Outlook and Prevention

There is arguably no more feared complication in mastoid surgery than unintentional injury to the facial nerve. Not only are there significant negative medical consequences to such an injury (e.g., corneal exposure, paralytic ectropion, oral incompetence), but the psychosocial effects of facial disfigurement are profound, including negative self-image, depression, and social rejection. It is therefore imperative for surgeons to go to great lengths to avoid this complication.

The incidence of iatrogenic facial nerve injury is variable and depends on the skill and experience of the surgeon. Reported rates of injury are around 1 case in 1,000 with experienced surgeons, but may be higher with inexperienced surgeons at a teaching facility.6–8 For revision surgery, the risk of injury is probably increased. The most common site of injury during mastoidectomy has been reported to be the second genu at the junction of the tympanic and mastoid segments. Unlike the tympanic segment, which is often noted to be partially dehiscent in small areas, the second genu is usually covered by bone, except in rare cases of very extensive erosive cholesteatoma. Hence, most of these injuries can be traced to mistakes in drilling of the overlying bone.

Drill-related injuries to the facial nerve are usually related to a failure to properly identify the nerve in a controlled and systematic manner or failure to assure sufficient irrigation to prevent thermal injury. This phenomenon can be witnessed in the setting of training in the temporal bone laboratory, where novice surgeons often recklessly drill small, deep, and narrow mastoidectomy cavities with the aim of rapid and direct entry into the antrum. In a sclerotic mastoid, this faulty technique may result in drilling in a trajectory that is more inferior than intended, resulting in potential fenestration of the lateral semicircular canal and injury to the adjacent facial nerve. In contrast, proper safe technique requires wide methodical saucerization of the mastoid cavity that progresses with stepwise identification of one known anatomical landmark after another.

The authors’ preferred sequence in mastoid drilling is as follows (see Fig. 4.2 ). First, the boundaries of the Macewen triangle are vaguely delineated. Then, broad strokes are used with a large bur around the temporal line (only a rough guide) until the tegmen is clearly identified at its lateral then inferior aspects. The sigmoid sinus is then widely demarcated in a similar manner. Next, with broad drill strokes, triangular dissection is executed that allows wide passage through the central tract of air cells and Koerner septum before progressing to controlled entry into the antrum. To be executed properly, one of the corners of the triangular dissection field must be located far enough anteriorly to lie deep to the zygomatic root. The lateral semicircular canal and the lateral process of the incus are then identified with careful widening of the antral opening. Next, drilling of the sinodural angle posteriorly and delineation of the digastric ridge inferiorly are undertaken.

The final sequence proceeds with copious irrigation and a medium-sized coarse diamond bur. This involves identification of the facial nerve by thinning the bone of the external auditory canal with slow controlled strokes that span from just inferior to the lateral semicircular canal toward the mastoid tip and digastric ridge. The latter acts as a rough depth gauge of where one should expect to encounter the inferior aspect of the facial nerve. As is the case with skeletonization of the tegmen and sigmoid, exposure of the nerve over a broad front is desired. In most cases, it is preferable to preserve a thin layer of bone over the nerve once it is properly identified. In doing so, focal punctate bleeding vessels may be encountered in a vascular area supplied by the stylomastoid artery, commonly known as “sentinel bleeders.” If hemostasis is required, gentle application of bone wax or other topical hemostatic agents are used in lieu of cauterization.

As a policy, it is beneficial to identify (but not expose) the facial nerve in every mastoidectomy procedure. Not only does this facilitate completeness of the operation, but it also leaves no room for doubt in the mind of the surgeon as to the status of the nerve at the completion of surgery. As one saying goes, “make the facial nerve your friend.” Once identified, subsequent advanced techniques, such as removal of the mastoid tip or posterior tympanotomy, can be safely and confidently executed under direct visualization of a valuable landmark.

There is some debate as to the role of facial nerve monitoring as an adjuvant in mastoid surgery.9,10 This pertains not only to the general question of use or nonuse, but also to whether it is indicated routinely or only in complicated and revision cases. There is no definitive evidence that facial nerve monitoring lowers the incidence of iatrogenic facial nerve injury in mastoidectomy. Nevertheless, the authors recommend routine monitoring in centers where otologic surgical training is undertaken and otherwise in cases that portend an increased risk of injury (e.g., congenital anomaly, cholesteatoma, trauma). The facial nerve monitor provides the additional advantage of affording nerve stimulation for identification when this is in question, such as in the case of extensive mastoid granulation tissue.

Management

Clinical trials in this area are generally not feasible, so acute management of iatrogenic facial nerve injury is based on both anecdotal guidelines and a general knowledge of principles applicable to motor nerve injury.11 Fig. 4.3 outlines a general scheme of management based on the timing of recognition and the severity of the injury, versions of which have been frequently cited over decades in otologic surgical teaching. In addition, it is common practice for most surgeons to treat these injuries with courses of high-dose intravenous corticosteroids that may be extended well into the postoperative recovery period with an oral dosing taper.

Outlook and Prevention

The sigmoid sinus is a major landmark in mastoid surgery; for this reason, the need to manage sigmoid sinus bleeding will arise on at least a few occasions throughout the career of most otologic surgeons. For those unfamiliar with this situation, it can be a very dramatic and fear-invoking experience as the surgical field may be rapidly and completely flooded with blood. Fortunately, the vast majority of these injuries can be easily controlled with simple measures if they are properly anticipated and calmly handled.12 Sigmoid sinus bleeding is low-flow venous output.

Most sigmoid sinus injuries are the result of drill-related trauma. In some cases the sigmoid may be located in a position only a few millimeters under the cortical bone of the mastoid, placing it at risk of trauma even from a few initial shallow drilling strokes with a cutting bur. Additionally, in a sclerotic mastoid, the sigmoid sinus is at risk by virtue of being displaced far further anteriorly than usual. Both of these conditions can be recognized on preoperative HRCT images. When drilling is undertaken in an intentional manner to completely remove overlying bone, the sigmoid is fairly resilient to direct contact with a large diamond bur; however, interface with a cutting bur or a small caliber diamond bur places the sigmoid at risk for tear or puncture, respectively.

Management

Small points of sigmoid bleeding, especially those encountered at the junction between the sigmoid and smaller feeding veins, can usually be controlled with focal bipolar cauterization. Use of monopolar cautery is not recommended because it may further open and widen the bleeding point.

For brisker bleeding ( Fig. 4.4 ), a large piece of Gelfoam (Baxter International, Deerfield, IL, USA) that is much larger than the injured area, to prevent embolization, or a piece of autologous muscle is applied at the bleeding source. The Gelfoam or muscle is then held in place under pressure by a suction tip with a cotton sponge acting as an interface. Generally, pressure with the suction tip is required for no longer than a minute, after which the suction may be withdrawn, leaving the cotton sponge and Gelfoam in situ. Work can be resumed at another site, with final removal of the cotton sponge occurring roughly 10 minutes thereafter. The vast majority of sigmoid sinus injuries can be successfully controlled in this manner.

Very rarely, a large sigmoid tear occurs that will require a more complex repair. If the lumen of the sigmoid is widely exposed, it can be occluded with dense packing of a single piece of muscle into the lumen that is fixed in place with sutures to prevent migration. Alternatively, vascular balloon catheters may be inserted and inflated proximal and distal to the injury site to allow primary suture repair (4.0 nonabsorbable monofilament, tapered needle) of the sinus wall. This nonocclusive primary repair technique may be particularly required if there is concern about the status of contralateral venous outflow.

In the case of a very large sigmoid sinus injury, especially when the lumen and inner walls of the sinus can be seen, an alert for the possibility of an air embolus should be raised and communicated to the anesthesiologist. To minimize this risk, Trendelenburg′s position is instituted immediately and the surgical field is temporarily flooded with physiologic solution while direct pressure is maintained on the bleeding site and preparations for definitive repair are finalized.

Management principles for the jugular bulb are the same as these described for the sigmoid sinus.

Outlook and Prevention

Similar to the discovery of a transected facial nerve, the unexpected discovery of “snake eyes,” indicating inadvertent violation of a semicircular canal, is a sight that all otologists hope to avoid.

Although labyrinthine fistulas are regularly managed in the setting of erosive cholesteatoma, experienced surgeons who are adept at recognizing the hallmark characteristics of dense ivory-colored labyrinthine bone should rarely encounter iatrogenic fistulas.7,13,14

The lateral semicircular canal is at greatest risk because of its exposed location relative to the antrum. Injuries to the lateral semicircular canal in this location can be attributed to many of the same errors in technique that have been discussed in relation to facial nerve injuries, especially narrow-field drilling toward the antrum in a sclerotic mastoid. In fact, the horrific scenario of concurrent iatrogenic lateral semicircular canal fenestration and injury to the second genu of the facial nerve has been reported. The posterior and superior semicircular canals are also at risk of violation with drilling of the infralabyrinthine and supralabyrinthine air cell tracts, respectively.

Management

Although the presence of an iatrogenic labyrinthine fistula generates a significant risk of sensorineural hearing loss and severe vertigo, these do not occur with absolute certainty. In fact, there are numerous reports of iatrogenic labyrinthine fistulas wherein hearing and/or partial vestibular function has been preserved. Perhaps this is not surprising given what we know about similar results for surgery that involves intended and controlled fenestration or occlusion of the labyrinth.

The keys to optimal management of this complication seem to be early recognition and avoidance of further trauma to the membranous labyrinth. As such, if a labyrinthine fistula is recognized, drilling should immediately cease and suction to the area should be strictly avoided. A prompt seal of the fistula can then be achieved by plugging the exposed semicircular canal with bone wax and/or fascia. An extended course of antibiotic therapy with an appropriate medication that passes through the blood–brain barrier is prescribed to prevent bacterial labyrinthitis and meningitis, especially in the case of an infected surgical field. As with a facial nerve injury, high-dose systemic corticosteroids may also be of benefit.