Biopsy of sentinel lymph nodes after injection of methylene blue and lymphoscintigraphic guidance in 30 dogs with mast cell tumors

Objective – To report the outcomes associated with sentinel lymph nodes (SLNs) detection and extirpation guided by radionuclide and methylene blue injections in dogs with cutaneous and subcutaneous mast cell tumors (MCTs). Study Design – Clinical prospective cohort study. Animals – 30 client-owned dogs with MCTs amenable to wide-margin excision, without evidence of distant metastasis and abnormal regional lymph nodes (RLNs). Methods – Technetium-99m and methylene blue were injected peritumorally. Dogs underwent pre-operative gamma camera scintigraphy, and an intraoperative gamma probe guided SLN extirpation. Outcomes included technical and surgical complications, number of SLNs, SLNs location respecting the expected RLN, and histopathology results. Results – SLN mapping was applied to 34 MCTs in 30 dogs without any complication. SLNs were not identified in 3/34 tumors, all with previous scar tissue. SLNs did not correspond to expected RLNs in 19/30 (63%) tumors. Histological examination confirmed an early or overt metastasis in 32/57 (56%) SLNs extirpated. Conclusion – SLN mapping and biopsy with radionuclide and injection of methylene blue was associated with low morbidity and allowed detection of SLNs in dogs with MCT at first presentation without scar tissue. Clinical significance – Incorporation of SLN mapping and extirpation allows for a personalized staging approach in dogs with MCT. The presence of scar tissue in dogs with recurrent tumors seems to be a limitation for SLN mapping with this technique.