1. Small bowel tumors

2. Epidemiology of small bowel adenocarcinoma
Small intestine accounts for approximately 75% of the length of the GI tract and more than 90% of the mucosal surface
Fewer than 2% of GI malignancies arise in the small intestine
Incidence of small bowel malignancies is 1 per 100,000

3. Small bowel malignancies
30-50% are adenocarcinomas
25-30% are carcinoids
15-20% are lymphomas
10-20% are gastrointestinal stromal tumors

4. Risk factors for small bowel adenocarcinoma
Pre-existing adenoma, either single or multiple
300-fold increased risk in patients with FAP
Crohn’s
Celiac disease
IgA deficiency
Alcohol abuse
Neurofibromatosis
Urinary diversion procedures
? Red meat

5. Anti-neoplastic environment of the small intestine
Liquid contents cause less irritation than more solid contents of large bowel
Rapid transit of intestinal contents provides shorter exposure of mucosa to carcinogens
Lower bacterial load may result in decreased conversion of bile acids into potential carcinogens
Benzopyrene hydroxylase, enzyme responsible for the conversion of the known carcinogen benzopyrene, is present in higher concentrations in the small bowel
Increased lymphoid tissue and higher levels of IgA

6. Metastatic disease involving small bowel
Secondary neoplastic involvement of small intestine is more frequent than primary small bowel neoplasia
Primary tumors of the colon, ovary, uterus, and stomach typically involve the colon by direct invasion or intraperitoneal spread
Primary tumors from breast, lung, and melanoma metastasize to small bowel hematogenously

7. GASTROINTESTINAL LYMPHOMA
It is of non-Hodgkin lymphomas
the gut is the most common extra-nodal location.
It constitutes about 1% to 4% of all GIT malignancies.
classified into B-cell and T-cell lymphomas.

8. 1.    MALT lymphoma is a sporadic lymphoma, which arises from the B cells of MALT (mucosa-associated lymphoid tissue
It can arise anywhere in the gut: stomach (55% to 60% of cases); small intestine (25% to 30%), proximal colon (10% to 15%), and distal colon 10%).
History of IBD appears to increase the risk -Helicobacter-associated chronic gastritis). .

9. 2. IPSID is also referred to as Mediterranean lymphoma
  2.    IPSID is also referred to as Mediterranean lymphoma. immunoproliferative small-intestinal disease (IPSID),
B-cell lymphoma arising
children and young adults, and both sexes appear to be affected equally.
etiology not known

10. 3-The intestinal T-cell lymphoma is usually associated with a long-standing malabsorption syndrome (such as celiac disease)
(age 30 to 40),
Intestinal T-cell lymphoma
In the proximal small bowel

11. The large blue non-Hodgkin's lymphoma cells can be seen infiltrating through the mucosa.

12. the non-Hodgkin's lymphoma cells have prominent clumped chromatin and nucleoli with occasional mitotic figures.

13. Gastrointestinal stromal tumors
Visceral sarcomas, previously classified as leiyomyomas and leiyomyosarcomas
Now classified as GISTs with a range of biological behaviors from low grade to high grade malignancies
Traditionally, microscopic findings were used to define malignancy including:
Increased cell size
Increased cell irregularity
Lack of cell differentiation
Presence of cells with hyperchromic and multiple nuclei

14. GISTs – Tumor biology
Proposed to arise from the interstitial cell of Cajal, an intestinal pacemaker cell of mesodermal origin
Similar cell markers to those of normal Cajal cells
1) myeloid stem cell antigen CD34
2) KIT receptor tyrosine kinase
3) variably positive for smooth-muscle actin
4) usually negative for desmin
Previously thought to be smooth muscle neoplasms but now accepted to have:
1) myogenic features (smooth muscle GIST)
2) neural features (GI autonomic nerve tumor)
3) myogenic and neural features (mixed GIST)

15. Clinical features of GISTs
Most commonly present with pain and weight loss
Most commonly present in the 6th and 7th decades but may occur at any age
Distribution of occurrence is proportional to the length of the segments of the small bowel
Lesions occur in extraluminal, subserosal locations
Often develop central ischemia and necrosis that leads to bleeding

16. Carcinoid Tumors of the Intestine
Originally described by Oberndorfer in 1907
Arise from neuroendocrine cells
Cells of the amine precursor uptake decarboxylase (APUD) system which have the ability to synthesize biologically active substances

17. Clinical features of carcinoid tumors
Most commonly present in the 7th decade
Often present with nonspecific complaints
Up to 50% of patients present with obstruction
Increasing frequency from the duodenum to the ileum with the appendix is the most common site.

18. Pathological features of carcinoid tumors
Carcinoid invasion into the mesentery leads to fibrosis and often kinking of the small intestine
Thickening of the vessel wall is also present and may lead to ischemic changes in the gut
Serotonin is postulated to be responsible for these features

19. Carcinoid tumor. Multiple protruding tumors are present at the ileocecal junction

20. Seen here at the ileocecal valve is a tumor that has a faint yellowish color. This is a carcinoid tumor.

21. Carcinoid Tumor : Clumps or cords of polygonal monotonous cells, rounded nuclei, pink granular cytoplasm, delicate stroma

22. At high magnification, the nests of carcinoid tumor have a typical endocrine appearance with small round cells having small round nuclei and pink to pale blue cytoplasm. Rarely, a malignant carcinoid tumor can occur as a large bulky mass. Metastatic carcinoid to the liver can rarely result in the carcinoid syndrome.

23. Carcinoid Syndrome (Syndrome present when metastasis occurs
in liver or lung )
- Flushing of the face
- Bronchospasm
- Diarrhea and may rarely peptic ulcer.
- Right side heart failure due to fibrosis of endocardium and tricuspid valve.
- Pellagra-like lesion of skin and oral mucus membrane