Principles of Minimally Invasive Surgery

Minimally invasive surgery (i.e., endoscopy) is an important diagnostic and therapeutic tool in veterinary medicine. This chapter provides a brief overview of endoscopic techniques, including underlying principles and a description of equipment. Specific techniques (e.g., thoracoscopic pericardiectomy and removal of osteochondritis dissecans [OCD] lesions) will be found in the relevant chapter(s) for that system, disease, or condition.

Definitions and Terminology

Endoscopy is the use of an instrument (i.e., an endoscope) to visualize the interior of an organ or body cavity that otherwise cannot be examined without surgery. Flexible endoscopy uses an endoscope that can bend to look and/or move around corners. The degree of flexibility depends on the instrument, but the ability to make bends ≥180 degrees is typical for most flexible scopes. Flexible endoscopes have a handle (where the scope is held by the operator), an insertion tube (the part that is inserted into the patient), and an umbilical cord (the part that attaches the scope to the light source and video processor). The biopsy channel is a passage that allows one to place instruments through the scope (e.g., biopsy forceps, foreign body retrieval forceps, aspiration tubes, cytology brushes) and aspirate air or liquids. Immersible scopes can have their handles placed in water without risk of damage.

Rigid endoscopy uses a plastic or metal scope that cannot bend. Sometimes a lens at the tip of the scope may allow one to look at various angles, even back on oneself. An obturator is a device placed through a hollow endoscope to facilitate insertion of the scope into the organ desired (e.g., esophagus, colon). When the obturator has a sharp point designed to facilitate penetration through tissue, it is termed a trocar.

Equipment is inserted into the body through the skin and soft tissue or a natural orifice. Insertion through the skin is done through portals. Portals are defined by their use. The scope is inserted through a scope or camera portal, whereas power and hand tools are inserted through an instrument portal. Cannulas are metal tubes that maintain the portals and protect the instruments. Triangulation refers to successful visualization of the instruments through the scope in a manner that is conducive to performing biopsies or therapeutic procedures within the body cavity.

Arthroscopy is endoscopy of a joint. Arthroscopes are always used through cannulas. Other instruments and fluid outflow devices may be used with or without cannulas. Instrumenting refers to the insertion of an endoscope, arthroscope, or other tool into the joint. Triangulation refers to successful visualization of the instruments through the scope in a manner that is conducive to performing biopsies or therapeutic procedures within the joint. The scope is inserted through a scope or camera portal, whereas power and hand tools are inserted through an instrument portal. Fluid flowing into the joint is referred to as inflow or ingress; fluid flowing out of the joint is referred to as outflow or egress. Repeat arthroscopic examination of a joint that has been previously scoped is referred to as second-look arthroscopy. In all endoscopies, a “red out” or a “white out” refers to having the viewing tip of the endoscope so close to the surface of what is being examined that one cannot focus on the surface (i.e., a blur occurs) or to having debris on the viewing end of the scope.

Endoscopy: General Principles, Equipment, and Techniques

Endoscopy is used to biopsy organs, remove foreign objects, examine the interior surface of hollow structures, and perform procedures typically done by more invasive surgery. This technique is valuable only when it is successful and eliminates the need for more invasive surgery. However, if for any of a number of reasons tissue samples obtained endoscopically are inadequate for diagnosis, unacceptable trauma occurs during endoscopic removal of foreign objects, or mucosal surfaces cannot be adequately examined endoscopically, then endoscopy ceases to be useful. Unfortunately, endoscopy sometimes has become more of a “hobby” than an important procedure to be learned and practiced diligently. Flexible endoscopy of the upper gastrointestinal tract in particular is much more difficult to properly perform than is widely appreciated, especially with regard to biopsying the mucosa. Much as is the case for a hemilaminectomy or a tibial plateau leveling osteotomy (TPLO), if the veterinarian is not sufficiently trained or is not going to perform the procedure often enough to maintain expertise, then it is probably best if patients are referred for this procedure.

Although flexible endoscopy of the alimentary and respiratory tracts occasionally is performed to dilate a stricture, control hemorrhage, remove part or all of an organ, insert a tube, or remove a foreign object, its primary use in veterinary medicine is to visualize and obtain tissue or cytologic samples (Box 13-1). Biopsy should always be performed regardless of the gross mucosal appearance unless there is a specific reason not to biopsy (e.g., coagulopathy, increased risk of perforation). Tissue samples obtained by flexible endoscopy are limited to the mucosa and adjacent submucosa as opposed to the full-thickness samples obtained surgically. However, endoscopic samples are typically adequate for diagnosis in probably >90% of patients (personal observation of author M.D.W.) with gastric or intestinal infiltrative disease (e.g., inflammatory bowel disease, histoplasmosis, neoplasia), assuming the operator has been well trained. Endoscopy cannot diagnose disorders beyond its reach (e.g., focal carcinoma of mid-jejunum). Nor can endoscopy reliably diagnose infiltrates that are too deep in the mucosa for the endoscopic biopsy forceps to reach or those that are hard, densely fibrotic lesions (e.g., pythiosis, scirrhous carcinoma).

Box 13-1 Primary Indications for Endoscopic Procedures in Dogs and Cats

Gastroduodenoscopy

• Gastric and intestinal biopsy/cytology for diagnosis of infiltrative and lymphatic disorders

• Identification of a mass, ulceration, erosion, lymphangiectasia, or Physaloptera infestation

• Identification and removal of foreign objects

• Placement of a gastrostomy tube

• Location of lesions (e.g., ulcer, site of bleeding) before or during surgery

• Removal of gastric polyps causing clinical signs

Esophagoscopy

• Identification and removal of foreign objects

• Diagnosis and dilation of strictures

• Aid in placing stents

• Diagnosis of esophagitis

• Biopsy of tumors

Proctoscopy and Colonoileoscopy

• Biopsy of the colon, rectum, ileum, or cecum for infiltrative disorders

• Identification of occult whipworm infestation

• Diagnosis/removal of polyps

• Diagnosis of cecocolic intussusception

Laryngoscopy

• Identification of laryngeal paralysis

• Identification of elongated soft palate and/or everted laryngeal saccules

• Location and removal of foreign objects

• Biopsy of a mass or other infiltrative lesions

Cystoscopy

• Diagnosis of ectopic ureters

• Biopsy of proliferative lesions in urethra and bladder, especially carcinomas

• Injection of collagen into the urethra to control incontinence

Thoracoscopy

• Identification/biopsy of masses and other infiltrative lesions, including lung biopsy

• Assistance in placing chest tubes in animals with severe pyothorax

• Determination of whether thoracotomy is appropriate, and if so, the best approach

• Performance of minimally invasive surgery, such as pericardiectomy, ligation/resection of PRAA

Bronchoscopy

• Identification of lesions (e.g., collapsed trachea, Oslerus osleri infestation)

• Bronchoalveolar lavage or brushing of trachea/bronchus for cytology/culture

• Identification and removal of foreign objects

• Identification of lung lobe torsion

• Biopsy of mucosa (e.g., with chronic bronchitis)

• Aid in placement of stents/evaluation of stents that were previously placed

Rhinoscopy

• Identification and removal of foreign objects

• Biopsy/cytology of mass lesions and mucosa for infiltrative disorders

• Identification and biopsy of aspergillomas

• Identification of source of epistaxis or chronic nasal discharge

Posterior Nares (Choanal) Examination

• Identification and removal of foreign objects

• Cytology/culture of the caudal nares

• Identification of and biopsy of proliferative disorders

• Identification, dilation, and stenting of nasopharyngeal stenosis

• Identification of nasal mites

Laparoscopy

• Examination and biopsy of abdominal viscera

• Determination of whether celiotomy is warranted (e.g., Is there evidence of metastasis that means surgery cannot be curative?)

• Performance of minimally invasive interventional surgery (e.g., gastropexy, placement of jejunostomy tube, ovariohysterectomy, removal of retained testicle)

Arthroscopy

• Identification/biopsy of lesions

• Removal of loose bodies (cartilage fragments, bone fragments, torn meniscus)

• Topical management of osteoarthritis—abrasion arthroplasty, microfracture

• Joint lavage for sepsis

• Arthroscopic assisted fracture repair

• Arthroscopic assisted joint stabilization

PRAA, Persistent right aortic arch.

Cytologic studies from endoscopic brushings or washes are occasionally diagnostic for disorders such as cancer, histoplasmosis, protothecosis, and eosinophilic enteritis. Histoplasmosis occasionally has been diagnosed cytologically when it was missed histologically. However, most inflammatory bowel diseases (especially lymphocytic-plasmacytic infiltrates) cannot be definitively diagnosed cytologically. Washings are especially useful in the respiratory tract to diagnose inflammatory or infiltrative problems, but they may also be useful in the search for gastric Ollulanus tricuspis infestation or duodenal giardiasis.

Rectal and gastric polyps can be removed endoscopically, although endoscopic snares fitted for electrocautery are required. However, because rectal polyps usually are found close to the rectum, surgical removal typically is easier and more certain to remove the entire polyp. Endoscopic polypectomies should be attempted only if the practitioner has been trained in endoscopic electrocautery; inappropriate use of electrocautery can damage or destroy the endoscope and/or video processor.

Percutaneous placement of gastrostomy feeding tubes can be done with or without endoscopy (see p. 107). Endoscopic placement of such tubes is indicated when the nonendoscopic apparatus for placement cannot be safely passed through the esophagus (e.g., esophageal stricture, esophageal dilation), when the operator is inadequately trained in the use of nonendoscopic apparatus, or when the endoscope is already in the stomach for other purposes. Endoscopic placement includes insufflation of the stomach, which is advantageous because insufflation helps prevent other abdominal organs from becoming trapped between the stomach and the abdominal wall.

Endoscopic dilation of benign esophageal strictures caused by post-esophagitis scarring is preferred to surgical resection. Strictures can recur after either method, but surgery may be associated with greater postprocedural morbidity and mortality and has a higher recurrence rate.

Severe upper gastrointestinal hemorrhage and persistent vaginal hemorrhage are indications for endoscopy. Endoscopy may help determine whether surgery is indicated and ensure that all bleeding sites are located. Intraoperative endoscopy can find bleeding gastric mucosal lesions if the surgeon cannot identify them at surgery; large ulcers may be missed when the stomach is examined only through a gastrostomy incision. Severely hemorrhaging lesions may require endoscopic electrocautery or injection with alcohol. Endoscopy may also detect small mucosal tumors undetectable from the serosal surface.

Rigid Endoscopy

Rigid endoscopy can be used for the gastrointestinal and respiratory tracts, urinary bladder, peritoneal cavity, pleural cavity, and joints. Indications for rigid endoscopy include many of those for flexible endoscopy (see Box 13-1), but rigid endoscopy (especially laparoscopy, thoracoscopy, and arthroscopy) is used more often than flexible endoscopy for interventional procedures.

Tissue samples obtained by rigid biopsy forceps during rigid colonoscopy typically procure large, deep colonic or rectal samples that include relatively large amounts of submucosa. Therefore rigid endoscopy is appropriate even when dense, fibrotic, submucosal lesions (e.g., carcinoma, pythiosis) are suspected.

Foreign Bodies

Rigid and flexible endoscopy is used to remove foreign objects. Rigid endoscopy is the best way to remove most esophageal foreign objects. Most esophageal, nasal, tracheal, and laryngeal foreign objects—and many gastric and duodenal foreign objects—can be removed endoscopically without undue risk to the patient. Objects that are out of reach of the endoscope, that cannot be firmly grasped or trapped by endoscopic devices, or that may cause severe damage if endoscopic removal is attempted (e.g., linear foreign objects that have been present for several days, objects with sharp edges or points that cannot be covered during removal) usually should be removed surgically.

Equipment

Flexible Endoscopes

Endoscopes: The equipment needed depends on the type of endoscopy and the body system to be investigated. Rigid and flexible endoscopes are available in a large assortment of sizes and lengths; both types have advantages and disadvantages (Box 13-2). Flexible endoscopes most often used in veterinary medicine are gastroduodenoscopes, bronchoscopes, and colonoscopes. Flexible scopes have a handle, an insertion tube, and an umbilical cord (Fig. 13-1). Bronchoscopes usually have a 2- to 6-mm outer diameter, gastroduodenoscopes a 7.9- to 10-mm outer diameter, and colonoscopes a 10- to 16-mm outer diameter. All scopes should have a biopsy-suction channel (usually 2 mm in diameter for bronchoscopes and 2- to 3.2-mm for gastroduodenoscopes and colonoscopes). Gastroduodenoscopes and colonoscopes have four-way deflection of the tip of the scope and an air-water channel that is used to insufflate air and wash off the viewing lens; bronchoscopes and ultrathin gastroduodenoscopes typically have only two-way deflection of the tip. Bronchoscopes do not have an air-water channel. The insertion tube typically has a working length of 40 to 60 cm in bronchoscopes, 100 to 135 cm in gastroduodenoscopes, and 130 to 220 cm in colonoscopes.

Box 13-2 Comparison of Flexible and Rigid Endoscopes