 3 of 8 vasorum and IDEXX SNAP 4Dx (Idexx Laboratories, Surgical intervention Wetherby, UK) for Dirofilaria immitis antigen and Bor- The dog underwent a L2-L3 right-sided hemilaminec- relia burgdorferi, Ehrlichia ewingii, Anaplasma phago- tomy. A reddish, soft extradural lesion resembling a cytophilum, and Anaplasma platys antibodies were blood clot was found adherent to the dura mater, inner negative. However, C-reactive protein (CRP) was ele- periosteum, and nerve root. The lesion was successfully vated (64.0 mg/L, RI < 10), indicating the presence of sys- removed, and its histopathological evaluation confirmed temic inflammation. the diagnosis of epidural haemorrhage. Magnetic resonance (MR) (Siemens MAGNETOM Following surgery, the dog’s condition gradually Essenza 1.5T) imaging of the thoracolumbar spine improved, showing moderate ambulatory paraparesis revealed a right-sided ill-defined extradural lesion, and pelvic limb proprioceptive ataxia. After a six-day extending from mid-L2 to mid-L3 vertebral body lev- of hospitalisation, the patient was discharged with a els, and causing severe compression of the spinal cord. course of gabapentin to manage neuropathic pain (Acta- The lesion was heterogeneous, hyperintense on both vis Ltd, Castleford, UK; 12 mg/kg, PO, q8h, for 2 weeks), T2-weighted (T2W) and T1-weighted (T1W) images rel- diazepam to promote relaxation of skeletal muscles in ative to the normal spinal cord. The T2*-gradient recalled the urethra and facilitate voiding (Teva Ltd, Runcorn, echo (GRE) images showed a complete hypointense rim UK; 0.2 mg/kg, PO, q8h, for 1 week), and paracetamol/ and hyperintense centre within the extradural lesion, codeine for pain management (Pardale-V, Dechra Ltd, with faint peripheral contrast enhancement (Fig. 1). Northwich, UK; 8 mg/kg, PO, q8h, for 1 week). Consider- Additionally, there was a poorly defined hyperintensity ing the dog’s history of recurrent gastrointestinal signs, on the dorsal short tau inversion recovery (STIR) images non-steroidal anti-inflammatory drugs (NSAIDs) were within the epaxial muscle at the same level. All vertebrae not used. were normal, and all visible intervertebral discs were well-hydrated without evidence of herniation. These find- Follow-up and surgical revision ings were consistent with a right-sided epidural haemor- At two months after the initial presentation, the dog rhage causing secondary spinal cord compression. The showed significant improvement, with only mild residual observed muscular changes were likely associated with pelvic limb ataxia. secondary inflammation and/or oedema. However, one year later, the dog was presented again at ChesterGates Veterinary Specialists with a his- tory of intermittent lethargy, hyporexia, vomiting, and pelvic limb ataxia. Physical examination was normal. Fig. 1 Comparison between different magnetic resonance images at the level of L2-L3 vertebrae. Sagittal T2W (A), dorsal T1W post-contrast (B), and transverse T2*GRE (C), T2W (D), T1W post-contrast (E) magnetic resonance images at the level of L2-L3 vertebrae, showing a right-sided extradural lesion (white arrow), extending from mid-L2 to mid-L3 vertebral body levels. The lesion showed heterogeneous, hyperintensity on T2W and T1W images, and had a complete hypointense rim and hyperintense centre on T2*-GRE images. The lesion exhibited faint peripheral contrast enhancement. Tavola et al. Acta Veterinaria Scandinavica (2023) 65:37 Page 4 of 8 Neurological examination showed mild pelvic limb signal intensity pattern indicated a likely mineralised ataxia, worse on the right side, while the rest of the nature (Fig. 2). In addition, there was a mild contrast neurological examination was unremarkable. The neu- enhancement of the adjacent meninges interpreted to be roanatomical localisation was consistent with a T3-L3 likely due to meningeal fibrosis, secondary to the previ- myelopathy. Haematology, serum biochemistry profile, ous surgery. urinalysis (including urine culture), and ACTH stimu- Computed tomography (CT) study of the entire spine lation test were normal. However, CRP was increased confirmed the MR findings of a mineralised vertebral (104.0 mg/L, RI < 10). lesion. CT of thorax and abdomen did not identify any Repeat MR study of the thoracolumbar spine revealed metastatic neoplastic disease. a small laminar defect (H 1 mm x L 4.5 mm) on the right The dog underwent a revision L2-L3 right-sided hemi- side of the caudal aspect of the L2 vertebra, which was laminectomy. However, the surgical procedure presented the site of the previous surgery. Adjacent to this site and challenges due to the loss of normal anatomical land- extending caudally, there was an ill-defined lesion arising marks caused by bone overgrowth. To ensure the accu- from the vertebra, affecting the right articular processes, racy of the surgical approach, a perioperative spinal CT the ventral aspect of the spinous process of L2-L3, and scan was performed. The scan revealed that the initial the contiguous vertebral laminae. This lesion was expan- surgical approach was too dorsal, and that the hemilami- sive in all directions, distorting the normal shape and nectomy, performed using a pneumatic-powered drill, joint space of the articular processes. It projected into the was initially targeting the spinous processes of L2-L3. vertebral canal as an extradural lesion, causing mild spi- To address this issue, a wider surgical approach was nal cord compression. The lesion appeared slightly het- undertaken, and intra-operative fluoroscopy was used erogeneous but markedly hypointense in all sequences, as a guiding tool. The remaining anatomical landmarks, with mild heterogeneous contrast enhancement. The including the accessory processes of L1-L2 and L3-L4, Fig. 2 Advanced diagnostic imaging performed a year post-routine hemilaminectomy. Transverse T2W (A) (B), and sagittal T2W (C) magnetic resonance images and transverse (D) (E) and sagittal (F) computed tomography images at the level of the L2-L3 vertebrae, showing a relatively sharp and small laminar defect (H 1 mm x L 4.5 mm) (white arrow) on the right side of caudal aspect of L2 vertebra. Adjacent to this site and extending cau- dally, there was an ill-defined expansive lesion (yellow arrow) lesion arising from the vertebra, affecting the right articular processes, and ventral aspect of the spinous process of L2-3 and the contiguous vertebral laminae, causing mild spinal cord compression. The lesion was slightly heterogeneous in all sequences, with mild heterogeneous contrast enhancement. Tavola et al. Acta Veterinaria Scandinavica (2023) 65:37 Page 5 of 8 as well as the transverse process of the L2-L3 vertebrae, further neurological progression was noted, and the dog were identified. The L2-L3 right-sided hemilaminectomy was re-admitted 6 months later (i.e., 9 months after the was accomplished and revealed an oedematous spinal revision surgery) for repeating lumbar spinal MR and cord with a pinkish granulated appearance of the dura CT studies to investigate whether the dog’s occasional mater. The dorsolateral compression was evident and vocalisation was related to spinal pain and to assess the mainly affecting the L2 vertebra. Multiple samples, which condition of the surgical site. CRP was now within nor- had a mixed consistency of bone and fibrocartilage, mal limits (3 mg/L; RI < 10) and SNAP 4Dx test (Idexx were collected intraoperatively and sent for histopatho- Laboratories, Wetherby, UK) for vector-borne diseases logical evaluation. Following the spinal cord decompres- was repeated and the result was negative. MR and CT sion, a postoperative CT scan showed a minimal amount studies of the thoracolumbar spine showed mineralised of residual bone overgrowth at the level of the rostral expansive lesion, similar in shape, margination and signal edge of L2, which did not cause significant spinal cord intensity compared to the pre-revision surgical images. compression. The right vertebral lamina of L2 and L3 showed smooth Following surgical procedure, the dog’s condition bone almost completely filling the previous laminec- gradually improved, showing mild ambulatory parapa- tomy defect, similar to the pre-operative state but with resis and pelvic limb ataxia. The patient was discharged a smaller laminar gap (H 1 mm x L 1 mm), on the right three days after surgery. In addition to diazepam (Teva side of caudal aspect of L2 vertebra. There was a notice- Ltd, RuncornUK; 0.2 mg/kg, PO, q8h, for 10 days), able bone growth in an eccentric manner, incorporat- paracetamol / codeine (Pardale-V, Dechra Ltd, North- ing the slightly deviated L2 and L3 spinous processes. wich, UK; 8 mg/kg, PO, q8h, for 2 weeks), and gabapen- It is important to note that during the revision surgery, tin (Actavis Ltd, Castleford, UK; 12 mg/kg, PO, q8h, for these spinous processes were mistakenly targeted (Fig. 3). 2 weeks), the patient received a tapering course of corti- Overall, the healing process had resulted in the verte- costeroids to reduce the local oedema and inflammation brae being reconstructed similarly to their pre-revision (Wockhardt Ltd, Wrexham, UK; prednisolone, 0.3 mg/kg, surgery state. Despite the presence of slight eccentric PO, q24h, for 10 days, then 0.2 mg/kg, PO, q24h, for 10 and concentric bone regrowth that extended beyond the days, then 0.1 mg/kg, PO, q24h, for 10 days, the 0.1 mg/ normal vertebral margins, the resulting minimal spinal kg, PO, q48h, for 10 days) and pentoxifylline to improve cord compression was not deemed significant enough to microcirculation, reduce inflammation, and enhance the require another surgical intervention. No intramedullary healing process (Trental, Sanofi Ltd, Reading, UK; 16 mg/ lesions were observed, and the mild meningeal enhance- kg, PO, q8h, for a month). ment seen before was still faintly present. Analysis and culture of the cerebrospinal fluid (CSF) Histopathological evaluation collected via a lumbar puncture were normal (CSF pro- The histological sections were stained with haematoxy- tein 39.8 mg/dL, RI < 45; TNCC 1 cell/uL, RI < 5). lin and eosin and scanned images were evaluated digi- The patient was discharged with pentoxifylline (Tren- tally. The submitted specimens consisted of histologically tal, Sanofi Ltd, Reading, UK; 16 mg/kg, PO, q8h for a normal or reactive connective, adipose and osseous tis- month) and paracetamol / codeine (Pardale-V, Dechra sues with no evidence of active inflammatory, prolif- Ltd, Northwich, UK; 8 mg/kg, PO, q8h, PRN). Phys- erative reaction, or neoplasia. In some fragments this iotherapy and hydrotherapy were recommended, and reactive fibrous tissue surrounded fragments of thin further monitoring of the clinical progress via video osseous trabeculae of compact bone containing well recording was advised. Approximately 18 months after organized osteons surrounding cavities filled with bone the revision surgery, the patient was re-examined and marrow. In other fragments, between a hyaline fibril- found to be stable with mild proprioceptive ataxia of the lary matrix, multiple lacunae containing one or two cells pelvic limbs with no evidence of discomfort. mimicking isogenous group of chondrocytes were pres- ent. Some changes were supportive of regenerating activ- Discussion and conclusions ity of connective tissue (fibrosis). The absence of active The present case report is the first to document exces- inflammatory reaction could not rule out a possible sive bone overgrowth causing vertebral stenosis following chronic stage of the underlying process. lumbar spinal decompression in a canine patient. While references to bone overgrowth as a surgical Follow-up imaging and outcome complication in lumbar stenosis exist in human litera- Three months after the revision surgery, the dog was pre- ture [4–8, 13], there is a lack of specific veterinary lit- sented with signs of occasional vocalisation suspected erature addressing bony defect resolution following to be secondary to discomfort and showed slight pel- hemilaminectomy. vic limb ataxia. Additional monitoring was advised. No Tavola et al. Acta Veterinaria Scandinavica (2023) 65:37 Page 6 of 8 Fig. 3 Advanced diagnostic imaging performed 9 months post-revision surgery. Transverse (A) (D) (E) and sagittal (F) computed tomography images and transverse T2W (B) and sagittal (C) magnetic resonance images at the level of the L2-L3 vertebrae, showing a right-sided expansive lesion (orange arrow) similar to the Fig. 2, with smooth bone almost completely filling the previous laminectomy defect, but leaving a small laminar gap (H 1 mm x L 1 mm), on the right side of the caudal aspect of L2 vertebra (white arrow). The lesion has grown more eccentrically, and incorporates the slightly deviated L2 and L3 (green arrow) spinous processes. In human patients, post-surgical bone overgrowth in our canine patient, as we believe that a different patho- typically evolves over several months to years, primar- physiological mechanism may be responsible for the ily in elderly patients over the age of 50. Various factors observed bone overgrowth. We hypothesised that an can influence this process [7, 13], such as post-operative excessive inflammatory response triggered by the surgical vertebral instability [8] or micromotion [5]. This is com- insult could have contributed to the post-surgical bone monly observed at the L4-L5 level, known to be the most overgrowth. The initial presentation of our patient with mobile intervertebral level in humans [4–8]. Excessive an extradural haematoma and increased CRP level may motion or inadequate mechanical environment can dis- supports the presence of an excessive systemic inflam- rupt normal bone remodelling, leading to cartilage and matory response. Additionally, the history of intermittent bone formation, as well as an excessive inflammatory gastrointestinal signs may further suggest an abnormal response to the initial trauma [5, 14]. This can subse- immune response; although, this could not be confirmed. quently lead to abnormal bone growth. It is important to The main limitation of our report includes the perfor- note that systemic abnormalities are not typically appar- mance of CSF analysis only 9 months after the revision ent in these patients [5]. surgery, which may not have captured the complete In contrast to the human literature [4–10], our case picture of the inflammatory response during the initial report describes excessive bone overgrowth following a stages of the condition. Additionally, we acknowledge hemilaminectomy procedure performed in a young dog the absence of immunoglobulin A (IgA) concentration to remove an extradural hematoma. It is worth noting testing for canine steroid-responsive meningitis-arteritis that the affected spinal level in our case is not typically (SRMA) [15]. However, the resolution of the clinical signs considered the most mobile segment in dogs. Although without the use of corticosteroids at immune-suppressive overt signs of instability were not observed, a dynamic doses, along with the absence of typical clinical signs study was not conducted to confirm the absence of insta- such as pyrexia and spinal pain [15], make the diagnosis bility [5], [6]. Vertebral stabilization was not performed Tavola et al. Acta Veterinaria Scandinavica (2023) 65:37 Page 7 of 8 histopathological examination. PMA carried out the MRI and CT exams. AT of canine steroid-responsive meningitis-arteritis (SRMA) performed the clinical examination, conducted the surgery, provided clinical less likely. care to the patient, conceived and designed the study, and is the main author In our case, we opted for a course of anti-inflammatory of the paper. All authors were involved in revising the manuscript and making final corrections. All authors have read and approved the final version of the dose of corticosteroids and pentoxifylline in an attempt manuscript. to reduce the suspected inflammation and vasculopa- thy. Although the definitive benefit of these drugs in our Funding Not applicable. patient remains uncertain, we did not observe any side effects associated with their use. Data Availability In humans, a revision surgery is often required to treat The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. restenosis [5], and this approach was chosen for our canine patient, which also allowed for a histopathological Declarations evaluation of the bone overgrowth. Histopathological evaluation showed the presence of Ethics approval normal or reactive osseous tissue, rather than new bone This study did not require official or institutional ethical approval. The dog was handled according to high ethical standards and national legislation. and immature woven bone. This finding may be similar to heterotopic ossification reported in humans following Consent for publication trauma or injury. The presence of chondrocytes in some Not applicable. fragments could indicate a possible chondroid metapla- Competing interests sia and endochondral ossification, which are necessary The authors declare that they have no competing interests. for bone regrowth [5, 16]. Despite thorough histological Prior publications examination, we did not identify a definitive histological Data have not been published previously. reason for the bone overgrowth, in our case. However, it may be also that the bone biopsies, although obtained Received: 26 February 2023 / Accepted: 3 August 2023 from different sites, may not have been fully representa- tive of the entire lesion. 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