Introduction

In general, a biopsy should be performed before definitive treatment if the results will change the therapy or influence the owner's thoughts to treat their animals. The purpose of this lecture is to introduce basic sampling techniques that are used at the Japan Small Animal Cancer Center. During the presentation, all techniques will be demonstrated by pictures and video clips.

Fine Needle Aspiration (FNA)

1.  Indication: Cutaneous mass, subcutaneous mass, lymph nodes, intra-thoracic or intra-abdominal mass, fluid analysis, etc.

2.  Pros: Quick, easy, inexpensive and safe

3.  Cons: Limitation of cytology

4.  Precaution: Coagulopathy

5.  Instruments and supplies required: 22 or 23-gauge, 1–1.5 inch needles, 6–12 ml syringes, pre-cleaned microscope slides, cytology stains (e.g., Diff-Quick, Wright-Giemsa, other).

6.  Techniques and tips to obtain a good sample:

a.  Avoid blood dilution as much as possible

b.  When preparing slides for cytologic evaluation, please obtain the sample with a non-aspiration FNA technique and gently distribute the cellular material with a spreader slide using the gentle compression ("squash") technique with no downward pressure. A coverslip could possibly be used as the spreader slide. This approach will help maintain cellular integrity and facilitates cytologic evaluation, although some cells may be inherently fragile.

c.  Move the tip of the needle back and forth gently after needle insertion

d.  Make a smear as gentle and smooth as possible

Punch Biopsy

1.  Indication: Cutaneous mass, subcutaneous mass

2.  Pros: Quick, easy, inexpensive and safe. General anesthesia is not required in most cases. Tissue can be collected at the juncture between normal and abnormal tissue.

3.  Cons: Sample size and depth are limited

4.  Precaution: Coagulopathy: Instruments and supplies required: +/- sedation, surgical scrub set, local anesthesia, sterile surgical gloves, punch biopsy instrument (4 mm, 6 mm or 8 mm), 10% neutral buffered formalin, cassette, #11 scalpel blade, sterile gauze, 2.0–4.0 nylon suture.

5.  Technique and tips to obtain a good sample:

a.  Rotate the punch in one direction

b.  Before removing the punch, angle the punch at least 45 degrees, or almost parallel, with the skin while still applying pressure along the long axis of the instrument so that the base of the specimen can be cut (Figure 1).

c.  Biopsy sample is very fragile. Grab the biopsy sample as gently as possible to minimize handling artifact.

Figure 1. The illustrations indicate how the base of the tissue is cut. Repeat the action in the opposite direction.

Needle Core Biopsy (Tru-cut Biopsy, Figure 2)

1.  Indication: Cutaneous mass, subcutaneous mass, intra-abdominal and intra-thoracic mass

2.  Pros: Quick, easy and safe

3.  Cons: Small sample size, instrument cost

4.  Precaution: Coagulopathy

5.  Instruments and supplies required: +/- sedation, surgical scrub set, local anesthesia, sterile surgical gloves, (14-gauge, 16-gauge, 18-gauge; 9 cm) core biopsy needles, 23-gauge needle, 10% neutral buffered formalin, cassette, #11 scalpel blade, sterile gauze, ultrasound machine.

6.  Technique and tips to obtain a good sample:

a.  Use as large an instrument as possible

b.  After insertion in the tumor, lift the needle tip slightly before the outer cannula is advanced over the stylet. This action will increase the sample volume significantly.

c.  Multiple samples should be collected to increase the accuracy of diagnosis

Figure 2. Tru-cut biopsy needle.

Excisional / Incisional Biopsy (Wedge Biopsy, Figure 3)

1.  Indication: Cutaneous mass, subcutaneous mass, most suitable for ulcerated or necrotic mass (i.e., oral tumor)

2.  Pros: Can obtained larger tissue. Tissue can be collected at the juncture between normal and abnormal tissues.

3.  Cons: Deep sedation or systemic anesthesia generally required

4.  Precaution: Coagulopathy

5.  Instruments and supplies required: Deep sedation or systemic anesthesia, surgical scrub set, sterile surgical gloves, standard surgical instruments, sterile gauzes, suture material, 10% neutral buffered formalin, sterile container of appropriate size.

Figure 3. The difference between excisional and incisional biopsies.

Other General Precautions

 Obtain as large a sample or samples as possible to assist the pathologist in making a correct diagnosis

 Any needle tracts should be within the future surgical field since needle tracts can be contaminated by tumor cells. FNA should be avoided if transitional cell carcinoma is suspected clinically or by abdominal ultrasound.

 Do not burn, vaporize and/or crush the sample. Therefore avoid using electrocautery or lasers, especially for small tissue specimens to reduce damaging the tissue.

 Submit all tissues that have been resected and properly prepared in an adequate amount of neutral buffered 10% formalin. An optimized fixation ratio is 1 part tissue to 9 parts fixative.

 For FNA, do not expose glass slides to formalin fumes

Japan Small Animal Cancer Center, 2-27-4 Nakatomiminami, Tokorozawa, Saitama, 359-0003, Japan, Phone: 81-4-2943-8699, Fax: 81-4-2943-8698, Web page: www.jsamc.jp