Pathophysiology

Acute gastrointestinal emergencies are caused by gastrointestinal perforation, obstruction, or intraluminal hemorrhage. Perforation occurs as a sequelae to ulceration of gastric or intestinal tumors, poor wound healing after enterotomy, chemotherapy for lymphoma and mast cell tumors, or mast cell tumor-induced ulceration. Gastrointestinal perforation quickly induces fulminant peritonitis resulting in fluid, electrolyte and protein losses, acid-base imbalances, hypoglycemia, diffuse intravascular coagulopathy, circulatory collapse, and septic shock. Gastrointestinal obstruction is caused by tumor encroachment or by adhesions from intraabdominal masses. Obstruction causes fluid and gas accumulation proximal to the site of obstruction and an increase in intraluminal pressure. Continued distension results in venous congestion, mural edema, decreased absorption, and increased secretion. Fluid and electrolytes are lost and significant vascular compromise may result in devitalization of the intestinal wall. At this point, the mucosal barrier is impaired and bacterial translocation results in progressive septic and hemodynamic shock. Intraluminal hemorrhage is commonly seen after ulceration of such tumors as mast cell tumors, gastrinomas, gastric and intestinal carcinomas, lymphoma, and metastatic tumors. Gastric and intestinal tumors are relatively uncommon in dogs and cats and include adenocarcinoma, leiomyoma, leiomyosarcoma, malignant lymphoma, mast cell tumor, polyps, and fibrosarcoma. Mainly older animals are affected and adenocarcinoma seems to be most common in dogs and lymphoma in cats. Relatively more nonlymphoid gastrointestinal tumors are reported in Siamese cats, Boxers, Collies, Staffordshire Bull terriers, and German shepherds compared to other breeds. Over two-thirds of gastrointestinal tumors are malignant and early metastasis to regional lymph nodes, liver, and lung in combination with ulceration are observed frequently.

Clinical Presentation and Diagnosis

Clinical signs associated with gastrointestinal tumors are nonspecific and include vomiting, diarrhea or constipation, anorexia, abdominal pain, ascites, and distension. Partial or total obstruction of the gastrointestinal tract is relatively common and the most common signs are protracted vomiting, abdominal pain, and abdominal distension. With perforation, signs quickly progress to severe depression, dehydration, and signs of cardiovascular and septic shock. Intestinal bleeding is associated with signs of anemia, weight loss, hematemesis, hematochezia, diarrhea, and melena. Ascites, dilated intestines, solitary masses, and excessive borborygmi can be detected during physical examination. Radiography and ultrasonography allow further examination and localization of abdominal masses, ileus, or free air. Diagnosis can be obtained using ultrasound-guided fine needle or cutting biopsy of the tumor. Barium or iodine (if perforation is suspected) contrast studies may locate the tumor if plain radiography does not. Endoscopy is useful in locating and obtaining biopsy specimens from gastric, duodenal, colonic, and rectal tumors, but is seldom used in an emergency situation. Gastrointestinal perforation is accurately diagnosed by paracentesis or peritoneal lavage and immediate exploratory surgery is necessary if intra and extracellular bacteria, or foreign material are found on cytological examination. Rarely, diagnostic peritoneal lavage may fail to demonstrate bacteria if the spillage caused by the perforation is localized. Repeat peritoneal lavage, radiography with water soluble contrast material, or exploratory surgery is indicated in these cases.

Surgical Therapy and Aftercare

Severe active bleeding into the digestive tract, partial or complete obstruction, or gastrointestinal perforation necessitate emergency explorative laparotomy. Preoperative supportive care is directed to correcting fluid, electrolyte, and acid-base imbalances; and treating septicemia and endotoxic shock. Supportive therapy may consist of blood transfusion, intravenous fluid or colloid, and antibiotic administration covering gram-negative and anaerobic bacteria (e.g., cephalosporins or aminoglycosides in combination with metronidazole). After routine celiotomy, the abdomen is explored and the extent of gastrointestinal involvement is assessed. Regional lymph nodes and liver are inspected for possible metastasis. At this point, biopsy specimens of tumor and regional lymph nodes can be obtained and submitted for cytological and histological examination. Histologic examination of frozen sections allows immediate diagnosis in most cases.

For gastric tumors, complete resection is the therapy of choice. Because of frequent involvement of antrum and pylorus (50% of cases), partial gastrectomy as a Billroth I or II procedure is often necessary to obtain wide surgical margins. Enlarged local lymph nodes are biopsied, or excised en-bloc. Partial gastrectomy is contraindicated in dogs with gastrointestinal lymphoma because of the diffuse nature of the disease, effective chemotherapy options, and associated complications with wound healing. Solitary lymphomatous lesions seem to respond better to surgery and adjunctive chemotherapy than to either surgery or chemotherapy alone. Intestinal neoplasms are usually treated by wide surgical resection and anastomosis. A simple end-to-end anastomosis often is sufficient but more complex intestinal reconstruction techniques are sometimes necessary. Tumors that already have metastasized may be effectively excised for palliation. Resection of regional lymph nodes and other sites of metastasis may decrease the total tumor burden enhancing the effect of adjuvant therapy. The use of serosal or omental patching at the surgery site is indicated for extensive resections or in patients with suspected impaired wound healing. The need for esophageal, gastric or intestinal feeding tubes should be assessed before closure. Placement of an esophagostomy, gastrostomy or jejunostomy tube is relatively easy. The benefits of improved nutritional status in cachectic cancer patients far outweigh the management disadvantages of surgically placed feeding tubes. General peritonitis after intestinal perforation is treated aggressively. Intraoperative cultures are obtained and the abdominal cavity is lavaged with copious amounts of a warm isotonic solution. Open abdominal drainage is used in severe cases of peritonitis. For open abdominal drainage, the linea alba is closed with a loose simple continuous polypropylene suture pattern and the subcutis and skin are left open. A sterile bandage is placed over the wound and changed as often as required. Periodic surgical lavage under strict aseptic conditions may be of benefit. The use of sterilized commercial diapers decreases the need of frequent bandage changes caused by fluid penetrating the outer bandage.

Postoperative care includes continuing fluid and electrolyte therapy. Initially small quantities of water are offered, and if vomiting does not occur, small quantities of soft food can be fed. Anorectic animals may be force fed by nasogastric, esophageal, endoscopically or surgically placed gastrostomy, or jejunostomy tubes. After intestinal anastomosis, breakdown of the suture line most commonly occurs during the second and fourth day postoperatively and signs of physical deterioration during that time should be aggressively investigated. Non-perforating ulceration of the gastrointestinal tract directly or indirectly caused by tumors can be treated medically using antacids (e.g., aluminum hydroxide), histamine2-antagonists (e.g., cimetidine), coating agents (e.g., sucralfate), and proton pump inhibitors (e.g., omeprazole). Malignant tumors of the gastrointestinal tract may benefit from adjunct chemotherapy because of their aggressive metastatic behavior. The effect of chemotherapy for canine gastric adenocarcinoma and canine and feline intestinal adenocarcinoma have been discouraging, however. Gastrointestinal malignant lymphoma appears less responsive to chemotherapy than the multicentric type. Also, complications associated with intestinal perforation after chemotherapy should be taken into consideration. Due to their aggressive metastatic behavior (up to 75%), the overall prognosis for gastrointestinal malignancies is guarded. The prognosis is poor if the tumor is extensive, if metastases are present, or when the tumor erodes through the serosal surface. The mean survival time of 12 dogs with malignant nonlymphoid gastrointestinal tumors, that survived the first two weeks after surgery, was 114 days without adjunctive chemotherapy. The mean survival of cats with resected adenocarcinoma was 15 months.

Conclusion

Surgical abdominal emergencies are relatively common in small animal cancer patients and pose a clinical and ethical challenge for the oncologist. The most common abdominal emergencies include abdominal hemorrhage, and urogenital, or gastrointestinal obstruction or perforation. After emergency stabilization, the question of whether surgical intervention is proper and necessary needs to be answered. Immediate surgery is only indicated in life-threatening situations where the risk versus benefit of surgery has been weighed, and should be accompanied by adequate preoperative and postoperative supportive care.

Reference

1.  Kirpensteijn J, et al. Vet Clinics of North America [Small Animal] 1995; 25: 207-223