BIOLOGIC BEHAVIOR
+ General Considerations
Majority of large intestinal tumors are malignant in dogs
+ Adenocarcinoma
- Mean age 8.5 years (range, 2-14 years)
- Sex predilection: 60%-70% male
- Sites: large intestine and mid-to-distal rectum
- Gross appearance is variable:
- Nodular (single or multiple)
- Pedunculated (mid-to-distal rectum)
- Annular constriction or obstruction (colon to mid-rectum)
- Metastatic rate is highly variable depending on the study
+ Leiomyoma and Leiomyosarcoma
- Smooth muscle tumors are the most common intestinal mesenchymal tumor
- Mean age 11 years (range, 8-13 years)
- Sites: small intestine and cecum
- Paraneoplastic syndromes include hypoglycemia and high plasma erythropoietin causing secondary erythrocytosis
- 50% have localized peritonitis as a result of tumor rupture
- 38%-54% metastatic rate with metastatic sites including the liver, spleen, lungs, kidneys, and diaphragm
+ Other Large Intestinal Tumors
- LSA
- Polyp
+ Clinical Signs
- Tenesmus, hematochezia, dyschezia, and rectal bleeding unassociated with defecation
- Other signs can include vomiting, diarrhea, and weight loss
- Hematochezia uncommon in mesenchymal tumors due to lack of mucosal involvement
- Cecal tumors often present with collapse and septic peritonitis due to perforation
Diagnosis
+ Physical Examination
- Cachexia is common
- Abdominal mass is frequently palpable via either abdomen and rectal palpation
- Other findings include dehydration and abdominal pain
+ Laboratory Tests
Anemia and leukocytosis reported but occur less commonly than small intestinal tumors
+ Abdominal Radiographs
- Abdominal mass is detected in 40%-50% of canine mesenchymal large intestinal tumors
- Abdominal effusion is detected in 20% of cecal leiomyosarcoma secondary to perforation
+ Contrast Radiography
- Contrast radiographs: mural lesions include luminal filling defect, intestinal wall thickening, mucosal ulceration, abnormal positioning of intestinal loops and constricting annular lesions
- Only 25% of large intestinal leiomyosarcoma required contrast studies for identification
+ Endoscopy
- Endoscopy is recommended prior to definitive treatment
- Biopsy samples should be interpreted histologically as cytologic misdiagnosis is common with intestinal ADC being misdiagnosed as either septic inflammation or LSA
- Biopsy samples are often small and superficial resulting in false-negative diagnosis if lesion is either submucosal or associated with surface ulceration and necrosis
+ Exploratory Celiotomy
- Definitive diagnosis with exploratory celiotomy and biopsy
- 50% of large intestinal ADC are associated with annular constrictions
- Leiomyomas and sarcomas are usually large solitary masses growing through the intestinal serosa
TREATMENT
+ Surgery
- Debilitation and hypoproteinemia may complicate treatment
- Exploratory celiotomy with resection and end-to-end anastomosis with 4-8 cm margins and serosal patching of anastomosis
- Mesenteric and regional lymph nodes should be assessed ± aspirated
+ Chemotherapy
no effective chemotherapy for ADC
Prognosis
+ Leiomyoma and Leiomyosarcoma
- Cecal leiomyoma: 28 month ST (n=1)
- Colorectal leiomyoma: 26 month MST
- Cecal leiomyosarcoma: 7.5-31.0 month MST
- 54% metastatic rate with spleen and liver common metastatic sites
- 1-year survival rate 75% and 2-year survival rate 66%
- Furthermore, metastasis at the time of surgery is not a poor prognostic factor with a MST 21.7 months