Within the Temporal Bone · Chapter 07 · Part II · Core dissections
The Antrum, Aditus and Epitympanum
Two routes to one space, and what changes when a landmark goes
Bench mode: one step per screen, large type, screen kept awake. Tap, use the arrow keys or say “next”.
- Specimen
- The bone from Chapter 6: cortical mastoidectomy done, canal wall and chain intact, side recorded
- Bench time
- One session; your instructor sets the target
- Tools
- Small diamond burr, round knife, curette, fine pick; angled endoscope if available
- View
- Low power for both routes; higher power at the incudostapedial joint
- Before this
- Chapter 5 (transcanal flap) and Chapter 6 (antrum, lateral canal, short process of the incus)
By the end you can
- Relate the antrum, aditus and attic from the mastoid and from the canal
- Open the lateral attic wall without touching the ossicles
- Divide the incudostapedial joint under vision before the incus is moved
- Remove the incus and malleus head as separate, recorded steps
- Reorient on the landmarks that remain and describe the final exposure exactly
Antrum, aditus and attic shown from the mastoid and from the canal; incus and malleus head removed as separate recorded steps; posterior canal wall kept.
Opening the facial recess (Chapter 8), drilling the anterior attic towards the geniculate region, or taking down the posterior canal wall.
The landmark chain
Each landmark leads to the next. Tap any one to see every station where it appears.
07.1 Connect the two routes
The antrum, aditus and epitympanum are one air space reached from two directions. From the mastoid you look forwards through the aditus to the short process of the incus; from the canal you look up past the scutum into the attic. Make the two views agree before you change either, then change the anatomy one recorded step at a time.
The antrum opens forwards through the aditus into the posterior attic. On its medial wall the lateral canal shows as smooth, dense, yellow-ivory bone; just in front, the short process of the incus points back into the fossa incudis, towards the facial recess. The attic holds the malleus head and incus body with their attachments; its roof, the tegmen, relates to the middle cranial fossa, and below lie the rest of the chain and the tympanic facial nerve. Movement given to the incus body reaches the stapes even when the stapes is out of sight.
Begin with the chain intact: it is the reference for every later, destructive step. If an ossicle is already lost, or Chapter 6 changed the anatomy, describe what is actually there and carry it forward in the record. Repeat the two-route comparison after every extension.
Never prove that two spaces communicate by passing an instrument through the aditus. Prove it with the view.
07.2 Decide the extent before you drill
Write down whether the exercise is inspection, atticotomy, ossicular removal or a wider epitympanectomy. Complete the limited inspection first; ossicular removal is a separate, planned extension, and a change of endpoint midway is recorded.
Keep the incus buttress while it helps orientation and support; an obstructing structure is not disposable just because a wider view is possible. The plan sets the endpoint, not the wish to show every recess through one opening: rotate the specimen or change route instead.
In the Harris and Linder atlas, epitympanotomy is a limited opening of the lateral attic wall with the ossicles kept; epitympanectomy adds removal of the incus and malleus head and a wider clearance. Usage varies, so record which wall you altered, which ossicles you kept and which space you exposed.
07.3 · The 6 stations
The antrum from the mastoid
- Clear debris and recover the orientation: tegmen above, sinus behind, canal wall in front. Record whether the canal wall and chain are intact.
- Name the antrum, the lateral canal on its medial wall and the short process of the incus in front.
- Look forwards through the aditus and describe the direction of the attic, without passing an instrument through it.
- Photograph the view, labelled for side and direction, with one landmark that the canal view will share.
Antrum, lateral canal and short process named from the mastoid; the photograph labelled.
You cannot see the incus. Widen the cavity under the tegmen at the antrum before you look further.
The attic from the canal
- Raise a tympanomeatal flap as in Chapter 5 and fold it forwards over the handle of the malleus.
- Remove the scutum and lateral attic wall from below upwards, the burr off the ossicles, mindful of the tegmen, lateral canal and facial nerve.
- Name the malleus head, the incudomalleolar joint, the incus body and the short process pointing back towards the aditus; find the suspensory ligaments and the tegmen above.
- Photograph the attic with the chain untouched and match it to the mastoid view.
Malleus head, incus body and short process seen from the canal and matched to the mastoid view.
The burr touches an ossicle. Stop, record it, and inspect the chain before going on.
Divide the incudostapedial joint
- Find a view that actually shows the joint; through the canal it lies posterosuperiorly.
- Separate the lenticular process from the stapes head, moving parallel to the footplate, never towards it; this limits movement transmitted during later attic work.
- Watch the stapes, not the knife: it must not rock. In a patient, movement reaching the footplate can injure the inner ear.
- Confirm the gap by eye. A concealed joint is not divided because the incus feels mobile.
A visible gap between the lenticular process and the stapes head, the stapes unmoved.
The stapes moves with the incus. Stop and review the direction of force with your instructor.
Remove the incus and reorient
- Release the incudomalleolar joint and the remaining incudal attachments deliberately, under vision.
- Lift the incus out with a controlled movement; never lever it against the footplate or rely on a sudden pull. Keep it, or its fragments, in a labelled container for study and reconstruction practice, recording side, prior state and any damage.
- Compare the field with your Station 2 photograph: the lateral canal and tympanic facial nerve now lie open on the medial wall. Describe the field from these.
- Trace the route from the mesotympanum to the attic through the tympanic isthmus, between the tensor tendon in front and the stapes behind.
The incus removed intact, and the field described from the landmarks that remain.
You are still navigating on the absent incus. Reorient on the lateral canal and the facial nerve.
The anterior attic
- Treat malleus head removal as a further planned step, not a consequence of removing the incus; agree the method with the supervising otologist and record what is retained.
- Divide the neck above the tensor tendon; keep the handle on the drum.
- Find the cog (the bony ridge dropping from the tegmen in front of the malleus head), the supratubal recess in front of it, the cochleariform process with the tensor tendon, the facial nerve running forwards to the geniculate region, and the tube below.
- Inspect the tensor fold area as an individual arrangement, not a diagram, leaving delicate folds intact. Review roof, canal wall and medial relations before more bone work.
Cog, supratubal recess, cochleariform process and facial nerve named in this bone.
You cannot tell where the attic ends and the geniculate region begins. Further anterior removal is an advanced extension, not this exercise.
Describe the final exposure
- Demonstrate the antrum, aditus and exposed attic from the mastoid and from the canal.
- Record side, routes, canal wall, chain and bone removed. Name the route that showed each recess; one you could not see is not visualised, never normal or absent.
- Separate observation from interpretation: soft tissue or erosion in a harvested bone cannot be diagnosed by appearance. Record a technical error alongside the anatomy it still shows.
- Save the exposure for Chapter 8: a good view through the aditus is not an identified facial recess.
Another surgeon could reconstruct your dissection from your record, without its title.
Your record says only “epitympanectomy done”. Rewrite it as a description.
07.4 Compare the routes
The microscope down the canal gives a straight line of sight and two free hands but misses the anterior recesses and the corners behind the ossicles; an endoscope looks round them, but a view is not an instrument path. The mastoid route keeps the canal wall but shows neither the anterior attic nor the stapes. Before enlarging an opening, decide whether the limit is the direction of view or the access for an instrument.
A low tegmen, dense bone or narrow attic may limit the exposure: accept it and agree the route with your instructor. A neat photograph can hide an unexamined space, so assessment covers the sequence and the specimen itself.
An exposed cavity and an inspected cavity are not the same thing.
07.5 Fault finding
| What you see | Probable cause | Correction |
|---|---|---|
| Tegmen breached above the attic | Bone removed upwards without a seen roof | Thin from below; keep the roof in view |
| Anterior attic declared normal | Seen only straight down the canal | Use an angled view; record what was not seen |
| Incus process broken on removal | Attachments not released before lifting | Release joint and ligaments first; keep and record the pieces |
| Work went on after the chain loosened | The change was not acknowledged | Stop, record the change and reorient before going on |
07.6 Viva at the bench
Does a view of the incus establish a complete anterior attic exposure?
No. The incus is in the posterior attic. The anterior attic (cog, supratubal recess, tensor fold area) is often hidden from a straight canal view and needs an angled view or a planned extension; a recess not seen is recorded as not visualised.
Why divide the incudostapedial joint before moving the incus, and how do you know it is divided?
Movement given to the incus reaches the stapes and, in a patient, can injure the inner ear. You know it is divided when you see a gap between the lenticular process and the stapes head, with the stapes unmoved, not because the incus feels mobile.
What is the cog, and what lies in front of it?
The cog is the bony ridge dropping from the tegmen in front of the malleus head. The supratubal recess lies in front of it, above the Eustachian tube.
One best answer
07.7 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 |
|---|---|---|---|
| Mastoid and canal views matched | |||
| Lateral attic wall opened, ossicles untouched | |||
| Incudostapedial joint divided under vision | |||
| Incus removed intact and recorded | |||
| Anterior attic landmarks named | |||
| Final record another surgeon could reconstruct |
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 you open an attic in the theatre
Sources and credits
- Harris T, Linder T. Mastoidectomy and epitympanectomy. The Open Access Atlas of Otolaryngology, Head & Neck Operative Surgery (Fagan J, ed.). University of Cape Town. CC BY-NC 3.0. med.libretexts.org/
- Companion video: Recurrent Cholesteatoma, endoscopic approach. Dr Bhushan Kathuria & Team. youtu.be/drC2paNs1jM
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 6: Cortical MastoidectomyChapter 8: The Facial Recess and Posterior Tympanotomy ›
Appears in: