Mastering “The Mystic Mastoid” Part 1

As discussed in the previous blogs, due to various reasons, it has become difficult to have the experience of cadaveric bone dissection. And as virtual methods of dissection lack the feel of real size three dimensional bones, only option remaining is the artificial temporal bone.

The first ever recorded hands-on dissection workshops were conducted by the Father of Surgery, Sushruta, born in Varanasi around 800 BCE.

In his elaborate treatise on surgery, named Sushruta Samhita, there is a detailed description of his methods of teaching surgery to his students. Using gourds and melons and such to represent the bodily cavities and using various types of threads and needles made from different materials, he used to encourage his disciples for hands-on practice of various surgeries. Sushruta used to perform not less than 300 different surgeries. Some of his surgical methods are followed in modern surgery till date. There is no doubt about the benefits of the preop hands-on practice of the surgery.

Dissection

Having the correct anatomical details and having the matching haptic feel is the main asset of these artificial bones which the writer uses during his hands-on dissection workshops.

These bones, as they mimic the hardness of the cadaveric bones, can be easily fitted in any temporal bone holder. The instrumentation needed is also similar, a microdrill with proper set of burrs of different sizes, suction-irrigation apparatus, operating microscope, and microear instruments are all that are needed.

Photograph: faculty guiding a delegate — appears on the live site

Every delegate drills their own bone under faculty guidance, station by station.

1. The layerwise removal of outer cortex of the bone opens up the superficial air cells. The thick plate of bone, which is the Koerner’s septum, can be easily identified. Drilling out this septum leads to the mastoid antrum. To identify the antrum, the most reliable landmark is the bulge of the lateral semicircular canal. Widening the antrotomy and skeletonizing the dural and sinus plates completes the cortical mastoidectomy procedure.
2. Next to practice is the facial recess approach to the middle ear. It has to be done in a sequence as, thinning out the posterior meatal wall, finding the tip of short process of incus, starting the dissection in line of the fossa incudis, finding the layout of the facial nerve and the chorda tympani, and then opening the recess in between the angle of these two nerves. Widening the facial recess, which is a triangle between the facial nerve, the chorda tympani, and the incudal buttress, leads to the identification of the round window niche.
3. For the cochlear implant workshops, the techniques of cochleostomy and the insertion of a dummy electrode along the correct trajectory are taught.
4. Thinning of the sinus plate and the bone medial to it give the topologic layout of the posterior fossa dural plate. Here, below the level of Donaldson’s line, the dura is opened to give the idea of the endolymphatic sac surgery.
5. Then the dissection proceeds for the facial nerve decompression technique. Keeping the posterior canal wall intact, it is taught to decompress the facial nerve from stylomastoid foramen to the first genu. Though skillful, if done with proper care, it is possible to decompress the nerve in its entirety.
   Photograph: facial nerve & vascular anatomy — appears on the live site
   The complete middle ear cleft with facial nerve and vessels, for decompression and re-routing work.
6. Next comes the hands-on practice of extended facial recess approach. Very useful for the removal of glomus tympani tumours, this approach gives access up to the depths of the hypotympanum.
7. Removal of the outer attic wall and the exposure of the ossicles completes the atticotomy or epitympanotomy procedure. If the head of malleus and the body of incus are taken out, the procedure will be epitympanectomy.
8. Hands-on dissection then proceeds to the removal of the posterior meatal wall so as to complete the modified radical mastoidectomy.
9. Labyrinthectomy is the most difficult and the most destructive procedure. Sequential opening of the semicircular canals is the skill to be learnt only by hands-on practice under a proper tutelage.
10. More difficult to learn is the translabyrinthine approach to the internal auditory meatus. In this dissection, the translabyrinthine approach yields the confidence to identify all the four nerves in the internal auditory meatus. Selective sectioning of the superior vestibular nerve can also be practiced.
11. Bones having weaker incudostapedial joints are made for hands-on practising the stapedotomy surgery. Similarly, the bones sans incus are used for hands-on practising of ossiculoplasty by incus interposition techniques.
12. Tympanoplasty practice is taught on bones with a tympanic membrane.
13. Many other procedures can be learnt on these artificial bones. Bill’s island technique for a very forward lying sinus plate, if learnt on this bone, will always prove helpful during surgeries on a contracted mastoid. Repair of lateral semicircular canal fistula, or of the dural breech, or even sinus plate erosion, and many more are possible to learn on these artificial bones.

Get a good instrument set for dissection and procure this artificial bone, then you are ready for the hands-on practice of all the mastoid surgeries on a single artificial temporal bone. If want to practice in an advanced way, ask for a difficult bone. If not able to do any of this, be on a lookout for the KBI SkillBridge hands-on workshops held periodically at the KBI Skill Lab. And never hesitate to write in with anything you want to ask about this hands-on experience.

Train on this bone

The models and programmes described above, at ProGuide.

• The temporal bone models— basic, complete and task-based
• Your own model from a CT scan— built from your patient’s own anatomy
• KBI SkillBridge workshops— dates, fees and registration
• Ask a question— our programme experts answer seven days a week

Writer

Dr Prashant M Naik

MS (ENT), DLO

Nagpur, India