Lateral canthoplasty for facial nerve paralysis and exposure keratitis in a mouse

An 11-month old entire male mouse was presented with mucopurulent discharge and corneal scarring of the left eye. This mouse previously had a history of ear mites that responded to therapy, and had undergone surgery to remove a large discharging mass from the left side of the neck. The eye problem was noted prior to surgery, but after the ear mite infection. Examination revealed absence of a palpebral reflex in the left eye, and no spontaneous movements of the left ear or lip and whiskers. Examination of the left eye revealed extensive corneal vascularisation and pigmentation. Intraocular structures were not visible. A diagnosis of facial nerve paralysis and secondary exposure keratitis was made. Surgery was performed to close the lateral canthus and reduce corneal exposure. Following surgery the eye discharge ceased and corneal vascularisation resolved, however corneal pigmentation persisted.     

Congenital unilateral facial nerve paralysis in a Warmblood filly

A 17-month-old Warmblood filly was referred to our clinic for evaluation of congenital facial nerve (FN) paralysis. Clinical examination revealed a right-sided facial paralysis with mild masticatory muscle atrophy, mild dysphagia and exposure keratitis. Apart from the FN deficits, neurological examination of the remaining cranial nerves showed no abnormalities. Magnetic resonance imaging (MRI) examination using a 3.0 Tesla scanner showed that in comparison to the left FN, the intracranial section of the right FN between the pons and internal acoustic canal was thinner, whereas it appeared indistinct and thickened within the internal acoustic canal and facial canal. Signs of meningitis or encephalitis were not present on MRI. Cerebrospinal fluid analysis showed mild pleocytosis. The owner of the filly requested euthanasia due to the guarded prognosis. At necropsy, the intracranial section of the right FN was macroscopically thinner than the left side and within the facial canal, a 5 mm tissue stump could be identified with an absent extracranial part of the right FN. Histological examination of the brain stem showed different architecture of the left and right motor nuclei of the FN: in the left nucleus, motor neurons of a normal size and well stainable Nissl bodies were present, whereas in the right nucleus, neurons with Nissl bodies were decreased in number and size. Further, a cytoplasmic rich cell population with a nucleus size compatible with normal neurons was present. These cells were suspected to be atrophic neurons. The tissue stump within the facial canal was histologically identified as connective tissue. Unilateral malformation of the FN has not previously been described in the horse. This filly showed a right-sided, intracranial hypoplasia accompanied by an extracranial aplasia of the FN causing complete, congenital facial nerve paralysis, which corresponded to a difference in the architecture of the affected motor nucleus of the FN.     

A cadaver study comparing two approaches to perform a maxillary nerve block in the horse

Reasons for performing study: Anaesthesia of the maxillary nerve of the horse has been described using several approaches, but sparse data exist to evaluate the accuracy of these methods. Objectives: This study compared 2 previously described approaches to the maxillary nerve to assess their relative accuracies. Methods: Thirty severed heads from horse cadavers were arranged to approximate the position of a live horse. Methylene blue (0.25 or 0.1 ml) was injected using a 19 gauge 90 mm spinal needle by one of 2 approaches, the method used being randomly allocated in each instance. Method ANG: angulated needle insertion on the ventral border of the zygomatic process of the temporal bone and directed rostromedially. Method PER: needle inserted perpendicular to the skin surface, ventral to the zygomatic process of the malar bone, level with the temporal canthus of the eye. Accuracy of dye deposition was assessed following dissection. Placement was categorised as ‘full hit’ (complete nerve coverage or dye deposition centred on nerve), ‘partial hit’ (partial nerve discolouration but dye not centred on nerve) or ‘miss’ (no nerve discolouration). Deposition of dye relative to the nerve and whether injection was performed on the left or right side of the head was recorded. A Chi‐squared test was performed to examine the relationship between the 2 methods. Results: Method ANG was performed 31 times, Method PER 28 times. Full hits were 10/31 (32%) vs. 9/28 (32%), partial hits 15/31 (49%) vs. 14/28 (50%) and misses 6/31 (19%) vs. 5/28 (18%) (Methods ANG vs. PER, respectively). Results were not statistically significantly different between the methods. Dye was deposited in the deep facial vein once by each method. Bone was contacted consistently with Method PER and 8/31 times with Method ANG. Conclusion and clinical relevance: Both methods appeared equivalent in terms of accuracy. Aspiration should always precede injection.     

Investigation into intraoral approach for nerve block injection at the mental foramen in the horse

Invasive dental procedures performed in the standing, sedated horse are facilitated by local and regional anaesthesia. The traditional transcutaneous approach to the mental foramen is used to desensitise the incisive region including the mandibular incisors, but is not well tolerated by many sedated patients. In this study, a new, intraoral needle insertion technique for nerve block at the mental foramen was investigated. In 15 equine cadaver heads and two live horses, computed tomography (CT) was used to verify Tuohy needle placement into each mental foramen using an intraoral technique. Varying volumes of contrast medium (3, 6, 10 mL) were injected into the mandibular canal with and without digital occlusion of the mental foramen. The distance of retrograde flow was measured. Additionally, measurements were taken to determine the position of the mental foramen within the interdental space. Correct placement of Tuohy needles and injection of contrast medium into the mandibular canal using an intraoral approach at the mental foramen was achieved in all injections. Retrograde flow of contrast medium was accomplished with all volumes, regardless of occlusion. Although not statistically significant, the 10 mL group appeared to have a greater distance of flow. The needle insertion technique described here appears to be a potential alternative to traditional transcutaneous approaches to mental nerve block for procedures involving the incisive region. In addition, it was found that 79% of the mandibular canals injected with 10 mL of contrast medium had retrograde flow to the position of PM4, suggesting this method may be a useful alternative technique for nerve block for the more rostrally located cheek teeth. The location of the mental foramen was consistently found in the distal third of the interdental space (approximately 60–80% of the distance between the distal aspect of the lateral corner incisor and the mesial aspect of the second premolar).     

Successful treatment of hyperkalaemic periodic paralysis in a horse during isoflurane anaesthesia

HistoryA 3-year-old, 400 kg, gelding Quarter Horse was presented for investigation of epistaxis.Physical examinationThe horse was bright, alert and responsive with rectal temperature, heart rate and respiration rate within normal limits.ManagementDuring a second general anaesthetic for surgical treatment of guttural pouch mycosis by balloon-tipped catheter occlusion of the right major palatine artery and ligation of the right external carotid artery, signs consistent with hyperkalaemic periodic paralysis (HYPP) were exhibited. These included concurrent hyperkalaemia, hypercapnoea, sinus tachycardia, and muscle fasciculations in the presence of normothermia. Stress associated with an acute haemorrhage pre-operatively, and intra-operative hypercapnoea may have precipitated the episode. There were no signs of HYPP during a general anaesthetic, 1 week earlier, when an initial attempt at surgical treatment of guttural pouch mycosis was performed. Treatment consisted of fluid therapy and administration of calcium gluconate (0.1–0.2 mg kg^?1 minute^?1), dextrose 5% (5 mL kg^?1 hour^?1) and insulin (0.05 IU kg^?1). Treatment resulted in the resolution of clinical signs and an uneventful recovery.Follow-upThe diagnosis of HYPP was confirmed by DNA analysis post-operatively.ConclusionsClinical cases of intra-operative HYPP can present despite a previous history of uneventful general anaesthesia. Rapid diagnosis and treatment can result in the successful management of HYPP. This report documents an unusual presentation of HYPP, a disease that remains present in the Quarter Horse population.     

Treatment and ophthalmic sequelae in a horse with facial cellulitis and orbital abscess

A 22‐year‐old Quarter Horse gelding with a history of dental (107) extraction 2 weeks previously was presented with facial cellulitis and an orbital abscess. The abscess was drained surgically dorsally and ventrally to the zygomatic arch and the horse was treated with parenteral antimicrobial and anti‐inflammatory drugs. The affected eye was protected with a temporary tarsorrhaphy and treated via a subpalpebral catheter. Six months after presentation, the horse was in excellent general condition and returned to previous level of exercise but showed blindness on the affected side. Pallor of the optic disc and severe attenuation of the retinal vessels, suggestive of optic disc atrophy, were present.     

Caudal anaesthesia of the infraorbital nerve for diagnosis of idiopathic headshaking and caudal compression of the infraorbital nerve for its treatment,in 58 horses

Reasons for performing study: Idiopathic headshaking is often a facial pain syndrome, but a diagnostic protocol has not been described. In a previous study, caudal compression of the infraorbital nerve for treatment offered a fair success rate, but low case numbers and short follow‐up time were limitations. Objectives: To describe a diagnostic protocol for headshaking, examining the role of bilateral local analgesia of the posterior ethmoidal nerve (PET block). To report longer‐term follow‐up after surgery of the original cases and further cases and to determine whether changes to the technique influence success rates and complications. Methods: Records of horses that had undergone PET block and caudal compression surgery at 3 hospitals were reviewed. Modifications to the surgical technique included placing additional coils into the infraorbital canal and/or performing concurrent laser cautery of the nerve. Follow‐up information was obtained by telephone contact with owners. Results: The PET block was performed in 27 horses, with a positive result in 23 of 27 (85%). Surgery was performed in 58 horses. A successful outcome was initially achieved in 35 of 57 (63%) horses, but recurrence occurred between 9 and 30 months later in 9 (26%). Surgery was repeated in 10 of 31 (32%) horses. Final success rate, considering only response to the last performed surgery, was 28 of 57 (49%) horses with median follow‐up time of 18 months (range 2–66 months). Nose‐rubbing was reported post operatively in 30 of 48 (63%) horses. This resolved in all but 4 horses, which were subjected to euthanasia. Response to PET block or change in surgical technique did not appear to influence outcome or complications. Conclusions and potential relevance: The diagnostic protocol described is recommended for the investigation of headshakers. Caudal compression offers the best prognosis for a successful outcome compared with other treatments, for horses in which the only alternative is euthanasia. Surgical treatment of the disorder requires refinement, and the pathogenesis of the disorder requires investigation.     

Temporohyoid osteoarthropathy and unilateral facial nerve paralysis in a horse

A 13-year-old broodmare was referred for weight loss and left facial nerve paralysis. Bilateral temporohyoid osteoarthropathy was diagnosed based on proliferation of the temporohyoid joints and stylohyoid bones on radiographs and guttural pouch endoscopy. The left side was more severely affected. Treatment resulted in little or no improvement.     

Shockwave therapy for treatment of a burn injury in a horse

This article describes a horse that sustained burn injury wounds over the back extending from the withers to the tail head as a result of a fire in a trailer. The extensive nature of the burn prompted investigation into treatment options which may stimulate healing. Based on current applications in human medicine, shockwave therapy was administered. This horse recovered from a substantial burn injury. Shockwave therapy may be a viable supplemental option for treating burn injuries in the horse, with no noted adverse effects.     

Paravertebral malignant peripheral nerve sheath tumour (MPNST) in a horse

A 10‐year‐old Lipizzaner gelding was presented with intermittent ataxia and hindlimb weakness. Ultrasonographic examination identified a mass cranial to the tuber sacrale. A provisional diagnosis of a soft tissue sarcoma was made based on a biopsy specimen. Owing to the extensive nature of the tumour and the associated poor prognosis, the horse was subjected to euthanasia on humane grounds. A post mortem examination revealed a locally infiltrative soft mass within the left lumbosacral epaxial musculature. Histologically, an infiltrative neoplasm predominantly composed of pleomorphic spindle or stellate‐shaped cells was identified. Neoplastic cells exhibited strong S‐100 protein and GFAP expression and variable vimentin, NSE, NGFR and myoglobin expression. They were uniformly negative for pan‐cytokeratin, melan A, laminin and desmin. The ultrastructural examination revealed pleomorphic cells with long cytoplasmic processes and an absence of melanosomes. Based on these results, a diagnosis of malignant peripheral nerve sheath tumour was made. This report contributes further information to assist in the diagnosis of these poorly defined neoplasms in animals, especially when they occur in uncommon locations.     

Hyperkalaemic periodic paralysis‐like syndrome in a Criollo Argentino horse

Hyperkalaemic periodic paralysis (HYPP) is a relatively new genetic disease that, so far, appears to be confined to descendants of the American Quarter Horse Impressive, a stallion identified as the link between the pedigrees of all affected horses, and that predominantly affects Quarter Horses but also Paint horses, Appaloosas and Palominos. This study suggests that an episode of muscle weakness, which was reported in a Criollo Argentino genetically unrelated to Impressive, was related to marked hyperkalaemia. The symptoms in this case were reproducible following a KCI challenge test although DNA testing for HYPP was negative. Based on these findings, a diagnosis of a HYPP‐like syndrome was made.     

Ultrasound‐guided retrobulbar nerve block in horses: a cadaveric study

Objective To develop an ultrasound‐guided technique for retrobulbar nerve block in horses, and to compare the distribution of three different volumes of injected contrast medium (CM) (4, 8 and 12 mL), with the hypothesis that successful placement of the needle within the retractor bulbi muscle cone would lead to the most effective dispersal of CM towards the nerves leaving the orbital fissure. Study design Prospective experimental cadaver study. Animals Twenty equine cadavers. Methods Ultrasound‐guided retrobulbar injections were performed in 40 cadaver orbits. Ultrasound visualization of needle placement within the retractor bulbi muscle cone and spread of injected CM towards the orbital fissure were scored. Needle position and destination of CM were then assessed using computerized tomography (CT), and comparisons performed between ultrasonographic visualization of orbital structures and success rate of injections (intraconal needle placement, CM reaching the orbital fissure). Results Higher scores for ultrasound visualization resulted in a higher success rate for intraconal CM injection, as documented on the CT images. Successful intraconal placement of the needle (22/34 orbits) resulted in CM always reaching the orbital fissure. CM also reached the orbital fissure in six orbits where needle placement was extraconal. With 4, 8 and 12 mL CM, the orbital fissure was reached in 16/34, 23/34 and 28/34 injections, respectively. Conclusion and clinical relevance The present study demonstrates the use of ultrasound for visualization of anatomical structures and needle placement during retrobulbar injections in equine orbits. However, this approach needs to be repeated in controlled clinical trials to assess practicability and effectiveness in clinical practice.     

A new approach for perineural injection of the lateral palmar nerve in the horse

OBJECTIVE: To evaluate the accuracy of a new technique for perineural injection of the lateral palmar nerve and to determine frequency of inadvertent injection into the carpal synovial sheath with this technique. STUDY DESIGN: Prospective experimental study. ANIMALS: Thirty equine cadaver forelimbs. METHODS: Each of 3 clinicians injected 0.5 mL of a 1% aqueous solution of new methylene blue as a marker at the medial aspect of the accessory carpal bone of 10 limbs. Immediately after each injection, the lateral palmar nerve was identified by dissection of and inspected for proximity of dye, and the carpal synovial sheath was inspected for the presence of dye. RESULTS: New methylene blue solution was observed to surround the nerve (29 limbs) or to lie within 2 mm of it (1 limb). Dye was not found in the carpal synovial sheath of any specimen. CONCLUSIONS: Using this technique, perineural injection of the lateral palmar nerve can be consistently achieved, and the carpal synovial sheath is unlikely to be penetrated by the needle during the procedure. CLINICAL RELEVANCE: The technique described provides an accurate and simple method for perineural injection of the lateral palmar nerve proximal to the origin of its deep branch. This technique can be used to anesthetize the lateral palmar nerve for diagnosis of pain originating in the palmaroproximal aspect of the metacarpus without risk of inadvertently desensitizing structures within the carpal synovial sheath.     

Tracheal rupture following general anaesthesia in a horse

A Dutch Warmblood, with no other underlying clinical disease, presented for surgical excision of a sarcoid tumour on the distal right pinna under general anaesthesia. At the end of the procedure, immediately before being moved to recovery, the horse became light and made repeated attempts to move whilst attached to the hoist. Anaesthesia was deepened with intravenous thiopental sodium (Thiopentone)¹ and the horse was moved into the recovery room. The trachea was extubated with the cuff of the endotracheal tube inadvertently left partially inflated. Recovery was smooth and the horse stood uneventfully. The following day subcutaneous emphysema was noted along the neck and tracheoscopy revealed an abnormal dorsoventrally flattened trachea and a 5 cm tear in the dorsal aspect of the trachea. Symptomatic treatment resulted in progressive healing of the lesion and the horse recovered fully with no evidence of respiratory complications.