MINIMALLY INVASIVE SURGERY FOR HORSES:
WHERE ARE WE NOW?
A. M. Trent, DVM, MVSc, Diplomate ACVS
U. MN College of Veterinary Medicine
"Minimally Invasive Surgery" is an umbrella term for a group of techniques that allow conduct of major surgical procedures through very small incisions or through natural body orifices. Arthroscopy and flexible endoscopy are very familiar and well established minimally invasive approaches for equine surgery. Both techniques were established first in human medicine and, with some initial resistance, worked their way into veterinary practice. Laser surgery and, more recently, rigid endoscopy (laparoscopy and thoracoscopy) are making a similar transition. Keyhole arthroplasty (joint replacement through small incisions), interventional radiography (use of real time imaging techniques such as fluoroscopy to diagnose and treat poorly accessible lesions), and transluminal endoscopy (introduction of endoscopes into body cavities across visceral walls) are techniques that are now gaining acceptance in human medicine and may make their way into veterinary practice in the next decade.
Minimally invasive procedures have, as a group, several major advantages and a few significant disadvantages. By reducing the size of the incision used to provide access for a procedure, there is a significant reduction in approach related morbidity, including pain, incisional inflammation and infection. In addition, the amount of trauma to the target organ (ex. ovary or joint surface) and surrounding tissue (ex. abdominal cavity or joint capsule) is also reduced, resulting in a reduction in inflammation related morbidity (ex. Adhesions). As a sum result, people and horses treated with minimally invasive techniques can be returned to work in days as opposed to the months necessary for complete incisional healing following traditional surgical approaches.
Equine surgeons were early adopters of endoscopic laser surgery because it provides surgical access to areas in the upper respiratory tract that are very difficult to access safely by traditional surgical approaches. Common respiratory applications for horses with the early Nd:YAG laser included ablation of cysts, lymphoid follicles, arytenoid chondromas, and ethmoid hematomas, and incision of entrapping aryepiglottic folds and cicatricial membranes. With advances in technology, the Nd:YAG has been largely replaced by the diode laser in human and equine medicine. The CO2 laser operates on a different wavelength and offers very precise tissue incision and evaporation. It is a fairly fragile machine and the beam cannot be delivered through a flexible scope. This limits use to surface structures, structures accessible with rigid endoscopes, and structures that can be exposed via a standard surgical approach. The most common uses for the CO2 laser in equine surgery include resection or ablation of skin tumors and sarcoids. Since lasers seal many vessel and nerve endings and are generally more precise than other incisional methods, laser surgery is generally less painful than alternative approaches.
Rigid endoscopy offers the most quickly expanding area of minimally invasive surgery in horses. Laparoscopy (insertion of scopes into the abdomen) and thoracoscopy (insertion of scopes into the thorax) provide diagnostic and therapeutic access to the abdomen and thorax in horses for a continually increasing range of procedures. Laparoscopy and thoracoscopy are performed by inserting a long rigid fiberoptic scope and long modified instruments through rigid portals inserted through small incisions.
Rigid endoscopic approaches offer a number of advantages over traditional surgical approaches. Instead of the 30-50 cm incision needed to visualize and manipulate structures by a standard surgical approach, several small 1-2 cm incisions are used. As a result, incisional healing is rapid and relatively pain free, and complications are infrequent and of relatively minor concern. As an example, a horse treated by laparoscopic ovariectomy (removal of ovaries) can be returned to work within a week, while a layoff of 3 months is recommended for the same procedure performed via a standard flank or ventral midline approach. In most cases, trauma to peritoneal and pleural surfaces is also reduced and complications such as adhesions are less common. This is a particularly valuable attribute for abdominal surgery in foals. The rigid endoscope provides superior visualization of many structures in the equine abdomen and allows more precise dissection than traditional approaches. Of perhaps greatest benefit, laparoscopy and thoracoscopy can often be performed in the standing horse, eliminating the risks associated with general anesthesia and providing an opportunity for diagnostic evaluation or treatment in horses that might not be able to tolerate anesthesia or recumbency. Laparoscopy is also used very effectively in combination with a small (8-10cm) incision for exteriorization of structures for external manipulation such as biopsy (laparoscope-aided procedures) or for insertion of a hand to aid in manipulation of larger structures (hand-assisted laparoscopy).
Rigid endoscopy is not without disadvantages and risks. Specialized equipment is necessary. Trained personnel are essential and the learning curve is steep. Horses with distended viscera and those that are poorly responsive to sedation in stocks may not be candidates for rigid endoscopy for safety reasons. There is a small risk of visceral trauma during instrument insertion and manipulation. Insufflation with CO2 or filtered air is necessary for many laparoscopic procedures and there is a small risk of inappropriate gas dissemination, although this risk appears to be very low in horses. Not all structures are accessible or amenable to manipulation with the available equipment at this time. Large tumors and masses may be approached laparoscopically, but removal will require enlargement of one of the portal incisions to fit the mass.
When should rigid endoscopy be considered for your horse or for your client's horse? The following applications are now being performed on a regular basis with established or emerging evidence of benefit over traditional techniques.
- Diagnostic abdominal exploration – Indicated for horses with chronic intermittent colic or weight loss (at a time when bowel distention is absent). A standing approach allows excellent visualization of adhesions and common sites of entrapment and abscessation, and allows visualization of the entire small intestine as well as cecum and dorsal colons.
- Biopsy – Indicated for biopsy of multiple solid (liver, kidney, spleen, pancreas) and hollow (small intestine, bladder) organs, particularly when focal lesions are suspected. The direct visualization provides valuable information about the health of the organ in question, increases the likelihood of obtaining a diagnostic sample over ultrasound guided biopsy, and allows control of hemorrhage or tissue trauma.
- Diagnostic thorascopic exploration – Use for this purpose is limited but growing in cases of chronic pleural or pericardial disease. In most cases this is performed as a standing procedure.
- Ovariectomy – Preferred approach for elective ovariectomy for behavioral or performance reasons, and ovarian tumors less than 20 cm in diameter. A standing approach is preferred unless tumors exceed 20 cm in diameter. Horses return to work within a week.
- Cryptorchidectomy – Excellent exposure to non-descended testicles with standing or recumbent approach, although temperament may dictate a recumbent approach. Inguinal testicles may also be retrieved. Preferred approach when the number and location of testicles can not be determined.
- Ruptured bladder repair – Very good access for most tears with reduced adhesion risk.
- Nephrosplenic space closure – Indicated for recurrent colic due to left dorsal displacement (Nephrosplenic entrapment)
- Bladder stone removal – Initial work suggests that a laparoscope aided approach may be preferred for removal of speculated stones in either gender, or large stones in stallions and geldings.
- Inguinal hernia repair – Inguinal hernias can be corrected and the inguinal ring closed with or without castration. The approach is preferred for foals.
- Adhesion lysis – Laparoscopic and thoracoscopic lysis of adhesions results in a lower recurrent rate in most human studies and has been used effectively in both foals and mature horses with chronic colic or weight loss due to adhesions.
- Drain placement – Thoracoscopy is gaining favor as a method to assist in effective pleural or abscess drainage in combination with diagnostic exploration in horses.
The University of Minnesota Veterinary Medical Center has identified minimally invasive surgery as an area of emphasis and we are pleased to offer a full range of services for horses. If you are interested in scheduling your horse for a minimally invasive surgery, or if you would like to learn more about options, please call our office (612-625-6700) and our receptionists can schedule an appointment or put you in touch with one of our surgeons for more information.