Multi-Center Retrospective Evaluation of Screw and Polymethylmethacrylate Constructs for Atlantoaxial Fixation in Dogs.

OBJECTIVE: To evaluate outcome and adverse events following ventral stabilization of the atlantoaxial (AA) joint in dogs with clinical AA subluxation using screw/polymethymethacrylate (PMMA) constructs in a retrospective, multi-center cohort study. STUDY DESIGN: Historical cohort study. ANIMALS: 35 client-owned dogs. METHODS: Medical records from 3 institutions were reviewed to identify dogs with AA subluxation treated with ventral screw and PMMA constructs. Data on signalment, pre- and postoperative neurologic status, imaging performed, and adverse events were retrieved. Neurologic examination data were abstracted to generate a modified Frankel score at admission, discharge, and re-examination. Telephone interview of owners >180 days postoperative was conducted. RESULTS: Thirty-five dogs with AA subluxation treated with ventral screw/PMMA constructs were included. Most dogs were young (median age 1 year), small breed dogs with acute onset of neurologic signs (median duration 22.5 hours). Most dogs were non-ambulatory at the time of admission (median modified Frankel score 3). Adverse events were identified in 15/35 dogs including 9 dogs with major adverse events. Four dogs required a second surgery due to vertebral canal violation (n = 2) or implant failure (n = 2). Re-examination at 4-6 weeks postoperative reported 15/28 dogs with improved neurologic status and 19/28 dogs were ambulatory. Telephone follow-up was available for 23/35 dogs with 23/23 reported as ambulatory (median follow-up 390 days). CONCLUSIONS: Ventral application of screw and PMMA constructs for AA subluxation, as described here, is associated with clinical improvement in the majority of dog. Major adverse events are infrequent and the technique is considered relatively safe.

Use of the T2*-weighted gradient recalled echo sequence for magnetic resonance imaging of the canine and feline brain.

T2*-weighted magnetic resonance imaging (MRI) has been reported to help improve detection of intracranial hemorrhage and is widely used in human neuroimaging. To assess the utility of this technique in small animals, interpretations based on this sequence were compared with those based on paired T2-weighted and fluid-attenuated inversion recovery (FLAIR) sequences in 200 dogs and cats that underwent brain MRI for suspected intracranial disease. Two sets of images (T2 + FLAIR and T2*) were reviewed separately in random order unaccompanied by patient information and were interpreted as normal or abnormal based on whether intracranial abnormalities were seen. The number and location of intracranial lesions were recorded. Eighty-five studies were considered normal and 88 were considered abnormal based on both sets of images, with good agreement (κ = 0.731) between the two. Susceptibility artifact was present in 33 cases (16.5%) on T2*-weighted images. In 12 cases (6%) a total of 69 lesions were seen on T2*-weighted images that were not seen on T2/FLAIR, all of which were associated with susceptibility artifact caused by presumed intracranial hemorrhage. Pseudolesions were seen on T2*-weighted images in five cases, none of which were associated with susceptibility artifact. Abnormalities were seen on T2/FLAIR images that were not seen on T2*-weighted images in 35 cases, confirming that T2* does not replace standard spin echo sequences. These results support inclusion of T2*-weighted sequences in small animal brain MRI studies and indicate that that a large number of abnormalities (especially hemorrhagic lesions) can go undetected if it is not performed.

Magnetic Resonance Imaging in 50 Captive Non-domestic Felids - Technique and Imaging Diagnoses.

Magnetic resonance imaging (MRI) is the recognized gold standard for diagnostic imaging of the central nervous system in human and veterinary patients. Information on the use of this modality and possible imaging abnormalities in captive non-domestic felids is currently limited to individual case reports or small case series. This retrospective study provides information on technique and imaging findings in a cohort of cases undergoing MRI at an academic Veterinary Medical Center. The University of Tennessee College of Veterinary Medicine MRI database was searched for non-domestic felids undergoing MRI of the brain or spine from 2008 to 2021. Medical record data were recorded, and MRI studies were reviewed. Fifty animals met the inclusion criteria. The most common brain diseases were Chiari-like malformation (n = 8) and inflammatory conditions (n = 8). Other abnormalities included pituitary lesions (n = 5), brain atrophy (n = 2), and one each of metabolic and traumatic conditions. Fourteen animals had a normal brain MRI study. The most common spinal abnormality was intervertebral disc disease (n = 7). Other disorders included vertebral dysplasia (n = 2), presumptive ischemic myelopathy (n = 1), subdural ossification causing spinal cord compression (n = 1), and multiple myeloma (n = 1). Spinal cord swelling of undetermined cause was suspected in two animals, and seven patients had a normal MRI study of the spine. MRI is a valuable tool in the diagnostic workup of non-domestic felids with presumptive neurologic disease.

Clinical and imaging findings in five dogs with intracranial blastomycosis (Blastomyces dermatiditis).

Fungal infections affecting the central nervous system are rare. The purpose of this study was to describe clinical and imaging findings in dogs with intracranial blastomycosis (Blastomyces dermatiditis). The radiology database was searched retrospectively for patients with a diagnosis of intracranial blastomycosis which had computed tomography performed as part of their diagnostic work-up. Medical records and imaging studies were reviewed. Five dogs met the inclusion criteria. Major presenting complaints were stertor/nasal discharge (n=2), exophthalmos (n=1), and seizures (n=2). Clinical and laboratory findings were variable. Computed tomographic examination revealed a single contrast-enhancing intra-axial mass (n=1), a nasal mass disrupting the cribriform plate (n=3), and an intracranial mass extending into the orbit and nasal cavity (n=1). Findings in intracranial blastomycosis in dogs are variable, and the disease may mimic other inflammatory disorders or neoplasia.

Malignant mediastinal extra-adrenal paraganglioma with spinal cord invasion in a dog.

A 1.5-year-old castrated, male, mixed-breed dog was evaluated because of a 2-week history of lethargy, stiffness, and progressive paraparesis. Spinal radiographs, myelography, and computed tomography of the region showed a locally invasive mass involving the thoracic wall. Upon necropsy, an encapsulated, fluctuant mass was noted attached to the right dorsal body wall in the region of the fifth to seventh thoracic vertebra. Churukian-Schenk staining revealed positive granules within the neoplastic cell cytoplasm and immunohistochemistry was positive for expression for cytoplasmic neuron-specific enolase and synaptophysin. Chromogranin A and S100 expression were found to be negative. Immunohistochemistry and silver staining did not allow further differentiation of the tumor, and the diagnosis remains consistent with either a chromaffin paraganglioma or a nonchromaffin paraganglioma (chemodectoma) with some production of catecholamines. Extra-adrenal paragangliomas are rare neoplasms in dogs but should be considered as a possible differential diagnosis for a primary paraspinal thoracic mass.

Large anaplastic spinal B-cell lymphoma in a cat.

A 5-year-old female spayed domestic shorthair cat was presented for evaluation of tetraparesis. The neurologic lesion was localized to the cervical spinal segment (C1-C6). A left axillary mass was identified, and the results of fine needle aspiration cytology indicated malignant round cell neoplasia of possible histiocytic origin. The cells were large, had marked anisocytosis and anisokaryosis, occasional bi- and multinucleation, and cytoplasmic vacuolation. Euthanasia was performed due to the poor prognosis associated with severe, progressive neurologic signs and a malignant neoplasm. Postmortem examination revealed spinal cord compression and an extradural mass at the C1-C2 spinal segment, with neoplastic cells in the adjacent vertebral bodies, surrounding skeletal muscle, left axillary lymph node, and bone marrow from the right femur. The initial histologic diagnosis was anaplastic sarcoma, but immunohistochemical results indicated the cells were CD20+ and CD45R+ and CD3-, compatible with a diagnosis of B-cell lymphoma. CD79a staining was nonspecific and uninterpretable. Weak to moderate CD18 positivity and E-cadherin positivity were also observed. Clonality of the B-cell population could not be demonstrated using PCR testing for antigen receptor gene rearrangement. To the authors' knowledge, this is the first reported case of a feline spinal anaplastic B-cell lymphoma exhibiting bi- and multinucleated cells. The prognostic significance of this cell morphology and immunophenotype is unknown.

Transient depression of pelvic limb reflexes in dogs with acute focal thoracolumbar myelopathy.

OBJECTIVE To determine the prevalence of depressed pelvic limb reflexes and changes in those reflexes over time in dogs with acute thoracolumbar myelopathy. DESIGN Prospective study. ANIMALS 34 dogs. PROCEDURES Dogs with acute pelvic limb paralysis caused by acute noncompressive nucleus pulposus extrusion (ANNPE), fibrocartilaginous embolism (FCE), or compressive intervertebral disk herniation (IVDH) within the T3-L3 spinal cord segments were enrolled in the study. Dogs with depressed or absent pelvic limb withdrawal reflexes as determined by 2 examiners were classified as affected and underwent additional testing to rule out multifocal lesions. Pelvic limb reflexes of affected dogs were reassessed every 12 hours until they returned to normal. Neurologic examinations were performed at 4 and 8 weeks after initial examination for some dogs. RESULTS Compressive IVDH, ANNPE, and FCE were diagnosed in 30, 1, and 3 dogs, respectively. Nine (5 with compressive IVDH and all 4 with FCE or ANNPE) of 34 (26%) dogs were classified as affected. Patellar reflexes were depressed in 2 of 9 affected dogs. The median time required for withdrawal reflexes to return to normal was 60 hours (range, 12 to 156 hours). Onset duration of paralysis was negatively associated with the odds of a dog being classified as affected. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that dogs with focal thoracolumbar spinal cord lesions, especially those with peracute onset of paralysis, can develop transient depression of pelvic limb reflexes. Awareness of this phenomenon is important for veterinarians to accurately localize lesions and develop appropriate diagnostic plans and prognoses.

Cerebral Blastomyces dermatitidis infection in a cat.

CASE DESCRIPTION: An 8-year-old domestic shorthair cat was evaluated because of signs of depression, circling, and visual deficits. CLINICAL FINDINGS: The cat had no cutaneous lesions, and results of an ophthalmologic examination and thoracic radiography were within reference limits. Computed tomography of the brain revealed a mass lesion involving the right parietal, temporal, and occipital lobes; the mass was in broad-based contact with the skull and smoothly marginated and had strong homogenous enhancement after contrast agent administration. During craniectomy, samples of the mass were collected for cytologic and histopathologic evaluations and microbial culture. A diagnosis of Blastomyces dermatitidis-associated meningoencephalitis with secondary pyogranulomatous inflammation was made. TREATMENT AND OUTCOME: Amphotericin B (0.25 mg/kg [0.11 mg/lb], IV) was administered on alternate days (cumulative dose, 1.75 mg/kg [0.8 mg/lb]). To minimize the risk of nephrotoxicosis, assessments of serum biochemical variables (urea nitrogen and creatinine concentrations) and urinalyses were performed at intervals. The third dose of amphotericin B was postponed 48 hours because the cat became azotemic. The cat subsequently received fluconazole (10 mg/kg [4.5 mg/lb], PO, q 12 h) for 5.5 months. Six months after discontinuation of that treatment, the cat appeared healthy and had no signs of relapse. CLINICAL RELEVANCE: Brain infection with B dermatitidis is typically associated with widespread disseminated disease. The cat of this report had no evidence of systemic disease. Blastomycosis of the CNS should be considered as a differential diagnosis for brain lesions in cats from areas in which B dermatitidis is endemic.

Pharmacokinetics of zonisamide following rectal administration to healthy dogs.

OBJECTIVE To evaluate the pharmacokinetics of zonisamide following rectal administration of 20 or 30 mg/kg suspended in sterile water or polyethylene glycol (PEG) to healthy dogs and determine whether either dose resulted in plasma zonisamide concentrations within the recommended therapeutic target range (10 to 40 µg/mL). ANIMALS 8 healthy mixed-breed dogs. PROCEDURES Each dog received each of 2 doses (20 or 30 mg/kg) of zonisamide suspended in each of 2 delivery substrates (sterile water or PEG) in a randomized crossover study with a 7-day washout period between phases. A blood sample was collected from each dog immediately before and at predetermined times for 48 hours after zonisamide administration. Plasma zonisamide concentrations were determined by high-performance liquid chromatography, and data were analyzed with a noncompartmental model. RESULTS Mean maximum plasma concentration, time to maximum plasma concentration, mean residence time, and elimination half-life did not differ significantly among the 4 treatments. The mean maximum plasma concentration for all 4 treatments was less than the therapeutic target range. The mean ± SD area under the concentration-time curve for the 30 mg/kg-in-water treatment (391.94 ± 237.00 h•µg/mL) was significantly greater than that for the 20 mg/kg-in-water (146.19 ± 66.27 h•µg/mL) and 20 mg/kg-in-PEG (87.09 ± 96.87 h•µg/mL) treatments. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that rectal administration of zonisamide at doses of 20 and 30 mg/kg failed to achieve plasma zonisamide concentrations within the recommended therapeutic target range. Therefore, rectal administration of zonisamide cannot be recommended as a suitable alternative to oral administration.

Evaluation of plasma diazepam and nordiazepam concentrations following administration of diazepam intravenously or via suppository per rectum in dogs.

OBJECTIVE: To evaluate the pharmacokinetics of diazepam administered per rectum via compounded (ie, not commercially available) suppositories and determine whether a dose of 2 mg/kg in this formulation would result in plasma concentrations shown to be effective for control of status epilepticus or cluster seizures (ie, 150 to 300 ng/mL) in dogs within a clinically useful interval (10 to 15 minutes). ANIMALS: 6 healthy mixed-breed dogs. PROCEDURES: Dogs were randomly assigned to 2 groups of 3 dogs each in a crossover-design study. Diazepam (2 mg/kg) was administered IV or via suppository per rectum, and blood samples were collected at predetermined time points. Following a 6- or 7-day washout period, each group received the alternate treatment. Plasma concentrations of diazepam and nordiazepam were analyzed via reversed phase high-performance liquid chromatography. RESULTS: Plasma concentrations of diazepam and nordiazepam exceeded the targeted range ≤ 3 minutes after IV administration in all dogs. After suppository administration, targeted concentrations of diazepam were not detected in any dogs, and targeted concentrations of nordiazepam were detected after 90 minutes (n = 2 dogs) or 120 minutes (3) or were not achieved (1). CONCLUSIONS AND CLINICAL RELEVANCE: On the basis of these results, administration of 2 mg of diazepam/kg via the compounded suppositories used in the present study cannot be recommended for emergency treatment of seizures in dogs.

Agreement between T2 and haste sequences in the evaluation of thoracolumbar intervertebral disc disease in dogs.

The purpose of this study was to compare half-Fourier-acquisition single-shot turbo spin-echo (HASTE) and T2-weighted (T2-W) sequences in dogs with thoracolumbar disc extrusion. MRI studies in 60 dogs (767 individual intervertebral disc spaces) were evaluated. Agreement between T2-W and HASTE sequences was assessed for two criteria: presence of an extradural lesion and treatment recommendation. There was moderate agreement between T2-W and HASTE sequences as to presence of an extradural lesion (kappa = 0.575). HASTE was in agreement in 96.1% of the sites where no extradural lesion was identified on T2-W images, but only in 58.1% of the sites where extradural lesions were identified on T2-W images. There was also moderate agreement between T2-W and HASTE sequences as to treatment recommendations (kappa = 0.476). HASTE was in agreement in 98.4% of the sites where a lesion was considered nonsurgical on T2 but only 82.1% of sites a lesion was considered surgical on T2. In 1.0% of sites considered not surgical and in 9.8% of sites considered equivocal based on T2-W images, a surgical lesion was identified on HASTE. Acquisition of a HASTE sequence in addition to conventional sequences may be beneficial in determining the severity of spinal cord compression in some cases when evaluating the canine spine.

Magnetic resonance imaging susceptibility artifacts due to metallic foreign bodies.

Susceptibility artifacts due to metallic foreign bodies may interfere with interpretation of magnetic resonance (MR) imaging studies. Additionally, migration of metallic objects may pose a risk to patients undergoing MR imaging. Our purpose was to investigate prevalence, underlying cause, and diagnostic implications of susceptibility artifacts in small animal MR imaging and report associated adverse effects. MR imaging studies performed in dogs and cats between April 2008 and March 2010 were evaluated retrospectively for the presence of susceptibility artifacts associated with metallic foreign bodies. Studies were performed using a 1.0 T scanner. Severity of artifacts was graded as 0 (no interference with area of interest), 1 (extension of artifact to area of interest without impairment of diagnostic quality), 2 (impairment of diagnostic quality but diagnosis still possible), or 3 (severe involvement of area of interest resulting in nondiagnostic study). Medical records were evaluated retrospectively to identify adverse effects. Susceptibility artifacts were present in 99/754 (13.1%) of MR imaging studies and were most common in examinations of the brachial plexus, thorax, and cervical spine. Artifacts were caused by identification microchips, ballistic fragments, skin staples/suture material, hemoclips, an ameroid constrictor, and surgical hardware. Three studies were nondiagnostic due to the susceptibility artifact. Adverse effects were not documented.

Evaluation of veterinary patients with brain disease.

The initial evaluation of patients with brain disease is focused on determining the neuroanatomic diagnosis and the etiologic diagnosis. This evaluation is based on obtaining a careful history and performing a neurologic examination. Based on these results, the clinician recommends further diagnostic tests to confirm the diagnosis. By following this orderly process of clinical reasoning, it is usually possible to determine the cause of the patient's brain disease, which provides a prognosis and allows specific therapy.

Hydrocephalus in dogs and cats.

Hydrocephalus is distension of the ventricular system of the brain related to inadequate passage of cerebrospinal fluid from its point of production within the ventricular system to its point of absorption into the systemic circulation. Developmental disorders are the most common causes of hydrocephalus, but there are other causes as well. Diagnosis is based on the clinical features and on brain imaging to assess ventricular size and to identify any specific causes. Medical therapy can provide temporary relief but definitive treatment usually involves placement of a ventriculoperitoneal shunt. This article discusses the pathophysiology and management of hydrocephalus.

Idiopathic epilepsy in dogs and cats.

Idiopathic epilepsy is the most common brain disease in dogs and also occurs in cats. Optimal management entails an accurate diagnosis and appropriate drug therapy. In dogs, either phenobarbital or bromide is appropriate as initial therapy. Phenobarbital is the drug of choice for cats. Several other drugs including zonisamide and levetiracetam have the advantage of fewer side effects and are being increasingly used in veterinary medicine. Treatment is successful in most cases, allowing the pet and client to enjoy a good quality of life.

Myelography vs. computed tomography in the evaluation of acute thoracolumbar intervertebral disk extrusion in chondrodystrophic dogs.

Myelography and/or computed tomography (CT) are commonly used to evaluate acute intervertebral disk extrusion in chondrodystrophic dogs. The purpose of this study was to evaluate the sensitivity of myelography and two different CT protocols in determining level and lateralization of acute thoracolumbar intervertebral disk extrusion in comparison with surgical findings, investigate interobserver variability, and determine examination duration times. Results of conventional CT, helical CT, and myelography were compared with surgical findings in 19 chondrodystrophic dogs with acute thoracolumbar intervertebral disk extrusion. Agreement among investigators was determined for different imaging modalities, and examination times were recorded. In the diagnosis of level of disk extrusion there was agreement of myelography, conventional CT, and helical CT with surgical findings in 94.7%, 100%, and 94.7% of dogs, respectively (P = 0.144). In the diagnosis of level and lateralization of disk extrusion there was agreement of myelography, conventional CT, and helical CT with surgical findings in 78.9%, 87.4%, and 85.3% of dogs, respectively (P = 0.328). Interobserver agreement was very good for all imaging modalities (myelography K = 0.87; conventional CT K = 0.86; helical CT K = 0.95). There were significant differences in median examination duration times between helical CT (4 min), conventional CT (8 min), and myelography (32 min) (P < 0.001). Both helical and conventional CT appear to be accurate for evaluation of acute thoracolumbar intervertebral disk extrusion in chondrodystrophic dogs and are faster to perform than myelography.