Surgical treatment of vertigo by utriculostomy: an experimental study in sheep

Sheep as a Large-Animal Model for Otology Research: Temporal Bone Extraction and Transmastoid Facial Recess Surgical Approach

PURPOSE

Sheep are used as a large-animal model for otology research and can be used to study implantable hearing devices. However, a method for temporal bone extraction in sheep, which enables various experiments, has not been described, and literature on middle ear access is limited. We describe a method for temporal bone extraction and an extended facial recess surgical approach to the middle ear in sheep.

METHODS

Ten temporal bones from five Hampshire sheep head cadavers were extracted using an oscillating saw. After craniotomy and removal of the brain, a coronal cut was made at the posterior aspect of the orbit followed by a midsagittal cut of the occipital bone and disarticulation of the atlanto-occipital joint. Temporal bones were surgically prepared with an extended facial recess approach. Micro-CT scans of each temporal bone were obtained, and anatomic dimensions were measured.

RESULTS

Temporal bone extraction was successful in 10/10 temporal bones. Extended facial recess approach exposed the malleus, incus, stapes, and round window while preserving the facial nerve, with the following surgical considerations: minimally pneumatized mastoid; tegmen (superior limit of mastoid cavity) is low-lying and sits below temporal artery; chorda tympani sacrificed to optimize middle ear exposure; incus buttress does not obscure view of middle ear. Distance between the superior aspect of external auditory canal and tegmen was 2.7 (SD 0.9) mm.

CONCLUSION

We identified anatomic landmarks for temporal bone extraction and describe an extended facial recess approach in sheep that exposes the ossicles and round window. This approach is feasible for studying implantable hearing devices.

Learning Curve of Two Handed Endoscopic Ear Surgery on Sheep Temporal Bone: A Fellow’s Perspective

The study puts forth the learning curve of two handed endoscopic middle ear dissection on a sheep temporal bone. It also highlights the usage of sheep temporal bone as an effective simulation technique for two-handed cadaveric temporal bone dissection. 6 sheep temporal bone models were dissected in a period of 15 days. Harvesting of cartilage graft, endoscopic myringotomy and grommet insertion, cartilage butterfly tympanoplasty, ossiculoplasty, stapes surgery and facial nerve decompression, using the Endohold®, were conducted on each bone. There was a remarkable decrease in the time required for subsequent temporal bone dissections, with significant improvement in efficiency, accuracy and neatness of dissection. Practice and experience resulted in upliftment in the level of confidence of the fellow. Striking similarities were noticed between sheep and human temporal bones. Availability of both the hands with a clear endoscopic view made it easier and more convenient to perform various procedures. Two handed endoscopic technique provides an excellent approach for ear surgeries. Availability of both the hands for the delicate surgery along with the spectacular endoscopic view contributes to increase in efficiency and surgery outcome. Cadaveric dissection of sheep temporal bones provides a great learning experience for a trainee to practice these delicate and skilful two-handed endoscopic middle ear surgical exercises. Its easy availability and striking similarity of the anatomy makes it a boon for the beginners. It gives ample opportunity to the trainee to explore and learn the complex anatomy, try new skills and develop an expertise in this field. The efficiency and accuracy increases significantly with each dissection, smoothening out the steep learning curve, that is, for such fine and intricate surgical skills.

Sheep as a large animal model for cochlear implantation

INTRODUCTION

In surgical training, large animal models are more suitable as their anatomy is more similar to humans. In otology, there have been relatively few studies about large animal models for surgical training.

OBJECTIVE

In this study, we aimed to do a neuroradiologic evaluation and surgical insertion of a cochlear implant electrode array on a sheep head model.

METHODS

Twenty cadaveric sheep heads were studied. A computed tomography scan and neuroradiologic evaluation was performed on each head, obtaining measurements of the inner ear for each sheep. Sheep measurements were compared to those from temporal bone computed tomography scans from 20 female humans. Surgical procedures were first trained with 13 of the sheep temporal bones, after which cochlear implantation was performed on the remaining 7 temporal bones. The position of the inserted electrode array insertion was confirmed by computed tomography scan after the procedure.

RESULTS

Neuroradiologic evaluation showed that, relative to the 20 female humans, the mean ratio for sheep was 0.60 for volume of cochlea, 0.70 for height of cochlea, 0.73 for length of cochlea; ratios for other metrics were >0.80. For the surgical training, the round window was found in all 20 sheep temporal bones. Computed tomography scans confirmed that electrode insertions were fully complete; the mean value of electrode array insertion was 18.3 mm.

CONCLUSION

The neuroradiologic and surgical training data suggest that the sheep is a realistic animal model to train cochlear implant surgery and collection of perilymph samples, but less so for surgical training of mastoidectomy due to pneumatization of the mastoid.

Comparison of sheep and human middle-ear ossicles: anatomy and inertial properties

The sheep middle ear has been used in training to prepare physicians to perform surgeries and to test new ways of surgical access. This study aimed to (1) collect anatomical data and inertial properties of the sheep middle-ear ossicles and (2) explore effects of these features on sound transmission, in comparison to those of the human. Characteristic dimensions and inertial properties of the middle-ear ossicles of White-Alpine sheep (n = 11) were measured from high-resolution micro-CT data, and were assessed in comparison with the corresponding values of the human middle ear. The sheep middle-ear ossicles differed from those of human in several ways: anteroinferior orientation of the malleus handle, relatively small size of the incus with a relatively short distance to the lenticular process, a large area of the articular surfaces at the incudostapedial joint, and a relatively small moment of inertia along the anterior-posterior axis. Analysis in this study suggests that structure and orientation of the middle-ear ossicles in the sheep are conducive to an increase in the hinge-like ossicular-lever-action around the anterior-posterior axis. Considering the substantial anatomical differences, outcomes of middle-ear surgeries would presumably be difficult to assess from experiments using the sheep middle ear.

Sheep as a large animal model for middle and inner ear implantable hearing devices: a feasibility study in cadavers

OBJECTIVE

Currently, no large animal model exists for surgical-experimental exploratory analysis of implantable hearing devices. In a histomorphometric study, we sought to investigate whether sheep or pig cochleae are suitable for this purpose and whether device implantation is feasible.

METHODS

Skulls of pig and sheep cadavers were examined using high-resolution 128-slice computed tomography (CT) to study anatomic relationships. A cochlear implant and an active middle ear implant could be successfully implanted into the sheep's inner and middle ear, respectively. Correct device placement was verified by CT and histology. The cochlear anatomy of the sheep was further studied by micro-CT and histology.

RESULTS

Our investigations indicate that the sheep is a suitable animal model for implantation of implantable hearing devices. The implantation of the devices was successfully performed by access through a mastoidectomy. The histologic, morphologic, and micro-CT study of the sheep cochlea showed that it is highly similar to the human cochlea. The temporal bone of the pig was not suitable for these microsurgical procedures because the middle and inner ear were not accessible owing to distinct soft and fatty tissue coverage of the mastoid.

CONCLUSION

The sheep is an appropriate large animal model for experimental studies with implantable hearing devices, whereas the pig is not.

Alterations in cochlear function during induced acute hyperinsulinemia in an animal model

Hyperinsulinism secondary to peripheral insulin resistance has been described as the most frequent etiologic factor in cochlear and vestibular syndromes.

Aim

This experimental study recorded and analyzed evoked auditory potential changes using transtympanic electrocochleography (EcochG) during induced acute hyperinsulinism in an animal model.

Materials and Methods

Six adult male sheep were randomly divided into 2 groups. The animals were submitted to EcochG under general anesthesia, and a peripheral blood sample was collected to measure glycemia and insulinemia. Animals in the intervention group (n=3) received regular human insulin IV (0.1 U/kg). The control group (n=3) received saline solution. Glycemia and insulinemia were measured simultaneously with the recording of evoked potentials at 10-minute intervals during 90 minutes.

Results

The intervention group experienced a progressive suppression in action potential amplitude when compared to the control group (p=0.001).

Conclusion

Data strongly suggest that acute induced hyperinsulinism suppresses cochlear function. Results may be attributed to loss of Na+K+ATPase activity in the stria vascularis, leading to loss of endocochlear potential and subsequent depolarization of cochlear hair cells as well as of neural cells in the auditory portion of cranial nerve VIII.

An alternative model for stapedectomy training in residency program: sheep cadaver ear

To determine the usefulness of sheep cadaver ear as a complementary model for training of stapedectomy at residency programs, 2 of our 4 year residents were included in the study and each operated 20 sheep ears. All routine steps of stapedectomy operation were performed, and their success and complication scores were recorded. Performance of residents for stapedectomy and teflon piston placement in sheep ears were evaluated by the authors. Success of both residents improved progressively. Success and complications were impressively better in the second 10 ears than the initial 10 for each resident. Both residents had better outcomes in last 10 ears. Sheep cadaver ear is an excellent model for stapedectomy training in residency and helps to improve surgical skills. We offer sheep cadaver ear training model especially in the countries where obtaining human cadaver temporal bone is difficult.

CT-Scan sheep and human inner ear morphometric comparison

INTRODUCTION

Studies about the use of sheep in surgical training and experimental otologic surgery are rare. This study intends to contribute to the knowledge on this field.

AIM

To study sheep inner ear structures using computerized tomography and serial cross-sections to collect more accurate morphometric data to compare sheep and human ears.

MATERIAL AND METHODS

This descriptive study compared the inner structures of sheep and human ears. Measurements were made using computerized tomography, and they were stored in a DICOM compact disc for later analysis and manipulation, with a program used for medical image analysis (Osíris 4.16).

RESULTS

Mean measures for sheep and human ears were found to be similar in this morphological study. Most structures (10 out of 15) maintained the 2/3 ratio of sheep to human ear.

CONCLUSION

The results of this morphometric study of sheep ear are an important contribution to the development of an animal model to be used for surgical training and experimental otologic surgeries.

Morphometric study of the external and middle ear anatomy in sheep: a possible model for ear experiments

Sheep are a potentially useful model for otologic surgical training and experimentation, currently limited by the scarcity of morphological comparisons between the structure of the ear in sheep and in humans. A detailed morphometric study of the ear in sheep was carried out using computed tomography. Measurements made with AutoCAD Release 14 were compared with measurements for the human ear reported in the literature. In general, ear structures in sheep are two-thirds the size of those in humans. The important anatomical similarities found in this study between the ear in sheep and in humans suggest that sheep may be a useful model for surgical training and experimentation in some middle ear procedures.

Tympanic membrane healing in myringotomies performed with argon laser or microknife: an experimental study in rats

Secretory otitis media (SOM) and recurrent acute otitis media (RAOM) may require surgical treatment to proper ventilate the middle ear. Incisional myringotomy is usually done under microscopy with a micro-knife, but it remains patent for just a few days. Recent research indicates that laser assisted myringotomies remain open much longer, allowing middle ear ventilation and healing. Material and methods: In this experimental study 34 white, male, adult, Wistar rats, without middle ear disease were submited to anesthesia with ketamine 27 mg/kg and xylazine 2,7 mg/kg. Incisional myringotomy was done on the right ear, while laser myringotomy was done on the left. Myringotomies were evaluated periodically until healing. Results: The healing times were equivalent. All myringotomies healed within 10 days. Conclusion: Argon laser assisted myringotomy healed just as early on as incisional myringotomy on Wistar rats without middle ear diseases.