Tree Shrew Secretory Otitis Media Animal Model Research

Objective:Anatomy of Eustachian tube and perform Micro-CT images of tree shrew temporal bone.To develop valid animal model for otitis media of effusion.Methods:We used 26 healthy adult tree shrew for the study.26 tree shrew were randomly divided into 2 groups:anatomy group and model group.Anatomy group:10 tree shrew were dissected under the aid of surgical microscope to study the general anatomy of Eustachian tube.Among the 10 tree shrew only 6 were performed Micro-CT examination.Model group:To develop the animal model for otitis media we usedl6 tree shrew.In our research we used electro coagulation method to create permanent blockage of Eustachian tube.16 healthy tree shrew without any inducing factor electro coagulation was done on the right pharyngeal orifice of Eustachian tube.All the experimental animals left ear was considered as control group.After the procedure in each group of animals middle ear status was assessed by otomicroscope and tymphanogaph recording and Micro-CT examination were performed.The experimental animals were at the end were killed for middle ear pathological study.Results:1.0Anatomy group:1.1 During the anatomy of Eustachian tube under surgical microscope we found;The tree shrews Eustachian tube is divided into three parts:the membranous part,membrano-cartilaginous part and bony portion.Cartilaginous portion lies with in medical bulla,bony portion lies with in lateral bulla and membranous portion lies with in nasopharynx.Muscles responsible for functioning Eustachian tube are found to be two;Tensor Veli Platini(TVP)and Levator Veli Platini(LVP).1.2.Cartilage is "C" shape;the mucosa is tightly attached to the cartilage.Towards the nasopharynx the cartilage gradually decrease in size and disappear to form membranous part of Eustachian tube.1.3.The Eustachian tube narrowest portion is on the border between cartilage and bony portions.1.4.The nasopharyngeal orifice of the Eustachian tube is surrounded by two soft lip like mucosal swelling one on the ventral and other on the cranial side,the mucosal lips can be easily movable.Tympanic orifice of Eustachian tube is bony structure which opens continuously.1.5.Tensor Veli Platini:TVP is composed of 2 groups of muscles,medial group,the bigger one,originates from in the bulla,sphenoid wing,pterygoid process and mainly related to muscle tension size,lateral group the smaller one,originates from in the lateral plate of cartilage near the junction of cartilage and bone,the main function of Eustachian tube expansion.Two groups of muscles form a tendentious intersection hook around the pterygoid hamulus and insert into the soft palate near the posterior border of hard palate.1.6.Levator Veli Platini:LVP originates from medial plate of cartilage nearly the junction of cartilage and bone.It has no origin on the membranous portion.Muscle bundle runs towards anterior medial,finally insert into the posterior portion of soft palate.It just forms a muscular sling suspending the soft palate from the cranial base.1.7.Micro CT scan;Micro CT scan can clearly showed the bony structure of the skull,palate,turbinate,temporal bulla,auditory ossicle,cochlear structures,etc.But for soft tissue display is poorer.Mcro-CT scan found that tree shrew tympanic bubble is divided into,lateral.medial and middle into three rooms,lateral bulla is bigger,the middle to bubble is smaller,Eustachian tube pharyngeal opening lies on lateral wall of medial bulla where as tympanic opening lies on lateral wall of lateral bullae.All these three bullae are separated by bony septum.Isthmus lies on the bony septum between anterior and posterior bulla.2.0 Model Group.2.1.Otomicroscopic examination;On the otomicroscope examination of experiment ear(right ear)air fluid level,dullness of tympanic membrane,budging of tympanic membrane were seen.On the control ears(left ears)no abnormalities were seen.Tympanic membrane seemed to be normal.2.2.Tympanograph:All the right ears showed B type curve.On the left ears no abnormalities were seen.Type A curve was recorded.No other typers of curves were recorded.2.3.Micro-CT Scan result:Based on Micro CT images and processing through Mimics 15.0 software the anatomical structure of the tree shrews temporal bone were successfully obtained.All the experimental group animals(right ears)low density CT images.Low density were specially seen on temporal bulla and middle ear cavity.Compare the middle ear mucosa with the opposite ear founded to be inflamed and thickened.All the left ear showed no abnormalities in CT images.2.4.Pathological Study;Under the light microscope showed presence of effusion in the middle ear and middle ear mucosal changes on 7th and 28th day.On the control group no abnormalities were seen.Conclusion:Eustachian tube is the main pathology for middle ear disease.There was relation between Eustachian tube pathology and middle ear disease.We developed easy way to induce otitis media in animal model.We proved otitis media is caused due to the obstruction in the Eustachian tube.On our anatomical study we found tree shrew Eustachian tube is divided into three parts;membranous,cartilaginous and bony parts.The normal function of Eustachian tube depends on two muscles namely Tensor Veli Platini and Levator Veli Platini.Substantial similarities were seen between tree shrew and human ears.It would be helpful for researchers to locate structures in nasopharynx and middle ear in further experiments with tree shrew.Our animal has benefit of easy handling,quick breeding,easily domesticated and relative small size.