Within the Temporal Bone · Chapter 05 · Part II · Core dissections
Transcanal Exposure and the Middle Ear
Raise the flap, read the medial wall, put it back
Bench mode: one step per screen, large type, screen kept awake. Tap, use the arrow keys or say “next”.
- Specimen
- Adult temporal bone with canal skin and drum preserved; side marked on the holder
- Bench time
- One session; most of it spent looking
- Instruments
- Speculum, round knife, sickle knife, fine suction, straight pick
- View
- Low power to inspect the drum; higher power to elevate and for the medial wall
- Before this
- Chapters 2–4: microscope, grip, orientation of a right and a left ear
By the end you can
- Document the intact drum and canal before any incision
- Raise a tympanomeatal flap in the right plane and enter the middle ear under control
- Preserve the chorda tympani and the ossicular chain throughout
- Name the structures of the medial wall and their relations
- Replace the flap and judge whether it would have healed
Middle ear entered and the medial wall named in order, chorda and chain intact, the flap replaced flat without tension and photographed beside the intact view.
Ossicular, stapes or posterior-recess work. A newly accessible structure is not in itself an indication to manipulate it; that work needs its own plan (Chapters 7, 11 and 12).
The landmark chain
Each landmark leads to the next. Tap any one to see every station where it appears.
05.1 Before you start
The transcanal approach is the shortest route into the middle ear and the one most often spoiled by haste. On the bench it teaches three things: a plane, a sequence of landmarks, and restraint.
A newly accessible structure is not in itself an indication to manipulate it; further ossicular, stapes or posterior-recess work needs its own plan.
The intact view is the first specimen. Record it before you change it.
05.2 · The 6 stations
Document the intact view
- Position the specimen so that the canal wall and annular region are visible. Choose a speculum that suits the canal without forcing it; improve position and light before enlarging access.
- Identify the handle of the malleus, its lateral process, the umbo, the cone of light anteroinferiorly, the pars tensa with its annulus, and the pars flaccida above the lateral process.
- Note canal curvature, bony overhangs, defects in the drum and any damage from harvesting.
- Photograph the view: it is the reference for flap replacement and ossicular assessment.
Malleus handle, umbo, pars tensa and pars flaccida named; the view photographed and labelled for side.
An overhang hides the annulus. Improve the position and light first.
Plan and cut the flap
- Plan the flap as your instructor demonstrates, long enough for the reconstruction you intend later: a short flap cannot be lengthened.
- Make two radial cuts, superior and inferior, and join them with a curved cut in the canal skin lateral to the annulus.
- Cut through skin and periosteum to bone in one deliberate pass, and leave the annulus uncut.
Three cuts that meet, through to bone, with the annulus untouched.
A cut runs into the drum. Record it; it will define what the flap can cover.
Elevate to the annulus
- Raise the skin from the canal bone with the instrument against bone, supporting the flap rather than stretching it; keep it moist.
- As the annulus is approached, identify its position and elevate it carefully from the sulcus.
- Recognise the transition into the middle ear; do not achieve it by an uncontrolled release of force.
- Protect the chorda tympani as it comes into view posterosuperiorly, running between the long process of the incus and the handle of the malleus. A delicate strand of uncertain identity is not expendable.
Annulus out of the sulcus, the middle ear entered under control, the chorda seen and intact.
The flap tears or the plane is lost. Return to bone and re-elevate from there.
Read the medial wall
- Keep the flap folded forwards without tension. Identify the promontory and the ossicular chain: long process of the incus, incudostapedial joint and stapes.
- Relate the oval and round window regions to them: the round window niche lies posteroinferior to the promontory.
- Above the oval window, the tympanic segment of the facial nerve; posteriorly, the pyramidal eminence and stapedius tendon; anteriorly, the cochleariform process with the tensor tympani tendon.
- Turn the view towards the epitympanum, hypotympanum and protympanum as far as it permits.
Every structure above named in order, in this bone, without a prompt.
You are reaching into a recess you cannot see. Change the view; never pass a hook whose tip you cannot see.
Test the chain
- Inspect the joints and attachments before any movement; record a pre-existing dislocation or missing structure first.
- Apply gentle, controlled movement at the handle of the malleus under supervision, and watch the stapes, not the instrument.
- Recognise how movement at the incus reaches the stapes. Fixation changes the chain: do not interpret its movement as live mechanics.
- If ossicular removal is planned later, document the intact relationships now. Separate a joint deliberately when that exercise comes; never pull an ossicle free.
Transmission observed and recorded, with the chain exactly as found.
The incus moves but the stapes does not. Record it and inspect the joint before any further touch.
Replace and judge the flap
- Return the annulus to the sulcus and lay the flap back on the canal bone to assess its reach and position.
- Check the annulus, drum, canal skin and chorda for damage made on the way in.
- Photograph the result beside the intact view of Station 1.
The flap lies flat without undue tension and would cover the bone if it healed.
The flap is short or torn. Record it and how the instrument movement or access contributed: a clean exposure through a torn flap is not a reconstructible approach.
05.3 Error lab · chorda tympani divided
On the bench: note where it was cut and which instrument did it. Trace both ends.
In the theatre: a divided chorda can alter taste on that side of the tongue, and a stretched one can be as troublesome as a cut one.
The lesson: the chorda appears as soon as the annulus is lifted posterosuperiorly. Look for it before you need to.
A good tympanotomy leaves the ear as it was found, except that you now know it.
◉ See it on real specimens
Real dissection and operative photographs published openly by other surgeons and institutions. They open on the original site with full credit to the authors; they are not copied into this companion. Compare them with the drawings above.
05.4 Fault finding
| What you see | Probable cause | Correction |
|---|---|---|
| Hole in the posterior drum | Instrument turned towards the drum at the sulcus | Keep the blade on bone; lift the annulus, not the membrane |
| Chorda stretched or divided | Taken as a band of mucosa | Treat every strand behind the annulus as the chorda |
| Middle ear entered with a jolt | Force applied before the annulus was free | Free the annulus before entering |
| Incus displaced | Ossicle used as a lever or hand rest | Test only at the handle; never work within the chain |
| Recesses reported as normal | Not visible from the canal axis | Record them as not seen; change the view |
05.5 Viva at the bench
Why inspect the chain before you move it?
So that a pre-existing dislocation, fixation or missing structure is recorded as found, and not mistaken for damage you caused or hidden by your own movement.
Where does the chorda tympani appear when the annulus is lifted, and how is it related to the incus and malleus?
Posterosuperiorly, as soon as the annulus is lifted; it runs forwards lateral to the long process of the incus and medial to the handle of the malleus.
What lies above the oval window, and what lies anterior to it?
Above it, the tympanic segment of the facial nerve; anterior to it, the cochleariform process with the tensor tympani tendon.
One best answer
05.6 My dissection log
Saved on this device only. Print it or send the summary to your fellowship coordinator for review.
Score the dissection · review order
| Item | 0 · not achieved | 1 · partly | 2 · achieved |
|---|---|---|---|
| Intact drum and canal documented | |||
| Flap cut through to bone, annulus uncut | |||
| Middle ear entered without a jolt | |||
| Chorda tympani found and intact | |||
| Medial wall named in order; unseen recesses recorded | |||
| Flap replaced flat without tension |
The review order is a teaching method, not a validated scoring instrument. Structured end-product scales such as the Welling scale have been studied for rater reliability; they assess the dissection, not operative outcome, but they make feedback specific.
Before your first tympanotomy in the theatre
Sources and credits
- Companion video: Endoscopic Tympanoplasty, hearing restoration (transcanal access to the middle ear). Dr Bhushan Kathuria & Team. youtu.be/QTeuGcIcSo4
Real dissection photographs with numbered drawings: Bassett Collection, Stanford University (CC BY-SA 4.0). Classic anatomical and operative plates: Gray’s Anatomy of the Human Body (1918, drawings by H. V. Carter) and Burghard’s A System of Operative Surgery (1909), both public domain, credited beside each plate. Remaining diagrams and charts: Dr Bhushan Kathuria & Team, not to scale. Operating-theatre frames and clips: our theatre, patient consent taken, identity not shown. Atlas photographs: Open Access Atlas of Otolaryngology (CC BY-NC 3.0), with their authors credited beside each image. This edition uses no AI-generated images. For professional education alongside supervised instruction and local protocols.
Dr Bhushan Kathuria & Team · Reg. No. HN-017323, Haryana Medical Council · A GeNext MedEd Foundation surgical education initiative.
‹ Chapter 4: Reading Temporal Bone ImagingChapter 6: Cortical Mastoidectomy ›
Appears in: