Summary Benign lymphoid aggregates are seen in only a minority of bone marrow specimens, but their distinction from non-Hodgkin lymphoma, particularly B-cell lymphomas, can represent a diagnostic challenge. Although criteria have been proposed to help distinguish between benign and malignant aggregates, a detailed description of the distribution patterns of B and T lymphocytes within benign lymphoid aggregates has not been investigated. One hundred thirty-seven cases of bone marrow specimens containing benign aggregates were studied with a panel of immunostains. A subset of these cases was also examined for immunoglobulin gene rearrangements by polymerase chain reaction. The aggregates were categorized based on size, location (paratrabecular or random), presence of infiltrating edges, and distribution of lymphoid cell populations. In addition, we examined 40 cases of bone marrow biopsies with documented malignant lymphoid aggregates for comparison purposes. We report that the distribution of B and T lymphocytes within lymphoid aggregates may serve as a useful criterion to aid in the separation between benign and malignant aggregates. When aggregates exhibit a predominance of T cells, consist of a central core of T cells surrounded by a rim of B cells, or have a mixed distribution of B and T cells, they are more likely to be benign. On the other hand, an increased likelihood of malignancy occurs when aggregates exhibit a predominance of B cells or consist of a central core of B cells surrounded by a rim of T cells (excluding germinal center formation), and assessing other features worrisome of malignancy (large aggregate size, presence of infiltrative edges, cellular atypia, and paratrabecular location, among others) is warranted.
Colorectal malignancies may be stented to alleviate obstruction. The stent is a polarized and braided network of metallic wires. Pathology associated with colorectal stents is yet to be described. The authors reviewed 7 cases involving stented colorectal segments from patients lacking clinical suspicion of Crohn disease. In 4 cases, orientation of the specimens and stents matched the corresponding anatomic landmarks. In 3 cases, the specimens lacked helpful anatomic landmarks, and orientation was possible only after correlating with the intrinsic polarity of the stents. Stented areas showed artifacts resembling Crohn disease, including rounded cobblestones, pseudopolyps, and simple fissures, as well as unique artifacts including rhomboid cobblestones, complex fissures, oblique fissures with remarkably straight edges, and conical fragments of tissue that appeared to float. Crohn disease was misdiagnosed in 1 case in which the stent was removed intraoperatively and was never received. Colorectal stents help orient ambiguous specimens and induce patterned injury that can be confused with Crohn disease.
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