5The Transcanal Approach to the Middle Ear

FA corridor that is already there

Every other route to the middle ear has to be made: the post-auricular approach lifts the whole auricle forward off an incision behind the ear, the endaural approach cuts between tragus and helix, and the transmastoid route drills a cavity through solid bone. The transcanal— or permeatal— approach is different in kind, because the corridor it uses is one nature has already provided: the external auditory canal itself. Nothing is incised on the outside of the head and no bone need be removed; the surgeon simply works down the existing lumen of the canal toward the tympanic membrane [2018].

That single fact — that the approach borrows an existing passage rather than creating a new one — is the source of all its strengths and all its limitations. Its strengths are the strengths of doing less: no external scar, less soft-tissue dissection, less postoperative pain, and a quicker return to normal life[2021]. Its limitations are the limitations of a fixed, narrow, slightly curved tube: whatever the canal will not let you see, you cannot reach. The art of the transcanal approach is therefore the art of judging, before you start, whether this particular canal will show you everything this particular operation needs.

For ossicular reconstruction this judgement is unusually clean, because much ossiculoplasty is, by its nature, a low-exposure operation. A prosthesis set from a stapes head to the underside of the drum, or a sculpted incus dropped between malleus and stapes, occupies a small, central, well-lit part of the middle ear — the mesotympanum — that the canal points almost directly toward. When the disease that damaged the chain has already been dealt with, the reconstruction that remains is frequently within the canal’s honest reach.

FHow the corridor is opened

The transcanal approach begins with exposure of the canal itself, classically through an aural speculum of the largest comfortable size that the canal will admit, held steady while the surgeon works coaxially down its axis with the operating microscope. The deep meatal skin is infiltrated with a vasoconstrictor to lift it and to keep the small field dry, because in such a confined space even minor bleeding floods the view.

Access to the middle ear is then gained by raising a tympanomeatal flap. A curved incision is made in the skin of the posterior bony canal, a few millimetres lateral to the annulus, and the flap of canal skin and the attached posterior drum is elevated medially until the annulusis lifted out of the tympanic sulcus and the middle ear is entered. The chorda tympani is identified and preserved as the flap is turned forward, and the mesotympanum — promontory, round window niche, oval window, stapes and the eroded ossicular remnant — comes into view. Because the whole working space is the diameter of the canal, the instruments are fine, the movements small, and good haemostasis is not a courtesy but a precondition[2019].

The key conceptual point for the beginner is that the line of sight is fixed by the geometry of the canal. The microscope looks straight down the tube; the surgeon can angle a little by tilting the patient’s head and the scope, but the canal walls define a cone of vision, and structures that lie outside that cone — tucked behind the anterior canal wall, or hidden in the posterior recesses — are simply not on display. The widget below makes that geometry explicit.

TWhen the canal is enough

The transcanal approach earns its place whenever the operation’s exposure demands are modest and the canal’s anatomy is favourable. The paradigm is the second-stage or otherwise isolated ossicular reconstruction: the tympanic membrane is intact and aerated, the middle-ear disease was cleared at a previous operation (or, in trauma, was never present at all), and what remains is a discrete conductive gap to close [2018]. In this setting a partial ossicular replacement prosthesis (PORP) onto a mobile stapes superstructure, or an incus interposition bridging malleus to stapes, is precisely the kind of central, low-profile work the canal points toward.

The advantages of choosing the canal in such cases are concrete. There is no external incision and therefore no visible scar; the natural architecture of the canal is preserved; operative time is reduced; and — because so little tissue is disturbed — postoperative pain and recovery are less than after a post-auricular or endaural operation [2021, 2021]. For a patient facing a second anaesthetic for a hearing operation, these are not trivial gains.

Use the selector below to see how these factors combine: a single adverse feature usually means addressing that feature (often by canalplasty) or simply keeping conversion in reserve, whereas several together argue for starting with a wider corridor.

TThe limits of the view, and how to read them

The honest weakness of the transcanal approach is exposure, and the trainee must learn to recognise the anatomy that defeats it before the operation begins rather than halfway through. The single most important obstacle is the anterior canal wall. A prominent anterior bony bulge, or a narrow and tortuous canal, throws the anterior tympanic annulus into shadow; the anterior mesotympanum, the protympanum and the eustachian-tube orifice disappear behind the overhang, and with a microscope looking straight down the tube there is no way to see around it. A medialised malleus handle compounds the problem by crowding the central field [2018].

When the bony anatomy obstructs the view, the surgeon has two honest options. The first is canalplasty— drilling away the obstructing anterior bulge to widen and straighten the corridor — but meaningful canalplasty needs the elbow room of an endaural or post-auricular incision and is itself a reason to abandon a purely permeatal plan. The second is simply to convert to a wider approach. Either way, the discipline is to decide deliberately rather than to persist with an inadequate view, because a prosthesis placed onto a structure the surgeon cannot clearly see is a prosthesis placed on hope.

Two further limits matter. The posterior recesses — the sinus tympaniin particular, and the depths of the facial recess — lie outside the microscope’s transcanal line of sight, so disease or anatomy in those recesses cannot be assessed or cleared this way. And the approach is intolerant of bleeding: in a field the diameter of the canal, even modest ooze obscures everything, which is why a wet, inflamed or actively discharging ear is a poor candidate for transcanal work and why haemostasis is laboured over from the first incision [2019].

TThe endoscope and the modern transcanal field

The single development that has most expanded the transcanal approach is the endoscope. Passed down the same canal the microscope uses, a rigid endoscope reaches pastthe narrow isthmus and sits close to the structures of interest, where its wide-angle optics light up a far broader field than a microscope looking in from the canal mouth. Angled telescopes — 30° and 45° — then let the surgeon look around corners that no straight microscopic line of sight can reach: the anterior epitympanum, the entrance to the antrum, the facial recess and even the lip of the sinus tympani all become visible through the canal alone[1999]. Transcanal endoscopic ear surgery (TEES)has, in effect, enlarged the cone of vision without enlarging the corridor.

The trade-off is equally characteristic. Because one hand must hold the endoscope, all the operative steps are performed single-handed, which costs the two-handed control that microscopic surgery takes for granted; and because the lens sits in the field, the endoscopic view is even less forgiving of bleedingthan the microscopic one — a brisk bleed simply paints the lens and blinds the surgeon [2019]. These are real constraints, not deal-breakers, and they shape what the endoscopic transcanal approach is good at: focused, central, low-bleeding work such as ossiculoplasty, rather than long dissections in inflamed tissue.

Crucially, the hearing results do not suffer. In incus long-process defects managed exclusivelythrough the canal with an endoscope, both bone-cement rebridging and incus interposition close the air-bone gap reliably, with success rates around 70–80% for a gap within 20 dB [2022]. Across the wider literature, systematic reviews and a meta-analysis find no significant difference in audiometric outcome between endoscopic transcanal and microscopic ossiculoplasty, while the transcanal endoscopic route is associated with less postoperative pain and often shorter operating times [2021, 2025, 2021]. The chart below sets out the verified figures.

CChoosing the approach, keeping conversion in reserve

For the clinician, the decision to operate transcanally is a single, defensible judgement made before the knife touches the canal: will this corridor show me everything this operation needs?The modern consensus frameworks treat the surgical approach as an explicit, reportable choice — transcanal, transmeatal/endaural, or retroauricular — precisely because the approach is a deliberate decision with consequences, not an afterthought [2018]. The transcanal route is selected when the exposure demands are modest and the anatomy is kind, and the clinician should be able to articulate why on both counts: an intact aerated drum, disease already cleared, a wide straight canal, and a central reconstruction onto a mobile stapes.

The corollary is just as important as the indication. Because the transcanal approach is chosen on a prediction about exposure, the surgeon must always plan, consent and drape so that conversionto an endaural or post-auricular approach is immediately available if the prediction proves wrong — if the anterior annulus cannot be brought into view, if bleeding will not settle, or if the chain proves more damaged than the audiogram suggested. There is no virtue in persisting transcanally once the view is inadequate; the better surgeon converts early and reconstructs under a view that is honest.

Read this way, the transcanal approach is not the “lesser” operation but the appropriately minimalone — the least the patient needs to have the chain rebuilt safely and well. Choosing it correctly spares an external scar, a longer recovery and unnecessary tissue dissection; choosing it incorrectly, or clinging to it past the point where the canal stops cooperating, risks a prosthesis set onto structures half-seen. The skill, in the end, is the same skill that runs through all of ossicular surgery: matching the size of the approach to the size of the problem, and changing the plan the moment the anatomy asks you to[2018, 2021].