Introduction
Magnetic resonance imaging is the optimal imaging modality for diseases of the thoracolumbar vertebral column, compared with CT and myelography, especially when distinguishing IVDD from other vertebral column disorders that may have similar clinical presentations.1 It has been previously reported that IVDD is the most common lesion found in dogs with clinical signs associated with thoracolumbar disease,2,3 but to the authors’ knowledge, no study has been performed that compares the incidence of various thoracolumbar diseases in dogs with regard to body weight.
The purpose of the study presented here was to compare the incidence of lesions found on MRI in dogs weighing < 15 kg (33 lb) with that of dogs weighing ≥ 15 kg. Information regarding the incidence of differing causes of thoracolumbar disease can aid a client's decision-making about whether to perform advanced imaging and surgical intervention. We hypothesized that dogs weighing ≥ 15 kg would have a significantly higher incidence of nonintervertebral disk–related lesions, compared with dogs weighing < 15 kg, and the occurrence of spinal neoplasia (ie, neoplasia of the spinal cord or vertebral column) and FCEM would also be significantly higher in dogs weighing ≥ 15 kg.
Materials and Methods
Case selection criteria
Electronic medical records for client-owned dogs admitted to BluePearl Veterinary Partners–Stone Oak (San Antonio, Tex) between January 31, 2016, and July 18, 2018, that underwent MRI of the thoracolumbar vertebral column were reviewed. Dogs that were admitted to the hospital for evaluation and treatment of clinical signs consistent with thoracolumbar disease were included as cases in the present study. Dogs were excluded from the study if the primary concern and reason for thoracolumbar imaging was not limited to the thoracolumbar vertebral column, such as generalized neurologic disease or acute trauma, or if the patient had incomplete medical records (ie, missing patient's weight, breed, sex, or MRI findings). If a patient was admitted to the hospital more than once during the study period for evaluation of thoracolumbar disease, only the first incident was included for statistical analysis.
Medical records review
Data collected from the medical records of dogs in the study population included the patient's age at time of imaging, body weight, breed, sex, MRI findings, and lesion location. Additional data collected included further diagnostic testing for patients in which no lesions were seen on MRI, or that had findings that were inconclusive and did not directly lead to a diagnosis. Further diagnostic testing was aimed at ruling out genetic, infectious, or inflammatory causes of thoracolumbar disease and consisted of cytologic analysis of CSF, infectious disease testing (ie, testing for Toxoplasma gondii, Neospora canis, Cryptococcus spp, and Coccidioides spp infections and for vector-borne infections), and genetic testing for a predisposition for DM. If indicated, tissue samples were collected and submitted for histologic evaluation and microbial culture.
MRI
Magnetic resonance imaging scans of all patients were completed under general anesthesia (isoflurane inhalation anesthesia). Patients were premedicated with hydromorphonea (0.1 mg/kg [0.045 mg/lb], IV or IM) administration and underwent anesthetic induction with propofolb (4 to 6 mg/kg [1.8 to 2.7 mg/lb], IV) administration. Patients were subjected to MRI in a high-field scanner.c The patients were positioned in dorsal recumbency, and the thoracolumbar region was examined by use of a body coil, with the area of concern centered in the field. The examinations began with the scout sequence to identify the affected area of the vertebral column, and focused diagnostic sequences were performed on the affected region. A T2W sagittal sequence and a T2W axial sequence were performed first, and if the lesion was disk related, no further sequences were performed. If there was no identifiable lesion and IVDD or spinal neoplasia was suspected, T1W sagittal, axial, and coronal sequences were performed with both precontrast and postcontrast images obtained by use of gadoversetamided (0.2 mL/kg [0.09 mL/lb]) administration as a contrast agent. In select cases, spectral fat suppression techniques were used for precontrast T1W sequences and were compared with precontrast T2W images. In the sagittal plane, slice thickness was 3 mm with no gap; in the axial plane, slice thickness was 3 to 5 mm with a 0- to 2-mm gap; and in the coronal plane, slice thickness was 3 mm with a 0- to 1-mm gap, adjusted depending on the patient's size and extent of the lesion.
All MRI imaging studies were reviewed and interpreted by a board-certified specialist, which included a surgeon (diplomate of the American College of Veterinary Surgeons), neurologist (diplomate of the American College of Veterinary Internal Medicine-Neurology), or radiologist (diplomate of the American College of Veterinary Radiology).
Statistical analysis
Age at diagnosis was compared between body weight groups (ie, dogs weighing ≥ 15 kg vs dogs weighing < 15 kg) by use of the Mann-Whitney U test. Comparison of proportions between body weight groups was made by use of the Fisher exact test or χ2 test. Binary logistic regression models were built with IVDD (yes or no), or neoplasia (yes or no), or lesion location, which included T11-12 (yes or no), L4-5 (yes or no), L5-6 (yes or no), or no lesion seen, as the dependent variables and age, weight, and sex as independent variables. Significance was set at a value of P < 0.05.
Results
During the study period, 494 dogs with thoracolumbar disease that underwent MRI were admitted to the hospital. The affected dogs included 28 sexually intact females, 61 sexually intact males, 207 spayed females, and 198 neutered males (Table 1). The study population was divided into dogs weighing < 15 kg (n = 393) and dogs weighing ≥ 15 kg (101). The mean ± SD age at time of MRI for all dogs was 83 ± 35.1 months (range, 12 to 174 months). Age at time of MRI was significantly (P = 0.003) higher in dogs weighing ≥ 15 kg (mean, 90.9 ± 32.4 months), compared with dogs weighing < 15 kg (81.1 ± 35.5 months).
Comparison of characteristics of dogs in the present study between dogs weighing < 15 kg and dogs weighing ≥ 15 kg.
| Characteristics | Dogs weighing < 15 kg (n = 393) | Dogs weighing ≥ 15 kg (n = 101) |
|---|---|---|
| Sex and reproductive status | ||
| Spayed female | 170 (43.3) | 37 (36.6) |
| Sexually intact female | 24 (6.1) | 4 (4) |
| Castrated male | 153 (38.9) | 45 (44.5) |
| Sexually intact male | 46 (11.7) | 15 (14.9) |
| Breed characteristics | ||
| Chondrodystrophic | 371 (94.4) | 25 (24.8) |
| Dachshund | 174 | 0 |
| French Bulldog | 17 | 1 |
| Shih Tzu | 18 | 0 |
| Other chondrodystrophic breeds | 162 | 24 |
| Nonchondrodystrophic | 22 (5.6) | 76 (75.2) |
| Labrador Retriever | 0 | 13 |
| German Shepherd Dog | 0 | 9 |
| Pit bull–type dog | 0 | 5 |
| Other nonchondrodystrophic breeds | 22 | 49 |
| Age at time of MRI (y) | 6.8 ± 3 | 7.6 ± 2.7 |
Data for sex and reproductive status and breed characteristics are reported as number (%) of dogs, and data for age are reported as mean ± SD.
Seventy breeds or types of dogs were included in the present study. Breeds were classified as either chondrodystrophic or nonchondrodystrophic, and dogs listed as mixed (eg, Dachshund mixed) were categorized on the basis of the primary breed described. Dachshunds (including Dachshund mixed, Longhaired Dachshunds, and Miniature Dachshunds) were overrepresented and accounted for 43.5% (215/494) of all dogs. Of the study population, 94.4% (371/393) of dogs weighing < 15 kg were chondrodystrophic breeds, compared with only 24.8% (25/101) of dogs weighing ≥ 15 kg. Characteristics of the 3 breeds with the largest sample size from the chondrodystrophic and nonchondrodystrophic categories are summarized (Table 1).
The most common imaging findings included IVDD (87.2% [431/494]), spinal neoplasia (5.7% [28/494]), FCEM (2.2% [11/494]), and no clinically important imaging findings (2.8% [14/494]). These 4 categories accounted for approximately 98% of all findings. Other findings were found for 2.0% (10/494) of dogs, which included diagnoses of granulomatous meningoencephalitis, diskospondylitis, meningoencephalitis, lumbosacral stenosis, hemivertebra, sterile epidural empyema, and syringomyelia.
In dogs weighing < 15 kg, the incidence of IVDD was 94.7% (372/393 dogs), compared with 58.4% (59/101) in dogs weighing ≥ 15 kg. Dogs weighing < 15 kg had a significantly (P = 0.034) higher incidence of IVDD lesions in the T12-13 segment, compared with dogs weighing ≥ 15 kg (Table 2). Chondrodystrophic dogs (P = 0.032) and dogs weighing < 15 kg (P = 0.008) had a significantly higher incidence of disk-related lesions in the T13-L1 segment, compared with nonchondrodystrophic dogs and dogs weighing ≥ 15 kg, respectively. Dogs weighing < 15 kg (P < 0.001) that were either sexually intact males (P = 0.038) or sexually intact females (P = 0.004), had a significantly higher incidence of IVDD lesions located in the region of the L5-6 segment, compared with dogs weighing ≥ 15 kg. Significantly (P < 0.001) more dogs weighing ≥ 15 kg had IVDD lesions at sites L4-5 and caudally, compared with dogs weighing < 15 kg.
Localization of lesions seen on MRI categorized on the basis of body weight for the dogs* of the present study.
| Lesion location | ||||||
|---|---|---|---|---|---|---|
| Body weight | Type of lesion | No. of lesions | T1-2 to T5-6 | T6-7 to T10-11 | T11-12 to L2-3 | L3-4 to L7-S1 |
| < 15 kg | IVDD | 405 | — | 4 (1) | 362 (89.4) | 39 (9.6) |
| Spinal neoplasia | 8 | 3 (37.5) | 1 (12.5) | 1 (12.5) | 3 (37.5) | |
| FCEM | 9 | — | — | 6 (66.7) | 3 (33.3) | |
| ≥ 15 kg | IVDD | 79 | — | 3 (3.8) | 60 (75.9) | 16 (20.3) |
| Spinal neoplasia | 34 | 3 (8.8) | 4 (11.8) | 9 (26.5) | 18 (52.9) | |
| FCEM | 9 | — | — | 6 (66.7) | 3 (33.3) | |
Data for lesion localization are reported as number (%) of lesions at each spinal region.
Some patients had lesions at more than 1 site or had lesions that spanned multiple sites.
— = No lesions identified.
The incidence of spinal neoplasia was significantly (P = 0.005) higher in dogs weighing ≥ 15 kg (19.8% [20/101]), compared with dogs weighing < 15 kg (2% [8/393]). Dogs weighing ≥ 15 kg had a significantly (P < 0.001) higher incidence of spinal neoplasia in the region of L4-5, compared with dogs weighing < 15 kg. Dogs weighing ≥ 15 kg were 11.9 times (95% CI, 5.1 to 27.9) as likely to have a neoplastic lesion as were dogs weighing < 15 kg. Binary logistic regression models showed that for each 1-kg (2.2 lb) increase in body weight, the odds of neoplasia increased by 8% (OR, 1.08 [95% CI, 1.05 to 1.12]). The mean age of dogs with spinal neoplasia at the time of MRI was 98.9 ± 36.4 months and was not significantly different from the mean age of all dogs (ie, 83 ± 35.1 months). Dogs weighing < 15 kg with spinal neoplasia were 109.9 ± 37.5 months old at the time of MRI. However, results of logistic regression analysis revealed that age was not an independent predictor of neoplasia. Multiple manifestations of spinal neoplasia were noted in the dogs of the present study that included extradural, intradural-extramedullary, and intramedullary spinal cord lesions. Biopsy and subsequent histologic examination were only performed in 1 dog and resulted in a diagnosis of a plasma cell tumor. In all remaining dogs with spinal neoplasia, owners elected either euthanasia or palliative care because of the poor prognosis and lack of treatment options.
In the study population, the overall incidence of an MRI lesion consistent with FCEM was 2.2% (11/494), with 6.9% (7/101) incidence in dogs weighing ≥ 15 kg, compared with 1% (4/393) incidence in dogs weighing < 15 kg. Dogs weighing ≥ 15 kg with thoracolumbar disease were 7.4 times (95% CI, 2.3 to 23) as likely to have an MRI lesion consistent with FCEM as were dogs weighing < 15 kg. No lesion location predilection was identified.
The overall incidence of MRI studies with no clinically important findings was 2.8% (14/494), with an incidence of 10.9% (11/101) in dogs weighing ≥ 15 kg and 0.8% (3/393) in dogs weighing < 15 kg. Of the 14 dogs with no MRI lesions, 3 dogs weighed < 15 kg. Two of these dogs had negative infectious disease test results and unremarkable findings on cytologic analysis of CSF but were identified as either carriers or at risk for DM on genetic testing. The remaining dog had unremarkable findings on cytologic analysis of CSF, negative infectious disease test results, and no predisposition for DM on genetic testing.
Of the 14 dogs with no MRI lesions, 11 dogs weighed ≥ 15 kg. Three of these dogs had a presumptive diagnosis of acute FCEM or ANNPE and were admitted to the hospital within hours of onset of clinical signs. In light of negative infectious disease test results and unremarkable findings on cytologic analysis of CSF in the 3 dogs, it was possible that the insult was minor, or that it was too early in the disease process for detection of MRI lesions. One dog weighing ≥ 15 kg that initially had nonambulatory paraparesis and no MRI lesions detected in the thoracolumbar vertebral column was hospitalized and the neurologic status progressed to nonambulatory tetraparesis. An MRI of the brain and entire vertebral column revealed a large cavitated mediastinal mass, consistent with a thymoma. A edrophonium test was performed, and results were strongly positive, indicating likely myasthenia gravis. Two dogs weighing ≥ 15 kg presented with neurologic signs consistent with thoracolumbar disease, but subsequently had a diagnosis of generalized neurologic disease not limited to the thoracolumbar vertebral column. One of these dogs was found to have meningomyelitis on the basis of CBC results and cytologic analysis of CSF, and 1 dog was found to have lymphoblastic leukemia on the basis of cytologic analysis of CSF. The 5 remaining dogs weighing ≥ 15 kg without an MRI lesion had negative infectious disease test results and unremarkable findings on cytologic analysis of CSF but were identified as either carriers of or at risk for DM on genetic testing.
Discussion
Magnetic resonance imaging was used in the present study as it has been shown to be the best diagnostic method for early identification of intervertebral disk degeneration in humans4 as well as for imaging the spinal cord, vertebral column, and associated structures in dogs.5 A strong correlation has been found between MRI and surgical findings (reportedly up to 100% for lesion localization and lateralization).6,7 Magnetic resonance imaging has a reported sensitivity of 98.5% for the diagnosis and characterization of intervertebral disk herniation in dogs.8 Spectral fat suppression techniques were used for precontrast T1W sequences in the present study, as this has been shown to differentiate normal fat in the bone marrow, epidural space, and fascial planes from other tissues, which may be pathological in nature.9 Ideally, both precontrast and postcontrast T1W images would be obtained as fat-suppression techniques to help identify subtle contrast enhancement. However, in reviewing MRI records of patients in the present study, only the precontrast T1W fat-suppression images were obtained and compared with T2W precontrast images. Therefore, some patients in the present study that had no identifiable lesions on MRI may have had appreciable lesions if both precontrast and postcontrast fat-suppression images had been obtained.
Patients in the present study were placed into 2 body weight groups (ie, dogs weighing < 15 kg and dogs weighing ≥ 15 kg) to identify differences in likelihood of types of lesions seen on MRI with regard to patient weight. The body weight cutoff of 15 kg for dichotomization of data was selected on the basis of the typical (high-end) body weight of American Kennel Club breed standards (approx 11 kg [24.2 lb]) for the chondrodystrophic breeds represented in the present study. Selection of this body weight cutoff resulted in nearly 95% of dogs in the < 15 kg body weight group representing chondrodystrophic breeds, and approximately 75% of dogs in the ≥ 15 kg body weight group representing nonchondrodystrophic breeds. The authors believed this would best highlight the differences both between the body weight groups as well as between chondrodystrophic and nonchondrodystrophic breeds. Because information regarding body condition scores was not available in most medical records, it is possible that some patients in the present study could have been misclassified into a higher or lower body weight group if they were over- or underconditioned.
The most common MRI findings in the present study included IVDD (87.2% [431/494]), spinal neoplasia (5.7% [28/494]), FCEM (2.2% [11/494]), and no lesion seen on MRI (2.8% [14/494]). In the remaining 2% (10/494) of dogs, lesions were consistent with either congenital malformations or inflammatory and infectious disease processes that required further testing for diagnosis.
The overall frequency of intervertebral disk–related disease in dogs is reported as 2.3%.10 Although all intervertebral disks are susceptible to herniation, 66% to 87% of all disk herniations occur in the thoracolumbar vertebral column.11 Several breeds have been previously noted to have a significantly increased risk of IVDD and include Basset Hounds, Beagles, Cocker Spaniels, Dachshunds, French Bulldogs, Lhasa Apsos, Pekingese, Pembroke Welsh Corgis, and Shih Tzus.12,13,14,15 Dachshunds are particularly predisposed, and 19% to 24% of all Dachshunds (including up to 62% within certain lineages) are predicted to develop intervertebral disk herniation within their lifetimes.16,17 Dachshunds have been found to be 12.6 times as likely to develop intervertebral disk herniation as are dogs of other breeds,18,19 and account for 45% to 73% of all cases of acutely herniated intervertebral disks in dogs.11,16,17,18,20,21,22,23,24 In the present study, Dachshunds (including Dachshund mixed, Longhaired Dachshunds, and Miniature Dachshunds) were overrepresented and accounted for 43.5% (215/494) of dogs in our study population. Disks located between the T12 and L3 vertebrae are the most commonly implicated sites for IVDD, and the most commonly affected disk spaces in chondrodystrophic dogs are T12-13 and T13-L1.11,21,24,25,26,27,28,29 The disk between L1-2 has been shown to be the most commonly affected site in large-breed dogs, followed by T13-L1 and L2-3.3,30 In the present study, significant differences were found in IVDD lesion location between the 2 body weight groups; dogs weighing ≥ 15 kg had significantly more disk herniations identified at L4-5 and caudally, compared with dogs weighing < 15 kg. Also, dogs weighing < 15 kg that were sexually intact, had a significantly higher incidence of IVDD lesions located in the region of the L5-6, compared with dogs weighing ≥ 15 kg.
The overall incidence of spinal neoplasia in dogs of the present study was 5.7% (28/494). The incidence of neoplasia in dogs weighing ≥ 15 kg was 19.8% (20/101). Dogs weighing ≥ 15 kg with clinical signs of thoracolumbar disease were 11.9 times (95% CI, 5.1 to 27.9) as likely to have a neoplastic lesion as were dogs weighing < 15 kg. In the present study, the mean age of all dogs with spinal neoplasia was 98.9 ± 36.4 months. Interestingly, dogs weighing < 15 kg with spinal neoplasia were 109.9 ± 37.5 months old at the time of MRI. The higher age at presentation of dogs weighing < 15 kg could possibly be attributed to longer lifespans of smaller-breed dogs. Although age was not an independent factor in determining the probability that a dog weighing ≥ 15 kg would have spinal neoplasia, compared with dogs weighing < 15 kg, body weight was shown to be a significant factor in the present study. The incidence of neoplasia of the spinal cord and vertebral column in the present study may be an underestimation in the general population; it is possible that other diagnostic imaging modalities, such as plain radiography, may reveal spinal lesions resulting in patient euthanasia before advanced imaging, such as MRI, is performed.
Fibrocartilaginous embolic myelopathy refers to embolization of the spinal vasculature with fibrocartilaginous material, resulting in ischemic insult to the associated spinal cord parenchyma.31,32,33,34,35,36,37,38,39,40,41,42 The fibrocartilaginous material is histologically consistent with nucleus pulposus.35,36,37,40,41 Acute noncompressive nucleus pulposus extrusion results in contusion of the spinal cord. In ANNPE, an increase in intradiskal pressure, often following exercise or trauma, causes acute extrusion of the hydrated nucleus pulposus from the underlying intervertebral disk.29,31,43,44,45 Both FCEM and ANNPE lesions can be seen as hyperintensity of the spinal cord on MRI but can only be definitively diagnosed after death by gross and histologic examination of the affected spinal cord segment.31 However, considering the generally fair to good prognosis associated with FCEM and ANNPE, clinical studies on these conditions have been performed on presumptive diagnoses made by combining clinical and MRI findings.32,37,38,42,43,44,46,47,48 In 1 study35 of confirmed FCEM in purebred dogs, giant-breed dogs had an incidence of 49%. The higher incidence of confirmed FCEM in giant-breed dogs in that study32 was believed to be in part attributed to the owners of the giant-breed dogs electing euthanasia and subsequent necropsy earlier than owners of smaller dogs, as a result of the logistic or financial obstacles of managing a large, paralyzed dog.
In the present study, dogs with FCEM (or potentially ANNPE) did not receive a definitive histopathologic diagnosis as these patients were not euthanized; dogs weighing ≥ 15 kg were 7.4 times (95% CI, 2.3 to 23) as likely to have MRI lesions consistent with FCEM as were dogs weighing < 15 kg. Clinical outcomes of dogs with presumptive FCEM and ANNPE have previously been investigated separately, with favorable recovery reported in 84%36 and 66.6%44 of dogs, respectively. In the present study, presumptive FCEM was diagnosed on the basis of MRI findings when findings of a T2W hyperintense noncompressive intramedullary lesion with minimal to no contrast-enhancement were present. This was often combined with clinical signs of an acute onset of lateralized myelopathy, often with no paraspinal hyperesthesia. Diagnosis of FCEM was also made on the basis of additional diagnostic test results when clients authorized them, including cytologic analysis of CSF to rule out inflammatory or infectious causes of clinical signs. If no additional diagnostic testing was performed, a diagnosis was made on the basis of clinical response to conservative medical management, exercise restriction, and physical rehabilitation.
Fourteen dogs (2.8% [14/494]) in the present study had no identifiable lesions on MRI. Additional diagnostic testing was performed in these dogs to investigate underlying causes of neurologic signs. Further diagnostic testing was aimed at ruling out genetic, infectious, or inflammatory causes of thoracolumbar disease and consisted of cytologic analysis of CSF, infectious disease testing (ie, testing for T gondii, N canis, Cryptococcus spp, and Coccidioides spp infections and for vector-borne infections), and genetic testing for predisposition for DM. Five of 14 dogs without MRI lesions had positive tests for affected or at-risk carriers for DM. Degenerative myelopathy is a diagnosis of exclusion, and definitive diagnosis requires histologic evaluation.49 Therefore, diagnosis of DM was made in these dogs when all other diagnostic testing results were negative, and was often combined with clinical signs of progressive deterioration of neurologic status.
The limitations of the present study included those inherent to a retrospective study. Incomplete medical records and lack of body condition score data could have contributed to misclassification of patients into their respective body weight groups. The MRI technique and images acquired could have potentially resulted in missed subtle contrast-enhanced lesions because spectral fat-suppression images were only obtained with precontrast T1W images; ideally these would be obtained with precontrast and postcontrast images for comparison. The lack of electro-diagnostic testing could have led to missed diagnoses of diseases affecting the peripheral nerves or neuromuscular junction.
The findings from the present study confirmed our hypothesis that dogs weighing ≥ 15 kg with thoracolumbar disease had a significantly higher incidence of nonintervertebral disk–related lesions, compared with dogs weighing < 15 kg. We also confirmed that dogs weighing ≥ 15 kg with thoracolumbar disease had a significantly higher incidence of spinal neoplasia; we found that these dogs were more often affected by a neoplastic lesion or FCEM than dogs with thoracolumbar disease weighing < 15 kg. A body weight cutoff of 15 kg highlighted the differences that existed between dogs of varying body weight, as dogs weighing < 15 kg were mainly chondrodystrophic breeds, and these dogs most often had IVDD. This finding may have important clinical relevance, as this information could allow for informed conversations with owners in managing expectations. When discussing advanced imaging with clients for dogs that weigh < 15 kg with thoracolumbar disease, the conversation could be focused on IVDD as this was the most likely diagnosis in the present study. For dogs that weigh ≥ 15 kg, the client education could include other likely diagnoses (ie, neoplasia and FCEM). For some clients, knowing that there is an increased likelihood of neoplasia may be a driving factor in deciding whether to pursue advanced imaging or surgical intervention.
Acknowledgments
This work was supported by the BluePearl Veterinary Partners internal review board and the BluePearl Science Study Design and Review Committee.
The authors declare that there were no conflicts of interest.
The authors thank Dr. Erik Hofmeister for assistance with statistical analysis.
Footnotes
Hydromorphone hydrochloride (10 mg/mL), TEVA Pharmaceuticals Inc, North Wales, Pa.
Propoflo (10 mg/mL), Zoetis Inc, Kalamazoo, Mich.
GE Signa Advantage 1.5T, GE Medical Systems, Milwaukee, Wis.
OptiMARK (0.5 mmoL/mL), Liebel-Flarsheim Company LLC, Raleigh, NC.
Abbreviations
| ANNPE | Acute noncompressive nucleus pulposus extrusion |
| DM | Degenerative myelopathy |
| FCEM | Fibrocartilaginous embolic myelopathy |
| IVDD | Intervertebral disk disease |
| T1W | T1-weighted |
| T2W | T2-weighted |
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