Histological Study of the External, Middle and Inner Ear of Horses

Geometric and Morphometric Analysis of the Auditory Ossicles in the Red Fox (Vulpes vulpes)

The use of carnivores as experimental models in auditory biology has led to a significant improvement regarding our understanding of the structure and function of the ear. Considering that data regarding the anatomy of the middle ear in the red fox are rare, this study aimed to describe the morphological and morphometrical features of the auditory ossicles in the red fox, as well as to provide their shape characteristics by geometric analysis. Nine adult red foxes were used in the study. The malleus, incus and stapes were extracted from the middle ear, prepared, photographed and measured using the software. For the geometric analysis, 19 landmarks were used. Following Principal Component Analysis (PCA), PC1 was found to explain approximately half of all variance (incus: 49.97%; malleus: 49.93%; stapes: 58.49%). The study demonstrated the similar anatomical organization of the auditory ossicles in line with important morphometric and basic geometric data, which can contribute to this field and add a useful perspective to the literature.

Gentamicin-induced sensorineural auditory loss in healthy adult horses

Background

Irreversible sensorineural auditory loss has been reported in humans treated with aminoglycosides but not in horses.

Objective

Investigate if auditory loss occurs in horses treated using the recommended IV daily dosage of gentamicin for 7 consecutive days.

Animals

Ten healthy adult horses (7‐15 years; females and males, 5 each).

Methods

Prospective study. Physical and neurological examinations and renal function tests were performed. Gentamicin sulfate was administered at a dosage of 6.6 mg/kg via the jugular vein on alternating sides for 7 days. Gentamicin peak and trough concentrations were measured. Horses were sedated using detomidine hydrochloride IV to perform brainstem auditory evoked responses (BAER) before the first dose, immediately after the last dose, and 30 days after the last dose. Peaks latencies, amplitudes, and amplitude ratios were recorded. Data from the second and last BAER were compared to results at baseline. Bone conduction was performed to rule out conduction disorders.

Results

Seven horses had auditory loss: complete bilateral (N = 1), complete unilateral (N = 2), and partial unilateral (N = 4). Based on physical examination and BAER results, sensorineural auditory loss was suspected. Absent bone conduction ruled out a conduction disorder and further supported sensorineural auditory loss in horses with completely absent BAER. Auditory dysfunction was reversible in 4 of 7 horses.

Conclusions and Clinical Importance

Gentamicin at recommended doses may cause sensorineural auditory loss in horses that might be irreversible. Follow‐up studies are needed to investigate if other dosing protocols present a similar risk.

Morphological and morphometrical aspects of the auditory ossicles in goat (Capra hircus)

The present paper deals with a detailed description of the auditory ossicles in Capra hircus. The paper focuses on the morphological and morphometrical description of the ossicular assembly, formed by malleus, incus and stapes. The malleus (overall length, as average- 8.16 mm) comprises the head of malleus (Caput mallei), a slightly strictured part-neck (Collum mallei) with 3 distinctive processes (lateral, rostral and muscular) (Processus lateralis, Processus rostralis and Processus muscularis) and a handle (Manubrium mallei). The head of malleus has an oval aspect with an obtuse articular surface on its medial surface (Facies articularis). The neck is evident with three bony processes described-the anterior, almost triangular, the muscular one quite reduced and the lateral one which is the most developed one. The manubrium is the longest sector-4.4 mm and appears as a slightly curved piece. The incus presents a body of 1.3 mm and two processes-the short and long crus (Crus breve and Crus longum). The overall shape of the ossicle resembles a biradicular molar. The lenticular process is a continuation of the distal part of the long crus. The stapes-the smallest in size of the three ossicles (2.7 mm), has a head (Caput stapedis), an anterior (Crus rostrale) and a caudal (Crus caudale) arm and a footplate (Basis stapedis). The two processes are slightly different in size and morphology, delimiting the intercrural space that shows the presence of a bony spicule. The footplate (1.6 mm² area) is ellipsoidal, with an anterior narrower extremity.

Otitis externa in eight horses - clinical signs, treatment and prognosis

BACKGROUND

Otitis externa is rare in horses and the condition is poorly described in the literature.

OBJECTIVE

To describe clinical signs, treatment regimens and prognosis of otitis externa in horses.

ANIMALS

Eight horses diagnosed with otitis externa during 2011-2018.

METHODS

Retrospective review of medical records and follow-up contact with owners.

RESULTS

Common clinical signs seen in affected horses were pruritus, ear discharge and ear droop of affected ears. The most common cytological findings were neutrophils, bacteria and yeast. All horses responded well to treatment; two horses were reported to have recurrent problems.

CONCLUSION AND CLINICAL IMPORTANCE

Otitis externa in horses is a rare and treatable condition. The condition may be present for prolonged periods before owners become aware, compromising the welfare of affected horses. Untreated otitis externa is a suggested cause of otitis media and temporohyoid osteoarthropathy, emphasizing the importance of identifying and treating this condition at an early stage. For this reason, clinicians should include a brief inspection of the pinnae and external ear canal in the clinical examination of horses.

Morphological and morphometrical study of the auditory ossicles in chinchilla

This study is meant to illustrate and describe the features of the auditory ossicles of the chinchilla (Chinchilla lanigera), one of the species used more and more frequently in otology and ear surgery as animal model. Cephalic extremities of 12 C. lanigera individuals obtained from a private farm, where this species was bred for fur, were used in this study. The ossicles were obtained either by direct surgical harvesting by mastoid approach or after a dermestid beetle exposure followed by anatomical dissection. The three ossicles that form the assembly are the malleus, incus and stapes. After the removal of these ossicles, a series of anatomical descriptions were made, followed by seriate sets of measurements. The malleus and incus form a joined-single unit called the maleo-incal complex, with an elongated straight appearance, also due to the development of the anterior process. The handle of the malleus and the long process of incus are almost perpendicular to the main axis of the maleo-incal complex. The presence of the muscular process on the handle of the malleus is recorded. The overall shape of the incus is given by the uneven development of the two processes and the reduced neck part. The stapes is the smallest of the components that maintains the well-known architecture in accordance with the general model. The morphology of all three ossicles is backed by a series of measurements, some standard, some adapted to the morphology of the ossicles. From the very reduced comparative metrical data at our disposal, our study presents an average of 10% lower values for the ones presented earlier by other researchers in the same species.

Dynamic property changes in stapedial annular ligament associated with acute otitis media in the chinchilla

Located at the end of the ossicular chain, the stapedial annular ligament (SAL) serves as a closed yet mobile boundary between the cochlear fluid and stapes footplate. It is unclear how SAL properties change with acute otitis media (AOM). This paper reports the measurements of SAL dynamic properties in chinchilla AOM model using dynamic mechanical analyzer (DMA) and frequency-temperature superposition (FTS) principle. AOM was analyzed in two infection groups: 4 days (4D) and 8 days (8D) post induction. SAL specimens were measured using DMA at three temperatures: 5, 25, and 37°C. To extend the testing frequencies to higher levels, FTS principle was employed. Then generalized Maxwell model was utilized to define the constitutive equations of the SAL. The complex shear moduli were obtained from seven samples of control, 4D, and 8D groups. Results show that the storage and loss shear moduli of SALs decreased due to AOM. The storage moduli for 4D and 8D ears were similar below 100Hz, and the loss modulus for 4D was significantly larger than 8D across the entire frequency range. This study reports data that contributes to ear biomechanics and improves understanding on the effects of AOM in middle ear tissues.

Neurologic Deficits Including Auditory Loss and Recovery of Function in Horses with Temporohyoid Osteoarthropathy

BACKGROUND

Auditory loss is a common deficit in horses with temporohyoid osteoarthropathy (THO), however, recovery of function is unknown.

HYPOTHESIS/OBJECTIVES

To investigate neurologic function with emphasis in audition in horses with THO after treatment. To describe anatomical alterations of the petrous temporal bone that might result in auditory loss.

ANIMALS

Twenty-four horses with a clinical diagnosis of THO.

METHODS

Prospective study. A brainstem auditory evoked response (BAER) study was done as part of the criteria for inclusion in horses with a clinical diagnosis of THO from the years of 2005 to 2014. Physical and neurologic status and BAER findings were recorded. Brainstem auditory evoked response variables were compared by using Wilcoxon sign test. Fisher's exact test was also used. Significance was set at P < 0.05.

RESULTS

The most common signs included auditory loss (100% of horses), vestibular and facial nerve dysfunction (83%), and exposure ulcerative keratitis (71%). Concurrent left laryngeal hemiparesis was observed in 61% of horses through endoscopy. Auditory dysfunction was bilateral in 50% of the cases (complete and partial), and unilateral affecting more commonly the right ear (R = 8, L = 4). Short- and long-term follow-up revealed persistent auditory loss in all horses based on abnormal response to sound, and further confirmed through a BAER in 8 horses.

CONCLUSIONS AND CLINICAL IMPORTANCE

Auditory dysfunction appears to be a permanent neurologic deficit in horses diagnosed with THO despite overall neurologic improvement.