These lymphomas usually arise from MALT (mucosa associated lymphoid tissue)- also known as Marginal Zone B - cell lymphoma (Low and High grade).

Diffuse large B-cell lymphoma include high grade lymphoma of MALT origin and non-MALT type and they are indistinguishable.

Other types include mantle cell lymphoma (malignant lymphomatous polyposis) , follicular lymphoma, Burkitt's lymphoma and rare solitary plasmacytoma.

Helicobacter pylori infection is a risk factor for gastric lymphoma 

Some MALT lymphomas have been reported in immunocompromised patients (in AIDS and following organ transplantation). High grade lymphoma following organ transplantation may be related to Epstein-Barr virus.

     Images: 1 ;  2

Note: Diagnosis of gastric lymphoma is made on the morphological features. Lymphoma should not be diagnosed or refuted on the basis of clonality studies by immunohistochemistry or molecular techniques alone.

Gross features:
Commonly located in the gastric antrum.
May be polypoid and fungating like gastric carcinoma. In low grade cases, multiple erosions or superficial ulceration may be present.

                          
Microscopic features:

LOW GRADE:  3 ; 4  ; 5

- Diffuse polymorphous population of B-cells expanding the lamina propria. Reactive lymphoid follicles are present. Numerous plasma cells are also  noted, some of these may have Dutcher bodies (true intranuclear inclusion made up of immunoglobulin).

- Small or medium sized irregular  (centrocyte-like) cells forming lymphoeithelial lesions and destroying the epithelium, leaving epithelial remnants and sometimes invading the follicles.

- In some, cases the neoplastic cells resemble small lymphocytes or monocytoid B cells with abundant pale staining cytoplasm.

Note:    
Lymphoepithelial lesions defined as glandular structures expanded and destroyed by groups of more than 3 lymphoid cells.

Immunostaining for CD20, CD79 and cytokeratin are useful for demonstrating lymphoepithelial lesions. CD5, CD10, CD23 or cyclin D1 are negative.

Occasional non destructive lymphoepithelial lesions alone are not sufficient to diagnose lymphoma.

Carefully look for compact clusters, confluent aggregates or sheets of blast cells that makes the tumour high grade.

Problem in distinguishing low grade lymphoma from heavy  chronic inflammatory cell infiltrate in chronic gastritis (lymphoepithelial lesion is diagnostic of lymphoma).

HIGH GRADE:  Images: 6 ;  7
- Lesion does not regress  with H. pylori eradication.

- Destructive infiltrate of clusters or sheets of blast cells.

- Few or no lymphoepithelial lesions.

- Mitoses and apoptotic bodies frequent.

- Problem in distinguishing from diffuse carcinoma, sarcoma, or even T-cell lymphoma or metastatic melanoma. Epithelial lesions infiltrated by melanoma cells may mimick lymphoepithelial lesions.

- Mucin stains and immunostaining for cytokeratin , CEA , common leucocyte antigen, B and T cell markers are very helpful.

http://www.histopathology-india.net/EsophagealPathology.htm

Normal histology of the small intestine for anatomic pathologists

An approach to evaluation of small intestinal biopsy.

Malabsorption syndrome (causes  and clinical investigations)

Tropical Sprue

Coeliac Disease

Enteropathy-associated T-cell lymphoma

Intestinal lymphangiectasia

Peptic Ulcer

Lesions causing small bowel obstruction and bleeding - 
Intussusception : Adhesions : Volvulus

Meckel's diverticulum

Ischemic bowel disease 

Brunner's Gland Adenoma

Duodenal  Gangliocytic Paraganglioma

Lymphoma of the small intestine

- Interpretation of Large Intestinal Biopsies

- Assessment of abnormalities -1 (lumen, surface epithelium, subepithelial zone)

- Assessment of abnormalities - 2  (crypt density , architecture and epithelium)

- Assessment of abnormalities - 3 (changes in the lamina propria,muscularis mucosae and submucosa) 

Juvenile polyp ; Peutz-Jeghers polyp ; Inflammatory fibroid polyp ; Multiple Lymphomatous polyposis ; Lymphoid polyp

AN APPROACH TO THE  REPORTING  OF ESOPHAGEAL BIOPSIES

BARRETT'S   ESOPHAGUS   (INTESTINAL METAPLASIA  DYSPLASIA  &   ADENOCARCINOMA)

BENIGN TUMOURS AND  TUMOUR - LIKE CONDITIONS  OF  ESOPHAGUS

 1. SQUAMOUS PAPILLOMA OF THE ESOPHAGUS

 2. INFLAMMATORY FIBROID POLYP OF THE ESOPHAGUS

 3. LEIOMYOMA OF THE ESOPHAGUS

 4. GRANULAR CELL TUMOUR OF THE ESOPHAGUS

 5. ESOPHAGEAL CYSTS

 6. GLYCOGENIC ACANTHOSIS

 7.FIBROVASCULAR POLYPS

REPORTING  OF  ESOPHAGEAL  RESECTION SPECIMENS

SQUAMOUS  EPITHELIAL  DYSPLASIA INCLUDING SQUAMOUS CELL CARCINOMA IN-SITU OF THE ESOPHAGUS

SMALL CELL CARCINOMA OF THE ESOPHAGUS

DRUG  RELATED  LESIONS  OF  THE GASTROINTESTINAL TRACT

Mycobacterium Leprae Inf.

Mycobacterium Marinum Inf.

Mycobacterium Ulcerans Inf.

Necrotizing Enteritis (pig-bel)

Norwalk Virus related Diarrhea

Rotavirus diarrhea

Salmonellosis (Gastroenteritis and Septicemia)

Shigellosis

Tuberculosis

Staphylococcal Infection

Streptococcal Infection

Trichinosis

Trichosporonosis

Trichuriasis

Tuberculosis

Tularemia

Typhoid fever