Geometric, landmark-guided technique reduces tissue trauma, surgery time, and subjective difficulty for canine peripheral lymphadenectomies: an educational crossover study

Natalie J. Worden Department of Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL

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Judith Bertran Department of Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL

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Penny S. Reynolds Department of Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL
Department of Anesthesiology, College of Medicine, University of Florida, Gainesville, FL

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Ellis C. Chase Department of Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL

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Chiquitha D. Crews Department of Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL

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Kathleen Ham Department of Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL

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Carlos H. de Mello Souza Department of Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL

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Penny J. Regier Department of Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL

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Christopher A. Adin Department of Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL

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Elizabeth A. Maxwell Department of Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL

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Abstract

OBJECTIVE

To compare the effect of a geometric, landmark-guided lymphadenectomy (LL) approach to peripheral lymph nodes (LNs) on successful LN identification, surgical time, tissue trauma, and ease of LN identification compared to standard lymphadenectomy (SL) and methylene blue–guided lymphadenectomy (MBL).

SAMPLE

18 adult, mixed-breed canine cadavers operated on by 7 veterinarians and 5 fourth-year veterinary students between July 23 and October 12, 2022.

METHODS

Participants were provided standardized, publicly available materials regarding the anatomy and surgical techniques for SL of 3 peripheral lymphocentrums: superficial cervical, axillary (ALN), and superficial inguinal (SILN). Participants performed the 3 SLs unilaterally on canine cadavers. Thereafter, they were randomly assigned to 2 crossover groups: MBL and LL. All dissections were separated by at least 2 weeks for each participant. Primary outcome measures included successful LN identification, surgical time, tissue trauma scores, and subjective difficulty.

RESULTS

Successful LN identification was highest with LL (86%) compared to SL (69%) and MBL (67%). Subjective difficulty scores were reduced with LL for SILN dissections. Tissue trauma scores were reduced when using LL for ALN and SILN compared to MBL and SL. Time to LN identification was reduced for ALN with LL. No significant differences were observed between MBL and SL, or for the superficial cervical dissections.

CLINICAL RELEVANCE

Peripheral lymphadenectomies are time consuming and difficult for veterinarians in early stages of surgical training. Little surgical guidance is provided within current literature. Geometric, landmark-guided lymphadenectomies may improve LN identification success and reduce surgical time, tissue trauma, and procedure difficulty, which could encourage their clinical application.

Abstract

OBJECTIVE

To compare the effect of a geometric, landmark-guided lymphadenectomy (LL) approach to peripheral lymph nodes (LNs) on successful LN identification, surgical time, tissue trauma, and ease of LN identification compared to standard lymphadenectomy (SL) and methylene blue–guided lymphadenectomy (MBL).

SAMPLE

18 adult, mixed-breed canine cadavers operated on by 7 veterinarians and 5 fourth-year veterinary students between July 23 and October 12, 2022.

METHODS

Participants were provided standardized, publicly available materials regarding the anatomy and surgical techniques for SL of 3 peripheral lymphocentrums: superficial cervical, axillary (ALN), and superficial inguinal (SILN). Participants performed the 3 SLs unilaterally on canine cadavers. Thereafter, they were randomly assigned to 2 crossover groups: MBL and LL. All dissections were separated by at least 2 weeks for each participant. Primary outcome measures included successful LN identification, surgical time, tissue trauma scores, and subjective difficulty.

RESULTS

Successful LN identification was highest with LL (86%) compared to SL (69%) and MBL (67%). Subjective difficulty scores were reduced with LL for SILN dissections. Tissue trauma scores were reduced when using LL for ALN and SILN compared to MBL and SL. Time to LN identification was reduced for ALN with LL. No significant differences were observed between MBL and SL, or for the superficial cervical dissections.

CLINICAL RELEVANCE

Peripheral lymphadenectomies are time consuming and difficult for veterinarians in early stages of surgical training. Little surgical guidance is provided within current literature. Geometric, landmark-guided lymphadenectomies may improve LN identification success and reduce surgical time, tissue trauma, and procedure difficulty, which could encourage their clinical application.

Introduction

Lymphadenectomy is known to be an important surgical procedure for the identification and treatment of metastatic lymph nodes (LNs) in veterinary medicine.1,2 In addition to guiding prognosis and treatment plans, excisional LN biopsy for histopathology is the gold standard for detection of metastatic disease, and removal of metastatic LNs can improve survival rates in dogs with certain neoplasms.14 Despite the high clinical importance of lymphadenectomies, surgical approaches to the peripheral lymphocentrums, such as the superficial cervical LN (SCLN), axillary LN (ALN), and superficial inguinal LN (SILN), are infrequently described or absent within the veterinary literature.1,5

Peripheral LN identification is known to be time consuming and difficult, with 1 study2 demonstrating that 40% (± 27%) of the total surgical time for mass removal and LN extirpation was dedicated solely to LN identification and removal. In the same study, surgeons’ subjective difficulty scores for LN identification were as high as 85/100 for more challenging LNs, such as the ALN.2 The lack of described surgical approaches to these peripheral lymphocentrums likely increases the risk of prolonged operative times and excessive tissue trauma due to the challenge of identifying the LNs. Additionally, changes in patient positioning may alter the necessary incisional orientation and location due to shifting of anatomy, supporting a demand for alternative surgical approaches to the peripheral lymphocentrums to prevent the need for intraoperative patient repositioning.

Previously, these challenges have been addressed through the use of intraoperative LN mapping techniques, most commonly injection of methylene blue (MB) dye.69 MB injection is a readily available method of intraoperative LN identification that does not require any specialized equipment and therefore is suitable for use in both specialty and general practice. However, blue dye injection may have inconsistent tissue uptake, can be challenging to discern from normal tissue coloration, and can reduce visualization of fascial planes.8,9 These limitations are important to consider when selecting intraoperative methods for LN identification.

In a previous study, we proposed novel, geometric, landmark-guided, surgical approaches to the SCLN, ALN, and SILN in canine cadavers with the goal of reducing dissection times, tissue trauma, and subjective difficulty of these lymphadenectomies.10 These approaches were based on superficial anatomical landmarks expected to be readily identifiable in most dogs, which could be used to triangulate the expected locations of these peripheral lymphocentrums. The advantages of the geometric technique include the following: (1) its applicability in a range of clinical settings, as it does not require specialized dye or equipment; (2) its descriptions of deep anatomical landmarks, which can be referenced even when identifying lymphocentrums from alternative approaches; and (3) the definitive guidelines regarding patient positioning and incisional orientation.

The objectives of the present study were to evaluate the previously described landmark-guided surgical approaches (SCLN ventral approach, ALN, and SILN) compared to standard and MB-guided lymphadenectomies (MBL) performed by novice surgeons in canine cadavers. The outcome measures were surgical time, successful LN identification, degree of tissue trauma, and subjective difficulty. The null hypothesis was that there would be no differences in successful LN identification, surgical times, tissue trauma scores, or subjective difficulty scores between the 3 lymphadenectomy techniques.

Methods

Study design and participant recruitment

An Institutional Review Board (IRB)–approved prospective, randomized, blinded, 2-period, 2-treatment crossover study was performed at the University of Florida College of Veterinary Medicine between July 23, 2022, and October 12, 2022, with IRB approval obtained on April 26, 2022 (IRB202200416). Participants were recruited via a standardized recruitment email sent out to fourth-year veterinary students, rotating interns, and first-year small animal residents at the University of Florida College of Veterinary Medicine. The first 12 participants who were willing to enroll in the study were selected. Randomization was used to assign identification numbers to participants to maintain anonymity and assign both cadavers and dissections (QuickCalcs Random Number Calculators; GraphPad Software). Six veterinary student volunteers were similarly recruited to assist with data collection during the study days. Volunteers received written instructions 1 week prior and verbal instructions 1 hour prior to each dissection day. Volunteers were randomly assigned to cadavers on dissection days.

Cadavers

Eighteen adult mixed-breed canine cadavers (13 males and 5 females) of medium size and similar average body condition score were obtained from a local animal shelter after euthanasia for reasons unrelated to the present study and were free of grossly apparent diseases that could result in lymphadenomegaly. Cadavers were randomly assigned to dissection days, and participants were randomly assigned to 1 side of each cadaver on the dissection day. Cadavers were stored at –16 °C and thawed at room temperature for 72 hours prior to dissection. Hair was clipped bilaterally around the proposed surgical sites, ensuring that all proposed anatomical landmarks were included within the surgical field. Drapes were used to conceal the contralateral side of each cadaver while participants were performing dissections.

Dissection groups

Dissection days were assigned to each participant on the basis of their reported availability. All participants (n = 12) performed the control, standard lymphadenectomy (SL), on their first available dissection day. Each participant then performed the following 2 additional dissection days over the next several months: MBL and landmarks lymphadenectomy (LL). Participants were randomized to 1 of 2 sequences of surgical approaches (MBL-LL vs LL-MBL) in a 2-period, 2-sequence (2 X 2) crossover design, with 6 participants/sequence. A minimum of 2 weeks between each of the 3 dissection days was ensured for every participant. All participants received standardized instructional materials (printed copy and/or emailed) with instructions for the specific dissection day 1 week prior to each dissection day.

Dissection days

On each dissection day (SL, MBL, and LL), participants were handed an envelope containing their assigned cadaver and dissection side (right/left). The instructions for the dissection day were repeated verbally to each participant. Participants then performed the 3 lymphadenectomies in the same order: SCLN, ALN, and SILN. The ventral approach to the SCLN was used in all cadavers.10

For each lymphadenectomy, participants were allowed to palpate the lymphocentrum for as long as they desired prior to initiating their dissections. Volunteers assigned to each cadaver recorded palpation and dissection times as directed by the participants, as described later. A nonblinded investigator (NJW) was present to confirm identification of LNs via palpation and visual inspection. All participants were given a 20-minute time limit for surgical identification of the LN, as this was thought to be a reasonable amount of time allocated to LN dissection in a clinical setting and was extrapolated from the average surgical times reported in a previous study.2

Standard lymphadenectomy—One week prior to the SL dissection day, participants were provided with a standardized educational packet containing publicly available information on the regional anatomy and, if available, surgical guidelines for extirpation of the superficial cervical, axillary, and superficial inguinal lymphocentrums.1,11 At the time of study design, no published surgical guidelines were available for lymphadenectomy of the ALN or SILN. Participants were not allowed to consult the provided materials while performing dissections.

Methylene blue lymphadenectomy—Cadavers assigned to MBL dissections received a subdermal injection of 1 mL of 1% MB (ProvayBlue; American Regent) at each injection site prior to the start of dissections. Injection sites were chosen on the basis of established lymphosomes and consisted of the cranial ipsilateral midhumeral region for the SCLN, medial ipsilateral elbow for the ALN, and medial ipsilateral stifle for the SILN.12 Injection sites were massaged for 5 minutes postinjection to encourage uptake and spread of MB. Participants were instructed to use the MB uptake as a guide to help them identify the 3 lymphocentrums and were asked not to reference any previously provided SL or LL materials in preparation for the MBL dissection day.

Landmarks lymphadenectomy—One week prior to the dissection day, participants were provided with an informational packet containing the dissection figures and landmark-guided surgical approaches for the SCLN, ALN, and SILN described previously.10 Participants were not allowed to reference the provided materials while performing dissections.

Outcome measures

Outcome measures were recorded on standardized score sheets labeled with the randomly assigned participant identification numbers, cadaver information, dissection group (for nonblinded investigator score sheets only), date, and time of dissection. All outcome measures were obtained for each lymphocentrum on each dissection day unless otherwise stated.

Participant data—Participant title (veterinarian/student), crossover group assignment, dissection date, time of day, cadaver assignment, cadaver sex, and cadaver side were recorded for each participant on every dissection day.

Timed outcome measures—Palpation time was recorded from the moment participants verbalized the beginning of palpation until they verbalized completion. Time to LN identification (T1) was recorded from the moment participants verbalized the start of the skin incision until they verbalized completion of LN identification. Time for T1 was cumulative until the LN was correctly identified by the participant, as confirmed by the supervisor (NJW). Time to LN removal (T2) was started the moment the participant verbalized continuation of dissection after their LN identification had been confirmed and ended when the participant verbalized completion of LN removal. If participants verbalized a request for early termination of the procedure prior to the 20-minute limit, volunteers were instructed to record the time at which the request was made and participants were asked to continue searching for the LN until the 20-minute time limit was reached. If a participant reached the 20-minute time limit without having correctly identified the LN, the outcome was recorded as “not identified” and participants continued to the next lymphocentrum.

Dissection scoring—Descriptive scoring of the dissections was performed by a single nonblinded investigator (NJW) and included incision length, incision orientation (parallel, perpendicular, or oblique to the described LL approach), and successful LN identification (yes/no). Dissection quality was scored by a single blinded investigator (JB) using a scale from 1, “very good,” to 5, “very poor,” which was a modified version of a previously published scoring system used to evaluate dissection quality in gross anatomy courses (Figure 1).13 This assessor also recorded the number of muscles incised (excluding the deep pectoral muscle for the ALN), number of other structures damaged, and number of additional incisions created for each surgical site. An overall tissue trauma score (TTS) was later calculated as the sum of the dissection quality score, number of muscles incised, number of structures damaged, and number of additional incisions created, with a higher TTS indicating more tissue trauma.

Figure 1
Figure 1

Representative images of superficial inguinal lymph node (LN) dissections performed by 7 veterinarians and 5 fourth-year veterinary students for 18 canine cadavers, presented in order of the dissection scoring system used in a crossover study to evaluate the effect of a geometric, landmark-guided approach for peripheral lymphadenectomy between July 23 and October 12, 2022. Dissections must have met at least one of the described criteria for their assigned score.

Citation: Journal of the American Veterinary Medical Association 261, 11; 10.2460/javma.23.04.0206

Participant outcome measures—At the end of each lymphadenectomy, participants were provided with a visual analog scale on which they rated the subjective difficulty of the LN identification from 1 (“extremely easy”) to 100 (“extremely difficult”), regardless of LN identification success. For MBL dissections, participants were asked whether they were able to appreciate MB uptake in the following locations for each LN: skin, subcutaneous tissues/fascia, and LN(s). For LL dissections, participants were asked to indicate whether they found the landmarks to be helpful for LN identification (yes/no).

Data analysis

Descriptive statistics—Summary statistics (mean and SD, SD) for continuous variables (palpation time and incision length) were calculated with SAS proc means (version 9.4; SAS Institute Inc). TTSs were summarized by counts for each score category.

Because identification times were censored, mean time to LN identification was estimated by fitting a right-censored linear parametric failure time model with SAS proc lifereg (version 9.4; SAS Institute Inc) and summarized as means and 95% CI.

Dye versus landmark comparisons—Performance outcomes were evaluated separately for each LN type (SCLN, ALN, and SILN). The standard 2 X 2 crossover design was used to compare LL and MBL methods directly. Time to event (time to LN identification and removal) was analyzed by Cox proportional-hazards regression with method, sequence, and period as fixed effects. Continuous outcome variables were analyzed with mixed-model ANOVA (SAS proc mixed version 9.4; SAS Institute Inc) on method, sequence, and period.14 TTSs were analyzed by cumulative logit regression on method, sequence, and period (SAS proc logistic version 9.4; SAS Institute Inc).15 Incision lengths were compared as a 2 X 2 crossover design (SAS proc mixed version 9.4; SAS Institute Inc). Method (MB and LL), sequence, and period were modeled as fixed effects, participants as random effects, and within-participant correlation modeled by unstructured variance-covariance structure.14 Model estimates are presented as means and 95% CI.

Results

Participant data

Seven veterinarians (2 rotating interns, 2 surgical specialty interns, 1 first-year medical oncology resident, and 2 first-year small animal surgery residents) and 5 fourth-year veterinary students participated in the study. All participants were assessed at each of 3 dissection days, with no dropouts. Time between dissection days averaged 18 days (SD, 6) between days 1 and 2, and 23 days (SD, 10) between days 2 and 3, with a minimum of 2 weeks (14 days) between each participant’s dissection days.

Timed outcome measures

Median palpation times were 27 seconds (IQR, 16 to 43 seconds) across all LNs; 1 participant spent 5 to 7.5 minutes palpating each LN during MB dissections.

Successful LN identification was highest with LL dissections (30/36 [86%]) compared to SL (25/36 [69%]) and MBL (24/36 [67%]) dissections. The 4 participants who failed to identify the SCLN with the LL method did not have the incisions correctly positioned in the described anatomical location (Table 1). Lymph node identification was similar between student and veterinarian participants for all techniques. Students identified 9 of 15 (60%) LNs with the SL method, 12 of 15 (80%) with the LL method, and 10 of 15 (67%) with the MBL method. Veterinarians identified 16 of 21 (76%) LNs with the SL method, 18 of 21 (86%) with the LL method, and 14 of 21 (67%) with the MBL method.

Table 1

Numbers of cadaveric canine lymph nodes (LNs; axillary LN [n = 12], superficial cervical LN [12], or superficial inguinal LN [12]) identified by 7 veterinarians and 5 fourth-year veterinary students in a crossover study conducted between July 23 and October 12, 2022, to compare geometric landmark lymphadenectomy (LL) versus standard lymphadenectomy (SL) and methylene blue–guided lymphadenectomy (MBL) performed on cadavers of 18 adult mixed-breed dogs euthanized for unrelated reasons.

LN identified LL MBL SL
Axillary
 Yes 10 5 6
 No 2 7 6
Superficial cervical
 Yes 8 9 8
 No 4 3 4
Superficial inguinal
 Yes 12 10 10
 No 0 2 2

The LL dissection method reduced T1 for the ALN by 8 to 20 minutes (P = .03) compared to the SL and MBL dissection methods (Table 2). Participants who successfully identified SILN and SCLN took approximately 10 minutes on average. Two subjects in each of the MBL and SL trials exceeded the 20-minute limit for identification of SILN, and 4 subjects exceeded the allotted time for SCLN identification for all 3 dissection methods. One subject was unable to complete 7 of 9 LN identifications. The T1 for the SILN LL dissection was 2 to 8 minutes, less than half the time of SL and 1 to 4 minutes faster than MBL. Measurements for T2 were not significantly different for any LN (P > .05); with 1 exception (1 SCLN with SL dissection), all identified LNs had a T2 of ≤ 20 minutes.

Table 2

Comparisons of the mean (95% CI) time to LN identification (T1) and LN removal (T2) for LL versus SL and MBL in the study described in Table 1. P values test the overall difference between dissection methods. Significance was set at P < .05.

LN and dissection group T1 (min) P value T2 (min) P value
Axillary
 SL 18 (11–29) .03 15 (5–42) .05
 MBL 23 (14–39) 20 (7–53)
 LL 10 (6–15) 6 (2–13)
Superficial inguinal
 SL 8 (5–15) .34 6 (3–11) .06
 MBL 6 (3–12) 6 (3–11)
 LL 4 (2–8) 3 (1– 5)
Superficial cervical
 SL 13 (7–23) .88 15 (7–29) .97
 MBL 12 (7–21) 9 (4–17)
 LL 14 (8–26) 9 (5–17)

Dissection scoring

ORs for the overall TTS were significant for the ALN and SILN and demonstrated reduced tissue trauma with the LL method compared to the SL and MBL methods (Table 3). For the ALN, the LL method was about 7 times more likely to have a lower TTS than the SL method and 15.6 times more likely to have a lower TTS than the MBL method. For the SILN, the odds of the LL method having a lower TTS were 22.86 times greater than the SL method and 17.98 times greater than the MBL method. There was no significant difference between the MBL and SL methods for any LN (P > .05). There was no difference in TTS between any of the dissection methods for the SCLN.

Table 3

Comparisons of tissue trauma scores for the SL, LL, and MBL LN dissections performed in the study described in Table 1. Number of participants in each score category by LN and method. OR (95% CI) describes likelihood of a lower score for each paired comparison. Larger OR indicates a higher likelihood of a lower tissue trauma score for the first method in the pair compared to the second. Significance was set at P < .05.

Lymphadenectomy method LN and trauma score
SL LL MBL
Axillary
  < 4 2 5 3
  4–6 7 5 5
  > 6 3 2 4
LL:SL LL:MBL MBL:SL
OR (95% CI) 7.03 (1.51–32.65) 15.6 (3.32–73.34) 0.45 (0.10–2.04)
P value .013 .0007 .30
 Superficial inguinal
  < 4 3 11 5
  4–6 8 1 7
  > 6 1 0 0
LL: SL LL: MBL MBL: SL
OR (95% CI) 22.86 (4.48–116.57) 17.98 (3.55–90.96) 1.27 (0.32–5.03)
P value .0003 .0007 .73
 Superficial cervical
  < 4 3 5 3
  4–6 7 5 5
  > 6 1 2 4
LL: SL LL: MBL MBL: SL
OR (95% CI) 1.95 (0.44–8.83) 3.96 (0.80–19.77) 0.49 (0.12–2.09)
P value .38 .09 .33

Incision lengths, reported as mean (SD), for the SCLN were similar between lymphadenectomy methods (P = .86): SL, 7.5 cm (2.5 cm); LL, 7.3 cm (2.3 cm); and MBL, 7.5 cm (2.6 cm). Incision lengths increased by approximately 1.5 cm for both LL and MBL methods in the last period, although period effects were not statistically significant (P = .14). For the ALN dissections, mean incision lengths were reduced with LL (5.4 cm; SD, 0.9 cm), compared to SL (7.8 cm; SD, 3.3 cm) and MBL (8.4 cm; SD, 2.4 cm). Incision length averaged 3 cm shorter (95% CI, –4.3 to –1.6 cm) for LL compared to MBL (P = .0002). Incision lengths increased by 1.3 cm in the last period, although period effects were not statistically significant (P = .07). For SILN lymphadenectomy, incision length for SL averaged 7.0 cm (3.1 cm). The LL method resulted in the shortest incisions; incision lengths averaged 2.0 cm less for LL compared to the MBL method (95% CI, –3.4 to –0.9 cm; P = .002). Incision lengths for both methods increased by 2.1 cm in the last period (P = .002).

Second incisions were made in 5 dissections: 1 SL and 1 MBL for the SCLN, 2 MBL for the ALN, and 1 SL for the SILN. No secondary incisions were made in any of the LL dissections.

Participant outcome measures

Subjective difficulty of LN identification using the LL method was approximately half that of both the SL and MBL methods for the ALN (P = .06) and SILN (P = .008; Table 4). Across all methods and LNs, the mean subjective difficulty scores decreased over time. After completing their LL dissections, most participants reported that landmarks were helpful for identification of the LNs, with 8 of 12 (66.7%) responding “yes” for SCLN, 10 of 12 (83.3%) for ALN, and 11 of 12 (91.7%) for SILN.

Table 4

Comparison of subjective difficulty scores (0 to 100) between the SL, LL, and MBL LN dissections performed in the study described in Table 1. For each LN, dissection method, and dissection period, the mean (95% CI) subjective difficulty scores are reported. Statistical significance was set at P < .05.

LN and dissection group Subjective difficulty score
Period Mean (95% CI) P value
Axillary
 SL
1 68 (43–107) .06
 MBL
2 62 (37–104)
3 60 (33–108)
 LL
2 35 (21–59)
3 26 (14–46)
Superficial cervical
 SL
1 47 (29–76) .63
 MBL
2 43 (25–75)
3 38 (20–71)
 LL
2 35 (20–61)
3 28 (15–53)
Superficial inguinal
 SL
1 45 (26–78) .008
 MBL
2 28 (15–52)
3 25 (12–50)
 LL
2 14 (8–27)
3 9 (4–19)

For the MBL dissections, all cadavers were confirmed by the investigators to have MB dye uptake within the dermis after injection and prior to the beginning of dissections. For participants, visible MB uptake into LNs was poor, with only 5 of 12 SCLN, 4 of 12 ALN, and 7 of 12 SILN having MB uptake within the LN that was appreciated by the participants. The MB was otherwise dispersed in the surrounding tissues and skin (Table 5). Participants were able to appreciate MB dye uptake within at least 1 tissue location in 7 of 12 cadavers for the SCLN, 9 of 12 cadavers for the ALN, and 11 of 12 cadavers for the SILN.

Table 5

Comparison of MB dye uptake perceived by participants during MBL dissections in the study described in Table 1. The number of cadavers out of 12 with MB uptake that participants visualized within the tissues is listed for each lymphocentrum.

Type MB uptake
Skin Subcutaneous and/or fascia LN
Superficial cervical 1 5 5
Axillary 3 7 4
Superficial inguinal 10 8 7

Four participants requested to end their LN dissections early. One participant performing SL dissection of the SCLN requested to quit multiple times throughout the dissection starting at 9 minutes, 1 participant requested to quit after 18 minutes during MBL dissection of the SCLN, and 2 participants requested to quit after 7 minutes when performing SL dissection of the ALN. All participants who requested to quit ultimately did identify the LN within the 20-minute time limit. No participants requested early termination during any of the LL dissections.

Discussion

The present study demonstrated the utility of a previously proposed geometric, landmark-guided technique for superficial cervical, axillary, and superficial inguinal lymphadenectomies in canine cadavers compared to standard and MB-guided lymphadenectomies performed by veterinarians and veterinary students early in their surgical training.10 On the basis of the findings of this study, the null hypothesis was rejected for the ALN and SILN; the findings indicated that LN identification time was reduced for the ALN, tissue trauma was reduced for the ALN and SILN, and subjective difficulty was reduced for the SILN with the landmark-guided technique compared to the standard and MB-guided techniques. However, the null hypothesis could not be rejected for the SCLN, as no significant differences were noted in identification times, TTSs, or subjective difficulty scores between lymphadenectomy techniques for the SCLN.

The lack of improvement seen with the LL method for the SCLN was suspected to be secondary to a few factors. First, participants were suspected to be either unfamiliar with or unable to identify the recommended landmarks; all 4 participants who did not identify the SCLN with the LL method had incisions that were too far dorsal and cranial, resulting in the incisions being completely outside of the bounds of the described landmarks. The incorrect positioning of these incisions likely led to excessive tissue dissection and higher subjective difficulty scores, making those participants unsuccessful in identifying the SCLN. Second, it is the authors’ impression that, despite correct landmark identification and incision orientation, the dissection of the SCLN with the patient positioned in dorsal recumbency is more challenging compared to approaching with the patient in lateral recumbency. When the patient is in dorsal recumbency, the LN tends to fall dorsally due to gravity, resulting in the need to pull the perinodal fat up from a deeper plane. Despite successful identification of the SCLN not being improved with the LL method in the present study, it is possible that with a larger sample size or more experienced surgeons, improvements in successful LN identification, T1, and TTS may be observed for the SCLN. Similarly for the SILN dissections, the average T1 for the SILN LL dissection method was approximately half that of the SL method and two-thirds of the average MBL T1. These time reductions could be relevant in a clinical setting, as they would reduce time under general anesthesia and may encourage veterinarians to perform lymphadenectomies due to their improved efficiency.

The 20-minute time limits for LN identification and removal were based on the expected amount of time that a veterinarian might spend searching for an LN before giving up, which was extrapolated from the mean surgical times reported in a previous study.2 Four participants requested to give up before the 20-minute limit, despite eventually identifying those LNs within the allotted time. All requests for early termination were made during the SL and MBL dissections, which could indicate a higher level of frustration with these methods. Similarly, 2 participants in the SL group and 3 participants in the MBL group made second incisions to help with LN identification, but no participants made second incisions in the LL group, even when they were unable to identify the LN. This could indicate a higher level of confidence for some participants with the landmark-guided technique.

The use of intraoperative MB injection for LN mapping has been well described within the veterinary literature and demonstrated to improve the learning curve and success of sentinel LN identification in human medicine.6,7,1619 As a result, MB-guided lymphadenectomy has been considered the gold standard of intraoperative LN identification for veterinarians without access to more advanced mapping techniques. In the present study, the MBL method did not reduce T1, TTS, or subjective difficulty scores for any LNs. The volume of MB used for injection in the present study (1 mL/lymphocentrum) was much higher than what is described within the current veterinary literature; however, MB uptake within the cadaver lymphatics was very inconsistent and often not appreciated by study participants, which may have contributed to the lack of differences seen between the MBL and SL methods.9,20,21 Additionally, while MB uptake was confirmed to be present in the dermis of all cadavers in the present study, the participants reported that they did not perceive uptake of MB within all tissues, which is consistent with the known challenge of discerning dye uptake from normal tissue coloration and was likely exacerbated by the fact that none of the participants in the study had previously used intraoperative MB dye for LN mapping.6,1719,22 Given that poor dye uptake and difficulty discerning dye from surrounding tissues are known challenges of MB dye injection, cadavers in the MBL group were still included in statistical analysis even if participants reported that they were unable to visualize MB in any of the tissues.

Despite its use in sentinel LN mapping, MB has been reported to have several disadvantages, including permanent or prolonged skin staining, increased difficulty with evaluation of surgical margins, interference with pulse oximetry, discoloration of urine, a steep learning curve, poor or incomplete uptake in tissues, difficulty discerning dye uptake from normal tissue coloration, and the need for wider surgical margins when tracing lymphatics.6,9,1719,22 Given the lack of apparent advantage for LN identification, surgical times, tissue trauma, and subjective difficulty observed with the use of MB in the present study, MB guidance for lymphadenectomy outside of sentinel LN mapping may not be worth the associated disadvantages. The highly variable dye uptake observed in the present study further supports the advantage of using anatomical landmarks as a more reliable method of identification than MB injection.

Mean subjective difficulty scores decreased over time for participants regardless of dissection method or LN, which could indicate that participants found the lymphadenectomies to be easier with repetition despite the time between dissection days. Additionally, participants trended toward making longer incisions over time. However, more objective measures indicate that participants’ surgical skills did not improve with repetition; the surgical speed of participants did not improve between SL and later dissection days. For all LNs, T2 was not different between dissection methods, indicating that the dissection method and day likely had no impact on a participant’s ability to remove an LN. Therefore, the decreased difficulty scores and longer incisions were interpreted as evidence of increased participant confidence levels, despite the fact that their surgical skills and knowledge of LN location did not actually improve throughout the course of the study.

Major limitations to this study included the small sample size, variability in scheduling and cadavers, and reliance on participants to read the provided materials. Different lengths of time between dissections may have influenced the quality of dissections or subjective difficulty; however, scheduling for the study was limited by the participants’ individual schedules. Freezer storage time for cadavers was variable and could have affected the quality of tissues for dissection or MB uptake, and cadaveric dissections are not completely representative of a clinical setting. The degree to which each participant prepared for the dissection days and each participant’s prior knowledge base was beyond the control of the study and may have impacted the success of LN identification. Additionally, participants may have utilized additional resources beyond what was provided for them or may not have read the LL surgical guidelines beforehand, which could have affected surgical skill level. Furthermore, MB injection for LN mapping in canine cadavers has been infrequently reported within the veterinary literature and the technique used in this study was developed on the basis of the validated technique and lymphosome map published in a previous study,12 which demonstrated that cadaveric skin can show normal lymphatic contrast agent uptake. Unfortunately, LNs were not transected postdissection to confirm the presence or absence of MB dye uptake, so the true uptake rates in this study are not known and results are only based on participant perception of dye uptake. For novice surgeons with no prior experience with MB dye for LN mapping, it is possible that discoloration of cadaveric tissues could have made it more challenging to identify dye uptake. Finally, the presence of MB staining within the MBL cadaver dissection sites could have introduced bias during the dissection scoring, which was intended to be blinded. Nevertheless, similarities between the MBL and SL groups were still consistent across objective scores (successful LN identification and surgical times) and subjective difficulty.

In conclusion, the use of the landmark-guided lymphadenectomy technique reduced time to LN identification for the axillary LN and subjective difficulty of superficial inguinal lymphadenectomy compared to standard and MB-guided techniques. Additionally, tissue trauma is more likely to be reduced during axillary and superficial inguinal lymphadenectomies when using the landmark-guided technique compared to both the standard and MB-guided techniques. Therefore, landmark-guided lymphadenectomy methodology may be useful in reducing surgical times, tissue injury, and difficulty in a clinical setting for veterinarians early in their clinical training. Additionally, this technique is feasible for veterinarians who do not have access to more advanced methods of intraoperative LN mapping, without the disadvantages associated with MB injection. Further investigation into this topic could include evaluation of the landmark technique using a larger sample size, in a clinical setting, or with veterinarians with a different range of experience levels.

Acknowledgments

The authors would like to thank Dr. W. Alex Fox-Alvarez for his assistance with study design, as well as all participants and volunteers for their participation in the study.

JB and NJW contributed to the study conception. JB, NJW, KH, PJR, and CAA contributed to the study design. NJW, JB, CDC, and ECC contributed to data collection. NJW, JB, and PSR contributed to data analysis and interpretation. CHMS and EAM contributed to data interpretation. PSR contributed to statistical analysis. All authors contributed to drafting, revising, and approval of the submitted manuscript.

Disclosures

The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.

Funding

The authors have nothing to disclose.

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