Biopsies should be fixed in 10 percent neutral buffered formalin (NBF). Maximum tissue thickness to allow optimal penetration of NBF is 10mm.
You can take multiple representative samples from different areas of the lesion, or for large samples, you can slice through the tissue using parallel slices which do not quite reach the bottom of the sample and fix in NBF ideally for 48 hours at your practice before wrapping in wet paper towel prior to packaging.
Margins can be inked, or tagged using different colours, lengths or numbers of sutures. Please do not use needles to mark margins.
Small/friable specimens, such as endoscopic samples, punch biopsies and needle core biopsies, are best placed in pre-soaked cell safe capsules. Pre-labelling the cassettes using an N2 pencil before immersion in NBF means that multiple cassettes can be placed in the same pot. Samples can be fixed free in NBF; however, although we endeavour to sieve these samples, inevitably some fragments can be left behind – particularly if they are placed in the same pot as larger biopsies. Submission on gauze or card can cause samples to rip when removing for processing. A single line drawn along the centre of skin punch biopsies in the direction of hair growth prior to biopsy can help with orientation.
Bone biopsies can be difficult to obtain and frustrating to interpret. This is because of the high risk of fracture during the biopsy procedure and, histologically, due to the presence of large quantities of reactive periosteum in most lesions, regardless of pathogenesis. A diagnosis of reactive hyperplasia is often of little clinical help. It is useful to take as large a sample as possible and/or to take multiple biopsies with some from the centre of the lesion. This is more likely to demonstrate the true lesion. Multiple biopsies reduce the risk of obtaining only haemorrhagic or necrotic tissue. Fixation in 10 percent NBF is adequate for routine diagnostic biopsies.
Eyes can be submitted whole in 10 percent NBF. There is no need to section the eye or inject the fixative as this causes significant artefactual damage.
Claws need to be softened and bones decalcified before processing. The digital site is naturally very restrictive, therefore any expansile mass will cause similar clinical signs: abnormal nail growth, swelling, pain, lameness and lysis of the bone. For this reason, amputation of one or more phalanges is the biopsy technique of choice. This includes inflammatory conditions of the nail bed, such as lupoid onychitis. Punch biopsy techniques have been described; however, these can be very difficult to orientate and can result clinically in permanent disfigurement of the claw. If possible, an affected dew claw can be sacrificed.
