 So in this talk we shall discuss in detail the anatomy of the oval and round windows and the inner ear temporal bone anatomy part 2. The sound waves are conducted via the ossicles that is malleus, incus and staples through the oval window to the perilymph in the vestibule and scala vestibuli of the cochlea. These fluid waves get transmitted to the endolymph of the cochlea duct which is the scala media where basilar membrane displacement stimulates the hair cell receptors of the organs of the corti within the scala media. The electrical signal now is then sent via the cochlea nerve to the auditory cortex. So perilymph waves are transmitted from the scala vestibuli via the apex of the cochlea that is the helicotrimer to the scala tympani and eventually dissipated at the round window. So looking at the cross-sectional anatomy of these two windows, these are the axial and coronal sections demonstrating a rectangular shaped oval window where the two crura of steps are seen to overlie this window. Immediately lies the vestibule and anteriorly as we see on the axial section lies a part of bone the otec capsule between the cochlea and the vestibule and posteriorly is the sinus tympani marked by the yellow arrow on the axial image. On the coronal image superior to the oval window lies the lateral semicircular canal as shown by the red arrow. Between the oval window and the lateral semicircular canal lies the facial nerve a small circular dot seen between these two structures which is the tympanic segment of the facial nerve. So medially to this oval window is the vestibule and inferromedial is the cochlea. Axial and coronal sections at the level of the round window niche, this is the level of the basal turn of the cochlea and the round window niche can be well evaluated both on our axial and coronal sections. Moving on to inner ear, inner ear comprises of the oscis labyrinth which encloses the membranous labyrinth. So the oscis labyrinth constitutes of the bony cochlea, vestibule, semicircular canals and vestibular and cochlear aqueduct. Within the oscis labyrinth, within all these structures lie the components of the membranous labyrinth, cochlea duct that lies within the cochlea, utricle and saccule that lie within the vestibule, the semicircular ducts that lie within the semicircular canals and the endolymphatic duct and sac which lies in the vestibular aqueduct. Between the peri-lymph and between the oscis labyrinth and the membranous labyrinth lies the peri-lymph. So imagine these two channels, these two circles, the outer one represents the oscis labyrinth and the inner one is the membranous labyrinth. So between these two demarcated by red lies your peri-lymph fluid and within the inner membranous labyrinth the green arrow depicts the endolymph. Now these two fluids are different in their ionic compositions. The peri-lymph being very rich in sodium and low in potassium is similar to extracellular fluid or CSF. Endolymph on the other hand is rich in potassium and low in sodium reverse of what is happening in peri-lymph. And this ionic composition is similar to the intracellular fluid which is required for bathing and nourishing our sensory epithelium. Axial sections of the vestibule and semicircular canals, the top three images are axial CT images, the lower three are axial MR images. So we can see the superior semicircular canal, the two limbs on the top most scan. On a slightly inferior scan we see the vestibule and the lateral semicircular canal seen entering the vestibule. And on a further inferior section we can also see one limb of the posterior semicircular canal. Coming on to cochlea, cochlea is a coil structure forming two and a half to two, three by four turns around a central bony axis which is the modulus. Now we need to evaluate cochlea especially on these two important sections. The first one here is a mid-modular level. So the modulus where we can see the modulus which is the central trapezoidal bone and this curved arrow depicts the cochlear aperture through which the cochlear nerve enters the cochlea. At the round-window niche level that we have already seen in this talk, at this level we can see the basal, the middle and the apical turns of the cochlea which are separated by the interscalar septum that bone that separates these two is the interscalar septum. Now the internal anatomy of the cochlea is better demonstrated on MR. So on the left we have a schematic representation. Thick central modulus through which the cochlear nerve passes. Within each turn of the cochlea from the modulus there is a what's the structure that come the bony thin bony structure that comes out is the oscious spiral lamina. Now this divides each of these turns into the outer anterior scala vestibuli and posterior and inner scala tympani. Oscious spiral lamina is what houses the cochlear duct which is the membranous labyrinth. So what we see on MR is the peri-limb fluid within the scala vestibuli and scala tympani this black line is what houses the cochlear duct which further contains the endolim which is beyond the resolution of our current imaging techniques. Interscalar septum can be seen separating the turns of the cochlea. Coronal images from anterior to posterior CT on the left MR on the right so we can see the cochlear turns. Going behind we see the vestibule by this yellow arrow and the semicircular the three semicircular canals by the green. Coming on to internal structure of the internal auditory canal. Now internal auditory canal houses the seventh and the eighth nerves. Eighth nerve being the vestibulo cochlear nerve. Now we can't see these nerves directly on our CT images but what we can certainly see is the canals which carry these nerves. So this is our on the top right image we see the facial nerve canal coming out anteriorly and posteriorly is the superior vestibular nerve canal. So on this diagrammatic representation what we see is that the seventh nerve lies up and anterior and the superior vestibular nerve is in the superior and the posterior part of this canal and that is what we extrapolate on our axial CT image. On the bottom right image another axial image we see the cochlear aperture the canal for the cochlear nerve which enters the cochlea and a canal for the inferior vestibular nerve canal. So these are the two nerves lying in the inferior part of the IAC as is well seen in the diagram. The superior and the inferior compartments of the IAC are divided horizontally by this the transverse crest or the falciform crest which divides it horizontally which is seen on this coronal image on the bottom left depicted by the yellow arrow which divides it into the superior and the inferior compartments. The superior compartment also has an incomplete kind of bone that can separate the seventh nerve and the superior vestibular nerve which is called the Bills Bar. The nerves can however be directly seen on MR as we all know. So these the superiorly we have the facial and the superior vestibular nerve in the superior part of the IAC and the inferior part of the IAC we see the cochlear nerve and the inferior vestibular nerve. A mnemonic to remember that the seventh nerve lies up and the eighth nerve lies down is seven up and coke down. So in the superior part of the IAC where we see the facial and the superior vestibular nerves these are two parallel lines and the inferior part of the canal these are two kind of intersecting or diverging lines which represent the cochlear nerve and the inferior vestibular nerve. On MR we can additionally obtain sagittal oblique T2 weighted image cutting perpendicular to the nerves within the IAC which can depict all these four nerves for us in cross section facial superior vestibular, cochlear and inferior vestibular facial and cochlear being in the anterior part of the IAC superior and inferior vestibular being in the posterior part of the IAC. Vestibular aqueduct is a bony channel extending from the posterior superior part of the vestibule causing laterally and inferiorly along the posterior-petrus surface. This houses the endolymphatic duct and sac so this vestibular aqueduct is demarcated by the yellow arrow and this lies nearly parallel and posterior to the posterior semicircular canal. The endolymphatic duct and sac help in maintaining volume and composition of the endolymph. The measurement of the vestibular aqueduct should not generally exceed that of the posterior semicircular canal beyond which it is considered dirated. Cochlear aqueduct is a narrow channel that contains some perilymph and loose connective tissue and this lies roughly parallel and slightly inferior to the IAC as we see on these two sections the left one showing the IAC and the right one slightly inferior to the IAC shows us the cochlear aqueduct. This is a potential conduit between the posterior fossa and the inner ear and its narrow diameter buffers the inner ear from wide pressure variations that can occur within the posterior fossa subarachnoid space. With that I thank you for your kind attention.