PMC4020529_01
Axial (a) and coronal (b) CT images obtained after IV and oral contrast administration are shown. Note asymmetric wall thickening involving some of the ileal bowel loops (arrow in (a)). There is dilation of several small bowel loops with a transition point in the mid-lower quadrant (arrow in (b)) consistent with small bowel obstruction. There are also a few borderline enlarged mesenteric lymph nodes (arrowheads in (b)).
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Imaging including abdominal computed tomography (CT) scan with contrast showed small bowel loops distention up to 4.3 cm in diameter and edema with transition point in the mid-lower abdomen concerning moderate enteric obstruction (Figure 1).
Meckel diverticulum gross pictures before and after dissection to show (a) intact diverticulum and (b) mucosal ulcer with severe edema and erythema.
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MD was identified at the level of mid-ileum. Macroscopy showed a prominent, inflamed, and indurated MD (Figures 2(a) and 2(b).
Microscopic pictures of Meckel diverticulum to show (a) sheets of infiltrative small lymphocytes involving mucosa and submucosa, (b) epithelial erosion and lymphoepithelial lesion, and (c) small lymphocytes with irregular nuclear contour and abundant cytoplasm (monocytoid B-cells). (hematoxylin-eosin, original magnification x40 (a), x100 (b), and x400(c)).
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Furthermore, microscopy revealed extensive infiltration of sheets of small lymphocytes with abundant cytoplasm (monocytoid B-cells) prominently in mucosa and submucosa to form lymphoepithelial lesions (Figures 3(a), 3(b), and 3(c)) and focally transmural involving serosal adipose tissue extending to the surgical resection margins.
Microscopic pictures from Meckel diverticulum show (a) Diffuse positivity for CD20; (c) and (d) reactive germinal centers with negativity for BCL-2 (b) and positivity for BCL-6 (c) (original magnification x100 (a)-(c)).
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The vast majority of the lymphocytes were CD20-positive with weak coexpression of CD43 by immunohistochemical studies (Figure 4(a)). T-cell markers including CD3 and CD5. The germinal centers were reactive, which was confirmed by negative BCL-2 and positive BCL-6 immunohistochemical staining and did not show any evidence of follicular colonization by tumor cells (Figures 4(b) and 4(c)).
FlSH studies with (a) API2-MALT1  fusion signals (yellow) (arrow) with the dual color API2(green)/MALT1(red) dual fusion probe consistent with t(11;18)(q21;q21) and (b) dual color MALT1 "split" probe showing MALT1 gene rearrangement (arrows-abnormal cells show split signals).
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Finally, the fluorescence in situ hybridization (FISH) studies revealed MALT1 gene rearrangement signals pattern in 45.6% of the cells analyzed and was followed by positive API2-MALT1 fusion signals consistent with a reciprocal t(11;18)(q21;q21), in 56.3% of examined cells, confirming the diagnosis (Figure 5).