Small Intestinal Tumors

GENERAL CONSIDERATIONS

Biologic Behaviour

General Considerations

•intestinal tumors are uncommon and account for 3% of canine tumors

•intestinal tumors (small and large) account for 92% of all non-oral GI tumors

•large intestinal tumors are more common than tumors of the small intestine

•80% of dogs > 7 years

•88% malignant and 12% benign (i.e., leiomyoma and polyp)

•sex predilection: 60%-70% male for non-lymphoid intestinal neoplasia

•breed predisposition: GSD and Collie

Lymphosarcoma

•intestinal LSA is the most common intestinal tumor

•majority are multifocal and involve the small intestine

Adenocarcinoma

•age: mean 9 years (range, 1-14 years)

•sites: large intestine and mid-to-distal rectum

•pseudomyxoma peritonei has been reported in 1 dog with small intestinal ADC and is characterized by deposition of mucinous pools on serosal surfaces and gelatinous ascites

•44% metastatic rate for small intestinal ADC with metastatic sites including the regional lymph nodes, mesentery, and liver ± spinal meninges and testes

Leiomyoma and Leiomyosarcoma

•smooth muscle tumors are the most common intestinal mesenchymal tumor

•mean age 9 years (range, 4-14 years)

•sites: small intestine and cecum

•50% have localized peritonitis as a result of tumor rupture

•intestinal leiomyosarcoma has been reported as a cause of nephrogenic diabetes insipidus in 1 dog

•38%-54% metastatic rate with metastatic sites including the liver, spleen, lungs, kidneys, and diaphragm

Mast Cell Tumor

•signalment: purebred male dogs of miniature breeds

•clinical signs: anorexia, lethargy, vomiting, and diarrhea

•hematology: anemia, hypoproteinemia, and mastocytemia are common

•GI ulceration is a common finding

•100% metastatic rate with metastatic sites including regional lymph nodes (common), liver, spleen, heart, and lungs

Other

•intestinal carcinoids are rare

•Goblet cell carcinoid (characterized by features consistent with both carcinoid and ADC) has been reported

•secretory (IgG) and non-secretory extramedullary plasmacytoma

•FSA

CLINICAL FEATURES

Clinical Signs

•anorexia, weight loss, intermittent vomiting, and diarrhea

•severe, persistent vomiting is occasionally observed if proximal small intestinal tumor causes obstruction

Diagnosis

Physical Examination

•palpable abdominal mass and cachexia are common

•other findings include dehydration and abdominal pain

Laboratory Tests

•anemia and leukocytosis are common in dogs with non-lymphoid intestinal tumors

•anemia and hypoglycemia are common in dogs with intestinal leiomyosarcoma

•mesenchymal tumors are associated with microcytic hypochromic anemia, hypoproteinemia, and mild leukocytosis

Abdominal Radiographs

•abdominal mass, obstruction, or persistent irregularity of bowel appearance are identified in 25% of small intestinal tumors and nearly 50% of non-lymphoid intestinal tumors

•abdominal mass is detected in 60% of canine mesenchymal small intestinal tumors

Contrast Radiography

•intestinal mass identified in 57% of dogs with non-lymphoid intestinal tumors

•contrast radiographs: mural lesions include luminal filling defect, intestinal wall thickening, mucosal ulceration, abnormal positioning of intestinal loops, and constricting annular lesions

Ultrasonography

•intestinal mass identified in 87% (13/15) dogs with non-lymphoid small intestinal tumors

•intestinal ADC are transmural, poorly echogenic, and associated with complete loss of wall layering, increased intestinal wall thickness (median 12 mm), luminal fluid accumulation proximal to the lesion (81%), and regional lymphadenopathy (57%)

•loss of wall layering is an excellent predictive factor for differentiating intestinal neoplasia from enteritis in dogs (99% v 12%) with intestinal tumors 50.9-times more likely to have loss of wall layering

•intestinal tumors also have significant increases intestinal wall thickness (15 mm v 6 mm) and are significantly less likely to have diffuse intestinal involvement (2% v 72%)

Exploratory Celiotomy

•definitive diagnosis with exploratory celiotomy and biopsy

•majority of small intestinal ADC are associated with annular constrictions

•leiomyomas and sarcomas are usually large solitary masses growing through 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

•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 plasmacytoma and MCT