Compartmentalized ocular lymphatic system mediates eye-brain immunity.

The eye, an anatomical extension of the central nervous system (CNS), exhibits many molecular and cellular parallels to the brain. Emerging research demonstrates that changes in the brain are often reflected in the eye, particularly in the retina1. Still, the possibility of an immunological nexus between the posterior eye and the rest of the CNS tissues remains unexplored. Here, studying immune responses to herpes simplex virus in the brain, we observed that intravitreal immunization protects mice against intracranial viral challenge. This protection extended to bacteria and even tumours, allowing therapeutic immune responses against glioblastoma through intravitreal immunization. We further show that the anterior and posterior compartments of the eye have distinct lymphatic drainage systems, with the latter draining to the deep cervical lymph nodes through lymphatic vasculature in the optic nerve sheath. This posterior lymphatic drainage, like that of meningeal lymphatics, could be modulated by the lymphatic stimulator VEGFC. Conversely, we show that inhibition of lymphatic signalling on the optic nerve could overcome a major limitation in gene therapy by diminishing the immune response to adeno-associated virus and ensuring continued efficacy after multiple doses. These results reveal a shared lymphatic circuit able to mount a unified immune response between the posterior eye and the brain, highlighting an understudied immunological feature of the eye and opening up the potential for new therapeutic strategies in ocular and CNS diseases.

Current and Developing Lymphatic Imaging Approaches for Elucidation of Functional Mechanisms and Disease Progression.

Study of the lymphatic system, compared to that of the other body systems, has been historically neglected. While scientists and clinicians have, in recent decades, gained a better appreciation of the functionality of the lymphatics as well as their role in associated diseases (and consequently investigated these topics further in their experimental work), there is still much left to be understood of the lymphatic system. In this review article, we discuss the role lymphatic imaging techniques have played in this recent series of advancements and how new imaging techniques can help bolster this wave of discovery. We specifically highlight the use of lymphatic imaging techniques in understanding the fundamental anatomy and physiology of the lymphatic system; investigating the development of lymphatic vasculature (using techniques such as intravital microscopy); diagnosing, staging, and treating lymphedema and cancer; and its role in other disease states.

Kidney Lymphatics.

Following significant advances in lymphatic biology, the important role of kidney lymphatics in kidney function and dysfunction is now being more fully appreciated. Kidney lymphatics begin in the cortex as blind-ended lymphatic capillaries and then coalesce into larger lymphatics that follow the main blood vessels out through the kidney hilum. Their function in draining interstitial fluid, macromolecules, and cells underpins their important role in kidney fluid and immune homeostasis. This article provides a comprehensive overview of recent and more established research findings on kidney lymphatics and the implications of these findings for kidney function and disease. The use of lymphatic molecular markers has greatly expanded our knowledge of the development, anatomy, and pathophysiology of kidney lymphatics. Significant recent discoveries include the diverse embryological source of kidney lymphatics, the hybrid nature of the ascending vasa recta, and the effects of lymphangiogenesis on kidney diseases such as acute kidney injury and renal fibrosis. On the basis of these recent advances, there is now an opportunity to link information from across multiple research disciplines to drive a new era of lymphatic-targeted therapies for kidney disease. © 2023 American Physiological Society. Compr Physiol 13:4945-4984, 2023.

The lymphatic system of the uterine cervix: towards a more precise definition of the drainage routes.

PURPOSE: Lymph node involvement in cancer of the uterine cervix is a major independent prognostic factor for overall survival. The aim of our study was to examine the lymphatic drainage regions of the different parts of the uterine cervix. METHODS: An anatomical study of fresh cadavers was conducted by injecting patent blue in the anterior or posterior lip of the uterine cervix and dissecting drainage regions. Furthermore, a retrospective radiological and pathological studies were conducted on patients who were treated for early-stage cancer of the uterine cervix with lymph node involvement. Radiological analysis of pre-therapeutic MRIs and/or pathological analysis of surgical specimens showed the precise location of the tumour. A correlation between the anatomy of the primary lesion site and the lymphatic area involved was established. RESULTS: We administered 15 cadaveric injections: 8 in the anterior lip of the uterine cervix and 7 in the posterior one. For 100% of the anterior lip injections, lymphatic drainage was bilateral ileo-obturator (n = 8/8) combined with bilateral parametrial drainage. For the posterior injections, there was never any ileo-obturator drainage, and 6 of the 7 (75%) posterior injections drained in the posterior uterine serosa. Concerning the clinical study, we included 21 patients. We observed a non-significant tendency towards bilateral lymph node involvement when the tumour of the anterior lip. CONCLUSION: Physiological lymphatic drainage of the uterine cervix presents anatomical specificities, depending on the structure studied, anterior or posterior lip of the cervix. Better knowledge of these specificities should allow personalized surgery for each patient.

Lymphatic Intervention, the Frontline of Modern Lymphatic Medicine: Part I. History, Anatomy, Physiology, and Diagnostic Imaging of the Lymphatic System.

Recent advances in lymphatic imaging have provided novel insights into the lymphatic system. Interventional radiology has played a significant role in the development of lymphatic imaging techniques and modalities. Radiologists should be familiar with the basic physiology and anatomy of the lymphatic system to understand the imaging features of lymphatic disorders, which reflect their pathophysiology. This study comprehensively reviews the physiological and anatomical aspects of the human lymphatic system as well as the latest lymphatic imaging techniques.

Anatomy and pathology of lymphatic vessels under physiological and inflammatory conditions in the mouse diaphragm.

The lymphatic vessels in the parietal pleura drain fluids. Impaired drainage function and excessive fluid entry in the pleural cavity accumulate effusion. The rat diaphragmatic lymphatics drain fluids from the pleura to the muscle layer. Lymphatic subtypes are characterized by the major distribution of discontinuous button-like endothelial junctions (buttons) in initial lymphatics and continuous zipper-like junctions (zippers) in the collecting lymphatics. Inflammation replaced buttons with zippers in tracheal lymphatics. In the mouse diaphragm, the structural relationship between the lymphatics and blood vessels, the presence of lymphatics in the muscle layer, and the distributions of initial and collecting lymphatics are unclear. Moreover, the endothelial junctional alterations and effects of vascular endothelial growth factor receptor (VEGFR) inhibition under pleural inflammation are unclear. We subjected the whole-mount mouse diaphragms to immunohistochemistry. The lymphatics and blood vessels were distributed in different layers of the pleural membrane. Major lymphatic subtypes were initial lymphatics in the pleura and collecting lymphatics in the muscle layer. Chronic pleural inflammation disorganized the stratified layers of the lymphatics and blood vessels and replaced buttons with zippers in the pleural lymphatics, which impaired drainage function. VEGFR inhibition under inflammation maintained the vascular structures and drainage function. In addition, VEGFR inhibition maintained the lymphatic endothelial junctions and reduced the blood vessel permeability under inflammation. These findings may provide new targets for managing pleural effusions caused by inflammation, such as pleuritis and empyema, which are common pneumonia comorbidities.

Gaspare Aselli (1581-1625) and Lacteis Venis: Four Centuries From the Discovery of Lymphatic System.

The first half of the seventeenth century may be seen as the turning point of knowledge of human anatomy and physiology, as also demonstrated by the works by William Harvey (1578-1657) on the circulation of the blood. This article aims to present biographic context of the surgeon Gaspare Aselli (1581-1625) and his rather fortuitous discovery of the lacteals in Milan in 1622, that contributed to the comprehension of the lymphatic system. The experimentation on living animals (anatomia animata, living anatomy), and particularly the vivisection used by Gaspare Aselli provided the basis for much of the subsequent investigation of the human physiology. In particular, the discovery of lymphatics challenged the basis of the Galenic doctrine, denying the liver the central role it had formerly been granted in transforming food into blood and revolutionized the ancient hepatocentrism in favor of the modern concept of cardiocentrism.

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.

Fascial Organisation and Lymphatic Systems Around the Pelvic Floor: A Literature Review.

This review summarises the anatomy and lymphatic systems around the pelvic floor. We investigated the lymphovascular network in the anorectal region, focusing on the hiatal ligament, which comprises smooth muscle fibres derived from the longitudinal muscle and connecting the anal canal and coccyx, and the endopelvic fascia, which seems to comprise collagen and elastic fibres. During rectal surgery, endopelvic fascia is recognized as a sheet of fascia covering the levator ani muscle. Endopelvic fascia is extensively attached to the smooth muscle fibres diverging from the longitudinal muscle of the rectum. Analysis of the lymphovascular network using submucosal India ink injection and indocyanine green fluorescence imaging suggests a functional lymphatic flow between rectal muscle fibres and hiatal ligament and endopelvic fascia. Precise analysis of the lymphatic systems of fascial organization around the pelvic floor may be useful in formulating therapeutic strategies for low rectal cancer.

The lymphatics in kidney health and disease.

The mammalian vascular system consists of two networks: the blood vascular system and the lymphatic vascular system. Throughout the body, the lymphatic system contributes to homeostatic mechanisms by draining extravasated interstitial fluid and facilitating the trafficking and activation of immune cells. In the kidney, lymphatic vessels exist mainly in the kidney cortex. In the medulla, the ascending vasa recta represent a hybrid lymphatic-like vessel that performs lymphatic-like roles in interstitial fluid reabsorption. Although the lymphatic network is mainly derived from the venous system, evidence supports the existence of lymphatic beds that are of non-venous origin. Following their development and maturation, lymphatic vessel density remains relatively stable; however, these vessels undergo dynamic functional changes to meet tissue demands. Additionally, new lymphatic growth, or lymphangiogenesis, can be induced by pathological conditions such as tissue injury, interstitial fluid overload, hyperglycaemia and inflammation. Lymphangiogenesis is also associated with conditions such as polycystic kidney disease, hypertension, ultrafiltration failure and transplant rejection. Although lymphangiogenesis has protective functions in clearing accumulated fluid and immune cells, the kidney lymphatics may also propagate an inflammatory feedback loop, exacerbating inflammation and fibrosis. Greater understanding of lymphatic biology, including the developmental origin and function of the lymphatics and their response to pathogenic stimuli, may aid the development of new therapeutic agents that target the lymphatic system.

Surgical Approach to Lymphedema Reduction.

PURPOSE OF REVIEW: For patients who have or may develop lymphedema due to oncologic resection, surgical options are available to prevent and treat this chronic disease. Here, we review the current pathophysiology, classification systems, surgical preventive techniques, and treatment options for lymphedema reduction. RECENT FINDINGS: Preventive surgical techniques, including de-escalation of axillary surgery, sentinel lymph node biopsy (SLNB), axillary reverse mapping (ARM), and lymphedema microsurgical preventive healing approach (LYMPHA), have been shown to reduce the incidence of lymphedema. Water displacement remains the gold standard for measuring limb volume and classification of lymphedema; however, lymphoscintigraphy and ICG lymphography are two novel imaging techniques that are now utilized to characterize lymphedema and guide management. Complete decongestive therapy (CDT) remains the mainstay of treatment. Vascularized lymph node transfer (VLNT) and lymphovenous bypass have shown promising results, particularly in advanced lymphedema stages. Combination therapy, incorporating both surgical and non-surgical approaches to lymphedema, yields best patient outcomes. Lymphedema is a chronic disease wherein management requires a combination of surgical and conservative treatments. Standardization in lymphedema staging, key outcome indicators, and quantitative data will be critical to establish the absolute best practices in lymphedema diagnosis and treatment.

Using the venous angle as a pressure reservoir to retrogradely fill the subclavian lymphatic trunk with contrast agent for lymphatic mapping.

BACKGROUND: Visualizing the lymphatic system and recording the spatial relations between the subclavian lymphatic trunk (SLT) and the surrounding anatomical structures will improve radiotherapy treatment planning for breast cancer patients with lymphatic involvement. An experimental approach to retrogradely fill the SLT with contrast agent was explored. METHODS: Six Thiel embalmed specimens were bilaterally dissected in the cervical and clavicular region to optimize the new experimental approach. A conservative dissection with minimum distortion of spatial relations between different anatomical structures was developed. A pressure reservoir was created inside the venous angle to allow retrograde filling of the SLT under the influence of time and pressure. RESULTS: The new methodology proved feasible, showing successful pressure build-up inside the venous reservoir, resulting in filling of the proximal end of the subclavian lymphatic trunk. The pressures needed to significantly fill the subclavian lymphatic trunk proved to be higher than the pressures that the venous walls could withstand. CONCLUSIONS: Thiel embalmed specimens proved useful for optimizing the experimental approach, but the embalming products could have negatively affected the vessel strength. The authors suggest that their method will be applied on fresh frozen specimens in future studies, to obtain SLT filling up to the axillary lymphatic plexus. Our findings also pointed out that there is still a lot to be learned about the anatomical variability of the SLT and its termination sites. The detailed description of our experimental approach offers valuable information for future lymphatic mapping studies.

Anatomy of the lymphovenous valve of the thoracic duct in humans.

The majority of lymph generated in the body is returned to the blood circulation via the lymphovenous junction (LVJ) of the thoracic duct (TD). A lymphovenous valve (LVV) is thought to guard this junction by regulating the flow of lymph to the veins and preventing blood from entering the lymphatic system. Despite these important functions, the morphology and mechanism of this valve remains unclear. The aim of this study was to investigate the anatomy of the LVV of the TD. To do this, the TD and the great veins of the left side of the neck were harvested from 16 human cadavers. The LVJs from 12 cadavers were successfully identified and examined macroscopically, microscopically, and using microcomputed tomography. In many specimens, the TD branched before entering the veins. Thus, from 12 cadavers, 21 LVJs were examined. Valves were present at 71% of LVJs (15/21) and were absent in the remainder. The LVV, when present, was typically a bicuspid semilunar valve, although the relative size and position of its cusps were variable. Microscopically, the valve cusps comprised luminal extensions of endothelium with a thin core of collagenous extracellular matrix. This study clearly demonstrated the morphology of the human LVV. This valve may prevent blood from entering the lymphatic system, but its variability and frequent absence calls into question its utility. Further structural and functional studies are required to better define the role of the LVV in health and disease.

Organ-specific lymphatics play distinct roles in regulating HDL trafficking and composition.

Recently, peripheral lymphatic vessels were found to transport high-density lipoprotein (HDL) from interstitial tissues to the blood circulation during reverse cholesterol transport. This function is thought to be critical to the clearance of cholesterol from atherosclerotic plaques. The role of organ-specific lymphatics in modulating HDL transport and composition is, however, incompletely understood. This study aimed to 1) determine the contribution of the lymphatics draining the intestine and liver (which are major sites of HDL synthesis) to total (thoracic) lymph HDL transport and 2) verify whether the HDLs in lymph are derived from specific organs and are modified during trafficking in lymph. The mesenteric, hepatic, or thoracic lymph duct was cannulated in nonfasted Sprague-Dawley rats, and lymph was collected over 5 h under anesthesia. Whole lymph and specific lymph lipoproteins (isolated by ultracentrifugation) were analyzed for protein and lipid composition. The majority of thoracic lymph fluid, protein, and lipid mass was sourced from the mesenteric, and to a lesser extent, hepatic lymph. Mesenteric and thoracic lymph were both rich in chylomicrons and very low-density lipoprotein, whereas hepatic lymph and plasma were HDL-rich. The protein and lipid mass in thoracic lymph HDL was mostly sourced from mesenteric lymph, whereas the cholesterol mass was equally sourced from mesenteric and hepatic lymph. HDLs were compositionally distinct across the lymph sources and plasma. The composition of HDL also appeared to be modified during passage from the mesenteric and hepatic to the thoracic lymph duct. Overall, this study demonstrates that the lipoproteins in lymph are organ specific in composition, and the intestine and liver appear to be the main source of HDL in the lymph.NEW & NOTEWORTHY High-density lipoprotein in lymph are organ-specific in composition and derive mostly from the intestine and liver. High-density lipoprotein also appears to be remodeled during transport through the lymphatics. These findings have implications to cardiometabolic diseases that involve perturbations in lipoprotein distribution and metabolism.

Pelvic sentinel lymph node biopsy in endometrial cancer-a simplified algorithm based on histology and lymphatic anatomy.

OBJECTIVE: To achieve the full potential of sentinel lymph node (SLN) detection in endometrial cancer, both presumed low- and high-risk groups should be included. Perioperative resource use and complications should be minimized. Knowledge on distribution and common anatomical sites for metastatic SLNs may contribute to optimizing the concept while maintaining sensitivity. Proceeding from previous studies, simplified algorithms based on histology and lymphatic anatomy are proposed. METHODS: Data on mapping rates and locations of pelvic SLNs (metastatic and non-metastatic) from two previous prospective SLN studies in women with endometrial cancer were retrieved. Cervically injected indocyanine green was used as a tracer and an ipsilateral re-injection was performed in case of non-display of the upper and/or lower paracervical pathways. A systematic surgical algorithm was followed with clearly defined SLNs depicted on an anatomical chart. In high-risk endometrial cancer patients, removal of SLNs was followed by a pelvic and para-aortic lymphadenectomy. RESULTS: 423 study records were analyzed. The bilateral mapping rates of the upper and lower paracervical pathways were 88.9% and 39.7%, respectively. 72% of all SLNs were typically positioned along the upper paracervical pathway (interiliac and/or proximal obturator fossa) and 71 of 75 (94.6%) of pelvic node positive women had at least one metastatic SLN at either of these positions. Women with grade 1-2 endometroid cancers (n=275) had no isolated metastases along the lower paracervical pathway compared with two women with high-risk histologies (n=148). CONCLUSION: SLNs along the upper paracervical pathway should be identified in all endometrial cancer histological subtypes; removal of nodes at defined typical positions along the upper paracervical pathway may replace a site-specific lymphadenectomy in case of non-mapping despite tracer re-injection. Detection of SLNs along the lower paracervical pathway can be restricted to high-risk histologies and a full pre-sacral lymphadenectomy should be performed in case of non-display.

The underestimated posterior lymphatic drainage of the prostate: An historical overview and preliminary anatomical study on cadaver.

BACKGROUND: The evidence of pelvic lymph node metastases after radical prostatectomy (RP) with pelvic lymph node dissection (PLND) is one of the strongest prognostic factors for poor oncologic outcome. The extent of PLND, although representing a crucial step in RP, is still controversial. Currently, there is a critical drawback in clinical practice due to the lack of congruence between the known lymphatic drainage and cancer dissemination despite defined management by a surgical approach. We hypothesized the existence of alternative pathways for the lymphatic drainage of the prostate currently not considered in clinical daily practice. METHODS: We carried out a literature review of the anatomic description of nodal drainage of prostate reported by online databases (MEDLINE/PubMed, EBSCO, Web of Science, Ovid, and Scopus) and the original texts since the 18th century, with an additional anatomical dissection on a human cadaver to confirm theoretical data. RESULTS: The anatomical dissection study converged with the historical anatomical treatises in describing three groups of lymphatics devoted to carrying out prostatic nodal drainage. Apart from the ascending ducts from the cranial gland leading to the external iliac nodes; the lateral ducts leading to the hypogastric nodes; small lymphatic vessels from the posterior surface of the prostate, directed to the pararectal lymphatic plexus, in the direction of the lateral sacral lymph nodes and those at the sacral promontory (ie, pararectal and presacral lymph nodes) were observed. CONCLUSIONS: Our preliminary findings demonstrate that lymphatic drainage of the prostate extends beyond standard nodal templates actually considered in surgical daily practice, despite the knowledge reported by historical anatomical treatises. Further anatomical and experimental evidence are needed to investigate anatomical variability in humans, as well as to add more topographical details.

[Thoracic lymphatic system-principles, characteristics and advice for the practice]. / Das thorakale Lymphsystem ­ Grundlagen, Besonderheiten und Hinweise für die Praxis.

The lymphatic system of the lungs is complex. To maintain an effective gas exchange there is a need for a dense lymphatic network. The alveolae have no lymphatic vessels. There is no segment-specific lymph drainage. For both lungs there are fixed bronchopulmonary lymph nodes but the number and size of the lymph nodes are variable. There are seven mediastinal lymph node chains that vary in extent, each of which acts as an independent functional unit. The accurate assessment of the nodal status needs a simple reproducible nodal map. The division into compartments or zones makes this easier. Mediastinal lymph node metastases without involvement of bronchopulmonary lymph nodes are possible. The development mechanism of this skip metastasizing is multifactorial.

Call for a Multidisciplinary Effort to Map the Lymphatic System with Advanced Medical Imaging Techniques: A Review of the Literature and Suggestions for Future Anatomical Research.

This review intends to rekindle efforts to map the lymphatic system by using a more modern approach, based on medical imaging. The structure, function, and pathologies associated with the lymphatic system are first discussed to highlight the need for more accurately mapping the lymphatic system. Next, the need for an interdisciplinary approach, with a central role for the anatomist, to come up with better maps of the lymphatic system is emphasized. The current approaches on lymphatic system research involving medical imaging will be discussed and suggestions will be made for an all-encompassing effort to thoroughly map the entire lymphatic system. A first-hand account of our integration as anatomists in the radiotherapy department is given as an example of interdisciplinary collaboration. From this account, it will become clear that the interdisciplinary collaboration of anatomists in the clinical disciplines involved in lymphatic system research/treatment still holds great promise in terms of improving clinical regimens that are currently being employed. As such, we hope that our fellow anatomists will join us in an interdisciplinary effort to map the lymphatic system, because this could, in a relatively short timeframe, provide improved treatment options for patients with cancer or lymphatic pathologies all over the world. Anat Rec, 302:1681-1695, 2019. © 2019 American Association for Anatomy.