Criteria used to classify malignant lymphoma of small bowel include:
i) Cell lineage: B or T cell lymphoma
ii) Primary or systemic nature of tumour
iii)Associated  backround chronic illnesses.

Primary gastrointestinal lymphoma usually arise as a sporadic tumour. Sporadic lymphomas, also termed the 'Westerm type'  are B- cell lymphomas which appear to arise from the B- cells of the mucosa associated lymphoid tissue.
Some lymphomas develop in the backround  of chronic  diseases . Eg.  Sprue -like malabsorption syndromes, congenital immunodeficiency states, infection with HIV following organ transplantation with immunosuppresion (heart transplant recipients), those complicating Crohn's disease , hypogammaglobulinaemia with lymphoid hyperplasia, in patients with alpha chain disease.
Ileum is commonly affected followed by jejunum and duodenum.

B-cell lymphoma usually arises in children and young adults with Mediterranean ancestry.
Usually located in the distal portion of duodenum and upper jejunum.
Diffusely thickened bowel wall with small nodules or discrete tumour masses indicate high grade tumour.
Diagnosis can be made by endoscopic biopsy. Histologically the low grade tumour is characterized by an infiltrate of plasma cells and lympho-plasmacytoid cells in the mucosa. There is broadening & shortening of villi and separation of crypts. The cells appear mature. In the early stage the tumour responds to antibiotics.
High grade tumour is characterized by pleomorphic large cells with immunoblastic and plasmacellular features.
Immunohistochemistry reveals alpha heavy chains of immunoglobulins in the cytoplasm.

-Relatively common in the Middle east and Algeria.
-Usually located in the ileum and the ileocaecal region.
-May cause intussusception.
-Histologically, the tumour consists of lymphoblast like cells with high mitotic rate
interspersed with macrophage containing cellular debris (starry-sky). The infiltrating tumour  dissects through the muscle fibres and surrounds the regional lymphnodes without infiltrating them.
-Immunohistochemistry:  CD19,20,22 &79a : positive
CD 10: positive,
CD5 & 23:  negative
Ki67 : more than 85% cell are positive.

Presents as lymphoid polyps in elderly patients (around 60 years of age).
It is usually associated with leukemic spread.
Immunohistochemistry:  Cyclin D1 positive
CD5 positive
CD10 : negative / positive
CD19,20,22, 79a  positive
CD23 : negative

The tumour has a follicular growth pattern and consists
of a mixture of germinal
centre blasts and cleaved
cells ( centroblasts and centrocytes).
Immunohistochemistry:  CD5 : negative
CD10 : positive/negative
CD19, 20, 22, 79a : positive
BCL-2 : positive

Occasionally, these  tumours transform into diffuse tumour containing large centroblasts. (Diffuse large B- cell lymphoma).

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