1. A STEPWISE APPROACH TO MIDDLE EAR ANATOMY A STEPWISE APPROACH TO MIDDLE EAR ANATOMY Build-A-Box J McCarty | J Dornhoffer | R Riascos | E Angtuaco | RT Fitzgerald #1444 eEdE-156

2. PURPOSE & DISCLOSURE ANATOMY IMAGING PATHOLOGY MCQ’S To provide a step-by-step approach to the complex anatomy of the middle ear – building the tympanic cavity “box” and all of its contents from the ground up. John L. Dornhoffer, MD - inventor of the Olympus Dornhoffer Interpositional PORP Prosthesis, Dornhoffer HAPEX PORP/TORP & Dornhoffer Micron Titanium Footplate Shoes The remaining authors have no disclosures.

3. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box THE BOX However, the tympanic cavity floor & roof are more spherical, bowing outward from the center of the cavity. The tympanic cavity and its contents comprise the middle ear. Although irregularly shaped, this cavity within the temporal bone has been compared to a box with 6 sides.

4. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box Sound Collection ++ ExternalMiddleInner It is useful to keep a broad understanding of ear anatomy and function in mind when studying the detailed subject of otology. THE EAR The ear is divided into 3 parts. Pinna & External Auditory Canal Tympanic Cavity & All of Its Contents Cochlea, Vestibule, Semicircular Canals Sound Conduction Nerve Impulse Formation

5. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box Ossicular Chain = Malleus + Incus + Stapes STEP 1: OSSICULAR CHAIN The tympanic membrane converts sound collected by the external ear into vibrations. The ossicles then transmit and amplify sound towards the oval window and inner ear. The middle ear aids in sound conduction.

6. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box Short Process of the Incus Head of the Malleus Manubrium of the Malleus Long Process of the Incus Footplate of the Stapes Lateral Lenticular Process of the Incus Tympanic Membrane Anterior Process of the Malleus Lateral Process of the Malleus Anterior Crus of the Stapes OSSICULAR CHAIN ANATOMY LATERAL MEDIAL

7. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box CT OF THE OSSICULAR CHAIN MALLEUS INCUS STAPES 3DVRAxialCoronalSagittal Head Handle Head Lateral Process Neck Short Process Long Process Lenticular Process Body Short Process Body Long Process Short Process Lenticular Process Body Capitellum Footplate Capitellum Posterior Crus Anterior Crus Posterior Crus Anterior Crus Posterior Crus Anterior Crus Capitellum

8. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box CASE BASED MULTIPLE CHOICE QUESTION (MCQ) Case 1 is an example of a: A.Foreign body B.Stapedial prosthesis C.PORP D.TORP The most common repairable cause of ossicular prosthetic failure is: A.Migration B.Recurrent cholesteatoma C.Trauma Prostheses may migrate or dislocate. Stapes prostheses most commonly migrate inferiorly. Occasionally one may migrate medially through the oval window CASE 1 Malleal & incudal prosthesis “TORP” = Total Ossicular Replacement Prosthesis “PORP” = Partial Ossicular Replacement Prosthesis Native stapes Coronal Axial

9. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box STEP 2: MUSCULATURE S TAPEDIUS Dampens Sound Attaches to Head of the Stapes Innervation: CN VII T ENSOR T YMPANI Dampens Sound Attaches to Neck of the Malleus Innervation: V3 Two Muscles: Stapedius + Tensor Tympani

10. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box AXIAL IMAGING The tensor tympani is a thin elongated muscle that resides superior to the Eustachian tube. Only a small portion of this muscle traverses the tympanic cavity. The stapedius is not well visualized on CT. Tensor Tympani Eustachian Tube Sequential axial images (1 = cranial, 4 = caudal) 1 2 34 2 3 4 1

11. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box CASE BASED MCQ Tumor invasion of the facial nerve tympanic segment would cause: A.Hyperaccusis B.Conductive hearing loss C.Sensorineural hearing loss Facial nerve segments labeled 1 & 2 on the coronal image are: A.Canalicular & genu B.Genu & labyrinthine C.Labyrinthine & tympanic D.Tympanic & mastoid Damage to the proximal facial nerve could lead to denervation of the stapedius and inability to adequately dampen sound. Coronal Axial 2 1 The “snails eyes” are the labyrinthine & tympanic segments of the facial nerve on coronal CT. CASE 2

12. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box STEP 3: LIGAMENTOUS SUPPORT Several ligaments stabilize the suspended ossicular chain. Posterior Incudal Ligament Superior Malleal Ligament Anterior Malleal Ligament

13. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box MALLEAL SUPPORT Superior Malleal Ligament SCUTUM * 4 Ligaments + Tensor Tympani Muscle Lateral Malleal Ligament Anterior Malleal Ligament (attachment) TEGMEN TYMPANI The malleus has the strongest support of the 3 ossicles.

14. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box Annular Ligament Stapedius Incudostapedial Joint INCUDAL & STAPEDIAL SUPPORT Posterior Incudal Ligament STAPEDIAL The annular ligament surrounds the footplate of the stapes, and stabilizes it to the oval window. INCUDAL The single posterior incudal ligament stabilizes the incus within the tympanic cavity.

15. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box The ligaments stabilizing the ossicular chain may not be well visualized on CT. However, here the posterior incudal and anterior malleal ligaments are seen AXIAL IMAGING Posterior Incudal Ligament Anterior Malleal Ligament

16. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box CASE BASED MCQ CASE 3CASE 4 Which ossicle is most commonly dislocated secondary to trauma? A.Malleus B.Incus C.Stapes What is the most common ossicular traumatic injury? A. Incudal fracture B. Malleal fracture C. Malleoincudal joint disruption D. Incudostapedial joint disruption The incus is the largest ossicle. It also happens to have the weakest support. Disruption of the malleoincudal joint without lateral incudal displacement. Ice cream only separated from cone. Laterally dislocated incus abuts the lateral wall of the epitympanum. Ice cream that fell of the cone. Incudal body Malleal head Incudal body Malleal head Although malleoincudal joint disruption is more often identified on CT, incudostapedial disruptions occur more often. Axial

17. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box STEP 4: NERVES J ACOBSON ’ S N. Branch of CN IX Courses over Cochlear Prominence Innervation: Sensory C HORDA T YMPANI Branch of CN VII Courses b/w Incus & Malleus Innervation: Taste Anterior 2/3 of Tongue TRAVERSING NERVES

18. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box Nerves In & Around the Middle Ear J ACOBSON ’ S N. C HORDA T YMPANI S TAPEDIUS N. T YMPANIC S EGMENT OF F ACIAL N. M ASTOID SEGMENT OF F ACIAL N. CN IXCN VII Course Inferior tympanic canaliculus  cochlear prominence Mastoid segment origin  B/w incus & malleus Arises close to pyramidal eminence  stapedius Medial wall of tympanic cavity Pyramidal eminence to stylomastoid foramen InnervationSensory Taste Anterior 2/3 of Tongue Stapedius**

19. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box 2 3 4 1 2 4 1 CN VII Tympanic segment CN VII Mastoid Segment AXIAL IMAGING CN VII Posterior Genu CN VII Mastoid Segment 3 Sequential axial images (1 = cranial, 4 = caudal)

20. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box CASE BASED MCQ What are the findings on clinical otoscopy? A.Red retrotympanic mass B.Blue retrotympanic mass C.White retrotympanic mass What is the most likely diagnosis? A. Glomus tympanicum B. Glomus jugulotympanicum C. Aberrant carotid artery D. Persistent stapedial artery There’s a small red retrotympanic mass overlying the cochlear promontory without underlying erosions. Coronal CASE 5 Retracted TM Retracted TM Specimen Otoscopy Glomus jugulotympanicum would have dehiscence of the middle ear floor & warrant a different surgical approach. Intact middle ear floor Rounded mass on the promontory Malleal Handle Red Mass Stapedial Head Promontory

21. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box STEP 4: NERVES T YPE L OCATION N ERVE P ARAGANGLIA Glomus TympanicumCochlear PromontoryCN IX (Jacobson’s) Glomus JugulareJugular ForamenCN X Glomus VagaleB/w ICA & IJCN X Carotid Body Glomus Carotid bifurcation (splaying ICA & ECA) CN X “Glomus” = “Paraganglioma” Arise from paraganglia (normal structures which accompany CN & ganglia) “Glomus” = “Paraganglioma” Arise from paraganglia (normal structures which accompany CN & ganglia)

22. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box STEP 5: WALLS Sinus Tympani Facial N. Recess Pyramidal Eminence “Roof” or Tegmen Tympani “Anterior” or Carotid Wall “Floor” or Jugular Wall “Posterior” or Mastoid Wall “Medial” or Labyrinthine Wall

23. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box AXIAL IMAGING AAA = aditus ad antrum, E = Eustachian tube, Co = Cochlea, CP = cochlear promontory, ST = sinus tympani, PE = pyramidal eminence, FR = facial recess, RW = round window, CC = carotid canal, JB = jugular bulb 2 3 4 1 5 6 2 4 1 56 AAA h Lateral Wall/TM JB ST PE Medial wall Posterior Wall FR Lateral Wall/ TM CC CP E E RW Anterior Wall CP Floor Anterior Wall Medial wall

24. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box CASE BASED MCQ CASE 6 From which structure does the mass arise? A.Tympanic Membrane B.Ossicular Chain C.Tegmen Tympani What is the most likely diagnosis? A.Squamous Cell Carcinoma B.Cerumen C.Verruca Vulgaris D.Glomus A soft tissue attenuation stellate mass arising from the TM projects into the external auditory canal. A benign cutaneous wart cause by human papillomavirus (HPV). Axial Coronal TM involvement is very rare – until 2013, there were no reports of verruca on the TM in the English literature. This mass arises from the TM – the lateral wall of the middle ear – and protrudes into the EAC. Stellate mass TM Stellate mass

25. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box CASE BASED MCQ CASE 7 What is the diagnosis? A.Cholesteatoma B.Glomus Tympanicum (GTP) C.Glomus Jugulotympanicum (GJP) D.Metastasis This mass arises in association with which nerve? A.CN VII B.CN VIII C.CN IX D.CN X A destructive soft tissue mass erodes through the middle ear floor and extends superiorly – overlying the cochlear promontory. Arnold’s Nerve – a branch of CN X. Axial Coronal Involvement of the middle ear floor is the distinguishing factor differentiating GTP from GJP and necessitates a different surgical approach. This mass causes permeative changes of the tympanic cavity floor and protrudes into the middle ear. Rounded mass Permeative changes Mass

26. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box STEP 6: SPACES The middle ear is further divided into several spaces. Epitympanum Mesotympanum Hypotympanum

27. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box CROSS SECTIONAL IMAGING Epitympanum Mesotympanum Hypotympanum Posterior Tympanum Mesotympanum Protympanum Coronal CT Axial CT

28. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box CASE BASED MCQ CASE 7 In which space does the mass reside? A.Protympanum B.Mesotympanum C.Prussak’s What is the most likely diagnosis? A.Cholesteatoma B.SCC C.Cerumen A small soft tissue mass resides in the epitympanum, eroding the TM. Cholesteatomas can be either congenital (2%) or acquired (98%). Otoscopy Coronal This mass extends through Prussak’s space, blunts the scutum and abuts the TM. Epitympanic mass Acquired cholesteotomas are most often seen in the epitympanum, medial to the pars flaccida (82%).

29. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box PRUSSAK’S SPACE Lateral Malleal Ligament Malleal Neck Tympanic Membrane Lateral Process Prussak’s Space Coronal

30. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box STEP 7: ADJACENT STRUCTURES Eustachian Tube Cochlear Promontory Aditus Ad Antrum Round Window Oval Window

31. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box AXIAL IMAGING AAA = aditus ad antrum, FN = facial nerve, TT = tensor tympani, E = Eustachian tube, Co = Cochlea, CP = cochlear promontory, ST = sinus tympani, PE = pyramidal eminence, FR = facial recess, RW = round window, CC = carotid canal, JB = jugular bulb 2 3 4 1 5 6 2 4 1 56 AAA h TM JB ST PE FN TT FR TM CC CP E E RW Co CP

32. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box CASE BASED MCQ CASE 7 What is the most likely diagnosis? A.High riding jugular bulb B.Aberrant carotid artery C.Glomus jugulotympanicum What is the most common clinical presentation? A.Sensorineural hearing loss B.Conductive hearing loss C.Pulsatile tinnitus D.Otalgia The carotid canal is normal & there is no permeative destruction of the floor. GTP, GJP, & aberrant ICA’s also present with tinnitus. Coronal Axial An enlarged & high riding jugular bulb extends along the middle ear floor Thinned posterior wall JB The overlying bone is thin and remodeled.

33. Introduction Ossicles Muscles Ligaments Nerves Walls Spaces Adjacent Final Box FINAL MIDDLE EAR BOX Chorda Tympani N. Eustachian Tube Ossicular Chain Cochlear Promontory Tensor Tympani Sinus Tympani Facial N. Recess Pyramidal Eminence Aditus Ad Antrum Round Window Stapedius Oval WindowJacobson’s N.

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35. THANK YOU Jennifer McCarty, MD Twitter: @JMcCartyMD Email: jmccarty@uams.edu PGY5 Radiology Resident Department of Radiology University of Arkansas for Medical Sciences John L. Dornhoffer, MD, FACS Professor of Professor and Vice-Chair Samuel McGill Chair in Otolaryngology Research Department of Otolaryngology University of Arkansas for Medical Sciences Ryan T. Fitzgerald MD Assistant Professor of Radiology Department of Radiology, Neuroradiology Division University of Arkansas for Medical Sciences Roy Riascos, MD Associate Professor of Neuroradiology Chief, Division of Neuroradiology The University of Texas Health Sciences Center at Houston Edgardo Angtuaco, MD, FACR Professor, Department of Radiology Chief, Division of Neuroradiology and MRI University of Arkansas for Medical Sciences