Intraoperative methylene blue staining is effective as a single mapping technique in the identification of sentinel lymph nodes in dogs with low-grade mast cell tumours.

Abstract

Objectives: The aim of this prospective study was to assess the association between methylene blue staining pattern and the presence of histologic nodal metastasis in dogs with low-grade mast cell tumour in low-resource settings for the efficient diagnosis of lymphatic spread.

Methods: Dogs with a single, cytologically low-grade mast cell tumour and no documented distant metastases were prospectively included and underwent surgery. Along with primary mast cell tumour removal, intraoperative sentinel lymph node mapping with peritumoral mast cell tumour injection and regional lymph node excision, regardless of whether blue dye was visible in the lymph node, were performed. Association between the lymph nodes with dye uptake (stained) and their metastatic status was evaluated.

Results: Twenty-five dogs were enrolled, and at least one stained lymph node was identified in 22 (88%) of them. A total of 49 lymphocentres were surgically inspected, and a total of 53 lymph nodes were removed. Twenty-nine (54.7%) lymph nodes were stained, and 24 (45.3%) were unstained. Among the 29 stained lymph nodes, there were seven (24.1%) HN0, seven (24.1%) HN1, seven (24.1%) HN2 and eight (27.7%) HN3. Among the 24 unstained lymph nodes, 17 (70.8%) were HN0 and seven (29.2%) were HN1. No complications related to methylene blue injection were recorded.

Clinical significance: Peritumoral methylene blue injection is a cost-effective alternative technique for detecting sentinel lymph node for dogs with mast cell tumours, particularly in economically constrained settings. All metastatic lymph nodes (HN2/HN3) were stained, and all unstained lymph nodes were non-metastatic (HN0/HN1).