Diagnostics and Therapy in Veterinary Dermatology. Группа авторов

be injected subcutaneously directly underneath the area to be biopsied. The punch biopsy instrument is placed perpendicular to the lesion and then rotated with gentle pressure until the punch drops into the subcutaneous space. Grasp the subcutaneous fat with thumb forceps to avoid crushing the delicate dermal and epidermal layers of skin and place the biopsy upright on a piece of wooden tongue depressor. This maintains the normal anatomic orientation of the biopsy sample. Place the sample in 10% formalin with a 1:10 ratio of tissue to formalin.

Figure 4.1 Noninfectious diseases that should be biopsied.

Figure 4.2 Nodular lesions that should be biopsied and cultured.

Figure 4.3 Primary lesions.

Figure 4.4 Secondary lesions.

Figure 4.5 Appropriate sampling. (a) Inappropriately taken biopsy punch with half normal tissue (outlined in white) and half abnormal tissue (outlined in black). (b) Biopsy appearance once in formalin. The loss of color makes it very difficult to differentiate the lesion from normal tissue. (c) If the biopsy is cut in following the green lines, then the lesion is included and can be examined by the pathologist. If the biopsy is cut in following the red line, the lesion has been completely missed and cannot be examined by the pathologist.

Figure 4.6 Punch biopsy. (a) Instrumentation for punch biopsy. (b) Inject lidocaine subcutaneously. (c) Hold the biopsy punch perpendicular to the skin and gently twist until it drops into the subcutaneous space. (d) Be sure to grasp the tissue sample in the subcutaneous fat to minimize artifacts. (e) Place the tissue sample on a wooden stick so it will form a cylinder.

Figure 4.7 Double punch. (a) Rapidly growing mycobacteriosis. (b) Lateral view of mass: one 6 mm plug removed. (c) Lateral view of mass: several deeper plugs removed from the same opening in the skin.

Another biopsy technique used in veterinary dermatology is the double punch (Figure 4.7). This method is very useful for large subcutaneous lesions with little epidermal involvement that are being biopsied for both histopathology and culture. Unlike biopsies of lesions affecting the epidermis and dermis, these lesions should be scrubbed and disinfected before the biopsy is taken. This procedure is normally performed under heavy sedation or general anesthesia. A 6 mm punch is used to remove a core of tissue from the surface of the nodule. The punch is then placed back into this same area and is pushed deeper into the lesion, usually in several directions. Then small forceps and iris scissors are used to remove pieces of tissue for both culture and histopathology. The original site is closed with one or two simple interrupted sutures.

Where to Send

      Where the biopsy is sent is as important as taking appropriate samples. Whenever possible, biopsies should be sent to a veterinary dermatopathologist. If a facility has multiple pathologists on staff, be sure to request the dermatopathologist for skin biopsies. A short history of the case including progression, response to therapy, and current therapies should be included. A description of the lesions that were biopsied, where they were obtained, and a differential diagnosis list should also be included. If possible, include several photographs of the lesions. This information will help the pathologist narrow their differential list and may assist them with keying in on specific structures. The report from the pathologist should include a complete microscopic description of the lesions and a comment on what disease the histopathologic changes best fit, plus other possibilities if the histopathology is not pathognomonic for a specific condition. There should also be recommendations from the pathologist on special stains and immunohistochemistry if indicated.

      Remember that biopsies are just a diagnostic tool. The more complete information supplied to the pathologist about the patient and the clinical picture, the better the information the pathologist will be able to provide in return. If the results do not fit with the clinical picture or response to therapy, another biopsy should be taken.

Recommended Reading

      1 Gross, T., Ihrke, P., Walder, E., and Affolter, V. (2005). Skin Diseases of the Dog and Cat: Clinical and Histopathologic Diagnosis, 2e. Ames, IA: Blackwell Science.

      2 Yager, J. and Wilcock, B. (1994). Color Atlas and Text of Surgical Pathology of the Dog and Cat, Dermatopathology and Skin Tumors, vol. 1. St. Louis, MO: Mosby.