Large Intestinal Tumors

BIOLOGIC BEHAVIOUR

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 FEATURES

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

•multiagent protocols recommended for LSA as either adjuvant therapy or sole treatment for diffuse disease

•chemotherapy is also recommended for cats with intestinal plasmacytoma and MCT