Mapping the lymphatic system across body scales and expertise domains: A report from the 2021 National Heart, Lung, and Blood Institute workshop at the Boston Lymphatic Symposium

Enhancing our understanding of lymphatic anatomy from the microscopic to the anatomical scale is essential to discern how the structure and function of the lymphatic system interacts with different tissues and organs within the body and contributes to health and disease. The knowledge of molecular aspects of the lymphatic network is fundamental to understand the mechanisms of disease progression and prevention. Recent advances in mapping components of the lymphatic system using state of the art single cell technologies, the identification of novel biomarkers, new clinical imaging efforts, and computational tools which attempt to identify connections between these diverse technologies hold the potential to catalyze new strategies to address lymphatic diseases such as lymphedema and lipedema. This manuscript summarizes current knowledge of the lymphatic system and identifies prevailing challenges and opportunities to advance the field of lymphatic research as discussed by the experts in the workshop.

Superficial and Functional Lymphatic Anatomy of the Upper Extremity

BACKGROUND

Knowledge of detailed lymphatic anatomy in humans is limited, as the small size of lymphatic channels makes it difficult to image. Most current knowledge of the superficial lymphatic system has been obtained from cadaveric dissections.

METHODS

Indocyanine green lymphography was performed preoperatively to map the functional arm lymphatics in breast cancer patients without clinical or objective evidence of lymphedema. A retrospective review was performed to extract demographic, indocyanine green imaging, and surgical data.

RESULTS

Three main functional forearm channels with variable connections to two upper arm pathways were identified. The median forearm channel predominantly courses in the volar forearm (99 percent). The ulnar forearm channel courses in the volar forearm in the majority of patients (66 percent). The radial forearm channel courses in the dorsal forearm in the majority of patients (92 percent). Median (100 percent), radial (91 percent), and ulnar (96 percent) channels almost universally connect to the medial upper arm channel. In contrast, connections to the lateral upper arm channel occur less frequently from the radial (40 percent) and ulnar (31 percent) channels.

CONCLUSIONS

This study details the anatomy of three forearm lymphatic channels and their connections to the upper arm in living adults without lymphatic disease. Knowledge of these pathways and variations is relevant to any individual performing procedures on the upper extremities, as injury to the superficial lymphatic system can predispose patients to the development of lymphedema.

Sentinel Lymph Node in Aged Endometrial Cancer Patients "The SAGE Study": A Multicenter Experience

OBJECTIVE

The incidence of endometrial cancer is increasing in elderly people. Considering that aging progressively affects lymphatic draining function, we aimed to define its impact on IGC uptake during SLN mapping.

METHODS

A multicenter retrospective cohort of endometrial cancer patients with apparently early-stage endometrial cancer undergoing complete surgical staging with SLN dissection was identified in four referral cancer centers from May 2015 to March 2021. Patients were classified in Group 1 (<65 years old) and Group 2 (≥65 years old). The primary endpoint was the assessment of the overall, bilateral, and unsuccessful SLN mapping in the two groups. Secondary outcomes were the evaluation of SLN anatomical distribution and the identification of predictors for mapping failure applying a logistic regression.

RESULTS

A total of 844 patients were enrolled in the study (499 in Group 1 and 395 in Group 2). The overall detection rate, the successful bilateral mapping, and the mapping failure rate of the SLN were 93.8% vs. 87.6% (p = 0.002), 77.1% vs. 66.8% (p = 0.001), and 22.9% vs. 33.2% (p = 0.001), respectively, in Group 1 vs. Group 2. The advanced age affects the anatomical distribution of the SLN leading to a stepwise reduction of "unexpected" mapping sites (left hemipelvis: p < 0.001; right hemipelvis: p = 0.058). At multivariate analysis age ≥ 65 (OR: 1.495, 95% CI: 1.095-2.042, p = 0.011), BMI (OR: 1.023, 95% CI: 1.000-1.046, p = 0.047), non-endometrioid histotype (OR: 1.619, 95% CI: 1.067-2.458, p = 0.024), and LVSI (OR: 1.407, 95% CI: 1.010-1.961, p = 0.044) represent independent predictors of unsuccessful mapping. Applying binomial logistic regression analysis, there was a 1.280-fold increase in the risk of failed mapping for every 10-year-old increase in age (OR: 1.280, 95% CI: 1.108-1.479, p = 0.001). A higher rate of surgical under-staging (0.9% vs. 3.3%, p = 0.012) and adjuvant undertreatment (p = 0.018) was reported in Group 2.

CONCLUSIONS

Old age represents a risk factor for SLN mapping failure both intrinsically and in relation to the greater incidence of other independent risk factors such as LVSI, non-endometrioid histotype, and BMI. Surgeons should target the usual uptake along UPP during the SLN dissection in this subgroup of patients to minimize mapping failure and the consequent risk of surgical under-staging and adjuvant undertreatment.

Real-Time Visualization of the Mascagni-Sappey Pathway Utilizing ICG Lymphography

Background: Anatomic variations in lymphatic drainage pathways of the upper arm may have an important role in the pathophysiology of lymphedema development. The Mascagni–Sappey (M–S) pathway, initially described in 1787 by Mascagni and then again in 1874 by Sappey, is a lymphatic drainage pathway of the upper arm that normally bypasses the axilla. Utilizing modern lymphatic imaging modalities, there is an opportunity to better visualize this pathway and its potential clinical implications. Methods: A retrospective review of preoperative indocyanine green (ICG) lymphangiograms of consecutive node-positive breast cancer patients undergoing nodal resection was performed. Lymphography targeted the M-S pathway with an ICG injection over the cephalic vein in the lateral upper arm. Results: In our experience, the M-S pathway was not visualized in 22% (n = 5) of patients. In the 78% (n = 18) of patients where the pathway was visualized, the most frequent anatomic destination of the channel was the deltopectoral groove in 83% of patients and the axilla in the remaining 17%. Conclusion: Our study supports that ICG injections over the cephalic vein reliably visualizes the M-S pathway when present. Further study to characterize this pathway may help elucidate its potential role in the prevention or development of upper extremity lymphedema.