Discovering Middle Ear Anatomy by Transcanal Endoscopic Ear Surgery: A Dissection Manual

The overall goal of this endoscopic dissection manual is to teach endoscopic middle ear anatomy and train basic skills for endoscopic ear surgery. This method improves the understanding of middle ear anatomy and its variability as recorded through an endoscope. The proposed dissection manual offers a systematic guide through the endoscopic middle ear dissection techniques.

The main advantage of this technique are the wide angled, panoramic views offered by the endoscope. Moreover, the surgeon is able to approach and magnify the structures as much as needed. The use of angled scopes inside of the middle ear allows the surgeon to look around the corner.

Begin by introducing the zero degree, three millimeter diameter and 15 centimeter length endoscope into the external auditory canal of the prepared anatomical specimen. As a first task, use the suction tube to clean ear wax from the external auditory canal. Then, rinse with water.

Cut the hair inside the external auditory canal with a pair of small scissors to prevent the endoscope from becoming dirty. Inspect the tympanic membrane. Identify the malleus with its short process, manubrium, and umbo, the annulus of tympanic membrane and the pars flaccida, or shrapnel membrane.

Use a sickle or a round knife to incise the EAC skin superiorly, slightly anterior to the short process of the malleus. Extend the incision to the posterior, superior portion of the EAC, and lengthen the incision to the anterior and inferior border of the tympanic membrane to configure a triangular shaped flap. With the 45 degree angled round knife, expose the bone and elevate the skin until the annulus is reached.

Then, elevate the annulus with the round knife to access the tympanic cavity. Use the Thomasin dissector to mobilize the annulus inferiorly and anteriorly. Identify the posterior lateral ligament of the malleus.

Grasp the ligament with Hartmann forceps, and gently pull it in the direction of the umbo until the short process of the malleus is revealed. Gently dissect the anterior Prussak Space until the anterior, superior insertion of the annulus is visible. Now, identify the annulus, chorda tympani, posterior malleolar ligament, lateral malleolor ligamental fold, anterior malleolar ligamental fold, and Prussak Space.

Continue the dissection from the short process of the malleus, and then use a needle dissector to incise the periosteum of the malleolar handle towards the umbo. Detach the tympanic membrane from the manubrium. A dry cottonoid may be helpful, since it facilitates the identification of the correct layer and its dissection.

Once the umbo is reached, use micro scissors to cut the remaining fibrous layer of the TM.Now, position the whole flap on the anterior wall of the EAC to allow free access to the tympanic cavity. Enter the epitympanum with the zero degree endoscope. Identify the chorda tympani, the subdivisions of the malleus, and the incus.

Proceed with the identification of the epitympanic diaphragm and the tympanic isthmus, between the cochleariform process and the long process of the incus. Now, identify the tenser tympani muscle with its tendon and bony canal. Still using the zero degree endoscope, explore the mesotympanum and identify the subdivisions of the stapes, and the tendon of the stapedial muscle emerging from the pyramidal eminence.

Inspect the promontory bone and Jacobson nerve associated with the inferior tympanic artery. Next, remove any adherences around the entrance to the retro tympanum. Identify the facial recess, posterior sinus, sinus tympani, ponticulus, subiculum, styloid eminence, Fustice bone, subtympanic sinus, area conchimerida, round window niche with tegmen, anterior and posterior pillar, round window membrane, subcochlear canaliculus, and funiculus.

Change the position of the surgeon to the contralateral side to facilitate access to the retro tympanum. And repeat the exploration using a 45 degree angulated optic. Next, view the hypotympanum and estimate the localization of the jugular vein bulb if not visible.

Proceed to the protympanum, and identify the protyniculus, internal carotid artery, and Eustachian tube. To explore the medial epitympanum and the antrum, we need to perform an attichotomy. Start to remove the scutum with a curette.

Once the body of the incus is uncovered, disarticulate the incudostapedial joint and remove the incus. With a curette, complete the removal of the scutum. Identify the tympanic segment of the facial nerve, the lateral semicircular canal, the antrum, the COG, or transverse crest, and the tegmen tympani.

Finally, cut the anterior malleolar ligaments and the tendon of the tenser tympani muscle and remove the malleus. Explore the anterior epitympanum, and geniculate ganglion. Observe that the tenser tympani muscle and the lateral semicircular canal are in line, crossed by the facial nerve.

This concludes the complete anatomical dissection of the middle ear. In the following photographs, the anatomical structures are illustrated according to the progress of the dissection. This image illustrates the Prussak Space and the malleolar ligaments.

This photograph demonstrates the anatomy after complete TMF elevation. The wide angle view allows the visualization of the mesotympanum and hyptotympanum, as well as parts of the epitympanum, retrotympanum, and protympanum. Here, the superior retrotympanum is shown as it appears in a 45 degree endoscope, while the surgeon is standing on the opposite side of the table.

This photograph illustrates in detail the protympanum with a dehiscent ICA. Finally, after removal of the ossicular chain and the transcanal attichotomy, the epitympanum is inspected until the lateral semicircular canal and the antrum, as shown here. The endoscope allows the preparation and observation of the delicate middle ear structures through the external auditory canal.

Hence, no bone has to be removed for access purposes, and the anatomy may be studied in its natural state. Moreover, the endoscope allows very close observation of any anatomical structures, and therefore also magnification without losing elimination. Once mastered, this technique may be introduced into your daily surgical routine.

Since it is a one-handed surgical technique, we would like to remind you that it is important to start with basic otological procedures, such as ventilation tube insertion or type one tympanoplasty.