Vertebral vascular canal dysplasia in French and English Bulldogs: Clinical, CT, and MRI characteristics and prevalence.

The authors have observed a vertebral anomaly in French and English Bulldogs and termed this anomaly "vertebral vascular canal dysplasia (VVCD)." No previously published descriptions of this anomaly were found. The aims of this retrospective, multi-institutional, observational study were to (1) describe the clinical, CT, and MRI characteristics of VVCD, and (2) estimate the prevalence and describe the characteristics of VVCD in a group of French and English Bulldogs. For descriptions of the anomaly, medical records and imaging studies of nine clinical cases with VVCD from several countries were reviewed. For estimation of prevalence, imaging studies of French and English Bulldogs from the United Kingdom (UK) and Italy were reviewed. All clinical case dogs had ≥5 thoracic vertebrae with VVCD affecting >50% of vertebral body height (VBH). The prevalence of VVCD involving ≥1 thoracic vertebra in the UK population (CT identified) of English Bulldogs and French Bulldogs was, respectively, 83.3% (30/36) and 68.3% (28/41). English Bulldogs had significantly more thoracic vertebrae with VVCD than French Bulldogs (P = < 0.01). The prevalence of VVCD in ≥1 thoracic vertebra in the Italian population (MRI identified) of English Bulldogs and French Bulldogs was, respectively, 21.7% (5/23) and 6.6% (7/106). Vertebral vascular canal dysplasia was observed in normal as well as in malformed vertebrae (e.g., hemivertebrae). Findings from the current study introduced descriptions of VVCD that can be used as background for future studies.

High-field MRI using standard pulse sequences has moderate to substantial interobserver agreement and good accuracy for differentiation between intracranial extra-axial histiocytic sarcoma and meningioma in dogs.

Intracranial extra-axial histiocytic sarcoma shares common MRI features with meningioma. As histiocytic sarcoma carries a generally worse prognosis than meningioma, the ability to differentiate between these two neoplasms is of clinical value. The aim of this retrospective diagnostic accuracy and observer agreement study was to evaluate the accuracy and reliability of high-field MRI to differentiate between these two tumors, using standard pulse sequences and published MRI features. A total of 51 dogs were included (26 meningiomas and 25 histiocytic sarcomas). Magnetic resonance imaging examinations were independently assessed by three experienced board-certified radiologists, evaluating 18 imaging features. They were asked to assign each case to one of three categories (meningioma, histiocytic sarcoma, and undetermined). Agreement for the MRI diagnosis across all three reviewers was moderate (κ 0.54) while paired interobserver agreement ranged from moderate to substantial (κ 0.58-0.74) with percent agreement ranging between 86.1% and 87.7%. Overall, the probability of correctly diagnosing meningioma in a dog with this tumor ranged between 79.2% and 94.4%, and the probability of correctly diagnosing histiocytic sarcoma in a dog with this tumor ranged between 76.0% and 92.3%. The overall probability to diagnose the correct tumor, irrespective of type, ranged between 79.2% and 89.7%. Histiocytic sarcomas tended to have more extensive edema and more often had combined perilesional and distant meningeal enhancement affecting both pachy- and leptomeninges, while for meningiomas, meningeal enhancement tended to more commonly be perilesional and pachymeningeal. Imaging features that seemed more useful to make a correct diagnosis included "location/type of meningeal enhancement," "osseous changes in the adjacent neurocranium," "cystic changes," and "herniation severity."

Correlation of MRI with the Neuropathologic Changes in Two Cats with Bromethalin Intoxication.

Two cats were presented with multifocal neurological signs. One cat's signs progressed over 2 wk; the other cat progressed over 5 days. Examinations were consistent with a process involving the prosencephalon, vestibular system, and general proprioceptive/upper motor neuron systems. MRI of the brain and cervical spinal cord reveal widespread T2 hyperintensity of the white matter. Affected areas included the cerebrum, cerebral peduncles, corticospinal tracts of the pons and medulla, and the cerebellum. T2 hyperintensity was present in all funiculi of the spinal cord. Diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) maps were consistent with cytotoxic or intramyelinic edema. Differential diagnosis included toxic or metabolic/degenerative leukoencephalopathies. Necropsies revealed widespread spongy degeneration of the central nervous system white matter. Toxicologic assays of liver specimens revealed desmethylbromethalin, a metabolite of bromethalin. Bromethalin is a rodenticide that causes uncoupling of oxidative phosphorylation. Antemortem diagnosis is challenging. DWI and ADC maps were instrumental in narrowing the differential diagnosis and raised the index of suspicion for bromethalin. Bromethalin intoxication should be considered in all animals with a progressive course of multifocal neurologic deficits. MRI, specifically, DWI and ADC maps, may serve as a biomarker of cytotoxic or intramyelinic edema associated with spongiform leukoencephalomyelopathy.

Post-operative Salmonella surgical site infection in a dog.

Following decompressive surgery for degenerative lumbosacral stenosis, a 6-year-old German shepherd dog developed a subcutaneous infection at the surgical site and discospondylitis at the lumbosacral intervertebral disc. Salmonella enterica subsp. enterica, serotype Dublin was recovered from the surgical site. Salmonella of a different serovar was isolated from a sample of the raw meat-based diet that the owner fed the dog.

Infection postopératoire du site chirurgical parSalmonellachez un chien. Après une chirurgie de décompression pour une sténose lombo-sacrée dégénérative, un chien Berger allemand âgé de 6 ans a développé une infection sous-cutanée au site chirurgical et une discospondylite au disque intervertébral lombo-sacré. Salmonella enterica sous-esp. enterica de sérotype Dublin a été isolée du site chirurgical. Une salmonelle d'un sérovar différent a été isolée d'un échantillon de l'alimentation à base de viande crue donnée par le propriétaire au chien.(Traduit par Isabelle Vallières).

MASTICATORY MUSCLE MYOSITIS IN A GRAY WOLF (CANIS LUPUS).

A 10-yr-old male, neutered gray wolf ( Canis lupus ) was presented for atrophy of the temporalis and masseter muscles. Clinical signs and magnetic resonance imaging were consistent with a myopathy. Positive serology for antibody titers directed against Type 2M myofibers, and the observation of a mixed mononuclear inflammatory cell infiltrate along with eosinophils and neutrophils within the temporalis muscle, were diagnostic for masticatory muscle myositis. Importantly, protozoal myositis was excluded based on other clinicopathologic data. The case highlights the potential for immune-mediated polymyositis in canids other than the domesticated dog ( Canis lupus familaris). Additionally, awareness of a diet in which raw meat is used should prompt a thorough investigation for an underlying infectious myositis in the gray wolf.

Magnetic resonance imaging findings associated with lateral cerebral ventriculomegaly in English Bulldogs.

Multiple congenital or developmental anomalies associated with the central nervous system have been reported in English Bulldogs. The purpose of this retrospective study was to identify and describe the prevalence and MRI characteristics of these anomalies and their association with presence and degree of cerebral ventriculomegaly. Magnetic resonance imaging studies of 50 English Bulldogs were evaluated. Forty-eight dogs had some degree of cerebral ventriculomegaly, 27 of which had an otherwise normal brain. Presence of lateral ventriculomegaly was not significantly associated with presence of another intracranial lesion. Appearance of the septum pellucidum was variable, ranging from intact to incomplete or completely absent. The corpus callosum was subjectively thinned in all but three dogs, two of which had normal lateral ventricles. Fusion of the rostral colliculi was not found in any dog. A persistent craniopharyngeal canal was identified in one dog. Aqueductal stenosis caused by fusion of the rostral colliculi was not identified in any dog. Findings indicated that cerebral ventriculomegaly is a common finding in English Bulldogs with or without other intracranial lesions, aqueductal stenosis caused by fusion of the rostral colliculi is unlikely to be a common etiology leading to obstructive hydrocephalus, and a large craniopharyngeal canal is a rare finding that has unknown clinical significance at this time.

Insertion of the dorsal oblique muscle in the dog: an anatomic basis for ventral strabismus associated with oculomotor nerve dysfunction.

OBJECTIVE: To describe the insertion of the dorsal oblique (DO) muscle in relationship to the equator of the globe in dogs. PROCEDURE: The study was conducted on 10 fresh cadaver eyes from five dogs, which were euthanized for disease processes unrelated to ocular disease. A manual vernier caliper was used to determine the calculated measurements. RESULTS: The median anterior-to-posterior diameter of the globe was 21 mm. The median length from the vertex of the anterior pole to the anterior point of insertion of the DO tendon was 11.5 mm. The median length from the posterior pole to the posterior point of insertion of the DO tendon was 10 mm. The width of tendon of insertion of the DO tendon was 3.25 mm. CONCLUSIONS: In disorders involving the oculomotor nerve or the oculomotor nerve nucleus in the mesencephalon, the resultant strabismus is directed ventrolaterally. Based on the insertion of the superior oblique muscle in humans, we hypothesized that the DO muscle would likely explain the ventral deviation in disorders of the oculomotor nerve or its nucleus. In this study, the point of the insertion of the DO muscle tendon was posterior to the equator. Based on this anatomic location, unopposed function of the DO muscle would be expected to result in ventral deviation of the globe.

Clinicopathologic and MRI characteristics of presumptive hypertensive encephalopathy in two cats and two dogs.

Two dogs and two cats were evaluated for the acute-onset of abnormal mentation, recumbency, and blindness. All cases had systemic hypertension, ranging from 180 mm Hg to 260 mm Hg. MRI of the brain disclosed noncontrast-enhancing, ill-defined, T2-weighted (T2W) hyperintensities in the white matter of the cerebrum in the areas of the frontal, parietal, temporal, and occipital lobes. Lesions were also observed in the caudate nuclei and thalamus (n = 1 in each). Intracranial hemorrhage was observed in one animal. Diffusion-weighted imaging (DWI) was consistent with vasogenic edema in two animals. Retinal lesions were observed in three animals. Hypertension was secondary to renal disease in three animals. A primary underlying disorder was not identified in one animal. Normalization of blood pressure was achieved with amlodipine either alone or in combination with enalapril. In one cat, hypertension spontaneously resolved. In three cases, neurologic improvement occurred within 24-48 hr of normalization of blood pressure. The presumptive diagnosis of hypertensive encephalopathy was supported by the MRI findings and neurologic dysfunction coincident with systemic hypertension in which the neurologic dysfunction improved with treatment of hypertension. The prognosis appears good for the resolution of neurologic deficits with normalization of blood pressure in animals with hypertensive encephalopathy.

Microanatomical findings with relevance to trigeminal ganglion enhancement on post-contrast T1-weighted magnetic resonance images in dogs.

Introduction: Trigeminal ganglion contrast enhancement (TGCE) is reported to be a normal and a common finding on magnetic resonance imaging studies of dogs, cats and humans. The intent of the present study was to describe the anatomical characteristics of the trigeminal ganglion, its surrounding structures, and histological features that are relevant to explain or hypothesize on the reason for TGCE on T1-weighted post-contrast MRI studies of the brain in dogs. Methods: Eight dog cadavers were dissected to study the anatomy of the trigeminal ganglion. The presence and anatomy of vessels was studied by dissection and by histological techniques. Two trigeminal ganglia were isolated and stained with hematoxylin-eosin (HE). Two other trigeminal ganglia included in the trigeminal canal and trigeminal cavity were decalcified with formic acid/formalin for 12 weeks and stained with HE to study the related vessels. Additionally, a corrosion cast was obtained from a separate canine specimen. Results: Leptomeninges and a subarachnoid space were identified at the level of the trigeminal nerve roots and the trigeminal ganglion. No subarachnoid space was identified and leptomeninges were no longer present at the level of the three trigeminal nerve branches. Small arterial vessels ran to and supplied the trigeminal ganglion, passing through the dura mater. No venous plexus was visualized at the level of the trigeminal ganglion in the dissections. A complex arterial vascular network was identified within the leptomeningeal covering of the trigeminal ganglion and was best appreciated in the corrosion cast. Histological examination revealed small-to moderate-sized blood vessels located in the epineurium around the ganglion; from there a multitude of arterioles penetrated into the perineurium. Small endoneurial branches and capillaries penetrated the ganglion and the trigeminal nerve branches. Discussion: Limitations to this study include the limited number of canine specimens included and the lack of electron microscopy to further support current hypotheses included in our discussion. In conclusion, this study provides further support to the theory that TGCE in dogs may be due an incomplete blood-nerve barrier or blood-ganglion barrier at the interface between the central nervous system and the peripheral nervous system.

Case report: Nonsimultaneous bilateral triceps tendon rupture and surgical repair in a healthy dog.

A 7-year-old female spayed Australian shepherd dog was presented for an acute onset of inability to stand. On physical examination, the dog was unable to support weight on the thoracic limbs. On neurological examination, the thoracic limbs had absent hopping and paw placement and reduced withdrawal reflexes bilaterally. The remainder of the neurological examination was normal. The anatomic lesion localized to the C6-T2 spinal nerve roots, spinal nerves, or the named nerves of the thoracic limb, bilaterally. A lesion affecting the ventral gray column of the C6 through T2 spinal cord segments was considered less likely. In an effort to exclude an orthopedic disorder from consideration, radiographs of the shoulders, elbows, and manus were normal. Magnetic resonance imaging of the cervical and cranial thoracic vertebral column was normal. Analysis of synovial fluid from the carpi, elbows, and shoulders were normal. Ultrasonography of the triceps muscle and tendon of insertion revealed bilateral, acute-subacute tears of the tendon at insertion of the triceps muscles, bilaterally. Magnetic resonance imaging of both elbows revealed complete avulsion of the triceps tendons bilaterally. Surgical repair of both tendons was performed using the Arthrex FiberLoop system combined with autologous conditioned plasma soaked in a collagen sponge. Postoperatively, external coaptation was provided using Spica splints for 6 weeks followed by the use of soft padded orthotic braces for an additional 6 weeks. Concurrently, a front support wheelchair was used for 10 weeks postoperative. By 10 weeks postoperative, the dog was able to ambulate without support. To the authors' knowledge, this is the first report of bilateral triceps tendon avulsion in a dog. Tendon avulsion occurred without a known history of trauma or predisposing metabolic abnormalities. Magnetic resonance imaging provided excellent anatomical detail that aided in surgical repair.

Pathology in Practice.

In collaboration with the American College of Veterinary Pathologists.

OLIG2 immunolabeling in feline ependymoma.

Ependymoma, one of the most common gliomas in cats, occurs most often in the lateral and third ventricles and has variable histologic patterns that often form rosettes and pseudorosettes. Oligodendrocyte transcription factor (OLIG2) is expressed in oligodendrocyte precursor cells and mature oligodendrocytes. Although widely used as a diagnostic marker for most gliomas, OLIG2 is reported to have minimal immunolabeling in ependymomas. Here we characterize the OLIG2 immunolabeling pattern in 19 cases of feline ependymoma, which occurred predominantly in the lateral and third ventricles. Immunohistochemistry for GFAP was variable in 14 cases and was typically localized in the cytoplasmic processes of the neoplastic ependymal cells, especially in the rosettes and pseudorosettes. Nuclear OLIG2 immunolabeling was present in 17 cases and varied in intensity from weak (4 cases) to strong (13 cases). The distribution of OLIG2 immunolabeling within the neoplasms included none (2 cases), <25% (7 cases), 25-50% (6 cases), 51-75% (2 cases), and >75% (3 cases). OLIG2 immunolabeling intensity and distribution is widespread in feline ependymoma, in contrast to ependymomas in other species, and should not be relied upon as a specific marker for feline oligodendroglioma.

Effect of doxepin on quality of life in Labradors with laryngeal paralysis: A double-blinded, randomized, placebo-controlled trial.

BACKGROUND: Laryngeal paralysis commonly affects older Labrador retrievers. Currently, dogs with severe disease require surgical intervention, most commonly arytenoid lateralization. Anecdotally, doxepin has been proposed to help dogs with laryngeal paralysis. HYPOTHESIS: Doxepin will improve quality of life measures assessed by owners of Labrador retrievers with laryngeal paralysis not requiring emergency surgery. ANIMALS: Twenty-two Labrador retrievers with laryngeal paralysis. METHODS: Dogs were randomized to receive doxepin (3-5 mg/kg q12h PO) or placebo for 28 days. Owners completed quality-of-life assessments before and after completing the study. Data were compared between groups using Rank-Sum tests or Fisher's exact tests. RESULTS: The 2 groups of dogs did not differ at baseline except for owner-perceived degree of ataxia (owners of dogs receiving doxepin considered them more ataxic than owners of dogs receiving placebo). After 28 days, owner-assessed quality of life measures did not differ between dogs receiving doxepin or placebo (dogs worsening: doxepin = 2, placebo = 1; dogs unchanged: doxepin = 6, placebo = 7; dogs improved: doxepin = 4, placebo = 2; P = .84). Dogs receiving placebo had a greater improvement in client-assessed overall health than dogs receiving doxepin (mean ranks: doxepin = 4.36, placebo = 6.64; P = .04). The study was terminated at this interim analysis. CONCLUSIONS AND CLINICAL IMPORTANCE: Doxepin did not appear to improve any measures of owner-assessed quality of life in Labrador retrievers with laryngeal paralysis.

Clinical features and outcome of acquired myasthenia gravis in 94 dogs.

BACKGROUND: Factors known to be associated with outcome of acquired myasthenia gravis (MG) in dogs are limited. HYPOTHESIS/OBJECTIVES: Of dogs with MG, advancing age and comorbid neoplasia are associated with poor long-term prognosis and low rates of remission. ANIMALS: Ninety-four client-owned dogs with MG diagnosed by acetylcholine receptor antibody (AChR Ab) assay between 2001 and 2019 from a university clinic and 3 private clinics in the United States. METHODS: Cases were retrospectively evaluated and data were collected to determine clinical signs, treatment, and response to therapy defined by means of a clinical scoring rubric. Immunological remission was defined as a return of the AChR Ab concentration to <0.6 nmol/L. Multivariable binary logistic regression analysis was used to identify clinical criteria predicting remission. RESULTS: An anticholinesterase drug was used to treat 90/94 (96%) dogs, which in 63/94 (67%) was the sole treatment; other drugs included immune modulators. Clinical remission (lack of clinical signs ≥4 weeks after treatment cessation) was observed in 29 (31% [95% confidence interval (CI): 22.4-40.8%]) dogs, clinical response (lack of clinical signs on treatment) in 14 (15% [95% CI: 9.0-23.6%]) dogs, clinical improvement (on treatment) in 24 (26% [95% CI: 17.8-35.2%]) dogs, and no clinical improvement in 27 (29% [95% CI: 20.5-38.6%]) dogs. Immunological remission was observed in 27/46 (59%) dogs, with clinical remission in all 27. Younger age (P = .04) and comorbid endocrine disease (P = .04) were associated with clinical remission. Initial AChR Ab concentration (P = .02) and regurgitation (P = .04) were negatively associated with clinical remission. CONCLUSIONS AND CLINICAL IMPORTANCE: Clinical remission in MG is less likely in older dogs and dogs presenting with regurgitation or high initial AChR Ab concentration, but more likely in younger dogs and dogs with comorbid endocrine disease.

Utility of MRI for Evaluation of a Common Calcaneal Tendon Rupture in a Dog: Case Report.

An 8-year-old intact male German shorthaired pointer was presented for a left pelvic limb lameness. Examination revealed a plantigrade stance with flexed digits in the left pelvic limb, and swelling of the left common calcanean tendon distally. Magnetic resonance imaging revealed a partial rupture of the left common calcanean tendon, involving rupture to the tendons of the biceps femoris, gracilis, and semitendinosus muscles. Surgical repair was performed using a modified 3-loop pulley suture. Postoperatively, the tarsus was immobilized with external coaptation. Destabilization of the external coaptation occurred over 9 weeks followed by physical rehabilitation and complete return to function at 10 months post-operative. This case report illustrates the utility of MRI as a diagnostic tool for evaluation of tendon pathology. MRI provided exceptional detail of the tendons that comprise the common calcaneal tendon and the anatomical relationships to surrounding structures which facilitated appropriate surgical correction.

A lateral approach to the feline cerebellar fossa: case report and identification of an external landmark for the tentorium ossium.

OBJECTIVES: The aim of this study was to describe the use of an external landmark that defines the attachment of the tentorium ossium for planning a craniectomy to access the cerebellar fossa. The external landmark was defined by a line where the caudal aspect of the convexity of the cranium transitions to a flat surface in the caudal aspect of the temporal fossa. We also aimed to determine if this external landmark was present and readily visualized, and to establish its relationship to the nuchal crest using three-dimensional (3D) volume-rendered CT reconstructions created from cats with normal cranial morphology. METHODS: First, a case is presented for the description of an approach in a cat with a meningioma located dorsolateral to the cerebellum. Second, CT studies of five cats with normal cranial morphology were selected. Regions of interest (ROIs) were drawn at the attachment of the tentorium ossium to the cranium and nuchal crest. Three-dimensional reconstructions were developed with colored ROI overlays. The external landmark defined the tentorial attachment on all 3D reconstructions. Additionally, using the postoperative CT of the clinical case described herein, ROIs of the tentorial attachment and nuchal crest along with a third ROI, the craniectomy, were drawn and overlaid on the 3D reconstruction to illustrate the position of the craniectomy in relation to the tentorium ossium attachment and nuchal crest. RESULTS: The use of the external landmark provided for a craniectomy that enabled adequate visualization for excision of a meningioma. On all 3D reconstructions, the external landmark was present and readily visualized. CONCLUSIONS AND RELEVANCE: Between the attachment of the tentorium ossium and nuchal crest exists an area adequately sized for a craniectomy in cats. Clinicians can use an identifiable external landmark on the lateral aspect of the cranium to plan the rostral boundary for a craniectomy to access the cerebellar fossa in cats.

Poliomyelomalacia in three dogs that underwent hemilaminectomy for intervertebral disk herniation.

CASE DESCRIPTION: 3 dogs were examined because of a sudden onset of signs of pain (1 dog) or paraparesis (2 dogs). CLINICAL FINDINGS: Neurologic findings consisted of myelopathy affecting the lumbar intumescence (1 dog) and T3-L3 myelopathy (2 dogs). In all dogs, MRI revealed spinal cord compression caused by L3-4 disk herniation. All dogs underwent routine surgical decompression of the intervertebral disk herniation. During MRI and decompressive surgery, physiologic variables were monitored. Immediately after surgery, all dogs were paraplegic with pelvic limb neurologic dysfunction consistent with myelopathy affecting the L4 through caudal spinal cord segments. TREATMENT AND OUTCOME: Within 24 hours after surgery, repeated MRI in all dogs revealed hyperintensity in the spinal cord gray matter of the lumbar intumescence on T2-weighted images. In the absence of neurologic improvement, dogs were euthanized at 3, 91, and 34 days after surgery. Postmortem microscopic examination of each dog's spinal cord at the lumbar intumescence revealed necrosis of the gray matter with relative white matter preservation suggestive of an ischemic injury. CLINICAL RELEVANCE: Dramatic neurologic deterioration following decompressive surgery for intervertebral disk herniation in dogs may be associated with the development of poliomyelomalacia secondary to ischemia. In these 3 dogs, ischemia developed despite probable maintenance of normal spinal cord blood flow and perfusion during anesthesia. To exclude other causes, such as compression or hemorrhage, MRI was repeated and revealed hyperintensity of the spinal cord gray matter on T2-weighted images, which microscopically corresponded with ischemic neurons and neuronal loss.

Anatomic description and clinical relevance of the meningovertebral ligament in dogs.

OBJECTIVE: To determine whether dogs have a meningovertebral ligament (MVL) and to assess the effect that structure may have on pathological lesions within the ventral epidural space. SAMPLE: Cadaveric specimens from 6 neurologically normal dogs and 2 dogs with vertebral neoplasms that extended into the epidural space and MRI sequences and cytologic preparations from 2 dogs with compressive hydrated nucleus pulposus extrusion that underwent decompressive surgery. PROCEDURES: The vertebral column was removed for gross and histologic examination from the cadavers of neurologically normal dogs and dogs with vertebral neoplasms. For dogs with hydrated nucleus pulposus extrusion, MRI sequences to assess lesion location and topography and cytologic preparations of material surgically extirpated from the ventral epidural space were reviewed. RESULTS: All dogs had an MVL, which formed the ventral boundary of the epidural space and consisted of fibrous bands that attached the external ventral surface of the dura mater of the spinal cord to the dorsal surface of the vertebral bodies throughout the length of the vertebral canal. Both vertebral neoplasms had a bilobed appearance as did the extruded nucleus pulposus lesions on MRI sequences. CONCLUSIONS AND CLINICAL RELEVANCE: Results of the present study indicated that dogs have an MVL, which creates an anatomic barrier within the ventral epidural space and causes pathological lesions to adopt a bilobed shape regardless of the pathogenic process. Further anatomic studies of the MVL and vertebral canal of dogs are necessary to elucidate how those structures affect lesion progression within the ventral epidural space.