MRI CHARACTERISTICS OF FOURTH VENTRICLE ARACHNOID DIVERTICULA IN FIVE DOGS

Intracranial arachnoid diverticula (cysts) are rare accumulations of cerebrospinal fluid (CSF) within the arachnoid membrane. The purpose of this retrospective study was to describe magnetic resonance imaging (MRI) characteristics of fourth ventricle arachnoid diverticula in a group of dogs. The hospital's medical records were searched for dogs with MRI studies of the brain and a diagnosis of fourth ventricle arachnoid diverticulum. Clinical characteristics were recorded from medical records and MRI studies were reinterpreted by a board‐certified veterinary radiologist. Five pediatric dogs fulfilled inclusion criteria. Clinical signs included cervical hyperaesthesia, obtundation, tetraparesis, and/or central vestibular syndrome. In all five dogs, MRI findings were consistent with obstructive hydrocephalus, based on dilation of all ventricles and compression of the cerebellum and brainstem. All five dogs also had cervical syringohydromyelia, with T2‐weighted hyperintensity of the gray matter of the cord adjacent to the syringohydromyelia. A signal void, interpreted as flow disturbance, was observed at the mesencephalic aqueduct in all dogs. Four dogs underwent surgical treatment with occipitalectomy and durotomy. A cystic lesion emerging from the fourth ventricle was detected in all four dogs during surgery and histopathology confirmed the diagnosis of arachnoid diverticula. Three dogs made excellent recovery but deteriorated shortly after surgery and were euthanized. Repeat MRI in two dogs revealed improved hydrocephalus but worsening of the syringohydromyelia. Findings from the current study supported theories that fourth ventricle arachnoid diverticula are secondary to partial obstruction of the central canal or lateral apertures and that arachnoid diverticula are developmental lesions in dogs.     

Comparison of cell populations derived from canine olfactory bulb and olfactory mucosal cultures

OBJECTIVE: To evaluate the numbers and proportions of olfactory ensheathing cells (OECs) in cell cultures derived from the olfactory bulb (OB) and olfactory mucosa of dogs. ANIMALS: 7 dogs. PROCEDURES: OB tissue and olfactory mucosa from the nasal cavity and frontal sinus were obtained from euthanatized dogs and prepared for cell culture. At 7, 14, and 21 days of culture in vitro, numbers and proportions of OECs, astrocytes, and fibroblasts were determined via immunocytochemistry. Antibody against the low-affinity nerve growth factor receptor p75 was used to identify OECs, antibody against glial fibrillary acidic protein was used to identify astrocytes, and antibody against fibronectin was used to identify fibroblasts. RESULTS: Cultured OECs derived from the olfactory mucosa of the nasal cavity and frontal sinus had similar characteristics. However, whereas OECs in the OB cell cultures constituted approximately 50% of the cells at 7 days and approximately 75% at 21 days the proportion of OECs in cultures derived from both mucosal types was much lower, with approximately 40% OECs at 7 days and approximately 25% at 21 days. Analysis of OEC numbers revealed that these changes were accompanied by corresponding decreases and increases in the population of cells with fibronectin receptors. CONCLUSIONS AND CLINICAL RELEVANCE: Although olfactory mucosal cell cultures yielded a sufficient number of OECs for spinal cord transplantation procedures in dogs, modification of culture conditions would be required to ensure that the derived cell population contained a sufficient proportion of OECs.     

IDENTIFICATION OF ARACHNOID CYSTS IN THE QUADRIGEMINAL CISTERN USING ULTRASONOGRAPHY

The ultrasonographic findings in three small breed dogs with intracranial arachnoid cysts are described. Ultrasound images were obtained via the foramen magnum, temporal window and persistent bregmatic fontanelle (when possible). In transverse, dorsal and sagittal transcranial ultrasound images there was marked dilation of the lateral ventricles and a well-defined, oval to triangular-shaped anechoic area between the caudal aspect of the occipital lobes, dorsal to the midbrain, and rostral to the cerebellum. These findings were consistent with a diagnosis of concurrent hydrocephalus and an arachnoid cyst within the quadrigeminal cistern.     

A Surgical Approach to the Canine Olfactory Bulb for Meningioma Removal

Olfactory bulb lesions were diagnosed in four dogs presented for generalized seizure disorders. Surgery was performed on each dog using a transfrontal craniotomy. A free fascial-fat graft was used to cover the dural defect resulting from surgery. No major complications were observed during the immediate postoperative period. The histopathologic diagnosis in each case was meningioma. Generalized seizures recurred in all dogs, and three dogs were euthanized for this reason from 9 to 29 weeks postoperatively. One dog was euthanized 12 weeks after surgery due to pancreatitis and pneumonia. Necropsy showed that two dogs had recurrent olfactory bulb meningiomas, one dog had a meningioma of the opposite olfactory bulb, and one dog was tumor free.     

Magnetic resonance imaging of syringomyelia in five dogs

This report describes the use of magnetic resonance imaging (MRI) in five dogs to diagnose spontaneous syringomyelia. Four of the dogs had cervical syringomyelia associated with hydrocephalus, and one of these cases was analogous to the Dandy-Walker syndrome in humans. The fifth dog had thoracic syringomyelia without hydrocephalus. It was possible to diagnose the condition antemortem in all of the dogs by MRI. It is suggested that MRI is a straightforward and effective tool for the antemortem diagnosis of syringomyelia in dogs.     

Signs consistent with syringobulbia may be detected in dogs undergoing MRI

Syringobulbia is a pathologic condition characterized by one or more fluid‐filled cavities within the brainstem. This retrospective case series describes observations in eight dogs with syringobulbia diagnosed during MRI. All dogs were adult, small‐breed dogs with concurrent syringomyelia and neurologic deficits localized to sites rostral to the spinal cord, which cannot be explained by syringomyelia (eg, six dogs had vestibular signs). On MRI, the fluid‐filled cavities had signal intensity characteristics like cerebrospinal fluid, were in the medulla oblongata, and were solitary in each dog. Initially, the shape of the cavity was a slit in five dogs and bulbous in two dogs. Magnetic resonance imaging was repeated in five dogs (6‐55 months of age). One dog had progression of syringobulbia from slit‐like to bulbous, and four dogs had unchanged slit‐like syringobulbia. One dog developed slit‐like syringobulbia after cranioplasty. A variety of medical and surgical treatments were performed with improvement of some but not all clinical signs. One dog died following surgery due to cardiopulmonary failure and the other seven dogs were alive at least 1 year after the initial diagnosis, which was the least time of follow‐up. One surviving dog developed a unilateral hypoglossal nerve deficit 2 months after the initial diagnosis and megaesophagus 14 months later. In conclusion, detecting a fluid‐filled cavity in the medulla oblongata consistent with syringobulbia is possible in dogs undergoing MRI. The cavity is likely acquired, slit‐like or bulbous, progressive, or static, and might be associated with breed size and neurologic signs localized to the medulla oblongata.     

Phylogenic aspects of the amphibian dual olfactory system

The phylogenic significance of the subdivision of dual olfactory system is reviewed mainly on the basis of our findings by electron microscopy and lectin histochemistry in the three amphibian species. The dual olfactory system is present in common in these species and consists of the projection from the olfactory epithelium (OE) to the main olfactory bulb (MOB) and that from the vomeronasal epithelium (VNE) to the accessory olfactory bulb (AOB). The phylogenic significance of subdivisions in the dual olfactory system in the amphibian must differently be interpreted. The subdivision of the MOB into its dorsal region (D-MOB) and ventral region (V-MOB) in Xenopus laevis must be attributed to the primitive features in their olfactory receptors. The middle cavity epithelium lining the middle cavity of this frog possesses both ciliated sensory cells and microvillous sensory cells, reminding the OE in fish. The subdivision of the AOB into the rostral (R-AOB) and caudal part (C-AOB) in Bufo japonicus formosus must be regarded as an advanced characteristic. The lack of subdivisions in both MOB and AOB in Cynops pyrrhogaster may reflect their phylogenic primitiveness. Since our lectin histochemistry to detect glycoconjugates expressed in the olfactory pathway reveals the subdivisions in the dual olfactory system in the amphibian, the glycoconjugates may deeply participate in the organization and function of olfactory pathways in phylogeny.     

Lectin Histochemical Analysis of the Olfactory Bulbs in the Barfin Flounder (Verasper moseri)

Several lines of evidence have shown that the olfactory system of the fish contains the main and accessory olfactory systems. However, morphological data indicate that the accessory olfactory bulb, the primary centre for the accessory olfactory system, will not differentiate in the fish. Therefore, the fish olfactory bulb is supposed to engage in both main and accessory olfactory systems. To examine this possibility, we investigated the olfactory bulb of the barfin flounder ( Verasper moseri ) by histochemical examination using lectins. The olfactory bulb of the barfin flounder showed a laminar structure with four layers, and diffuse glomerular architecture was observed in the glomerular layer. Based on the expression patterns of sugar residues, the glomerular layer of the barfin olfactory bulb was largely divided into three portions. Heterogeneity in the lectin-binding pattern among olfactory glomeruli was clearly demonstrated by the fluorescent double-lectin staining. The results of this study suggest that the fish olfactory bulb contains both regions equivalent to the main and accessory olfactory bulbs, and they are subdivided into small subsets with different functions.     

Experimental infection of equine herpesvirus 9 in dogs

Equine herpesvirus 9 (EHV-9), a new neurotropic equine herpesvirus, was inoculated intranasally at 107 plaque-forming units in five dogs to assess its pathogenicity. Dogs showed weight loss, pyrexia, anorexia, and neurologic signs on the fourth day. The EHV-9 virus was recovered from the examined brains. Histologically, dogs had a fulminant nonsuppurative encephalitis characterized by severe neuronal degeneration and loss, with intranuclear inclusions, slight glial reactions, perivascular cuffing, and multifocal hemorrhage. The olfactory bulb and the frontal and temporal lobes were predominantly affected. Immunohistochemistry revealed reactivity for EHV-9 antigen in neurons. All dogs had mild bronchopneumonia and various degrees of lymphoid necrosis. These findings indicate that dogs are fully susceptible to EHV-9 and that EHV-9 can cause fulminant encephalitis with high mortality in dogs, as in gazelles and goats.     

HIGH FIELD STRENGTH (4.7T) MAGNETIC RESONANCE IMAGING OF HYDROCEPHALUS IN AN AFRICAN GREY PARROT (PSITTACUS ERITHACUS)

Hydrocephalus was diagnosed in a juvenile African Grey parrot by high-field strength (4.7-Tesla) magnetic resonance imaging (MRI). Excellent anatomic detail was achieved, and there was severe dilation of all ventricles. Relative obstruction was localized to the level of or beyond the outflow of the fourth ventricle. There have been several reports of hydrocephalus diagnosed postmortem in psittacines (i.e., hook-billed parrots), however, this is the first report of an antemortem diagnosis in a psittacine using high-field strength MRI.     

The Accessory Olfactory Bulb of the Mink, Mustela vison: a Morphological and Lectin Histochemical Study

The distribution of binding sites for the lectins Ulex europaeus agglutinin I. Soybean agglutinin, Bandeiraea simplicifolia agglutinin I-isolectin B₄, and Vicia villosa agglutinin in the mink olfactory bulb was investigated. All lectins except Ulex europaeus agglutinin I bound exclusively and systematically to a single area of the olfactory bulb. This area corresponded to that in which the vomeronasal nerves terminate, indicating that it is the accessory olfactory bulb, as confirmed by microdissection and by the study of transverse and parasagittal series of the olfactory bulb. The results, moreover, indicate that the accessory olfactory bulb of the mink comprises three isolated eminences, the largest in the dorsal part of the olfactory bulb, and the other two in the lateral and medial parts.     

Differential expression of neurofilament 200-like immunoreactivity in the main olfactory and vomeronasal systems of the Japanese newt, Cynops pyrrhogaster

Expression of neurofilament 200 (NF200)-like immunoreactivity was examined in the main olfactory system and the vomeronasal system of the Japanese newt, Cynops pyrrhogaster, using anti-porcine NF200 monoclonal antibody (clone N52) to investigate the differences in phenotypical characteristics between these systems. The entire nasal cavity was a flattened single chamber consisting of the main nasal chamber (MNC) and the lateral nasal sinus (LNS) communicating with each other. The olfactory epithelium (OE) was present in the MNC, and the vomeronasal epithelium (VNE) was in the LNS. The OE possessed only a small number of NF200-like immunoreactive receptor neurons. The olfactory nerve and the olfactory nerve layer of the main olfactory bulb also contained a small number of NF200-like immunoreactive axons. In contrast, the VNE possessed many NF200-like immunoreactive receptor neurons. The vomeronasal nerve and the vomeronasal nerve layer of the accessory olfactory bulb contained many NF200-like immunoreactive axons. These findings in the Japanese newt indicate that NF200-like immunoreactive receptor neurons constitute a major subpopulation in the VNE and a minor subpopulation in the OE. In addition, NF200-like immunoreactivity seems to be a useful marker to distinguish the vomeronasal system from the other nervous systems including the main olfactory system in the Japanese newt. The localization of a few NF200-like immunoreactive receptor neurons in the OE might indicate that pheromone-sensitive receptor neurons are intermingled in the OE of the Japanese newt.     

Congenital external hydrocephalus in a dog

A 4-year-old female Chihuahua was presented with progressive seizures, blindness and lethargy. Neurolocalisation was consistent with a diffuse brain lesion affecting the forebrain and cerebellum. MRI demonstrated dilation of the subarachnoid space dorsolaterally surrounding the cerebrum, filled with cerebrospinal fluid (CSF). Ventricular system size was normal, but mild cerebral atrophy was suspected. There was pachymeningeal contrast enhancement, but CSF analysis was unremarkable. This lesion was interpreted to be an external hydrocephalus of suspected congenital origin.     

Heterogeneous expression of glycoconjugates in the primary olfactory centre of the Japanese sword‐tailed newt (Cynops ensicauda)

Histochemical organization of the Caudata olfactory system remains largely unknown, despite this amphibian order showing phylogenetic diversity in the development of the vomeronasal organ and its primary centre, the accessory olfactory bulb. Here, we investigated the glycoconjugate distribution in the olfactory bulb of a semi‐aquatic salamander, the Japanese sword‐tailed newt (Cynops ensicauda), by histochemical analysis of the lectins that were present. Eleven lectins showed a specific binding to the olfactory and vomeronasal nerves as well as to the olfactory glomeruli. Among them, succinylated wheat germ agglutinin (s‐WGA), soya bean agglutinin (SBA), Bandeiraea simplicifolia lectin‐I (BSL‐I) and peanut agglutinin showed significantly different bindings to glomeruli between the main and accessory olfactory bulbs. We also found that s‐WGA, SBA, BSL‐I and Pisum sativum agglutinin preferentially bound to a rostral cluster of glomeruli in the main olfactory bulb. This finding suggests the presence of a functional subset of primary projections to the main olfactory system. Our results therefore demonstrated a region‐specific glycoconjugate expression in the olfactory bulb of C. ensicauda, which would be related to a functional segregation of the olfactory system.     

Polymicrogyria in Standard Poodles

Background: Polymicrogyria is a disorder of cerebrocortical migration resulting in increased numbers of small, disorganized gyri. This disorder occurs in Standard Poodles and in cattle.
Objectives: To describe the clinical, electroencephalographic, imaging, and histopathologic features in poodles with polymicrogyria.
Animals: Five Standard Poodles with histologically confirmed polymicrogyria.
Methods: Retrospective case series. Cases were obtained by personal communication with 1 of 2 authors (TJVW, DPO).
Results: All dogs had cortical blindness and other neurologic abnormalities including gait and behavioral changes. Magnetic resonance imaging of 3 dogs showed multiple disorganized gyri, which were especially apparent on T2-weighted dorsal plane images. Electroencephalogram (EEG) of 1 dog revealed epileptiform discharges, including both spike and spike and wave discharges with voltage maximum potentials over the parietal/occipital region. The EEG supported that the repetitive behavior displayed by the dog was a complex partial motor seizure. One dog had concurrent hydrocephalus. All dogs had occipital lobe involvement and 2 dogs had involvement of other lobes.
Clinical Importance: The cases presented here demonstrate a larger age range (7 weeks to 5 years) and a decreased frequency of associated hydrocephalus when compared with the previous report.     

Surgical treatment of lumbosacral foraminal stenosis using a lateral approach in twenty dogs with degenerative lumbosacral stenosis

Objectives— To describe clinical signs, magnetic resonance imaging (MRI) and surgical findings using a lateral approach to the lumbosacral intervertebral foramen and to evaluate clinical outcomes in dogs with or without concurrent dorsal decompression and annulectomy.
Study Design— Retrospective study.
Animals— Dogs (n=20) with degenerative lumbosacral stenosis (DLSS).
Methods— Medical records (2002–2006) of dogs that had lumbosacral lateral foraminotomy alone or in combination with dorsal decompression were reviewed. Degree of dysfunction was assessed separately for each pelvic limb; dogs with unilateral signs were included in group A, those with bilateral signs in group B. Retrieved data were: signalment, history, neurologic status on admission, 3 days, 6 weeks, and 6 months postoperatively, duration of clinical signs, results of MRI, surgical site(s), intraoperative findings, and outcome.
Results— Based on the clinical and MRI findings unilateral foraminotomy was performed in 8 dogs, bilateral foraminotomy in 1 dog, unilateral foraminotomy with concurrent dorsal decompression in 7 dogs, and bilateral foraminotomy with concomitant dorsal decompression in 4 dogs. Surgery confirmed the presence of foraminal stenosis in all dogs, with osteophyte formation and soft tissue proliferations being the most common lesions. Outcome was good to excellent in 19 dogs and poor in 1 dog. Mean follow-up was 15.2 months (range, 6–42 months).
Conclusion— Lateral foraminotomy addresses compressive lesions within exit and middle zones of the lumbosacral foramen.
Clinical Relevance— Successful surgical management of DLSS is dependent on recognition and correction of each of the compressive lesions within the lumbosacral junction.     

ASYMMETRIC NASAL MUCOSAL THICKENING IN HEALTHY DOGS CONSISTENT WITH THE NASAL CYCLE AS DEMONSTRATED BY MRI AND CT

The nasal cycle is a physiological phenomenon that causes regular cyclical congestion and decongestion of the venous sinusoids lining the nasal mucosa. The purpose of this prospective study was to describe magnetic resonance imaging (MRI) and computed tomographic (CT) features of the normal nasal cycle in a group of dogs. Five dogs were recruited that met the following criteria: 8 to 15 months old, nonbrachiocephalic breed, no clinical signs or history of nasal disease, and undergoing anesthesia for problems unrelated to the nasal cavity. Nasal MRI (n = 5) and CT scans (pre‐ and postcontrast, n = 5) were acquired. Images were evaluated subjectively by two board‐certified radiologists and objectively by a diagnostic imaging intern using regions of interest placed on each side of the nasal cavity. Findings were compared using Cohen's kappa coefficient and Students t‐test on log‐transformed data. All dogs showed diffuse unilateral mucosal thickening of the rostral part of the nasal cavity in both MRI and CT studies. This mucosal thickening shifted sides between examinations in three dogs. Changes appeared most marked on T2‐weighted scans. No asymmetric mucosal changes were seen in the mucosa of the ethmoturbinates, vomer–nasal septum, hard palate or the frontal sinuses in any patient on MRI or CT. Computed tomographic contrast enhancement of the thickened mucosa was not statistically significant (P‐value < 0.08). In conclusion, the normal nasal cycle may cause asymmetrical mucosal changes in the rostral part of the nasal cavity that mimic MRI and CT characteristics previously reported for inflammatory disease in dogs.     

Lectin histochemical study on the olfactory bulb of the newt, Cynops pyrrhogaster

The function and/or morphological features of the vomeronasal olfactory system remain unclear in aquatic animals, although the system appeared first in urodeles based on phylogenic data. We examined the lectin binding patterns in the olfactory bulb of a semi-aquatic urodele, the Japanese red-bellied newt, Cynops pyrrhogaster, using 22 different lectins. Eleven of the lectins showed specific binding to the nerve fibres and glomeruli in the olfactory bulb. Among these, Wheat germ agglutinin, pokeweed and peanut agglutinin preferentially bound the main olfactory bulb, reflecting variation in the expression of glycoconjugates between the main and accessory olfactory bulbs. By contrast, the types of lectins bound to the Cynops olfactory bulb were considerably different from those reported in other urodele families. These results suggest a histochemical distinction between the main and accessory olfactory bulbs, and that glycoconjugate expression may differ significantly among urodele families.     

Surgical management of perineal paraprostatic cysts in three dogs

Three intact male dogs were presented with faecal tenesmus and obvious perineal swelling. All three animals had paraprostatic cysts originating within the abdominal cavity and extending caudally through the pelvic canal, causing perineal swelling. Two of the dogs were found to have concurrent benign prostatic hyperplasia, while the third had chronic active prostatitis. This report describes the investigations, surgical management and outcome for the three dogs presented.