The effect of bilateral glossopharyngeal nerve anaesthesia on swallowing in horses

REASONS FOR PERFORMING STUDY: Dysfunction of the glossopharyngeal nerve has been implicated as a cause of dysphagia in horses. However, recent studies have indicated that this is not the case. OBJECTIVES: To determine whether bilateral glossopharyngeal nerve anaesthesia would cause dysphagia in horses or result in measurable alterations in the timing, function, or sequence of swallowing. METHODS: Swallowing was evaluated in 6 normal horses with and without bilateral glossopharyngeal nerve anaesthesia. Swallowing dynamics were assessed subjectively and objectively based on time from prehension of food until swallowing, number of tongue movements until initiation of swallowing, depth of bolus at the base of the tongue prior to initiation of swallow and evidence of tracheal aspiration using fluoroscopy and endoscopy. RESULTS: There was no evidence of aspiration or dysphagia in horses before or after bilateral glossopharyngeal nerve block. No observed or measured differences in swallowing sequence or function could be detected in blocked compared to unblocked horses. However, there was a trend in blocked horses for the number of tongue pushes and the time to swallowing to be increased. CONCLUSIONS: Glossopharyngeal nerve function may not be essential for normal swallowing function in otherwise healthy horses. POTENTIAL RELEVANCE: Clinically, normal swallowing is not an appropriate test of glossopharyngeal nerve function and dysphagic horses should not be assumed to have glossopharyngeal nerve dysfunction.     

Cervical neoplasia originating from the vagus nerve in a dog

An eight-year-old intact male Bernese mountain dog was referred with a history of chronic vomiting, coughing and signs of respiratory distress. Other historical findings included lethargy, weight loss and choking. On presentation, clinical findings were Horner's syndrome, ipsilateral laryngeal hemiplegia, coughing, gagging, respiratory distress and vomiting. Lateral cervical radiographs showed ill-defined mineralisation in the soft tissue ventral to the third cervical vertebra, while ultrasonography of the neck revealed a well marginated heterogeneous mass with focal hyperechogenic lesions and acoustic shadowing. Results of an ultrasound-guided fine needle aspirate suggested neoplasia. At necropsy, a large tumour was detected in the ventral cervical region, originating from the right vagosympathetic trunk. In view of the infiltrating pattern, the cellular pleomorphism and the numerous mitoses on histopathological examination, the tumour was classified as a malignant peripheral nerve sheath tumour.     

Gross anatomy of the accessory nerve and vagus nerve ofthe head and cranial neck region in the Bactrian camel

Seven heads and necks of Bactrian camels were dissected to investigate the origin, course, branches anddistribution of the accessory nerve and vagus nerve in the cranial cervical region. The spinal root and external branch of the accessory nerve were not present, but there was a delicate communicating branch between the dorsal root of the first cervical nerve and the root of the vagus nerve. The sternocephalic muscle was innervated by the second cervical nerve while the brachiocephalic and trapezius muscles were supplied by the sixth and seventh cervical nerves. In the head and cranial cervical region of the Bactrian camel the vagus nerve gave oft the auricular branch, pharyngeal branch, cranial laryngeal nerve, a common trunk to the larynx, oesophagus and trachea, and some communicating branches connecting with the glossopharyngeal, hypoglossal, first cervical nerves and the cranial cervical ganglion.     

Diagnostic outcome of contrast videofluoroscopic swallowing studies in 216 dysphagic dogs

Determining the anatomic and functional origin for dysphagia is critical for development of an appropriate therapeutic plan and determination of the prognosis. The purpose of this retrospective study was to report the quantitative and qualitative outcome of contrast videofluoroscopic swallowing studies in a large cohort of dysphagic dogs presenting to a tertiary veterinary care hospital. The videofluoroscopic swallowing studies were reviewed to generate values for pharyngeal constriction ratio, timing of swallowing events (maximum pharyngeal contraction, opening of upper esophageal sphincter, closing of upper esophageal sphincter, and reopening of epiglottis), type of esophageal peristalsis generated, and esophageal transit time. One or more anatomic locations for origin of dysphagia were assigned (pharyngeal, cricopharyngeal, esophageal (primary motility disorder), other esophageal (stricture, vascular ring anomaly, mass), lower esophageal sphincter/hiatus. Sixty‐one of 216 studies (28%) were deemed unremarkable. Twenty‐seven of 216 dogs (13%) had pharyngeal dysphagia, 17/216 dogs (8%) had cricopharyngeal dysphagia, 98/216 dogs (45%) had dysphagia secondary to esophageal dysmotility, 19/216 dogs (9%) had dysphagia secondary to focal esophageal disorders, and 97/216 dogs (45%) had dysphagia of lower esophageal sphincter/hiatus origin. Multiple abnormalities were present in 82/216 (38%) dogs. Elevated pharyngeal constriction ratio was associated with pharyngeal, cricopharyngeal, and esophageal motility disorders, delayed upper esophageal sphincter opening was associated with cricopharyngeal disorders, a lower percentage of primary esophageal peristaltic waves was associated with cricopharyngeal, pharyngeal, or primary esophageal motility disorders. In conclusion, videofluoroscopic swallowing studies was pivotal in the diagnosis of dysphagia with 155/216 (72%) dogs receiving a final diagnosis.     

Morphologic and morphometric studies of the vagus and recurrent laryngeal nerves in clinically normal adult dogs

Morphologic and morphometric studies were performed on the vagus nerve and its major branch, the recurrent laryngeal nerve (RLN): (1) to determine normal histologic data in myelinated fibers of clinically normal young adult dogs, (2) to establish reference values for mean fiber diameter in the vagus nerve and in the proximal and distal portions of the RLN, and (3) to delineate relative frequency distribution curves for each nerve. Few degenerative changes were observed in single teased-nerve fiber preparations. There was no statistical difference between left and right sides of the vagus nerve or between the proximal and distal portions of the RLN (right and left sides). In contrast to the unimodal distribution of fibers in the vagus nerve and the proximal portion of the RLN, the distribution of fibers in the distal portion of the RLN was bimodal. Mean (+/- SD) fiber diameters of the vagus nerve and in the proximal portion of the RLN (3.02 +/- 1.44 microns and 3.63 +/- 1.49 microns, respectively) were not significantly different, despite a shift to large-diameter fibers in the latter. However, mean fiber diameters of distal and proximal portions of the RLN (5.56 +/- 1.88 microns and 3.63 +/- 1.49 microns, respectively) were significantly (P less than 0.001) different. Approximately 86% of fibers in the vagus nerve and 76% of fibers in the proximal portion of the RLN, had a diameter less than 5 microns, and about 70% of fibers in the distal portion of the RLN had a diameter greater than 5 microns.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional electrical stimulation of the left recurrent laryngeal nerve using a vagus nerve stimulator in a normal horse

The aim of this study was to assess the feasibility of implanting an existing vagus nerve stimulating (VNS) electrode around the recurrent laryngeal nerve. The stimulus response characteristics required to achieve abduction of the ipsilateral arytenoid by the VNS electrode in the normal horse could then be determined. The electrode was wound around the left recurrent laryngeal nerve at the cervical level and connected to a pulse generator. Stimulus response characteristics were obtained by measuring stimulated arytenoid displacement endoscopically in the standing, non-sedated horse. A full and sustained abduction of the arytenoid was obtained with a stimulation frequency of 25 Hz and intensity of 1 mA with a pulse width of 250 μs.     

Noninvasive electrocardiographic parameters to assess interventricular dyssynchrony in dogs with bundle branch blocks

ObjectivesTo define electrocardiographic features of complete left bundle branch block (LBBB) and right bundle branch block (RBBB), and the use of R-peak time (RPT) to identify interventricular dyssynchrony in dogs with BBB.Animals, materials and methodsTwelve-lead ECG tracings of 20 dogs with RBBB, 20 with LBBB, and 60 healthy dogs were retrospectively analyzed and RPT was measured in precordial leads. Interventricular dyssynchrony index (IDI) was than calculated.ResultsIn RBBB, mean electrical axis (MEA) was −111° [−120/−100°], V₁RPT was significantly longer (61 ms [55–72 ms]) than left precordial leads RPT (V₂:25 ms [22–30 ms]; V₃:25 ms [22–29 ms]; V₄:24 ms [21–29 ms]; V₅:25 ms [22–29 ms]; V₆:25 ms [22–29 ms]) and when compared to normal dogs (P < 0.001). In LBBB, MEA was 76° [70/81°], RPT in left precordial leads was significantly longer (V₂:49 ms [34–58 ms]; V₃:49 ms [43–57 ms]; V₄:52 ms [45–62 ms]; V₅:53 ms [45–63 ms]; V₆:55 ms [45–63 ms]) than V₁RPT (17 ms [15–20 ms]) and when compared to normal dogs (P < 0.001). V₁RPT > 28 ms and V₅RPT > 36 ms were found to predict the presence of RBBB and LBBB with a sensitivity of 100% and 96.7%, and a specificity of 96.7% and 99.5%, respectively. The IDI was 23% [16–29%] in normal dogs and significantly greater in dogs with RBBB (33% [30–38%]; P < 0.001) and LBBB (32% [23–41%]; P = 0.006).ConclusionsThis study defines ECG features and RPT in dogs with BBB. Electrical interventricular dyssynchrony can be defined using IDI in dogs with BBB.     

The use of magnetic resonance imaging in the management of pharyngeal penetration injuries in dogs

Objectives: To investigate the correlation between the magnetic resonance imaging findings and subsequent surgical findings for a series of dogs presenting with suspected pharyngeal stick injuries to the Animal Health Trust, Newmarket, between 1995 and 2004. Methods: Magnetic resonance imaging findings were reviewed for patients undergoing a scan of the pharyngeal or cervical area for suspected foreign bodies during the years 1995 to 2004. Results: Case signalment, history and clinical signs were similar to those reported in previous studies. Magnetic resonance imaging demonstrated foreign material in six of seven cases where this was present. There was good correlation between diagnosis of a foreign body at magnetic resonance imaging and subsequent surgical identification. Clinical Significance: Compared with other imaging modalities, magnetic resonance imaging is very helpful for this type of injury, especially in chronic cases where radiographic evidence of a foreign body is unlikely. It is a valuable aid in the diagnosis of pharyngeal penetration injury and in surgical planning.     

The normal response to repetitive motor nerve stimulation in dogs

The responses of certain muscles to stimulation at different frequencies has been studied in normal dogs. Repetitive stimulation at 10 and 20 Hz resulted in a smooth, progressive decremental response when the compound muscle action potential (CMAP) was recorded from the plantar, and to a lesser extent the palmar, interosseous muscles. In contrast, there was a slight incremental response when the CMAP was recorded from the cranial tibial muscle. Studies using a competitive neuromuscular blocking agent have suggested that the plantar interosseous muscles have a greater proportion of low efficacy synapses in comparison with the other muscles studied. The cranial tibial muscle may therefore be more suitable for assessing neuromuscular transmission than the distal limb muscles.     

Fine structure of the retino-optic nerve junction in dogs

In most mammals, the optic nerve fibers are myelinated in its extraocular part (EON) but not in its intraocular part (ION) and also in the retina. Transitional zone from the myelinated to unmyelinated optic nerve usually lies in the central part to the lamina cribrosa. It has been known that dogs contain exceptionally myelinated fibers in ION by light microscopy. The aim of this study was to investigate electron microscopically the retino-optic nerve junction in dogs and re-evaluate the barrier to migration of oligodendroblasts into ION. Fourteen adult dogs were used. EON was largely myelinated. In ION the percentage of myelinated fibers decreased gradually toward the retina. A narrow area of ION adjoining the retina was completely unmyelinated. In most mammalian optic nerves, oligodendrocytes are not found in ION. It has been suggested that oligodendroblasts are prevented from migrating from EON into ION; that is to say, there is a barrier to migration of oligodendroblasts. The lamina cribrosa, a dense meshwork of fibrous astrocytic processes, and a defect in the blood optic nerve barrier have been proposed as a candidate for the barrier to migration. Our results suggest, however, that these factors, at least in dogs, would be not involved in the formation of a barrier to migration of oligodendroblasts.     

Diagnosis of pharyngeal disorders in dogs: a retrospective study of 67 cases

OBJECTIVES: To assess the frequency distribution of pharyngeal disorders and to compare clinical signs in diseases of the different pharyngeal areas. To review the investigation methods. METHODS: Medical records of 67 dogs presenting with abnormalities of the pharyngeal area were retrospectively reviewed and classified according to the anatomic area involved, i.e. the nasopharyngeal, oropharyngeal and laryngopharyngeal areas. Clinical signs, endoscopic findings and results of additional sampling were reviewed. RESULTS: Nasopharyngeal disorders were most frequently encountered (49 per cent), with choanal masses being the most frequent diagnosis (24 of 33), followed by laryngopharyngeal disorders (37.5 per cent) and oropharyngeal disorders (10.5 per cent). A rare condition, stenosis of the intrapharyngeal opening, was classified separately (3 per cent). An overall good correlation between matched cytology and histopathology samples was found. In all categories of diseases, clinical signs related to both the upper respiratory and digestive tracts were reported. CLINICAL SIGNIFICANCE: Pharyngeal disorders are more frequently localised in the nasopharyngeal area and include essentially choanal masses. The use of a flexible endoscope for retrograde rhinoscopy is essential for adequate investigation of the proximal nasopharyngeal area. Clinical signs do not allow differentiation of the pharyngeal disorder within the different pharyngeal areas.     

Tumours involving the nerve sheaths of the forelimb in dogs

Nerve sheath tumours were diagnosed in 10 dogs over a three-year period. The age at presentation ranged from three to 12 years (mean 6-3 years) and the sexes were equally represented. All the dogs were of medium to large breeds. The cases were assigned to two distinct clinical groups, which corresponded with the location of the neoplasia. One group presented as a chronic progressive, unilateral forelimb lameness; these dogs had peripherally located tumours. The other group had an acute onset of signs associated with spinal cord compression without previous forelimb signs. These were associated with tumours at the level of the spinal nerve roots.     

The feline dorsal nerve of the penis arises from the deep perineal nerve and not the sensory afferent branch

The cat has been used extensively as an animal model for urogenital studies involving the pudendal nerve. However, discrepancies persist in the literature regarding the origin of the dorsal nerve of the penis (DNP). This study used gross dissections and serial histological cross sections to demonstrate that the DNP arises from the deep perineal nerve and not the sensory afferent branch as previously reported. This finding indicates a better than previously appreciated neuroanatomical homology between the cat and human.     

The prevalence of dynamic pharyngeal collapse is high in brachycephalic dogs undergoing videofluoroscopy

The aim of this retrospective study was to determine the frequency of pharyngeal collapse in a large group of brachycephalic dogs undergoing videofluoroscopic assessment of swallowing or airway diameter. We hypothesized that brachycephalic dogs would have pharyngeal collapse more frequently than dolichocephalic or mesocephalic dogs with or without airway collapse. The medical records database was searched for brachycephalic dogs undergoing videofluoroscopy of swallowing or airway diameter between January 1, 2006 and December 31, 2015. A cohort of dolichocephalic/mesocephalic dogs with videofluoroscopically confirmed airway collapse was age and time matched for comparison. A control group of dolichocephalic/mesocephalic dogs that did not have documented airway collapse was also evaluated. All fluoroscopic studies were assessed by a board certified veterinary radiologist for the presence and degree of pharyngeal collapse. Results demonstrate that pharyngeal collapse was significantly more common in brachycephalic dogs (58/82; 72%) than in nonbrachycephalic dogs with (7/25; 28%) and without (2/30; 7%) airway collapse. Pharyngeal collapse is more prevalent in brachycephalic dogs undergoing videofluoroscopy than in dolichocephalic/mesocephalic dogs with or without airway collapse.     

Maturation of spinal-evoked potentials to tibial and ulnar nerve stimulation in clinically normal dogs

Spinal-evoked potentials were recorded from 2 litters of clinically normal mixed-breed dogs between 35 and 300 days of age. Summated responses to tibial nerve stimulation were recorded from percutaneous needle electrodes placed at L7-S1, L4-5, T13-L1, C7-T1, and the cisterna cerebellomedullaris. The ulnar nerve was stimulated with recordings at C7-T1 and the cisterna cerebellomedullaris. Amplitudes did not change significantly with age, but were significantly (P less than 0.05) different between various recording sites. On day 35, segmental and overall (L7-cisterna cerebellomedullaris) conduction velocities were less than half of the adult values. Spinal cord conduction velocities increased with age, reaching adult values at approximately 9 months of age. It was determined that quadratic equations best predicted the conduction velocities during maturation.     

A transorbital approach to the maxillary nerve block in dogs: a cadaver study

Objective

To describe a transorbital approach to the maxillary nerve block in dogs and compare it with a traditional approach.

Multicentric nerve sheath fibrosarcomas of multiple cranial nerve roots in two dogs

Nerve sheath fibrosarcomas of the left 5th through 8th cranial nerve roots were diagnosed in 1 dog and of the left 4th through 8th cranial nerve roots in another dog. Clinical signs in both dogs included head tilt to the left, circling to the left, left hemiparesis and proprioception deficits, rotary nystagmus, left-sided atrophy of masticatory muscles, and cutaneous hypalgesia of the left side of the face. Cranial nerve roots from both dogs were incorporated in discrete, firm, encapsulated, lobulated, tan masses of various sizes that compressed adjacent brain stem and cranial nerves. There were no regional or distant metastases; however, there was enlargement of nerve roots adjacent to the masses. The masses were composed of bundles and sheets of anaplastic, polymorphic to spindle-shaped cells that infiltrated cranial nerves and ganglia and extended into the brain along nerve roots. Masses contained various amounts of collagen and reticulin fibers, but no mucopolysaccharide ground substance. There was no myelin or S-100 protein associated with neoplastic cells. The tumors appeared to have a multicentric origin from cranial nerve sheaths.     

Evaluation of repetitive nerve stimulation in young dogs

Evaluation of neuromuscular transmission requires a complete electrodiagnostic evaluation including repetitive nerve stimulation. Supra-maximal stimulation of the peroneal nerve and recording of the compound muscle action potentials from the cranial tibial muscle were under-taken in 25 young dogs of two to 18 months of age. Proximal stimulation in the trochanteric fossa and distal stimulation in the popliteal fossa were chosen for small and large breeds, respectively. Highly consistent results were obtained when the examined muscle was kept at a constant temperature and the limb was firmly fixed. Neither sex- (14 females, 11 males) nor age- related (mean = 4·4 months] differences in neuromuscular transmission were found, but frequency-dependent phenomena were observed. These became more distinct with high frequency stimulation. Pseudofacilitation (n = 16/15 Hz; n = 7/50 Hz), was found to range within certain limits (6 to 26 per cent/15 Hz; 13 to 31 per cent/50 Hz). Its mean values at 50 Hz stimulation were apparently higher (26·88 per cent) than those at 15 Hz stimulation (11·3 per cent). Decremental responses occurred mainly with application of tetanic stimulation frequency (n = 1/15 Hz; n = 12/50 Hz) and may represent blocking of neuromuscular transmission. Each of these reaction patterns usually started to occur at the fourth potential of a series (81 per cent/15 Hz; 94 per cent/50 Hz) and remained constant during the second half of the stimulation train in most cases. The occurrence of post-tetanic phenomena in healthy dogs is poorly understood. Post-tetanic potentiation observed in the present material (24 per cent) may represent pseudofacilitation following high stimulation frequency (50 Hz/100 pulses).