Anatomy of the DISCLOSURE Temporal Bone Zorann Rumboldt I have no actual or potential conflict of interest in relation to this presentation Universityyj of Rijeka Medical Universityy of South Carolina Telemedicine Clinic Temporal bone parts: 5 Major components: 5 + 3 Squamous - Lateral wall of middle cranial fossa External Auditory Canal (EAC) Mastoid - Aerated posterolateral T-bone Middle ear-mastoid (ME-M) Inner ear (IE) Petrous - Pyramidal shape medial T-bone Internal auditory canal (IAC) containing inner ear, IAC, & petrous apex Petrous apex (PA) Tympanic - U-shaped bone forming bony EAC Cranial nerves VII & VIII (CN7, CN8) Styloid - Forms styloid process after birth Internal carotid artery (ICA) Zygomatic Process - Zygomatic arch Jugular bulb (JB) External auditory canal is made up of lateral cartilaginous and medial bony components. Infection can penetrate inferomedially to the skull base and associated spaces via the fissures of Santorini (gaps in the EAC cartilage). External ear and EAC lymphatic drainage is to the parotid nodal chain. The medial margin of the EAC is the tympanic membrane, which attaches to the scutum and tympanic annulus. 33% pneumatized Petrous Apex 5% asymmetric pneumatization Axial graphic shows the petrous apex. The carotid artery is located along the anterior margin; CN6 and the trigeminal division of CN5 course over the anterior superior margin; the internal auditory canal and inner ear are at the posterior margin. Eustachian Tube symmetry direct Middle Ear & Mastoid comparison of the Hypotympanum -Empty matching ME – 3 parts slices Hypo Mesotympanum (Middle ear proper) Meso Posterior wall: 3 key structures Epi facial nerve recess, pyramidal eminence, sinus tympani Medial wall: 3 key structures 3P + 3M tympanic segment CN7, oval & round window Epitympanum (Attic) - above the line from the scutum tip to tympanic CN7 Tegmen tympani: roof of middle ear cavity Prussak space = lateral epitympanic recess Middle ear is divided into 3 components: Epitympanum, mesotympanum, hypotympanum. The epitympanum is defined as the cavity above a line from the scutal tip and tympanic segment of CN7. Its roof is tegmen tympani. The mesotympanum extends from this line The tympanic segment of the facial nerve is seen from the anteromedial geniculate ganglion to the posterior genu, where it changes to inferiorly to a line connecting tympanic annulus to base of the cochlear promontory. The hypotympanum lies inferior to this line. become the mastoid segment. The cog is seen crossing the anterior epitympanum. Epitympanum The cochleariform process (high on the cochlear promontory) is the annulus through which the tendon of the tensor tympani muscle turns toward the malleus. Stapes crura are visible. The stapedius muscle in the pyramidal eminence is distinguishable from the mastoid Mesotympanum segment of CN7. Coronalal CT Middle Ear & Mastoid Facial Nerve Epitympanum (Attic) - above the line from scutum to tympanic CN7 Oval Window Tegmen tympani - roof of middle ear cavity Prussak space = lateral epitympanic recess Mastoid sinus 3 key structures Aditus ad antrum - Connects epitympanum to mastoid antrum Cochlea Mastoid antrum - Large, central mastoid air cell Tegmen mastoideum - Roof of mastoid air cells Ossicles At the level of upper internal auditory canal, the aditus ad antrum (L. "entrance to the cave") is seen connecting the epitympanumto Right ME ossicles viewed from the front shows that the anterolateral malleus has a head, neck, & manubrium with lateral & anterior mastoid antrum (L. "cave"). Körner septum separates the mastoid antrum from squamous portion of the mastoid air cells. processes. The incus has a large body and short, long, & lenticular processes. The stapes has a head, crura, and footplate. Axial CT Carotid Jugular Stapes Malleus Incus Axial CT Inner Ear/Labyrinth Cochlear Aperture - opening from IAC fundus Cochlea Modiolus - central bony axis of cochlea (spiral ganglion) Vestibule Spiral Lamina - projecting to Basilar Membrane from Modiolus 3 spiral chambers of cochlea – 2 contain perilymph: Scala Vestibuli anterior & ascending Scala Tympani posterior & descending Perilymph to subarachnoid space via Cochlear Aqueduct Spiral Lamina Scala Media (cochlear duct) – contains endolymph Separated from scala tympani by Basilar Membrane Organ of Corti (hearing apparatus) - on Basilar Membrane MRI Spiral Lamina Membranous labyrinth from above. Key elements include ~ 2 1/2 turns of the cochlea, the meeting point of the superior and posterior IAC semicircular ducts (crus communis), and endolymphatic duct and sac. Endolymphatic duct has intraosseous and intradural components. oblique sagittal Inner Ear/Labyrinth MEMBRANOUS LABYRINTH Vestibule (utricle & saccule) ENDOLYMPH Semicircular Ducts fluid within structures of Scala Media (cochlear duct) membranous labyrinth Endolymphatic Duct & Sac PERILYMPHATIC SPACES PERILYMPH surrounding utricle & saccule (vestibule) within bony and around around semicircular ducts (SCCs) membranous labyrinth within scala tympani & vestibuli (cochlea) Graphic depicts cranial nerve relationships in fundus of internal auditory canal. The crista falciformis separates cochlear nerve and inferior vestibular nerve below from CN7 and superior vestibular nerve above. Bill's bar separates CN7 from superior vestibular nerve. HEARING Movement of Stapes transmits fluid waves via Oval Window Cochlear recess wave is transmitted to Scala Vestibuli of cochlea Waves in perilymph of scala vestibuli are transmitted via vestibular membrane to endolymph of Cochlear Duct This transmission causes displacement of Basilar Membrane - stimulates hair cell receptors in Organ of Corti Hair cell movement generates electronic potentials - converted to action potentials in cochlear nerve High frequency sounds at Cochlear Base, Low at Cochlear Apex Axial view of cochlea shows 3 scalar chambers - scala media, scala vestibuli & scala tympani. Bipolar cell bodies of the spiral ganglia within the modiolus send distal fibers to the organ of Corti and proximal fibers into the cochlear nerve. The cochlear nerve passes through the cochlear aperture into the fundus of the IAC. Cochlear Aperture CT Cochlear Nerve MRI Axial T2 MR image of inner ear reveals high signal membranous labyrinth within low signal bony labyrinth. Cochlea is divided by osseous spiral lamina into an anterior scala vestibuli & a posterior scala tympani. Scala vestibuli & tympani have equal transverse dimensions. Arcuate Eminence bony covering of Superior SCC Subarcuate artery runs under SCC surrounded by dura & CSF (subarcuate canaliculus - involutes by 5 yrs ) - Petromastoid Canal Superior vestibular nerve: Afferent balance fibers from utricle, superior SCC, & lateral SCC - superior vestibular ganglion Inferior vestibular nerve: Afferent balance fibers from saccule & posterior SCC - inferior vestibular ganglion Singular Nerve In the mid-internal auditory canal, 4 discrete nerves are visible. The anterosuperior facial nerve is normally slightly smaller than the anteroinferior cochlear nerve. The superior and inferior vestibular nerves are often joined by connecting fibers. Axial CT in a 9 month old shows a prominent subarcuate canaliculus extending from the medial petrous ridge (solid arrow), beneath the superior semicircular canal (open arrow), to the medial mastoid antrum wall (curved arrow) - thin bony wall at its medial margin. The malleus head articulates with the body of the incus. The lateral epitympanic recess is seen lateral to the ossicles. The short process The labyrinthine segment of the facial nerve exits the anterosuperior fundus of the IAC. The vertical crest (Bill’s bar) separates the of the incus is pointing into the aditus ad antrum. Körner septum is separating the lateral mastoid air cells from the mastoid antrum. anterior labyrinthine segment of CN7 from the posterior superior vestibular nerve canal. The cochlear nerve canal is connecting the anteroinferior fundus of the IAC to the cochlea. The cochlear nerve accesses the modiolus of Mid-cochlear image shows both the cochleariform process and the tendon of the tensor tympani muscle extending over to the malleus. the cochlea through the cochlear nerve canal. The posterolateral fundal bony wall abutts the medial vestibule. Multiple branches of the The incudostapedial articulation is between the lenticular process of the incus and the stapes head. The round window is at the base of vestibular nerves pass through this wall (the macula cribrosa) to the vestibule and semicircular canals. the basal turn of the cochlea. In this image, the normal cortex of the sigmoid plate is well seen. The sigmoid plate separates the mastoid air cells from the sigmoid sinus. Notice the cochlear aqueduct on the medial temporal bone wall. The tensor tympani tendon turns 90 degrees at the cochleariform process to cross the medial ME and attach to the malleus. The The labyrinthine segment of CN7 is merging together with the anterior tympanic CN7 above the cochlea. The cochleariform process and stapedius tendon emerges from the pyramidal eminence to attach to the stapes hub area. The 4 ossicle ligaments include the superior, tendon of the tensor tympani muscle are both visible. The petrous internal carotid horizontal segment can be seen below the cochlea. lateral, and anterior (not shown) malleal ligaments and the (posterior) incudal ligament. Image through the mid-mesotympanum shows the more superior epitympanum with the long and short processes of the incus forming Image of posterior mesotympanum with the 3