Anatomical Effects of Axillary Nodes Dissection on Rat Lymphatic System Model: Indocyanine Green Mapping and Dissection

In Vivo Dynamic and Static Analysis of Lymphatic Dysfunction in Lymphedema Using Near-Infrared Fluorescence Indocyanine Green Lymphangiography

BACKGROUND

Near-infrared fluorescence indocyanine green lymphangiography, a primary modality for detecting lymphedema, which is a disease due to lymphatic obstruction, enables real-time observations of lymphatics and reveals not only the spatial distribution of drainage (static analysis) but also information on the lymphatic contraction (dynamic analysis).

METHODS

We have produced total lymphatic obstruction in the upper limbs of 18 Sprague-Dawley rats through the dissection of proximal (brachial and axillary) lymph nodes and 20-Gy radiation (dissection limbs). After the model formation for 1 week, 9 animal models were observed for 6 weeks using near-infrared fluorescence indocyanine green lymphangiography by injecting 6-μL ICG-BSA (indocyanine green-bovine serum albumin) solution of 20-μg/mL concentration. The drainage pattern and leakage of lymph fluid were evaluated and time-domain signals of lymphatic contraction were observed in the distal lymphatic vessels. The obtained signals were converted to frequency-domain spectrums using signal processing.

RESULTS

The results of both static and dynamic analyses proved to be effective in accurately identifying the extent of lymphatic disruption in the dissection limbs. The static analysis showed abnormal drainage patterns and increased leakage of lymph fluid to the periphery of the vessels compared with the control (normal) limbs. Meanwhile, the waveforms were changed and the contractile signal frequency increased by 58% in the dynamic analysis. Specifically, our findings revealed that regular lymphatic contractions, observed at a frequency range of 0.08 to 0.13 Hz in the control limbs, were absent in the dissection limbs. The contractile regularity was not fully restored for the follow-up period, indicating a persistent lymphatic obstruction.

CONCLUSIONS

The dynamic analysis could detect the abnormalities of lymphatic circulation by observing the characteristics of signals, and it provided additional evaluation indicators that cannot be provided by the static analysis. Our findings may be useful for the early detection of the circulation problem as a functional evaluation indicator of the lymphatic system.

Anatomy and relationships of forelimb lymph nodes in Sprague-Dawley rats: A detailed dissecting approach

Background

Constructing a reliable animal model for preclinical treatment of secondary lymphedema is challenging because the anatomical characteristics near the lymph nodes are understudied. Therefore, this study examined the detailed anatomical relationship between the axillary lymph node flaps (ALNFs) and brachial lymph node flaps (BLNFs) in the forelimb of Sprague-Dawley (SD) rats.

Materials and methods

Ten male rats, weighing 250–300 g, were used. The ALNFs and BLNFs on either side of the rat forelimbs were dissected. The two lymph node flaps (LNFs) were immediately harvested to analyze their physical characteristics (via imaging process software) and microscopic structure (via histology examinations).

Results

A total of 20 ALNFs and BLNFs from 10 rats were harvested and analyzed. ALNF dissection was simpler and lasted a shorter time than BLNF dissection (p < 0.0001). The left LNFs were more difficult to dissect than the right LNFs (p < 0.0001). In physical characteristics of LNFs, the area (p < 0.001) of LNFs and the number of lymph nodes (p < 0.0001) associated with ALNFs were greater than those associated with BLNFs, but the pedicle lengths of ALNFs were shorter than that of BLNFs (p < 0.0001). No significant difference in the diameter of the venous and arterial pedicles was noted between the two LNFs (p > 0.05).

Conclusion

This study reported detailed physical characteristics of ALNFs and BLNFs in SD rat forelimbs, assessing the respective area of LNFs, number of lymph nodes, and lengths and diameters of vascular pedicles. Moreover, this study suggested an efficient method to perform a study of LNFs by describing the operation process and repeatedly measuring the operation time.

A novel mouse tail lymphedema model for observing lymphatic pump failure during lymphedema development

It has been suggested that many forms of secondary lymphedema in humans are driven by a progressive loss of lymphatic pump function after an initial risk-inducing event. However, the link between pump failure and disease progression has remained elusive due to experimental challenges in the clinical setting and a lack of adequate animal models. Using a novel surgical model of lymphatic injury, we track the adaptation and functional decline of the lymphatic network in response to surgery. This model mimics the histological hallmarks of the typical mouse tail lymphedema model while leaving an intact collecting vessel for analysis of functional changes during disease progression. Lymphatic function in the intact collecting vessel negatively correlated with swelling, while a loss of pumping pressure generation remained even after resolution of swelling. By using this model to study the role of obesity in lymphedema development, we show that obesity exacerbates acquired lymphatic pump failure following lymphatic injury, suggesting one mechanism through which obesity may worsen lymphedema. This lymphatic injury model will allow for future studies investigating the molecular mechanisms leading to lymphedema development.