CHAPTER 4 OBTAINING A DIAGNOSTIC BIOPSY 37
Sampling only from the periphery of a lesion may cause pathology to be missed if the
active section of dermatitis is small and not within the sectioned tissue.
Choose representative lesions from multiple areas of skin; most laboratories permit
submission of 3–5 samples for dermatopathologic examination.
Submit samples from the tissue affected even if less amenable to biopsy (e.g., from
the planum nasale – this area heals well after biopsy).
Where to Biopsy
Choose several representative lesions because they may represent various stages of
the same disorder or multiple problems.
Include lesions characterized by scale, crust, erythema, erosion, ulceration, etc.; it is
not always necessary to biopsy the edge of a lesion, although a sample taken within
the center of an ulcer is rarely diagnostic.Pustules and vesicles should not be biopsied with a punch technique (unless smaller
than 4 mm); the twisting motion of the punch will rupture or remove the roof of
the lesion and disrupt the architecture of the sample; these lesions should be excised
in toto.Ulcers or deep draining lesions are best taken by excision, rather than by punch tech-
nique, because the twisting motion may separate the pathologic tissue from the more
normal tissue (e.g., vasculitis, panniculitis).If affected, biopsy footpads or the planum nasale; wedge samples are easier to close
than circular punched samples – these areas heal well.
Crusted lesions are excellent areas for biopsy; if the crust separates from the lesion
during sampling, include the crust in the formalin jar andmake a notation for the
technician to “please cut in the crust.”Heavily scaled areas are often good diagnostic sites.
BIOPSY TECHNIQUE
Skin biopsy sites should be gently clipped (if needed) and should not be scrubbed or
cleaned.
Excessive cleaning will remove or alter potentially significant pathologic changes.
Most skin biopsies can be obtained with local anesthesia; sedation may be necessary
with fractious animals.
When possible, use 6 mm or larger biopsy punches to avoid sampling error.
How to Biopsy
Never scrub or cleanse the area before excision – the surface crust may contain the
pathologic changes necessary to make a diagnosis.
Use a surgical blade to obtain a wedge-shaped or elliptic biopsy specimen when
sectioning the nose, footpad, vesicles, bullae, or deep lesions (e.g., vasculitis,
panniculitis).