How to get better pathology results - Veterinary Medicine
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How to get better pathology results
Find answers to your questions about submitting samples for cytologic and histologic examinations and communicating with pathologists—plus, tips for avoiding common mistakes.


Problem: Inconclusive histologic findings or unsatisfactory results

Collect as large a sample as possible (within reason) to increase the likelihood of obtaining representative tissue sections. Collect multiple samples if necessary, particularly if there appear to be large areas of hemorrhage or necrosis.

It is important that a sufficient amount of formalin is used for the size of the sample and container. At a minimum, a ratio of 10:1 of 10% neutral-buffered formalin-to-tissue volume should be used, though some pathologists recommend a 20:1 ratio. The rate of formalin penetration and fixation reduces dramatically with increasing thickness of tissue, and unfixed tissue will undergo autolysis, which will impair or prevent diagnostic interpretation. So practitioners need to be aware of the thickness guidelines and adhere to them whenever possible. This holds particularly true for vascular, often congested tissues such as the spleen, liver, and kidney.

Sample sizes 0.5 to 1 cm thick are ideal for optimum fixation and should be provided for representative lesions in which complete excision is not achieved or is impractical. For larger submitted specimens, incision into the tissue may be necessary to allow the formalin to completely penetrate the tissue (e.g. splenectomy with a mass lesion). For very small specimens, submission of the sample in a tissue cassette is recommended, with sponges used for specimens smaller than cassette grate size.

For excisional mass lesions when border evaluation is necessary (e.g. mast cell tumors, soft tissue sarcomas), the specimen should be submitted in full. Designate borders appropriately (e.g. ink, sutures), and provide an explanation to orient the technician or pathologist for tissue sectioning. For example, write, "Two sutures are placed at the cranial border, and one suture is placed at the caudal border." Aside from ink labeling or placing suture for orientation, the borders of the specimen should not be dissected or incised.

For endoscopic biopsies, samples should be numerous (eight to 10 per location) to offer the best opportunity for evaluation of full-thickness mucosa and submucosa. Samples of only superficial mucosa are less diagnostic.

Use care when collecting and handling tissues to avoid crush artifact. This complication is common with skin biopsies. The interface of lesions and normal tissue is important for the pathologist in general, but particularly with skin samples. Such interfaces should always be included with skin biopsies. If skin lesions are large or multifocal, multiple biopsies are recommended to help ensure that the samples are representative. Avoid sampling of only ulcerated areas, as an intact epidermis is often critical to a diagnosis. Traumatic removal of surface crusts should be avoided; any crusted debris removed should be included in the submission.

The tissues should be submitted in jars or containers labeled with patient name and tissue source. When specimens from multiple sites are collected, each container should be labeled individually with patient name and source. Tissues to be submitted for histologic examination should never be frozen, unless specifically requested by the laboratory or pathologist for special testing. As always, provide patient history and information or results pertinent to the case on the submission form.


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