General Principles for Submitting Cytology Samples
Proper labeling of slides with patient name and sample site will help ensure accurate record keeping and minimize error. Slides that have one edge that is frosted should be labeled with a pencil with the patient identification and sample site before the sample is put on the slides.
This is preferred to “permanent” ink marking pens because the preparation stains and fixatives used in the staining process will often wash off the ink.5 When submitting samples to a diagnostic laboratory, it is important to fill out a complete history including the patient signalment; tissue sampled; location; duration of the mass or illness; a description of the mass or lesion (color, three-dimensional size for masses, shape, texture, consistency, etc.); other important clinical findings (bloodwork, surgical, imaging results); and differential diagnoses. Minimizing the amount of blood present on slides is also important, especially in cases in which inflammation is suspected. In these cases, cytologic findings may need to be interpreted in conjunction with CBC data to aid in determining if inflammation is present or if leukocytes are blood associated. Samples can be obtained by fine-needle aspirate, impression smears, scrapings, and swabs of lesions. Depending on the sample, blood smear, squash, or roll preparations can be made to spread cells on the slide. Once air-dried samples are made, they can be stained with Romanowsky type stains (Wright-Giemsa, Diff-Quik, etc.). Although stained slides may be submitted, it is also important to include some unstained slides when submitting samples to a diagnostic laboratory. Keep unstained cytology slides/samples away from formalin during surgery and when biopsy samples are also being prepared and submitted because the formalin fumes can render cytology samples nondiagnostic.5Bone Marrow Aspirates and Core Biopsy Samples
Please refer to Chapter 28.
Lymph Node Aspirates
Lymph nodes should be manually stabilized, and aspiration or nonaspiration techniques as have been described elsewhere can be used to collect cells.6 In both techniques, the needle should be maintained within the lymph node and it can be redirected to obtain cells from multiple areas. Peripheral lymph node samples tend to be highly cellular because the lymphocytes tend to exfoliate well and blood contamination is often mild. As a result, it is important to spread the cells out well, which can be done by the squash preparation or blood smear technique. Evaluation of poorly stained thick areas should be avoided. Lymphocytes are often fragile and are prone to lysis; it is therefore important to be gentle when making the preparations. Evaluate only intact lymphocytes because ruptured lymphocytes can appear larger than normal, leading to the misdiagnosis of lymphoma.
The main differential diagnoses for lymph node aspirates include normal lymph node, reactive lymph node, various inflammations (lymphadenitis), lymphoma, and metastatic neoplasia.6 Normal lymph nodes are composed of mostly small lymphocytes with fewer medium and large lymphocytes. Low numbers of plasma cells, macrophages, eosinophils, nondegenerate neutrophils, and rare mast cells can also be seen. In reactive lymph nodes, small lymphocytes still predominate, but there are increased numbers of medium and large lymphocytes and plasma cells. Reactive lymph nodes are a relatively nonspecific finding in animals with antigenic stimulation, inflammation, or neoplasia. Increased numbers of degenerate or nondegenerate neutrophils, macrophages, or a combination of these 2 cell populations should prompt evaluation for an underlying infectious organism (bacteria or fungus) and for metastatic neoplasia. Eosinophilic inflammation can be seen with parasitic disease, some fungal diseases, and allergic conditions.6