[Problems in biopsy differential diagnosis in lymphomas of the small and large intestines]

Besides the problems inherent in endoscopically obtained tissue and the low incidence of intestinal lymphomas, the major difficulties reside in the distinction to reactive processes and in the differential diagnosis among several lymphoma entities. Knowledge of the microanatomical and biological properties of the intestinal MALT, supplemented by sufficient clinical information, are important prerequisites for the diagnostic work-up which has to include immunohistochemical studies. Whereas the diagnosis of aggressive B-cell lymphomas (diffuse large B-cell lymphoma, Burkitt's lymphoma) is usually straightforward, lymphomatous polyposis (LP, the intestinal equivalent of mantle cell lymphoma) and low-grade B-cell lymphoma of MALT-type may be difficult to diagnose and to separate from reactive lymphoproliferations. The characteristic immunohistochemical profile of LP (cyclin D1 + CD5 + CD43 + CD23 - CD10 - IgM kappa or lambda, is very helpful in this regard and similarly useful to exclude intestinal involvement by B-CLL or follicular center lymphoma. In addition, the endoscopic appearance characterized by seeds of small polyps along the colorectum favors LP although MALT-type lymphoma may occasionally produce polypoid lesions. Focal lymphoid hyperplasia occurs in the terminal ileum and may present with a mass in the right iliac fossa. The diagnosis of intestinal T-cell lymphoma (ITL) represents the most challenging task for both clinicians and pathologists. This disease is often associated with and may closely mimick celiac disease of adult onset type, or can be misdiagnosed as inflammatory bowel disease. The presence of an abnormal activated T-cell phenotype, i.e. different from that of normal intraepithelial lymphocytes, strongly suggests ITL and is of particular importance in cases that lack overt cytological atypia.