Description and validation of a magnetic resonance imaging-guided stereotactic brain biopsy device in the dog.

A stereotactic brain biopsy system that is magnetic resonance (MR) imaging-guided has not been validated in dogs. Our purpose was to determine the mean needle placement error in the caudate nucleus, thalamus, and midbrain of a canine cadaver brain using the modified Brainsight stereotactic system. Relocatable reference markers (fiducial markers) were attached to the cadaver head using a dental bite block. A T1-weighted gradient echo three-dimensional (3D) sequence was acquired using set parameters. Fiducial markers were used to register the head to the acquired MR images in reference to a 3D position sensor. This allowed the planning of trajectory path to brain targets in real time. Coordinates (X, Y, Z) were established for each target and 0.5 microl of diluted gadolinium was injected at each target using a 26-gauge needle to create a lesion. The center of the gadolinium deposition was identified on the postoperative MR images and coordinates (X', Y', Z') were established. The precision of this system in bringing the needle to target (needle placement error) was calculated. Seventeen sites were targeted in the brain. The mean needle placement error for all target sites was 1.79 +/- 0.87 mm. The upper bound of error for this stereotactic system was 3.31 mm. There was no statistically significant relationship between needle placement error and target depth (P = 0.23). The ease of use and precision of this stereotactic system support its development for clinical use in dogs with brain lesions > 3.31 mm.

Spinal neoplasms in small animals.

Tumors arising from or involving the spinal cord are important considerations in animals presented for pain and limb dysfunction. Clinical signs of spinal cord dysfunction, however, are not pathognomic for neoplastic disease in most instances. Advanced magnetic resonance imaging (MRI) often accurately identifies the location and extent of abnormalities. Although some spinal neoplasms have a characteristic appearance with MRI, in other instances the abnormalities may not be readily discernable as neoplastic. Histologic diagnosis, therefore, is imperative to provide information regarding potential treatment modalities and prognosis. Histologic diagnosis is most commonly performed following surgical biopsy and is often performed in combination with surgical removal.

Gamma-irradiated Calvarium Allograft Cranioplasty in a cat following brain tumor removal.

A 14-year-old domestic shorthair cat was evaluated for a 3-month history of head pressing and circling. Neurological examination suggested a supratentorial problem, predominantly on the left side. An extradural mass extending from the rostral frontal lobes caudally to the level of the caudal aspect of the corpus callosum was found with magnetic resonance imaging. A bilateral rostrotentorial craniectomy combined with a frontal sinus craniectomy was performed for mass removal. A gamma-irradiated calvarial allograft was used to repair the calvarial defect. At 14 months following surgery, the cat had no neurological abnormalities, and the skull and facial appearance was normal.

Confirmed 2,4-dichlorophenoxyacetic acid toxicosis in a dog.

A 2-year-old, intact male Weimaraner was evaluated for episodic extensor rigidity and a stiff gait of 24 hours' duration. Percussion of the proximal appendicular muscles with a reflex hammer resulted in formation of dimples consistent with myotonia. Electromyography identified myotonic potentials. Residues of 2,4-dichlorophenoxyacetic acid (2,4-D) were detected in both serum and urine. The dog was treated with intravenous fluid therapy for 36 hours, and clinical signs improved dramatically. Toxicosis with 2,4-D should be considered a differential for acquired myotonia in dogs with or without systemic signs. Exposed dogs with only clinical signs of myotonia can have good clinical outcomes. A confirmed clinical case of 2,4-D toxicosis in the dog has not previously been reported.

In vitro biomechanical evaluations of screw-bar-polymethylmethacrylate and pin-polymethylmethacrylate internal fixation implants used to stabilize the vertebral motion unit of the fourth and fifth cervical vertebrae in vertebral column specimens from dogs.

OBJECTIVE: To determine the change in stiffness as evaluated by the dorsal bending moment of cervical vertebral specimens obtained from canine cadavers after internally stabilizing the vertebral motion unit (VMU) of C4 and C5 with a traditional pin-polymethylmethacrylate (PMMA) fixation implant or a novel screw-bar-PMMA fixation implant. SAMPLE POPULATION: 12 vertebral column specimens (C3 through C6) obtained from canine cadavers. PROCEDURES: A dorsal bending moment was applied to the vertebral specimens before and after fixation of the VMU of C4 and C5 by use of a traditional pin-PMMA implant or a novel screw-bar-PMMA implant. Biomechanical data were collected and compared within a specimen (unaltered vs treated) and between treatment groups. Additionally, implant placement was evaluated after biomechanical testing to screen for penetration of the transverse foramen or vertebral canal by the pins or screws. RESULTS: Treated vertebral specimens were significantly stiffer than unaltered specimens. There was no significant difference in stiffness between vertebral specimen groups after treatment. None of the screws in the novel screw-bar-PMMA implant group penetrated the transverse foramen or vertebral canal, whereas there was mild to severe penetration for 22 of 24 (92%) pins in the traditional pin-PMMA implant group. CONCLUSIONS AND CLINICAL RELEVANCE: Both fixation treatments altered the biomechanical properties of the cervical vertebral specimens as evaluated by the dorsal bending moment. There was reduced incidence of penetration of the transverse foramen or vertebral canal with the novel screw-bar-PMMA implant, compared with the incidence for the traditional pin-PMMA implant.

P-glycoprotein contributes to the blood-brain, but not blood-cerebrospinal fluid, barrier in a spontaneous canine p-glycoprotein knockout model.

P-glycoprotein is considered to be a major factor impeding effective drug therapy for many diseases of the central nervous system (CNS). Thus, efforts are being made to gain a better understanding of P-glycoprotein's role in drug distribution to brain parenchyma and cerebrospinal fluid (CSF). The goal of this study was to validate and introduce a novel P-glycoprotein-deficient (ABCB1-1Delta) canine model for studying P-glycoprotein-mediated effects of drug distribution to brain tissue and CSF. CSF concentrations of drug are often used to correlate efficacy of CNS drug therapy as a surrogate for determining drug concentration in brain tissue. A secondary goal of this study was to investigate the validity of using CSF concentrations of P-glycoprotein substrates to predict brain tissue concentrations. Loperamide, an opioid that is excluded from the brain by P-glycoprotein, was used to confirm a P-glycoprotein-null phenotype in the dog model. ABCB1-1Delta dogs experienced CNS depression following loperamide administration, whereas ABCB1 wild-type dogs experienced no CNS depression. In summary, we have validated a novel P-glycoprotein-deficient canine model and have used the model to investigate transport of the P-glycoprotein substrate (99m)Tc-sestamibi at the blood-brain barrier and blood-CSF barrier.

Biomechanical evaluation of cervical intervertebral plug stabilization in an ovine model.

OBJECTIVE: (1) To determine the biomechanical stability of cervical spinal segment C5-C6 after ventral slot (VS) decompression and distraction-stabilization by a modified polymethylmethacrylate (PMMA) intervertebral plug technique (IVP) in an ovine model. (2) To determine if the distraction of the disk space is maintained after VS-IVP, and the frequency of bony intervertebral union. STUDY DESIGN: Experimental in vivo study in an ovine model with an in vitro control study. ANIMALS: Adult (>2 years age), intact sheep (n=18). METHODS: Ten sheep had VS/IVP surgery of C5-6 with computed tomography (CT) images obtained immediately before and after surgery, as well as 8 (n=10) and 24 (n=5) weeks postoperatively. Cervical spines harvested 8 weeks (8-week group; n=5) and 24 weeks (24-week group; n=5) after surgery had three-dimensional (3D) flexibility tests in flexion-extension, axial rotation, and lateral bending. Image data was analyzed qualitatively and quantitatively in 3D. Eight ovine cervical spines served as controls and had biomechanical testing in intact condition (n=5) and after in vitro VS/IVP (n=5). RESULTS: Significantly decreased range of motion (ROM) was noted in all loading modes when comparing in vitro operated spines and the 24-week group to intact spines. The 8-week group was not significantly different from the intact group, except in lateral bending. Quantitative CT analysis of treatment groups showed progressive disk space collapse and ventral implant migration. Intervertebral bony union did not occur. CONCLUSION: Biomechanical stability was obtained immediately after VS/IVP surgery, but ROM at 8 weeks was not different from intact spines. However, at 24 weeks, the operated level had regained stability similar to the immediate postoperative level. Distraction of the disk space was not maintained and bony union did not occur in this ovine model of VS/IVP. CLINICAL RELEVANCE: In clinical situations requiring constant increased stability of cervical segments for an extended time, more rigid stabilization techniques are required.

Magnetic resonance imaging of acquired trigeminal nerve disorders in six dogs.

The medical records and magnetic resonance (MR) images of dogs with an acquired trigeminal nerve disorder were reviewed retrospectively. Trigeminal nerve dysfunction was present in six dogs with histologic confirmation of etiology. A histopathologic diagnosis of neuritis (n=2) or nerve sheath tumor (n=4) was made. Dogs with trigeminal neuritis had diffuse enlargement of the nerve without a mass lesion. These nerves were isointense to brain parenchyma on T1-weighted (T1W) precontrast images and proton-density-weighted (PDW) images and either isointense or hyperintense on T2-weighted (T2W) images. Dogs with a nerve sheath tumor had a solitary or lobulated mass with displacement of adjacent neuropil. Nerve sheath tumors were isointense to the brain parenchyma on T1W, T2W, and PDW images. All trigeminal nerve lesions enhanced following contrast medium administration. Atrophy of the temporalis and masseter muscles, with a characteristic increase in signal intensity on T1W images, were present in all dogs.

Cerebrospinal fluid analysis and magnetic resonance imaging in the diagnosis of neurologic disease in dogs: a retrospective study.

BACKGROUND: Diagnosis of central nervous system (CNS) abnormalities in dogs can be challenging antemortem. Historically, cerebrospinal fluid (CSF) analysis has been used for routine diagnostic evaluation of animals with suspected neurologic disease; however, with increasing availability of magnetic resonance (MR) imaging, the need for concurrent CSF analysis may be questioned. OBJECTIVE: The purpose of this study was to retrospectively assess and compare the diagnostic information contributed from MR imaging and CSF analysis in a population of dogs presenting with neurologic disease. METHODS: Results of concurrent MR imaging and CSF analysis were evaluated in dogs presented for neurologic diseases. Based on clinical diagnosis, the sensitivity of CSF analysis and MR imaging for detecting a nervous system abnormality was calculated. Dogs with diagnoses confirmed by other diagnostic modalities were also evaluated separately. RESULTS: A total of 256 dogs were included in the study. For clinical diagnoses in which abnormalities were expected, MR imaging abnormalities were found in 89% and CSF abnormalities in 75% of dogs; CSF abnormalities were more common than MR imaging abnormalities only in inflammatory CNS disease. The majority of CSF abnormalities were nonspecific; an etiologic diagnosis was determined in only 2% of CSF samples. MR imaging excelled in detecting structural disorders, revealing 98% of vertebral abnormalities. In confirmed cases (n = 55), 76% of MR images and 9% of CSF samples were diagnostic. When intervertebral disk disease (IVDD) and vertebral malformation were excluded from analysis (n = 16 remaining), 25% of MR images and 6% of CSF cytology results were highly indicative of the confirmed diagnoses; CSF titer results provided the diagnosis in 25% of these cases. CONCLUSION: CSF analysis may not be necessary when MR findings of IVDD or vertebral malformation/instability are obvious; however, when the cause of neurologic disorder is uncertain, concurrent MR imaging and CSF analysis provides the greatest assistance in establishing a clinical diagnosis.

Fecal incontinence and spinal cord abnormalities in seven dogs.

Seven dogs with fecal incontinence and abnormal gaits were evaluated. Fecal incontinence was characterized as defecation of normal stools without posturing. Duration of clinical signs prior to evaluation ranged from 5 months to 3 years. Five dogs had upper motor neuron (UMN) paraparesis, and 2 dogs had UMN tetraparesis. With magnetic resonance imaging, spinal cord abnormalities primarily involving the dorsal aspect of the spinal cord were identified in all dogs. Five dogs had focal abnormalities, and 2 dogs had diffuse abnormalities of the spinal cord. Of the dogs with focal spinal cord lesions, 4 had cystic spinal cord abnormalities and 1 had a meningioma. Surgery was performed on all dogs with focal lesions; 4 of the 5 dogs had resolution of fecal incontinence after surgery. Results in these dogs suggest that fecal incontinence can be associated with spinal cord abnormalities and, depending on the characteristics of the lesion, can resolve after surgical treatment of the abnormality.

Radiographic diagnosis--paraspinal abscess in a dog.

A two-year-old intact male Brittany Spaniel was admitted for evaluation of progressive spinal pain. Previous treatment had been initiated for suspected lumbosacral intervertebral disk disease, however there was poor response to therapy. On presentation the dog was laterally recumbent and neurological examination revealed hyperesthesia over the lumbar vertebral segments. On survey radiography there was loss of detail in the sublumbar fascial planes and inconclusive lumbar vertebra proliferation. Magnetic resonance (MR) imaging was performed to better evaluate the lumbar spine and surrounding tissues, which revealed extensive paralumbar cellulitis, abscessation and osteomyelitis with extradural compression of the spinal cord. MR imaging allowed delineation of the abscessed area, and distinct visualization of its extension into and involvement of the surrounding tissues including muscle, fat, and retroperitoneal structures. In this case, MR imaging was instrumental in defining the extent of the infection and determining whether medical or surgical management of the diseased tissue was necessary. If available, MR may be the imaging method of choice for evaluation of paraspinal abscesses yielding a better insight to the spinal structures involved and facilitating medical or surgical intervention.

Outcomes and complications associated with ventral screws, pins, and polymethyl methacrylate for atlantoaxial instability in 12 dogs.

Clinical outcomes and complications of a technique used for atlantoaxial stabilization were evaluated in a group of 12 dogs. At surgery, the atlantoaxial joint was realigned and rigidly fixated using cortical bone screws, K-wire, and polymethyl methacrylate. Results in nine dogs were graded as excellent. Results in two dogs were judged as good. One dog was euthanized 17 months after surgery for recurrent cervical pain. Eight dogs had no postoperative complications. The surgical technique described provided an adaptable method for the correction of atlantoaxial instability.

Intramedullary spinal cord damage associated with intervertebral disk material in a dog.

Intervertebral disk extrusions into the spinal cord are rarely reported in veterinary medicine, and only necropsy findings are described in previous reports. It is hypothesized that a disk lesion results in forceful injection of disk material into the spinal cord. In the 3-year-old Miniature Doberman Pinscher of our report, acute clinical signs and results of magnetic resonance imaging were consistent with this disease and helped determine the extent and character of the lesions. Alteration in the appearance of the nucleus pulposus was important in determining that intervertebral disk disease may have been present in this dog. However, a definitive diagnosis of intramedullary disk extrusion can be made only via histologic examination of a biopsy specimen or at necropsy. The dog improved substantially after surgical decompression of the spinal cord, and histologic findings in a biopsy specimen of material found within the spinal cord were consistent with mature degenerate intervertebral disk material.

Surgical treatment of an intramedullary spinal cord hamartoma in a dog.

A 9-year-old spayed female Golden Retriever was examined because of progressive hind limb lameness. Magnetic resonance imaging of the thoracic and lumbar portions of the vertebral column revealed a focal, contrast-enhancing, intramedullary spinal cord mass. The history, signalment, and magnetic resonance findings were suggestive of spinal cord neoplasia. A hemilaminectomy, durotomy, and longitudinal myelotomy were performed, and a 1 X 1-cm mass that contained numerous blood vessels was removed with blunt dissection. Results of histologic examination and immunohistochemical staining of the mass suggested that it was a hamartoma. The dog improved after surgery, with no evidence of a recurrence of clinical signs 14 months after surgery. Vascular malformations of the CNS in dogs include hamartomas, hemangiomas, angiomas, hemangioblastomas, meningocerebral hemangiomatosis, and arteriovenous malformations. A hamartoma is a non-neoplastic overgrowth of cells or an improper proportion of cells that are normally in the involved tissue. Although magnetic resonance imaging may be helpful in determining the extent of the lesion in dogs with vascular malforrmations, it cannot be used to distinguish neoplastic from non-neoplastic formations. Excision may result in a good outcome for dogs with an intramedullary spinal cord hamartoma.