Laser in Otosclerosis

The word laser is an acronym for Light Amplification by Stimulated Emission of Radiation. Why are lasers the preferred tool to be used during stapedectomy surgery?
Laser’s avoid the use of manual physical force. Use of manual physical force can cause the footplate to get mobilized or subluxed. This situation can complicate stapedectomy surgery and result in suboptimal results in hearing both in the short term as well as the long term.
Laser creates the desired dimension of the footplate fenestra by avoiding the use of manual physical force. It is precise and thus allows for stapedotomy rather than stapedectomy. This has implications for short term as well as long term hearing results as well as avoids perilymphatic fistula.
The laser can accurately and relatively atraumatically divide the stapedius tendon.
Laser also provides for good control of bleeding thus allowing for better visualization of middle ear structures.
Laser is particularly useful in revision stapedectomy and is the instrument of choice. It lyses the adhesions between the utricle and saccule and the footplate and the prostheses without damaging these structures. Thus making the surgery as atraumatic as possible. Revision stapedectomy is notoriously associated with poor outcomes. When performed correctly with a laser the outcomes are better.

Ideal qualities required in a laser for use during a stapedectomy.

Precision. Precise optics in order to focus the laser beam at the place required.
It should be able to vaporize either the bone or the collagen at the oval window in a predictable and controlled manner.
The thermal footprint of the laser should not be beyond (deeper) than the site of application. If it penetrated deeper than the site of application it would cause thermal damage to the utricle and the saccule below.
The laser should not heat the perilymph

Optical Properties - Visible Lasers

The short wavelength lasers (argon =488 or514nm, KTP =532nm) have ideal optical properties for microscopic surgery.
The light can be delivered from a laser source to the microscope mounted micromanipulator through an optical fiber and can be focussed to a tiny spot size of 0.5mm or smaller.
The light of the aiming beam and the working beam is the same the spot size and the point of impact are identical that is to say they are parfocal and coaxial. Initially Perkins (1980), McGee (1983) used microscope mounted lasers. In 1990 Gherini and Horn introduced a hand held Endo Otoprobe (HGM Medical Lasers Systems, Salt Lake City, UT) to deliver an argon laser beam. This provided further refinement to the convenient use of lasers in stapedectomy.

Advantages of visible lasers

Flexible cable delivered CO2 lasers are now very popular though it is expensive. It avoids the use of attachment to the microscope and is thus less cumbersome.

Convenience of hand held probe for use of lasers during surgery
Spot size can be chosen accurately.

Disadvantages

The visible light lasers depend on char formation to begin creation of a rosette (fenestra) on the footplate. The char absorbs laser energy and creates heat. The laser energy can pass through either directly or by scatter and injure the neural tissue of the utricle or saccule

Optical Properties - Infrared Lasers

Long wavelength CO2 laser light (infrared =10,600nm) can be transmitted to the microscope via a series of carefully aligned mirrors and lenses. The infrared CO2laser is invisible to the naked eye and so a visible laser aiming beam is needed. For this purpose a Helium- Neon laser is used.

Advantages of the CO2 laser

The CO2 laser has near ideal tissue absorption characteristics. The CO2 laser energy is absorbed by water. The water component of bone is approximately 60%. At the high power density setting the pulsed laser vaporizes bone and releases heat and tissue into the vapor plume. Since the CO2 laser energy is absorbed by water, it does not penetrate.

Disadvantages

The laser apparatus is cumbersome. Recently this has been overcome by the use of a flexible cable deliverecCo2 laser
Increased working distance between the microscope and the operative site.
Diminished light through the microscope because of the use of the beam splitter.
The aiming beam and the working beam do not have the same wavelength and so it became difficult to focus both together at the same spot.

In short the CO2 Laser can be said to have optimal tissue characteristics but suboptimal optical characteristics for use in stapedectomy (Poe 2000).

Choice of laser for stapedectomy

At this time there is no ideal laser. The visible lasers, especially the argon Endo-Otoprobe has excellent optical precision and is superior to the CO2 laser. However the CO2 laser has superior interaction of laser energy with bone, collagen and perilymph.
Fluency threshold studies confirm that 15 to 20 times more argon or KTP energy is required to ablate bone (Lesinski and Newrock 1993). Transmission spectroscopy studies of both collagen and bone further verified the selective absorption of infrared electromagnetic energy compared with visible light (DiBartolomeo J 1981) Finally Thermocouple experiments show that should correct energy parameters and surgical care during surgery be taken, then both visible and invisible (infrared) lasers can be used safely for stapedectomy.(Perkins 1980)
A pulsed CO2 laser beam is ideal for revision stapedectomy.

Ideal situations for using the laser for stapedectmy

Revision stapedectomy.
Obliterative footplate.
Primary stapedectomy is also an ideal situation because in stapedectomy the first surgery is the best chance for an optimal outcome.

Advantages of Laser stapedectomy

A precise fenestra can be created in the oval window without the use of manual physical force which if improperly applied can result in suboptimal results.
Avoids trauma to the inner ear. Incidence of vertigo, sensorineural hearing loss and tinnitus are much less.
A floating footplate is more likely to occur with manual stapedectomy where the surgeon attempts to create a fenestra without the use of a laser. The use of a laser lowers the chance of such an event from occurring.
Good hemostasis
Good long term results in terms of hearing.

Ultimately it may be said that a laser is only a tool and is only as good or as bad as the hand that wields it.

The tympanomeatal flap is replaced. And the external auditory canal is packed.

Results

Virgin (primary)surgery
Almost all authors conclude that with whatever laser they use hearing results are uniformly good and are superior to those performed through conventional techniques without the use of laser (Perkins 1980, Lesinski and Stein 1989). Lesinski (1993) reports on 100 consecutive patients who have undergone CO2 laser stapedectomy. They were examined 1 to 3 years postoperatively. In his series 91% maintained an air bone gap within 10dB or better, 95% within 15dB. 3patients had an airbone gap of 20dB Sensorineural hearing loss
No patient was found to have a sensorineural hearing loss in the speech range of 500, 1000 , 2000 or 3000HZ.

Complications

Perilymph fistula
No patients in his series went on to develop a perilymphatic fistula. Vestibular symptoms
Intraoperatively no patient developed dizziness.
With 4 hours 13 developed mild dizziness However all symptoms resolved within a month of surgery.

Revision stapedectomy surgery with laser.

Lesinski (1993) reports better hearing results in those who were found to have a normal malleus and incus at the time of revision surgery. 90% maintained an air bone gap to within 10dB. Those patients who presented with incus erosion or malleus fixation the results were poorer. No patient developed a worse speech reception threshold. No patient developed a significant sensorineural hearing loss.

Newer lasers for the use of stapedectomy

The search for an ideal otological laser has been directed towards development of a laser with a good water absorption characteristics that could be delivered through a fiberoptic cable. The search has focussed on alternative wavelengths for lasers in the mid infrared range where water absorption is good.

Pulsed Infrared Lasers

The emerging lasers in the mid infrared region have been pulsed lasers to date. Pulsed lasers work by storage of large amounts of energy which is suddenly dissipated in a massive release that generates the laser emission in very short bursts. These high energy bursts rapidly exceed tissue vaporization levels with efficient tissue ablation that reduces the total energy required for ablation compared with continuous wave lasers. Pulsed lasers lose less energy to adjacent thermal spread, yielding a better quality perforation of the oval window. The high energy bursts over a brief period of time produce a transient plasma explosion with nonlinear (out of proportion for the amount of energy) acoustic effects not found in continuous wave lasers that follow only linear photothermal properties. Pulsed lasers have highly desirable wavelengths and are excellent at bone cutting. However the acoustic shockwave has been found to be a potential serious barrier for their use within the ear.
Esenaliev et al (1993) found that the shorter the pulse the greater the acoustic effect particularly when the duration of the pulse was less than the duration of the stress relaxation time as the tissue recoiled from each pressure wave. The pulsed or explosive ejection of tissue ablation products caused a compression and rarefaction recoil pulse that propagated through tissues could cause significant injury even at remote distances from the site of ablation. All of the acoustic effects caused tissue stresses and generated energy below levels required for tissue ablation so no secondary vaporization would be expected but widespread necrosis could result.

Erbium laser

The erbium laser is one such laser currently being investigated because of its clean bone cutting characteristics and it has a wavelength of 2.9um lying close to the maximal peak of water absorption (3.00um) in the visible and infrared spectrum. Shah et al (1996) examined the erbium laser. They found that ten pulses of the laser on the footplate produced a 2.00 elevation in temperature. It was noted that the errbium laser was capable of precise bony ablation and very limited collateral damage with much less char than either continuous wave or superpulsed CO2 lasers. The erbium laser was intensely absorbed by water and collagen and also by bone minerals calcium phosphate and hydroxyapatite. The excellent absorption of the laser energy meant that the majority of energy was consumed by tissue ablation and ejection of debris, leaving minimal residual energy to dissipate into adjacent tissues. Hemostasis was limited. It worked best only on very small vessels. It was also noted that a loud popping sound occurred when the laser impacted the bone. This was indicative of a significant shock wave phenomenon.
Jovanovic et al (1995) found that the Erbium :YSGG (ER:YSGG) laser produced a 3.60 elevation in temperature from the footplate, while the CO2 laser produced a 8.80 temperature increase. They were concerned that the shock waves could be introduced into the perilymph with the potential to damage the inner ear structures. They also found that the ER:YSGG laser created well formed fenestra in the oval window. The ER:YSGG laser require 2 to 4 times less total energy than the CO2 laser.

Diode Lasers

New semiconductor diode lasers, which are fiber delivered, inexpensive and available in continuous wave or pulsed modes are available in recent times. However the clinically available wavelengths lie between 800 and 1000nm fall between hemoglobin and water absorption peaks. While they are useful for pigmented bodies they cause deep extensive thermal damage.

Summary

CO2 laser energy (10.6 microns) is nearly completely absorbed by collagen and bone. It is the ideal tool to use in revision stapedectomy surgery.
Visible lasers like Argon and KTP lasers are poorly absorbed. However they can be delivered through a convenient hand held probe. It can be used ideally for primary stapes surgery.
Laser stapedectomy has to a certain extent reduced technical difficulties of a very technical surgery. It must be remembered that the laser, whichever one is used, is only as good as the hand that wields it.

References

Perkins R (1980): Laser stapedotomy for otosclerosis. Laryngoscope 90:228-241.
GheriniS, Horn KL (1990): Small fenestra laser stapedectomy utilizing a hand held argon laser in obliterative otosclerosis. Presented at the Western Section, The Triologic Society, Pebble Beach, CA January 06, 1990.
McGee T (1983): The argon laser in surgery for chronic ear disease and otosclerosis. Laryngoscope.93:1177-1182.
Smith MFW McElveen JE (1992): Neurological surgery of the ear.. Mosby Yearbook. St Louis , MO Pp131-162
Poe DS (2000): Laser Assisted endoscopic stapedectomy: A prospective study. Laryngoscope supplement no 95. 110:1-37.
Lesinski SG and Newrock R (1993): Carbon dioxide lasers for otosclerosis. Otolaryngologic Clinics of North America. 26: 417-441.
DiBartolomeo J (1981): Argon and CO2 lasers in otolaryngology. Which one, when and why? Laryngoscope 91 (Supplement 26) 1-16
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Kecke T, Wiebe M, Rettinger G and Riechelmann H (2002): Safety of the Erbium:Yttrium Aluminium- Garnet laser in stapes surgery in otosclerosis. Otology and Neurotology 23:21-24.
Huber A, Linder T, Fisch U (2001): Is the Err:YAG laser damaging to inner ear function? Otology and Neurotology 22:311-315.
Shah UK, Poe DS, Rebeiz EE, Perrault DF et al (1996) Erbium laser in middle ear surgery: in vivo and in vitro animal study. Laryngoscope 106:418-422.
Jovanovic S , Schonfeld U, Prapavat V et al (1995): Effects of pulsed laser systems on stapes footplate. Lasers Surg med 21:341-350
Nagel D (1997): The ER:YAG laser in ear surgery:First Clinical results. Lasers Surg. Med 21:79-87.
Bottrill I, Perrault DF, Pankratov MM. Poe DS (1994): Thulium:YAG laser for stapes surgery: preliminary observations SPIE Int Soc England. 2128:23-30.
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