Lymph Node Biopsy

• preferably received intact and fresh soon after excision.

• after assigning a lab number, dissect the lymph node free from surrounding fat/connective tissue.

• count the number of nodes and measure their size (length x width x depth (mm)).

• make parallel cuts along the transverse axis at 2-3 mm intervals with a sharp blade.

• a small portion is submitted for microbiological investigations if infectious disease is suspected clinically. If not submitted immediately, store at 4 °C. Make smears for Gram's/ Ziehl-Nielsen stain.

• make imprints of the cut surface on coated, alcohol-cleaned slides. Touch the glass slide gently to the cut surface of the node after ensuring it is not too wet or bloody. Avoid using force. Dry the slides in air. Heating or blow-drying is unnecessary and creates artefacts. For wet fixation, the smears are dipped in alcohol-based fixative immediately after taking imprints.

• submit the slices for histology. Fix in 10% formalin for 24-48 hours prior to paraffin processing. Prolonged fixation can bind antigenic sites and hamper immunohistochemistry. Good quality, thin (3-4 ^m) sections are required for H & E morphology. Correlate imprint findings with histology of the slice from which it was obtained.

Frozen section for immunohistochemistry: usually no longer necessary as the vast majority of diagnostic antibodies are readily applicable to good-quality paraffin sections, particularly with the advent of newer, robust antibodies and antigen-retrieval techniques (e.g., pressure cooking/ microwave).

Cytogenetics/flow cytometry: place a 0.5-1-cm3 piece of tissue in a bottle containing a culture medium such as RPMI/DMEM and send to the appropriate laboratory. Snap freeze tissue at -70 °C if tissue is not immediately processed.

Immunoglobulin heavy chain and T cell receptor gene rearrangement studies can be carried out using both fresh and paraffin-processed material as determined by local protocols.

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