Preoperative planar lymphoscintigraphy allows for sentinel lymph node detection in 51 dogs improving staging accuracy: Feasibility and pitfalls

Abstract

Sentinel lymph node (SLN) mapping is the current gold standard for the oncological staging of solid malignancies in humans. This prospective observational study describes the feasibility and the limits of preoperative lymphoscintigraphy for SLN detection in dogs with spontaneous malignancies and the improvements in staging accuracy. Client-owned dogs with confirmed malignant neoplasia and absence of distant metastasis were prospectively enrolled. Lymphoscintigraphy was performed after the peritumoral injection of Technetium-99m labeled nanocolloids. Regional dynamic and static images were acquired, with and without masking of the injection site with a lead shield. The dogs were then subjected to surgery for tumor excision and SLN extirpation. Intraoperative SLN detection was performed by combining methylene blue dye and a dedicated gamma probe. Overall, 51 dogs with a total of 60 solid malignant tumors were enrolled. Lymphoscintigraphy identified at least one SLN in 57 of 60 cases (95%). The SLN did not always correspond to the regional lymph node (35/57, 61.4%). The use of a lead shield, masking the injection site, markedly improved the SLN visibility. The median time of SLN appearance was 11.4 ± 9.3 min. No side effects were observed. Preoperative lymphoscintigraphy allows for SLN detection in dogs and can improve staging accuracy by either identifying the SLN in a different lymphosome than clinically expected or discriminating the draining node in uncertain cases. The combined use of preoperative and intraoperative techniques is recommended to increase the SLN detection rate.

Keywords: 99mTc; lymphatic metastasis; lymphoscintigraphy; sentinel lymph node; tumor staging.

FIGURE 1

Dorsal (A) and right lateral (B) planar static images (120 s/frame, matrix size 256 × 256) of the head of a dog with a single MCT at the planum nasale, acquired 3 minutes after injection. Injection site (arrow) was not masked and a bilateral radiopharmaceutical uptake was observed at the level of mandibular LNs (arrowheads)

FIGURE 2

Ventral (A) and left lateral (B) planar static images (120 s/frame, matrix size 256 × 256) of a dog with a digital MCT in the left hand. Injection site (arrow) was masked with a 2 mm thick lead shield. A focal radiopharmaceutical uptake is visible at the level of the left superficial cervical LN (arrowheads)