Page 4 - Clinical Connections - Summer 2023

RVC RESEARCH STUDY VETERINARY SERVICES RVC.AC.UK
Oncology
SENTINEL LYMPH NODE MAPPING –
LEADING THE WAY IN ONCOLOGY

Andy Yale, Lecturer in Veterinary Oncology

ancer is a common disease in the primary tumour or scar, followed by an
older cats and dogs but, as more imaging technique to visualise the exact
C advanced diagnostic and treatment LN(s) that drain the patient’s tumour. These
modalities become available, the prognosis ‘sentinel’ LNs are then sampled to check for
and quality of life of many pets with cancer metastasis.
can be good. This means LN sampling can be much
Sentinel lymph node (SLN) mapping is more specific and personalised, both
a diagnostic tool commonplace in human increasing the accuracy of metastasis
oncology and developing in veterinary detection and reducing patient morbidity.
oncology. It increases the accuracy of There are a variety of techniques available Beetle, following revision surgery (requiring an
detection of metastatic disease whilst for SLN mapping, although CT and advancement flap) of her incompletely excised
minimising patient morbidity. ultrasound-based techniques are most MCT of the dorsal head, and SLN extirpation
With increased detection of metastasis, common in veterinary oncology.
more patients can be offered additional were identified (left parotid LN, bilateral
therapies that may not have otherwise been Case study – Beetle mandibular LNs). Cytology of these did not
considered – thus improving outcomes. Beetle, a nine-year 11-month female identify MCT metastasis but, as cytology
Cancer commonly spreads to lymph neutered Labrador, was seen by RVC can miss MCT LN metastasis in around
nodes (LNs) and, historically, assessment Small Animal Referrals’ Oncology Service 25% of cases, the SLNs were extirpated
for LN spread would be based on cytology in 2021. Beetle had an incompletely excised for histopathology at the time of revision
of LNs that are anatomically closest to low-grade (Kiupel), intermediate-grade surgery for the incompletely excised MCT.
the tumour, and/or regional LNs that are (Patnaik) mast cell tumour (MCT) on the Histopathology identified the parotid
enlarged. However, there are limitations head, situated midline above both eyes. LN as pre-metastatic, with no evidence of
to this approach as tumours can develop Despite being low- to intermediate-grade, metastasis in either mandibular LN. Prior
unpredictable lymphatic drainage patterns the MCT had a high Ki67 index (>1.8%) cytology did not identify evidence of spread.
– meaning they may drain to LNs distant to – indicating a more aggressive biologic Beetle completed a course of adjuvant
the tumour location, bypassing more local behaviour. Therefore, thorough staging lomustine chemotherapy and has been
LNs. prior to revision surgery and adjuvant doing well since with no evidence of MCT
Additionally, many normal-sized LNs can chemotherapy was discussed. recurrence or metastasis.
still harbour metastatic disease. Thoroughly Staging without techniques such as SLN
assessing for LN metastasis without specific mapping would have involved sampling Benefits across species
techniques, such as SLN, mapping would many LNs as lymphatic drainage patterns As SLN mapping and biopsy is a more
therefore involve sampling multiple LNs, of head and oral tumours can be especially targeted and personalised staging
with associated increased patient morbidity. unpredictable. Lymph nodes targeted would approach, it significantly reduces morbidity
It may also risk missing LN metastasis as have included bilateral mandibular, medial compared to more extensive LN sampling.
LNs considered less likely to be draining retropharyngeal, parotid and prescapular It also increases the detection of metastatic
the tumour, based on anatomic location, are LNs (a total of eight, many of which require disease – in humans, 30% of patients
unlikely to be sampled with this approach. ultrasound-guided sampling). benefit from additional therapies that would
Sentinel LN mapping involves the Following SLN mapping via indirect not have otherwise been offered. For canine
administration of a contrast agent around CT lymphography (ICTL), three SLNs MCT, as in Beetle’s case, the extirpation of
metastatic LNs (and even the prophylactic
CT images following Beetle’s SLN mapping. Iohexol contrast was injected around the scar in four- removal of regional non-metastatic LNs) can
quadrants (asterisk), and afferent lymphatic drainage can be visualised (arrows) heading towards
two of the SLNs (left parotid and mandibular LN). The drainage towards the third SLN (right improve outcome, so accurate identification
mandibular) is not shown in this image. of SLNs is crucial.
The Oncology Service is committed to
providing the most up-to-date diagnostic
and therapeutic options to improve patient
quality of life and outcome and is one of few
centres to offer SLN mapping via both ICTL
and contrast-enhanced ultrasound.

For small animal referrals, please call:
01707 666399
Email:
qmhreception@rvc.ac.uk

4 Summer 2023