Surgical Technique

Transcanal Labyrinthectomy

Patients must undergo general anesthesia for surgical labyrinthectomies because of the nausea and vomiting that accompany removal of the labyrinth. A facial nerve monitor may be used during the procedure due to the proximity of the horizontal segment of the facial nerve to the operative site. Preoperative antibiotics and steroids are not required. Anesthesiologists should be asked not to use paralytic agents if facial nerve monitoring is performed.

The patient is placed supine on the operating table with the affected ear up. The ear is prepped with antiseptic solution and draped accordingly. The operating microscope is also draped after checking for proper balance. A transcanal approach is sufficient for most patients; however, if the canal is narrow, an endaural or postauricular incision may be necessary for full exposure. Local anesthetic with 1:100,000 epinephrine is injected into the canal. Using the largest speculum possible in a speculum holder, a long tympanomeatal flap is raised. Part of the scutum is then removed either using a curette or a small bur to expose the horizontal segment of the facial nerve. Full exposure of the facial nerve and oval and round windows is required (Fig. 25-1A). A portion of the posterior bony canal may also need to be removed. The incus can be removed and the stapedial tendon sectioned (Fig. 25-1B). The stapes is carefully removed by rocking in an anteroposterior

Tympanomeatal Flap
FIGURE 25-1 (A) Transcanal labyrinthectomy. A tympanomeatal flap has been raised and the incudostapedial joint separated. (B) Stapedial tendon is sectioned in preparation for removal of the stapes.

Round and uval windows

Tympanic Membrane Flap

Round and uval windows

Conncct round and oval windows to remove lateral aspect of promontory

FIGURE 25 —2 The oval and round windows are connected to remove the bony promontory.

Conncct round and oval windows to remove lateral aspect of promontory

FIGURE 25 —2 The oval and round windows are connected to remove the bony promontory.

motion to prevent fracture of the footplate. Avoid suctioning to prevent retraction of the utricle superiorly. The oval window is now enlarged using a microdrill, or the oval and round windows may be connected to remove the bony promontory (Fig. 25-2). The inferior portion of the round window niche is then removed to expose the posterior ampullary nerve (singular nerve). Sectioning of the singular nerve facilitates a full labyrinthectomy, as the crista of the posterior semicircular canal is difficult to remove using the transcanal approach. The nerve is approximately 1 mm medial to the posterior edge of the round window niche at a 45-degree angle. Sectioning is done using a small pick (Fig. 25-3A). Any cerebrospinal fluid (CSF) leak that occurs can be controlled using bone wax.

Carefully examine the facial nerve for areas of dehiscence. The utricle is now removed using a 3- or 4-mm right-angle hook, whirlybird, or utricular hook. It lies in a recess that is deep and superior to the horizontal facial nerve (Fig. 25-3B). Irrigating with saline may be helpful at this point to free the utricle from the walls of the recess. Removal of the utricle usually also results in removal of the membranous horizontal and superior semicircular canals. The saccule is then removed by aspirating the medial portion of the vestibule. Fracture of the cribrose area, in the medial portion of the vestibule, results in a CSF leak from the internal auditory canal. The bony semicircular canals are then probed to destroy any residual neuroepithelium.

The vestibule can be packed either with Gelfoam or fat. This is not absolutely necessary, but leaving the windows open results in a pneumolabyrinth. Packing also helps contain any CSF leaks that may have occurred. The flap is then replaced and the

Images Csf Leak Tegman Tympani

FIGURE 25-3 (A) The posterior ampullary nerve is sectioned with a pick. It is located 1 mm medial to the posterior edge of the round window at a 45-degree angle. (B) A hook is used to remove the utricle and semicircular canals, which are located deep and superior to the horizontal facial nerve. SCC superior semicircular canal; VII, facial nerve; S, saccule.

FIGURE 25-3 (A) The posterior ampullary nerve is sectioned with a pick. It is located 1 mm medial to the posterior edge of the round window at a 45-degree angle. (B) A hook is used to remove the utricle and semicircular canals, which are located deep and superior to the horizontal facial nerve. SCC superior semicircular canal; VII, facial nerve; S, saccule.

canal packed. If a postauricular incision was made, the incision is closed and a dressing placed.6,7

Transmastoid Labyrinthectomy

The patient is placed under general anesthesia and placed supine on the operating table. The table should be turned 90 or 180 degrees. The affected ear is up and the postauricular shave prep is extended several finger-breadths behind the ear. The exposure is usually a little more than that used in a standard mastoidectomy because of the need for greater exposure for the medial dissection. Place the facial nerve monitor leads and ensure that the monitor is working properly. A high-speed drill with multiple cutting and diamond burs should be available. Both monopolar and bipolar cautery should also be available. The postauricular area is then injected with epinephrine (1:100,000). If this is combined with local anesthesia, care must be taken not to inject at the mastoid tip and anesthetize the facial nerve. The anesthesiologist should be informed that nerve monitoring is taking place, and so paralytics should be avoided. If more than one anesthesiologist is giving agents during the procedure, it is important to communicate this instruction. In some operating room settings, this is instruction is posted in a prominent location. Preoperative antibiotics and steroids have not been shown to affect outcomes or postoperative infection rates.

The area is then prepped and draped in a sterile fashion. The surgeon should also check the operating microscope and ensure proper balance prior to draping. A postauricular incision is made and carried down to the temporalis muscle. Monopolar cautery is then used to make a T incision along the linea temporalis and down to the mastoid tip. A Lempert elevator is used to widely elevate the periosteum off the mastoid cortex, taking care to identify the spine of Henle anteriorly. The soft tissues are then held in place using self-retaining retractors. Any bleeding encountered during the dissection is controlled using electrocautery. A dry field is important for good visualization of the operative area.

A cortical mastoidectomy is then performed using a large cutting bur and continuous suction irrigation. The tegmen and sigmoid sinus are identified and the posterior bony canal thinned. The sinodural angle is opened widely for exposure of the vestibule. The antral air cell is entered and the horizontal canal, fossa incudis, and body of the incus should all be seen clearly (Fig. 25-4). The sigmoid sinus may also need to be decompressed for adequate exposure of the posterior semicircular canal. The bone over the sinus is carefully thinned and removed. Bipolar

Mastoid tip

Digastric ridge

Mastoid tip

Digastric ridge

Tympanic Membrane Irrigation

Middle fossa plate

S i nod u ral angle

Sigmoid sinus

FIGURE 25-4 Transmastoid labyrinthectomy. A view of the horizontal canal, fossa incudis, body of the incus, tegmen, and sigmoid sinus after the cortical mastoidec-tomy.

Middle fossa plate

S i nod u ral angle

Sigmoid sinus

FIGURE 25-4 Transmastoid labyrinthectomy. A view of the horizontal canal, fossa incudis, body of the incus, tegmen, and sigmoid sinus after the cortical mastoidec-tomy.

cautery is then used to collapse the sinus. Leaving an island of bone covering the sinus requires the use of a retractor. No ill effects usually result from superficial coagulation and contraction of the sig-moid sinus. The vertical segment of the facial nerve is now carefully identified using a large diamond bur.

The lateral (horizontal) semicircular canal identified during the mastoidectomy is completely delineated. Many surgeons prefer to completely remove all air cells surrounding the labyrinth. The horizontal canal is ''blue lined'' and followed posteriorly to the posterior semicircular canal. This process is usually done with a diamond bur to also identify the relationship of the canals and the second genu of the facial nerve. The posterior canal is then delineated in a similar manner (Fig. 25-5). Removal of bone is carried medially on both canals, being careful to keep a flat plane of dissection without irregularities that might cause the bur to skip and injure the facial nerve. The posterior canal dissection requires much more bone removal and goes further medial. The area where the posterior and superior canals join is the common crus. The superior canal establishes the medial limit of the dissection (Fig.

Oval Window Trans Canal View

sigmoid si mi s

FIGURE 25-5 The decompressed sigmoid sinus and vertical segment of the facial nerve are identified prior to opening of the semicircular canals.

sigmoid si mi s

FIGURE 25-5 The decompressed sigmoid sinus and vertical segment of the facial nerve are identified prior to opening of the semicircular canals.

25-6A). The anterior ampullated end is immediately superior to the ampullae of the horizontal canal. The superiormost point of dissection is the arcuate eminence. To see this point and the whole length of the canal, it may be necessary to angle the head of the microscope upward. The crus is then followed to the vestibule. The vestibule lies under (medial to) the facial nerve anteriorly. The bone covering the external genu of the facial nerve is thinned and the anterior and inferior portion of the posterior canal is opened to its ampulla. At the conclusion of drilling, it should be possible to see the open ampullae of all of the semicircular canals and the vestibule without any remaining bone dividing them. Once all the canals and vestibule have been opened, the neuro-epithelium is removed with a right-angle hook (Fig. 25-6B).

The mastoid periosteum is now closed in layers. It is not necessary to pack the cavity with tissue unless a CSF leak has occurred. The area of the leak must be identified and repaired with tissue prior to packing of the cavity. A mastoid dressing is placed over the ear and the patient is brought out of anesthesia.8 10

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