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EQUINE LASER SURGERY
Overview
LASER is the acronym for Light Amplification by Stimulated Emission of Radiation. But what is a laser? A laser is a device that generates an intense beam of light that can cut, seal or vaporize tissue. It is different than the light around us in several ways. The most important difference is that laser light consists of one wavelength while the light around us is composed of many different wavelengths. The light of a laser is created by energizing molecules to emit light at a certain wavelength. There are many different kinds of lasers, each of which operate at a unique wavelength. Three examples of popular lasers are the carbon dioxide (CO2), Nd:YAG and Diode lasers.
The CO2 laser is one of the most widely used lasers in the world. It operates at a wavelength of 10,600nm. When a CO2 laser is delivered to the soft tissue, the light energy is absorbed by the water existing in the soft tissue. This then heats up the soft tissue and vaporizes it. The CO2 laser is used for its ability to spare surrounding tissue from heat damage and its precise cutting.
The Nd:YAG laser (wavelength 1064nm) was the most commonly used laser in large animal surgery from 1984 to the mid 1990’s. The Nd:YAG is delivered through a small quartz fiber which allows it to be used through a videoendoscope. The endoscope is a long flexible tube with a camera on the end that allows the doctor to see into areas that he could not see otherwise – for example deep within the nasal passage. Thus, the laser can be transmitted down a fiber through an endoscope and used deep within the nasal passage (Figure 1). The light energy from this laser is absorbed by two major components of living tissue: melanin, the dark pigment in skin and hair; and, hemoglobin, the pigment in red blood cells that carries oxygen. The Nd:YAG laser is more readily absorbed by tissue than the CO2 laser leading to better coagulation (blood clotting), but the increased absorption leads to increased thermal damage to surrounding tissues.
Figure 1. The endoscopic view inside a horse’s throat with the laser fiber extending out from the scope, beginning to cut an epiglottic entrapment.
The diode (wavelength 810-10,600nm) laser has become increasingly popular in large animal surgery since it has a very similar wavelength to the Nd:YAG and therefore can also be delivered via a small quartz fiber through a videoendoscope. The advantage over the Nd:YAG is that the diode laser is small, portable, and more efficient.
Advantages and Disadvantages of Laser Surgery Versus Conventional Surgery
Advantages:
- Less Bleeding - The laser seals small blood vessels during surgery.
- Less Swelling – Decreased bleeding and no crushing of tissues decreases post-operative swelling.
- Shorter Hospitalization Times – Many procedures can be done with standing sedation and therefore, the horse does not require general anesthesia. This reduces the risk of complications as well as hospitalization time.
- Precision - The laser can be controlled precisely to remove thin layers of tissue.
- Less Pain - The laser seals nerve endings as it cuts therefore, the patient experiences less pain.
- Sterilization - The laser sterilizes the surgical site (kills bacteria) as it cuts.
- Faster Recovery – A decreased amount of bleeding and swelling will result in faster healing of tissue. This will lead to a faster return to activity and use.
Disadvantages:
- Requires specialized equipment and training.
- Can result in excessive thermal damage to adjacent or target tissue if not used appropriately.
Conditions Amenable to Laser Surgery
Laryngeal Hemiplegia (roaring):
Laryngeal hemiplegia is a condition of paralysis to muscles of the throat or voicebox (the larynx) weakening the animal’s ability to open their throat fully during breathing and close it during swallowing or vocalizing. This condition usually occurs on the left side of the larynx due to loss of nerve function in the left recurrent laryngeal nerve. Laryngeal hemiplegia is a common cause of exercise intolerance and a common cause of abnormal respiratory noise (roaring) in horses. The most common surgical treatment for the disease is a prosthetic laryngoplasty or a “tieback” procedure. This procedure involves permanently opening one side of the throat to avoid it from collapsing into the airway under the negative pressure as the animal breathes in. If the throat were to collapse, there would be an obstruction and abnormal respiratory noise (roaring). A common adjunctive therapy is the removal of the vocal folds and/or the laryngeal saccules that stabilize the bottom portion of the arytenoid cartilage in the airway. Removal of this tissue (ventriculocordectomy) has been shown to decrease the abnormal noise and increase the airway diameter for possible increased performance. This technique has been traditionally performed through an incision in the throat region (laryngotomy) under general anesthesia after the “tieback”. The laser can be used to perform a similar procedure but can be achieved in the standing horse (or under general anesthesia) through the endoscope (Figure 2). This obviates the need for a surgical incision.
Figure 2. Endoscopic view after the left vocal cord has been resected (removed) employing the laser. Arrow on remaining normal right vocal cord.
Epiglottic Entrapment:
Epiglottic entrapment is a condition in which a loose part of throat lining (in this case the aryepiglottic tissue) abnormally wraps over the epiglottis (a cartilage of the larynx). It can easily be diagnosed with upper airway endoscopy. It is a common cause of exercise intolerance and abnormal respiratory noise in racehorses. The condition can also occasionally cause coughing and nasal discharge. Traditional surgical correction involved splitting the tissue down the middle (axial division) with a curved blade (usually under general anesthesia) or surgical resection through an incision in the throat region (under general anesthesia). Laser division of the tissue can be performed using either the Nd:YAG or diode laser through the videoendoscope (Movie 1). This technique can be done on an outpatient basis (with the patient under sedation and application of a local anesthetic) with decreased surgical complications and reduced healing time (Figure 3). The re-entrapment rate is also slightly lower with the use of a surgical laser versus a traditional surgical approach.
Movie1 - The diode laser is being used under videoendoscopic guidance to perform an axial division of an epiglottic entrapment. Several cuts are being made through the tissue, and several more will be required to complete the procedure.
Figure 3. View of epiglottis from horse in Figure 1 after epiglottic entrapment has been treated.
Arytenoid Granulomas:
These are areas of “proud flesh” on the flaps of the voice box (the arytenoids) that can cause the horse to cough and lead to arytenoid infection. The laser can be used through the endoscopic to remove (resect) the granulomas. This procedure is performed in the standing horse under sedation and with the use of local anesthesia at the surgery site. Using the laser allows precision and minimizes bleeding.
Ethmoid Hematoma:
Ethmoid hematomas are encapsulated masses that arise from the ethmoid turbinates (an area of thin bony structures in the back of the nasal passage) or occasionally from the sinuses. Most common clinical signs of the disease include a mild, intermittent nose bleed from one nostril. If the mass is large it may cause abnormal respiratory noise and can occasionally cause malodorous breath. Definitive diagnosis can be made with a biopsy and a tentative diagnosis can be made using upper airway endoscopy. Treatment consists of removing the mass and the tissue of origin. With small masses that arise from the ethmoid region this can be accomplished by injection of the mass with formalin under standing sedation. This process may need to be repeated several times. For large masses, a sinus bone flap under general anesthesia may be necessary. Laser ablation of the mass can be achieved through an endoscope in the standing horse. This procedure can be done after formalin or sinus flap surgeries or by itself with small masses. The use of the laser decreases both hemorrhage during surgery and the chance of recurrence of the mass.
Guttural Pouch Tympany or Empyema:
The guttural pouch is unique to the horse. It is an air filled out-pouching of the eustachian tube. Guttural pouch tympany is a condition that occurs in foals. The exact cause of the condition is unknown but most agree that there is a malfunctioning of the mucosal flap in the pharynx that forms an opening to the guttural pouch. Instead of allowing air to flow in and out of the guttural pouch, the flap acts as a one-way-valve, allowing air in but not out. Thus, air gets trapped in the pouch and excessive air accumulation in the pouch leads to tympany. Foals affected with this condition have a large, non-painful swelling on one or both sides of the throat latch region. Diagnosis is based mostly on clinical signs. Traditionally, an opening is created between the two guttural pouches through a surgical incision in the throat latch region while the foal is under general anesthesia. The surgical laser can be used to create this opening; or, it can be used to create an opening from the pharynx into the affected pouch. Either approach can be performed through the videoendoscope on an outpatient basis with the foal standing under sedation (Figure 4).
Figure 4. Fistula created between the two guttural pouches of a foal affected by guttural pouch tympany.
Guttural pouch empyema is a condition that occurs when the guttural pouch gets filled with fluidy or somewhat solidified purulent material. It is extremely difficult to resolve the infection with flushing and antibiotic treatments alone. The laser can be used to create a surgical opening from the throat area directly into the guttural pouch (salpingopharyngeal fistula) allowing the infectious material to drain passively.
Dorsal Displacement of the Soft Palate:
Dorsal displacement of the soft palate consists of the displacement of the soft palate on top of the epiglottis. This causes exercise intolerance and abnormal respiratory noise in performance horses. Several techniques have been described with varying success for the treatment of dorsal displacement of the soft palate. One therapy in conjunction with traditional surgical techniques is application of a laser in several small areas at the free edge of the soft palate. The theory behind this treatment is to produce scar tissue and stiffen the edge of the soft palate to prevent further displacement. The laser can also be used to resect the free edge of the soft palate (staphylectomy) under videoendoscopic guidance. Previously, this type of surgery was only done with the horse under anesthesia and through a skin incision into the throat.
Upper Respiratory Tract Cysts and Masses:
Masses within the upper airway (trachea, pharynx, larynx) as well as cysts in the epiglottis, pharynx, and nasal passages can all be treated with laser surgery. Laser surgery can be used to remove the masses/cysts with minimal trauma to the surrounding tissue, decreased bleeding, and decreased recurrence when compared to traditional surgical approaches (Figure 5a,b).
Figure 5a. Granulation tissue obstructing the view of the normal larynx (voice box)
Figure 5b. One (1) month after the tissue was removed with the laser
Skin Tumors:
Most surgical skin diseases in large animals are neoplastic (cancer) in origin. Removal or destruction of the diseased tissue is the goal of any therapy. Laser surgery for these lesions both alone and in conjunction with chemotherapy can decrease recurrence rate and speed recovery. Laser excision of tissue causes less swelling to surrounding tissue and less spread of neoplastic cells to surrounding areas when compared to excision with sharp instrumentation. Typical skin tumors treated with laser surgery include sarcoids, squamous cell carcinomas, and melanomas.
Skin Grafts:
Lasers can be used to prepare the healing wound bed (granulation tissue) for skin grafting. They can be used to remove the exuberant healing tissue (“proud flesh”) that is often seen in horses and to sterilize the wound bed. The use of the laser also allows for less bleeding in the highly vascularized tissue and less swelling when compared to other methods. The laser creates an ideal environment for the new tissue to grow.
Neurectomy:
Neurectomy (removing a section of nerve) is a treatment in large animals to reduce pain from progressive, debilitating disease processes. Removal of a small piece of the nerve supplying sensation to the painful area eliminates the sensation of pain the animal feels. Although this does not treat the disease, it does relieve pain to the animal allowing a more comfortable life. The most common complication of a neurectomy is regrowth of the nerve or formation of a painful neuroma (swelling at the nerve end). Using a laser to remove the nerve seals the end of the nerve tissue decreasing the occurrence of neuroma formation.
Other:
Various other surgical procedures utilize lasers. Lasers can be helpful in breaking up bladder stones. Lasers are also being used to remove cartilage in the lower hock joints to aid in fusing a joint (arthrodesis) for treatment for chronic arthritis. Lasers are being used during laparoscopic procedures to seal vessels and prevent hemorrhage. As surgical techniques continue to advance, the laser will be used to treat an increasing number of diseases.
Conclusion
Laser surgery is a specialized technique of performing surgery. The great advantage of laser surgery in large animals is that it allows your surgeon to reach obscure areas and perform surgery through a minimally invasive approach without general anesthesia. If you have any questions about laser surgery, you should contact your ACVS board-certified veterinary surgeon. Find an ACVS Veterinary Surgeon.
—David Levine, DVM, Lecturer in Surgery
—Eric Parente, DVM, Diplomate, ACVS
Posted 9/8/2006
Reviewed and updated 10/4/2009 by Drs. Levine and Parente
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