Page 182 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 9 Biopsy and Sentinel Lymph Node Mapping Principles 161

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• Fig. 9.3 Excisional (top) contrasted with incisional (bottom) biopsy. The top tumor should be small
enough that excisional biopsy will not negatively influence other possible treatments. The bottom tumor,
however, requires knowledge of the tumor type before excision to ensure appropriate surgical “dose” is
used at the time of definitive removal. Note that the biopsy incision is oriented in such a way to make it
easiest to include during wide excision and minimize difficulty with closure.

techniques are convenient, cost effective, and generally safe, they splenic mass, testicular tumor, etc.). It is more frequently per-
may suffer from inadequate visualization and limited biopsy sam- formed than indicated but when used on properly selected cases,
ple size compared with other techniques. For example, an endo- it can be both diagnostic and therapeutic as well as cost effective.
scopic biopsy result of ulcerative gastritis in a dog with a firm,
infiltrative mass of the lesser curvature of the stomach does not Sentinel Lymph Node Mapping and Biopsy
rule out gastric adenocarcinoma. In veterinary medicine, assessment of nodal metastasis has been
largely predicated on palpation or imaging of nodal size and archi-
Laparoscopy and Thoracoscopy tecture with cytologic sampling when abnormal. Sentinel lymph
Evaluation of the abdomen and thorax via minimally invasive node (SLN) mapping and subsequent biopsy are performed to
techniques, when performed by an experienced operator, can yield identify the first lymph node (LN) to which a cancer is likely to
important information regarding stage of disease and can procure spread from a primary tumor and to sample that LN for evidence
tissue for biopsy. In addition, laparoscopic- and thoracoscopic- of metastasis. If the SLN is free of metastasis, subsequent LNs in
assisted removal results in smaller incisions and more rapid recov- the drainage pattern are also likely to be negative. This method
ery times compared with open procedures. The option to convert was initially studied in human cutaneous melanoma to detect
to an open procedure should be available if problems are encoun- lymphatic drainage patterns before surgery. It is now a widely uti-
tered that cannot be adequately addressed using minimally invasive lized staging procedure in many human cancers, but the evidence
methods. As specialists become more proficient at these techniques, for its usefulness in staging has been primarily from the applica-
more and more options are becoming available for tumor removal. tion of this technique in human breast cancer patients. The SLN
has been classically defined as the first node detectable after peri-
Image-Guided Biopsy tumoral injection of a radioactive marker and subsequent scintig-
Diagnostic imaging has greatly expanded the ability to stage raphy. Visual identification in surgery is typically aided by the use
various neoplasias. The use of positron emission tomography– of vital dye injection (e.g., methylene blue) in conjunction with
computed tomography (PET–CT) in veterinary medicine has also use of a portable gamma probe in the operating room to detect
led to significant advances in sentinel node mapping, novel staging the LN with the greatest radioactivity. In one study of 19 dogs
methods, and the ability to assess response to treatment. In addi- with cutaneous mast cell tumors, the SLN was different from the
3
tion, the use of radiographic-, fluoroscopic-, ultrasonographic-, regional anatomic LN in eight (42%) of these dogs. SLN map-
CT-, and magnetic resonance imaging (MRI)-guided needle ping and biopsy identified LN metastasis in these eight dogs and
aspirates or core biopsies can prevent the need for more invasive clients were offered adjunctive therapy that otherwise would not
diagnostic procedures. Commonly biopsied tissue includes lung, have been considered. 3
kidney, liver, spleen, prostate, and, more recently, brain. Indirect lymphography is an alternative to scintigraphic SLN
mapping. This procedure involves injection of a contrast agent in
Excisional Biopsy the periphery of the tumor and serial or real-time imaging to fol-
This method is utilized when the treatment would not be altered low contrast uptake in the draining lymphatic basin. This method
by knowledge of tumor type (e.g., “benign” skin tumors, solitary uses contrast enhancement of nearby LNs and lymphatic channels