Comparison of sentinel lymph node mapping patterns before and after surgical excision of mast cell tumors in dogs using indirect lymphography: A prospective clinical study

Abstract

Sentinel lymph node (SLN) mapping has been shown to be important for staging in dogs with mast cell tumors (MCTs). Despite this, many patients are referred to an oncologist after surgical intervention has been carried out. It is unknown whether lymphatic drainage patterns are altered by surgery and whether postoperative SLN mapping can be reliably conducted. The objective of this study was to compare lymphatic drainage patterns from MCT sites before and after surgical removal to determine whether the SLN changes following tumor excision. Twenty-nine client-owned dogs with 31 cytologically diagnosed MCTs were prospectively enrolled, with 14 dogs (N = 15 MCTs) completing the study. Preoperative SLN mapping was conducted using radiographic indirect lymphography (IL). Water-soluble iodinated contrast (WIC) medium was injected peritumorally using a 4-quadrant technique and digital radiography was then used to assess lymphatic drainage patterns. Orthogonal projections were obtained every 1 to 2 min until the SLN was visualized, up to 20 min post-injection. Dogs were re-evaluated 2 to 5 wk postoperatively and radiographic IL was carried out again using the same protocol as previously described with WIC injected around the surgical scar line in a 4-quadrant technique. An SLN was identified for 15 MCTs in 14 dogs preoperatively and in 13/15 MCTs postoperatively. Sixteen dogs with 16 MCTs did not have postoperative lymphography and did not complete the study. Agreement between preoperative and postoperative SLNs was a complete match in 7/15 MCTs, a partial match in 5/15 MCTs, and no match in 3/15 MCTs. A negative IL study was obtained in 2/15 MCTs postoperatively. Complete agreement between preoperative and postoperative SLN identification was detected in 46.7% of cases and there was no agreement in 20% of cases. Surgical intervention did not change the time to SLN identification when carrying out radiographic IL. Thus, surgical removal of MCTs affects lymphatic drainage and can alter the SLN(s) detected. Clinicians should be aware of this finding and interpret results of postoperative lymph node staging with caution.

Figure 1

Flow diagram depicting all dogs enrolled in the study and exclusion criteria for 14 dogs. MCT — Mast cell tumor.

Figure 2

Lymphography images from a dog with a mast cell tumor (MCT) in the right perianal region preoperatively (A) and 20 d after surgery (B). A — Left lateral radiograph of the caudal abdomen conducted 3 min after injection of water-soluble iodinated contrast (WIC) medium (Iopamadol) around an MCT in the right perianal region (arrow). Contrast uptake can be seen within the afferent lymphatics surrounding the tumor and within the right medial iliac lymph node (circled). B — Lateral radiograph of the caudal abdomen taken 5 min after injection of WIC medium at the scar line in the right perianal region. Contrast uptake can be seen within the lymphatics in the perineum, with uptake noted in the right medial iliac lymph node and right superficial inguinal lymph node (circled). This denotes a patient with partial agreement.