AITL : Cellular Infiltrate
In angioimmunoblastic T-cell lymphoma (AITL), the nodal architecture is effaced by a polymorphic infiltrate occupying the paracortical or interfollicular areas of the lymph node. The infiltrate usually extends beyond the node into the perinodal fat with sparing of the cortical sinuses. The infiltrate consists of small to medium-sized lymphocytes (neoplastic cells) admixed with neutrophils, eosinophils, plasma cells, dendritic cells, histiocytes, and epithelioid cells. In some cases, the epithelioid cells are quite prominent and may mask the key diagnostic features. The neoplastic T cell population ranges from small foci that may be easily masked by the background polymorphic infiltrate to large confluent sheets that are readily identified. Cases with a predominance of neoplastic T-cells in the form of large sheets are generally high-grade and show an overlap with peripheral T-cell lymphoma, NOS. The atypical T cells have round or irregular nuclei, clear cytoplasm, and well-defined cytoplasmic borders. Many cells with clear cytoplasm can be seen in this image.