Lymphatic Malformations: Genetics, Mechanisms and Therapeutic Strategies

Sirolimus for kaposiform hemangioendothelioma: Potential mechanisms of action and resistance

Kaposiform hemangioendotheliomas (KHEs) are vascular tumors that are considered borderline or locally aggressive and may lead to lethal outcomes. Traditional therapies, such as surgery and embolization, may be insufficient or technically impossible for patients with KHE. Sirolimus (or rapamycin), a specific inhibitor of mechanistic target of rapamycin, has recently been demonstrated to be very useful in the treatment of KHEs. Here, we highlight recent substantial progress regarding the effects of sirolimus on KHEs and discuss the potential mechanisms of action of sirolimus in treating this disease. The prevention of platelet activation and inflammation, along with antiangiogenic effects, the inhibition of lymphangiogenesis, the attenuation of fibrosis, or a combination of all these effects, may be responsible for the therapeutic effects of sirolimus. In addition, the mechanism of sirolimus resistance in some KHE patients is discussed. Finally, we review the somatic mutations that have recently been identified in KEH lesions, and discuss the potential of novel therapeutic targets based on these further understandings of the cellular and molecular pathogenesis of KHE.

Force-mediated recruitment and reprogramming of healthy endothelial cells drive vascular lesion growth

Force-driven cellular interactions are crucial for cancer cell invasion but remain underexplored in vascular abnormalities. Cerebral cavernous malformations (CCM), a vascular abnormality characterized by leaky vessels, involves CCM mutant cells recruiting wild-type endothelial cells to form and expand mosaic lesions. The mechanisms behind this recruitment remain poorly understood. Here, we use an in-vitro model of angiogenic invasion with traction force microscopy to reveal that hyper-angiogenic Ccm2-silenced endothelial cells enhance angiogenic invasion of neighboring wild-type cells through force and extracellular matrix-guided mechanisms. We demonstrate that mechanically hyperactive CCM2-silenced tips guide wild-type cells by transmitting pulling forces and by creating paths in the matrix, in a ROCKs-dependent manner. This is associated with reinforcement of β1 integrin and actin cytoskeleton in wild-type cells. Further, wild-type cells are reprogrammed into stalk cells and activate matrisome and DNA replication programs, thereby initiating proliferation. Our findings reveal how CCM2 mutants hijack wild-type cell functions to fuel lesion growth, providing insight into the etiology of vascular malformations. By integrating biophysical and molecular techniques, we offer tools for studying cell mechanics in tissue heterogeneity and disease progression.

Lymphedema in Turner syndrome: correlations with phenotype and karyotype

OBJECTIVES

Lymphedema (LD) in Turner syndrome (TS) is a commonly reported comorbidity, though its associations with karyotype and other comorbidities are poorly understood. Characteristics of patients with TS and LD, including correlation with phenotype and karyotype, are described.

METHODS

Medical records of patients with TS seen in two pediatric institutions from 2002 to 2020 were retrospectively reviewed. Demographic data (age, presentation onset, clinical features, genetics, LD presence, investigations, treatments) were collected.

RESULTS

393 girls with TS with mean age of 12.5 years (SD: 5.7) were identified. LD was noted in 37 % of patients (n=146). Among the 112 patients with TS and documentation of onset of LD, LD was noted within the first year of life in 78.6 % (n=88). 67.6 % (n=96) of total patients with TS and LD had non-mosaic 45, X karyotype. Frequency of webbed neck was significantly greater in girls with TS and LD compared with girls without LD (58 vs. 7 %, p<0.001). Congenital heart anomalies, hypertension, and renal anomalies were also more common in girls with LD. Nail abnormalities with presence of hypoplastic or dysplastic nails were significantly associated with LD (OR: 6.784, 95 % CI 4.235-11.046). The number of girls reporting presence of LD decreased with age.

CONCLUSIONS

LD in TS often occurs within the first year of life, is less prevalent in older children and adolescents, and is significantly associated with 45, X karyotype, presence of webbed neck, nail changes, congenital heart anomalies, and renal anomalies.

Sclerothrapy of giant lymphatic malformation in neonates

OBJECTIVE

To analyze the sclerotherapy of giant (≥8 mm) lymphatic malformations in neonates and discuss effective treatment.

METHODS

This was a single-center retrospective study. Twelve patients received bleomycin (BLM) (six patients) or BLM combined with polidocanol (POL) (eight patients). The safety and effects of BLM and BLM + POL were analyzed using a t-test for categorical data and likelihood ratios or Fisher's exact test for continuous data. Factors resulting in an increased number of treatment sessions were studied.

RESULTS

Treatment began 2-5 days after birth. The patients in the BLM group underwent more treatment sessions. Gestational age, lesion size and type, total response, and complications showed no significant differences between groups. Larger and mixed-ype lesions required more treatment sessions.

CONCLUSIONS

Both BLM group and BLM + POL group appear relatively safe and effective in neonates with giant lymphatic malformations. The combination of the two agents reduced the number of procedures and general anesthesia required.

Ultrasonography findings of pediatric head and neck lymphatic malformations: A 10-year experience of 140 surgical cases

OBJECTIVE

To discuss the usefulness of ultrasonography (US) in the diagnosis and management of pediatric head and neck lymphatic malformations (HNLMs).

METHODS

We conducted a retrospective analysis of 140 children who were referred to our hospital for the treatment of HNLMs.

RESULTS

The median age at presentation was 12 months (1 day-171 months; 66.4% under 2 years old; 35.7% neonatus). The majority clinical presentations were asymptomatic mass (65.7%, 92/140) and cosmetic deformity (25.7%, 36/140). HNLMs involved the neck accounting for 65.7% (92/140), especially posterior cervical trigone (22.1%, 31/140), and submandibular (20.0%, 28/140). The US diagnostic accuracy was 91.4% (128/140). Their boundary with the surrounding tissues was usually clear (87.9%, 123/140), whereas the shape was mostly irregular (97.1%, 136/140). Based on surgical findings, there were 67 pure HNLMs and 73 intracystic hemorrhage. Between the two groups, there were statistical differences in capsule contents (χ2 = 7.8299, p = 0.0051), flocculent echo floating (χ2 = 21.2964, p < 0.0001), overlying skin (χ2 = 9.0498, p = 0.0026), and palpation (χ2 = 13.4058, p = 0.0003).

CONCLUSIONS

US typically reveals the lesion with clear boundary, irregular morphology, anechoic contents, no blood flow signal, and echoic intracapsular septum with blood flow signal. In contrast, bluish appearance, tensional palpation, and capsule contents with low/mixed echo or flocculent echo floating may indicate intracystic hemorrhage.

Lymphatic System Development and Function

PURPOSE OF REVIEW

This review delves into recent advancements in understanding generalized and organ-specific lymphatic development. It emphasizes the distinct characteristics and critical anomalies that can impair lymphatic function. By exploring developmental mechanisms, the review seeks to illuminate the profound impact of lymphatic malformations on overall health and disease progression.

RECENT FINDINGS

The introduction of genome sequencing, single-cell transcriptomic analysis, and advanced imaging technologies has significantly enhanced our ability to identify and characterize developmental defects within the lymphatic system. As a result, a wide range of lymphatic anomalies have been uncovered, spanning from congenital abnormalities present at birth to conditions that can become life-threatening in adulthood. Additionally, recent research highlights the heterogeneity of lymphatics, revealing organ-specific developmental pathways, unique molecular markers, and specialized physiological functions specific to each organ. A deeper understanding of the unique characteristics of lymphatic cell populations in an organ-specific context is essential for guiding future research into lymphatic disease processes. An integrated approach to translational research could revolutionize personalized medicine, where treatments are precisely tailored to individual lymphatic profiles, enhancing effectiveness and minimizing side effects.

Targeted treatments for vascular malformations: current state of the art

Vascular malformations, which arise from anomalies in angiogenesis, encompass capillary, lymphatic, venous, arteriovenous, and mixed malformations, each affecting specific vessel types. Historically, therapeutic options such as sclerotherapy and surgery have shown limited efficacy in complicated malformations. Most vascular malformations stem from hereditary or somatic mutations akin to oncogenic alterations, activating the PI3K-AKT-mTOR, RAS-MAPK-ERK, and G-protein coupled receptor pathways. Recognizing the parallels with oncogenic mutations, we emphasize the potential of targeted molecular inhibitors in the treatment of vascular malformations by repurposing anticancer drugs. This review delves into the recent development and future use of such agents for the management of slow- and fast-flow vascular malformations, including in more specific situations, such as prenatal treatment and the management of associated coagulopathies.

A multi-step approach to overcome challenges in the management of head and neck lymphatic malformations, and response to treatment

BACKGROUND

Lymphatic malformations are vascular developmental anomalies varying from local superficial masses to diffuse infiltrating lesions, resulting in disfigurement. Patients' outcomes range from spontaneous regression to severe sequelae notwithstanding appropriate treatment. The current classification guides, in part, clinicians through the decision-making process, prognosis prediction and choice of therapeutic strategies. Even though the understanding of molecular basis of the disease has been recently improved, a standardized management algorithm has not been reached yet.

RESULTS

Here, we report our experience on five children with different lymphatic anomalies of the head and neck region treated by applying a multidisciplinary approach reaching a consensus among specialists on problem-solving and setting priorities.

CONCLUSIONS

Although restitutio ad integrum was rarely achieved and the burden of care is challenging for patients, caregivers and healthcare providers, this study demonstrates how the referral to expert centres can significantly improve outcomes by alleviating parental stress and ameliorating patients' quality of life. A flow-chart is proposed to guide the multidisciplinary care of children with LMs and to encourage multidisciplinary collaborative initiatives to implement dedicated patients' pathways.

Sclerotherapy vs. surgical excision for lymphatic malformations of the head and neck: a systematic review and meta-analysis

OBJECTIVES

Lymphatic malformations (LMs) are abnormal lymphatic vessels with cystic characteristics, categorized as macrocystic, microcystic, or a combination of both. They represent the second most common vascular malformations, and their management involves multidisciplinary approaches based on clinical assessments and imaging studies. LMs manifest as a challenge to medical professionals in the head and neck, posing functional and aesthetic concerns. Our systematic review aims to compare the efficacy of sclerotherapy and surgery for LMs, identifying optimal treatment modalities for each scenario.

METHODS

We searched four electronic databases for related studies. Data were extracted from the included studies. We calculated the pooled rate ratios with 95% confidence intervals (CIs). The I2 test was used to detect heterogeneity. The inclusion of the studies required the following prerequisites: 1- Studies focusing on any lymphatic malformations in the head and neck, whether microcystic, macrocystic, or a mix of both; 2- Studies performed on more than ten patients; 3- All interventions used as surgery, sclerotherapy, or both.

RESULTS

We included 58 studies in our systematic review, of which 45 were eligible for the meta-analysis. For macrocystic LMs, sodium tetradecyl sulfate (STS) mixed with ethanol and excision achieved the highest complete response rates at (92.9%) and (92.5%), respectively. Surgical excision showed the lowest poor response rate. Polidocanol microfoam had the highest poor response rate (11.1%). In microcystic LMs, combining sclerotherapy with excision showed the highest complete response rate (70.3%) and the lowest poor response rate (1.3%). Picibanil had the lowest complete response rate (9.1%) and the highest rate of poor response (61.4%). In mixed LMs, surgical excision had the highest complete response rate (70.3%).

CONCLUSION

Both surgical excision and STS combined with ethanol are highly effective for treating macrocystic LMs, achieving similar complete response rates. The combination of sclerotherapy and surgical excision demonstrated the best outcomes in microcystic LMs. Surgical excision demonstrates superior efficacy over sclerotherapy for mixed LMs. These findings suggest that excision is generally more effective in achieving complete and excellent responses across all LM subtypes. Further high-quality studies are necessary to standardize and optimize treatment protocols.

A 14-year single-center experience evaluating sclerotherapy efficacy in lymphatic malformations

OBJECTIVE

The aim of this study is to share our experience in treating patients with lymphatic malformations (LMs) over a span of 14 years, evaluating the efficacy and safety of sclerotherapy, particularly with the use of ethanol as sclerosant of choice.

METHODS

A retrospective review of pediatric patients diagnosed and later treated for LMs between 2008 and 2022 was conducted. We collected patient demographics, LM characteristics, treatment strategies, and outcomes, including response to treatment and complications.

RESULTS

The cohort included 36 patients (24 male patients), first presenting clinically at a median age of 5 months (range: 0-12 years). LMs were macrocystic (17), microcystic (3), and mixed types (16). In most patients (22), the malformation involved the cervicofacial area. Twenty-five patients underwent 54 procedures, averaging 2 procedures per patient (range: 1-13). Sclerotherapy resulted in 90% of patients exhibiting some response of the LM (P = .005). Ethanol was used in most procedures (31) and proved most efficacious, facilitating partial or complete response of the malformations in all cases compared with 72% with other sclerosants (P = .06). Sclerotherapy exhibited low complication rates among all sclerosants used (7%, P = .74).

CONCLUSIONS

Sclerotherapy is a safe and effective intervention for pediatric LMs. Ethanol demonstrated comparable efficacy and safety to other sclerosants, highlighting its potential as a preferred treatment option. This study supports the tailored use of sclerotherapy, guided by a thorough understanding of the risks and benefits, to provide optimized care for patients with LMs.

Targeting lymphatic function in cardiovascular-kidney-metabolic syndrome: preclinical methods to analyze lymphatic function and therapeutic opportunities

The lymphatic vascular system spans nearly every organ in the body and serves as an important network that maintains fluid, metabolite, and immune cell homeostasis. Recently, there has been a growing interest in the role of lymphatic biology in chronic disorders outside the realm of lymphatic abnormalities, lymphedema, or oncology, such as cardiovascular-kidney-metabolic syndrome (CKM). We propose that enhancing lymphatic function pharmacologically may be a novel and effective way to improve quality of life in patients with CKM syndrome by engaging multiple pathologies at once throughout the body. Several promising therapeutic targets that enhance lymphatic function have already been reported and may have clinical benefit. However, much remains unclear of the discreet ways the lymphatic vasculature interacts with CKM pathogenesis, and translation of these therapeutic targets to clinical development is challenging. Thus, the field must improve characterization of lymphatic function in preclinical mouse models of CKM syndrome to better understand molecular mechanisms of disease and uncover effective therapies.

Efficacy of Bleomycin-Lauromacrogol Foam in Pediatric Macrocystic Lymphatic Malformations With and Without Intracapsular Hemorrhage

BACKGROUND

Sclerotherapy is purportedly less effective in patients with hemorrhagic than with non-hemorrhagic lymphatic malformations (LMs). We aimed to compare the efficacy of bleomycin-lauromacrogol foam (BLF) sclerotherapy in the treatment of macrocystic LMs with and without intralesional hemorrhage.

METHODS

Fifty-five children with macrocystic LMs admitted to the Pediatric Surgery Department were retrospectively included. The patients were allocated into a hemorrhage group (23 cases) or a non-hemorrhage group (32 cases) based on the occurrence of an intracapsular hemorrhage. The diagnosis was confirmed by physical examination, color ultrasound, magnetic resonance imaging, and puncture findings. BLF was injected into the capsule after draining the cystic fluid under color ultrasound guidance. Patients whose lesions were unchanged or showed minor change after 1 month were treated again using the same method. Changes in lesion size and the number of treatments were recorded. Effectiveness was classified as excellent (volume reduction ≥90%), good (50%≤volume reduction<90%), or poor (volume reduction <50%).

RESULTS

In the hemorrhage group, 17, 6, and 0 patients' outcomes were classified as excellent, good, and poor, respectively. The overall efficacy rate was 100%. In the non-hemorrhage group, 23, 7, and 2 patients' outcomes were classified as excellent, good, and poor, respectively. The overall efficacy rate was 93.8%. There was no significant difference in efficacy rate between groups (P = 0.767).

CONCLUSIONS

BLF is an effective and safe treatment for macrocystic LMs with bleeding. The results were similar in patients with and without bleeding.

LEVEL OF EVIDENCE

Treatment, Level III.

Complex lymphatic anomalies: Molecular landscape and medical management

The lymphatic system is one of the most essential and complex systems in the human body. Disorders that affect the development or function of the lymphatic system can lead to multi-system complications and life-long morbidity. The past two decades have seen remarkable progress in our knowledge of the basic biology and function of the lymphatic system, the molecular regulators of lymphatic development, and description of disorders associated with disrupted lymphangiogensis. In this chapter we will touch on the clinical features of complex lymphatic anomalies, new molecular knowledge of the drivers of these disorders, and novel developmental therapeutics for lymphatic disease.

Imaging manifestations of head and neck lymphatic malformations: A single-center experience of 170 surgical cases

OBJECTIVES

To discuss the imaging manifestations and the utility of preoperative ultrasonography (US), contrast-enhanced computed tomography (CE-CT) and contrast enhanced magnetic resonance imaging (CE-MRI) in diagnosing the pediatric head and neck lymphatic malformations (HNLMs).

METHODS

We performed a retrospective review of 170 children who were referred to our hospital in the past 9 years for the treatment of HNLMs.

RESULTS

The diagnostic rates of US, CE-CT and CE-MRI were 93.0% (146/157), 94.7% (143/151) and 100% (45/45), respectively. As in multilocular cases, intracystic septa detection rate was 91.5% (130/142), 50.4% (68/135) and 88.1% (37/42), and which had a statistical difference (χ2 = 25.8131, p < 0.05). US showed capsule contents anechoic in 51.0% (80/157) cases, hypoechoic or mixed echoic in 49.0% (77/157) cases, and flocculent or dotted echo floating in 36.9% (58/157) cases. CT showed low density of the capsule contents without enhancement in 69.5% (105/151) cases and mixed density with enhancement in 30.4% (46/151) cases. Liquid-liquid levers were seen in 8.6% (13/151) cases. MRI showed T1WI high signal and T2WI low signal of the capsule contents without enhancement in 28.9% (13/45) cases and mixed density in 71.1% (32/45) cases. Liquid-liquid levers were seen in 46.7% (21/45) cases. There were statistically significant differences between pure HNLMs and intracystic hemorrhage in capsule content (echo, density, signal), enhancement, and liquid-liquid lever (all p < 0.05). Among US, CE-CT and CE-MRI, intracystic hemorrhage diagnostic accuracy had a statistical difference (χ2 = 25.4152, p < 0.05).

CONCLUSIONS

For clinical diagnosis and evaluation of HNLMs, we suggest that US combined with CE-CT for acute cases, and for stable cases, US combined with CE-MRI.

Lymphatic failure and lymphatic interventions: Knowledge gaps and future directions for a new frontier in congenital heart disease

Lymphatic failure is a broad term that describes the lymphatic circulation's inability to adequately transport fluid and solutes out of the interstitium and into the systemic venous circulation, which can result in dysfunction and dysregulation of immune responses, dietary fat absorption, and fluid balance maintenance. Several investigations have recently elucidated the nexus between lymphatic failure and congenital heart disease, and the associated morbidity and mortality is now well-recognized. However, the precise pathophysiology and pathogenesis of lymphatic failure remains poorly understood and relatively understudied, and there are no targeted therapeutics or interventions to reliably prevent its development and progression. Thus, there is growing enthusiasm towards the development and application of novel percutaneous and surgical lymphatic interventions. Moreover, there is consensus that further investigations are needed to delineate the underlying mechanisms of lymphatic failure, which could help identify novel therapeutic targets and develop innovative procedures to improve the overall quality of life and survival of these patients. With these considerations, this review aims to provide an overview of the lymphatic circulation and its vasculature as it relates to current understandings into the pathophysiology and pathogenesis of lymphatic failure in patients with congenital heart disease, while also summarizing strategies for evaluating and managing lymphatic complications, as well as specific areas of interest for future translational and clinical research efforts.

Changes in cell morphology and function induced by the NRAS Q61R mutation in lymphatic endothelial cells

Recently, a low-level somatic mutation in the NRAS gene (c.182 A > G, Q61R) was identified in various specimens from patients with kaposiform lymphangiomatosis. However, it is unknown how these low-frequency mutated cells can affect the characterization and surrounding environment of their lesions. To understand the pathogenesis and association of these gene abnormalities, we established NRASQ61R mutated lymphatic endothelial cells transfected with lentivirus vector and undertook morphological and functional characterization, protein expression profiling, and metabolome analysis. NRASQ61R human dermal lymphatic endothelial cells showed poor tube formation, a low proliferation rate, and high migration ability, with an increase in the ratio of mutated cells. An analysis of signaling pathways showed inactivation of the PIK3/AKT/mTOR pathway and hyperactivation of the RAS/MAPK/ERK pathway, which was improved by MAPK kinase (MEK) inhibitor treatment. This study shows the theoretical circumstances induced in vitro by NRASQ61R-mutated cells in the affected lesions of kaposiform lymphangiomatosis patients.

Central conducting lymphatic anomaly: from bench to bedside

Central conducting lymphatic anomaly (CCLA) is a complex lymphatic anomaly characterized by abnormalities of the central lymphatics and may present with nonimmune fetal hydrops, chylothorax, chylous ascites, or lymphedema. CCLA has historically been difficult to diagnose and treat; however, recent advances in imaging, such as dynamic contrast magnetic resonance lymphangiography, and in genomics, such as deep sequencing and utilization of cell-free DNA, have improved diagnosis and refined both genotype and phenotype. Furthermore, in vitro and in vivo models have confirmed genetic causes of CCLA, defined the underlying pathogenesis, and facilitated personalized medicine to improve outcomes. Basic, translational, and clinical science are essential for a bedside-to-bench and back approach for CCLA.

Lymphatic Malformation Initially Presenting as Snoring: A Case Report

We describe a case of lymphatic malformation (LM) with snoring as the primary symptom. The patient, an 11-year-old boy, sought medical attention due to "snoring that had worsened over 3 years, accompanied by shortness of breath for 1 month." The preoperative examination showed that the apnea-hypopnea index during sleep was 33.4. The average overnight blood oxygen saturation was 95.3%, reaching a lowest level of 79.9%. Magnetic resonance imaging identified a space-occupying lesion in the postpharyngeal space, leading to significant compression and narrowing of the pharyngeal cavity. This suggested the possibility of a vascular malformation, with a higher proportion of vascular components. The patient underwent resection of the pharyngeal mass and temporary tracheostomy under general anesthesia, and intraoperative freeze and postoperative pathological diagnoses confirmed LM. Postoperative prognosis was favorable.

Recent advances in nanomaterial-driven strategies for diagnosis and therapy of vascular anomalies

Nanotechnology has demonstrated immense potential in various fields, especially in biomedical field. Among these domains, the development of nanotechnology for diagnosing and treating vascular anomalies has garnered significant attention. Vascular anomalies refer to structural and functional anomalies within the vascular system, which can result in conditions such as vascular malformations and tumors. These anomalies can significantly impact the quality of life of patients and pose significant health concerns. Nanoscale contrast agents have been developed for targeted imaging of blood vessels, enabling more precise identification and characterization of vascular anomalies. These contrast agents can be designed to bind specifically to abnormal blood vessels, providing healthcare professionals with a clearer view of the affected areas. More importantly, nanotechnology also offers promising solutions for targeted therapeutic interventions. Nanoparticles can be engineered to deliver drugs directly to the site of vascular anomalies, maximizing therapeutic effects while minimizing side effects on healthy tissues. Meanwhile, by incorporating functional components into nanoparticles, such as photosensitizers, nanotechnology enables innovative treatment modalities such as photothermal therapy and photodynamic therapy. This review focuses on the applications and potential of nanotechnology in the imaging and therapy of vascular anomalies, as well as discusses the present challenges and future directions.

Lymphatic malformations: mechanistic insights and evolving therapeutic frontiers

The lymphatic vascular system is gaining recognition for its multifaceted role and broad pathological significance. Once perceived as a mere conduit for interstitial fluid and immune cell transport, recent research has unveiled its active involvement in critical physiological processes and common diseases, including inflammation, autoimmune diseases, and atherosclerosis. Consequently, abnormal development or functionality of lymphatic vessels can result in serious health complications. Here, we discuss lymphatic malformations (LMs), which are localized lesions that manifest as fluid-filled cysts or extensive infiltrative lymphatic vessel overgrowth, often associated with debilitating, even life-threatening, consequences. Genetic causes of LMs have been uncovered, and several promising drug-based therapies are currently under investigation and will be discussed.

The development of early human lymphatic vessels as characterized by lymphatic endothelial markers

Lymphatic vessel development studies in mice and zebrafish models have demonstrated that lymphatic endothelial cells (LECs) predominantly differentiate from venous endothelial cells via the expression of the transcription factor Prox1. However, LECs can also be generated from undifferentiated mesoderm, suggesting potential diversity in their precursor cell origins depending on the organ or anatomical location. Despite these advances, recapitulating human lymphatic malformations in animal models has been difficult, and considering lymphatic vasculature function varies widely between species, analysis of development directly in humans is needed. Here, we examined early lymphatic development in humans by analyzing the histology of 31 embryos and three 9-week-old fetuses. We found that human embryonic cardinal veins, which converged to form initial lymph sacs, produce Prox1-expressing LECs. Furthermore, we describe the lymphatic vessel development in various organs and observe organ-specific differences. These characterizations of the early development of human lymphatic vessels should help to better understand the evolution and phylogenetic relationships of lymphatic systems, and their roles in human disease.

Sirolimus treatment for intractable lymphatic anomalies: an open-label, single-arm, multicenter, prospective trial

Introduction

Intractable lymphatic anomalies (LAs) include cystic lymphatic malformation (LM; macrocystic, microcystic, or mixed), generalized lymphatic anomaly, and Gorham-Stout disease. LAs can present with severe symptoms and poor prognosis. Thus, prospective studies for treatments are warranted. We conducted a prospective clinical trial of sirolimus for intractable LAs.

Methods

This was an open-label, single-arm, multicenter, prospective trial involving five institutions in Japan. All patients with LAs received oral sirolimus once daily, and the dose was adjusted to ensure that the trough concentration remained within 5-15 ng/mL. We prospectively assessed the drug response (response rate for radiological volumetric change in target lesion), performance state, change in respiratory function, visceral impairment (pleural effusion, ascites, bleeding, pain), laboratory examination data, quality of life (QOL), and safety at 12, 24, and 52 weeks of administration.

Results

Eleven patients with LAs (9 generalized lymphatic anomaly, 1 cystic LM, 1 Gorham-Stout disease) were treated with sirolimus, of whom 6 (54.5%; 95% confidence interval: 23.4-83.3%) demonstrated a partial response on radiological examination at 52 weeks of administration. No patients achieved a complete response. At 12 and 24 weeks of administration, 8 patients (72.7%) already showed a partial response. However, patients with stable disease showed minor or no reduction after 12 weeks. Adverse events, such as stomatitis, acneiform dermatitis, diarrhea, and fever, were common with sirolimus. Sirolimus was safe and tolerable.

Conclusion

Sirolimus can reduce the lymphatic tissue volume in LAs and may lead to improvements in clinical symptoms and QOL.

A Large Adult Postcricoid Lymphatic Malformation: A Case Report and Literature Review

Adult-onset lymphatic malformations arising at the postcricoid, a subsite of the hypopharynx, are sporadic. Only one case has been previously reported. In this study, we presented a 36-year-old female presented with globus sensation, dysphagia, and upper airway obstruction, requiring a tracheostomy. A computed tomography scan identified a 5 cm × 4.5 cm × 3 cm multilocular hypodense lesion in the postcricoid. Due to its considerable size, complete resection with function preservation was crucial, and a standard microscopic direct laryngoscopy approach may result in inadequate exposure, while an open transcervical approach may affect functional outcomes and increase surgical complications. We successfully performed an en bloc resection with a transoral endoscopic approach, using laryngeal suspension and a laparoscopic ultrasonic scalpel to preserve aerodigestive functions, ensure rapid recovery, and avoid neck scarring. The patient was decannulated within 2 weeks and remained disease-free after 1 year. The reported cases of adult-onset lymphatic malformations at the postcricoid and hypopharynx were reviewed and summarized for educational purposes.

The role of key biomarkers in lymphatic malformation: An updated review

The lymphatic system, crucial for tissue fluid balance and immune surveillance, can be severely impacted by disorders that hinder its activities. Lymphatic malformations (LMs) are caused by fluid accumulation in tissues owing to defects in lymphatic channel formation, the obstruction of lymphatic vessels or injury to lymphatic tissues. Somatic mutations, varying in symptoms based on lesions' location and size, provide insights into their molecular pathogenesis by identifying LMs' genetic causes. In this review, we collected the most recent findings about the role of genetic and inflammatory biomarkers in LMs that control the formation of these malformations. A thorough evaluation of the literature from 2000 to the present was conducted using the PubMed and Google Scholar databases. Although it is obvious that the vascular endothelial growth factor receptor 3 mutation accounts for a significant proportion of LM patients, several mutations in other genes thought to be linked to LM have also been discovered. Also, inflammatory mediators like interleukin-6, interleukin-8, tumor necrosis factor-alpha and mammalian target of rapamycin are the most commonly associated biomarkers with LM. Understanding the mutations and genes expression responsible for the abnormalities in lymphatic endothelial cells could lead to novel therapeutic strategies based on molecular pathways.

Factors affecting the ability of patients with complex vascular anomalies to navigate the healthcare system

BACKGROUND

Vascular anomalies (VAs) are rare congenital disorders that can cause pain, disfigurement, coagulopathy, asymmetric growth, and disability. Patients with complex VAs experience multiple barriers to accessing expert care. It is imperative to understand which factors support these patients' ability to navigate the healthcare system.

RESULTS

We surveyed adult patients with VAs using previously validated measures, recruiting participants from five patient advocacy groups and multidisciplinary VA clinics. The primary outcome was self-reported ability to access needed medical care, using the "Navigating the Healthcare System" subscale of the Health Literacy Questionnaire. We evaluated factors associated with the ability to navigate the healthcare system using multivariate linear regression (n = 136). We also performed an exploratory model that included the primary care doctor's knowledge of VAs for the subset of participants with a primary care doctor (n = 114). Participants were predominantly women (n = 90, 66%), White and non-Hispanic (n = 109, 73%), and college-educated (n = 101, 73%). Most participants had PIK3CA-Related Overgrowth Spectrum (n = 107, 78%). Most participants reported that navigating the healthcare system was "sometimes" or "usually difficult" (mean score 16.4/30, standard deviation 5.6). In multivariate linear regression, ability to navigate the healthcare system was associated positively with quality of information exchange (β = 0.38, 95% Confidence Interval (CI) 0.22 to 0.55, p <.001) and whether patients had VA specialists (β = 2.31, 95% CI 0.35 to 4.28, p =.021), but not associated with patient self-advocacy, anxiety, education, age, race and ethnicity, gender, or having a primary care doctor. In exploratory analysis of participants with primary care doctors, ability to navigate the healthcare system was positively associated with quality of information exchange (β = 0.27, 95% CI 0.09 to 0.45, p =.004), having a VA specialist (β = 2.31, 95% CI 0.22 to 4.39, p =.031), and primary care doctors' VA knowledge (β = 0.27, 95% CI 0.04 to 0.50, p =.023).

CONCLUSION

Patients with VAs struggle to navigate the healthcare system. High-quality information from clinicians and more knowledgeable primary care doctors might help patients to access needed care. Relying on patient self-advocacy is insufficient. Future efforts should focus on patient-directed and clinician-directed educational interventions. Additionally, future work should assess the structural barriers that impede healthcare access for these patients.

Lymphatic vessel: origin, heterogeneity, biological functions, and therapeutic targets

Lymphatic vessels, comprising the secondary circulatory system in human body, play a multifaceted role in maintaining homeostasis among various tissues and organs. They are tasked with a serious of responsibilities, including the regulation of lymph absorption and transport, the orchestration of immune surveillance and responses. Lymphatic vessel development undergoes a series of sophisticated regulatory signaling pathways governing heterogeneous-origin cell populations stepwise to assemble into the highly specialized lymphatic vessel networks. Lymphangiogenesis, as defined by new lymphatic vessels sprouting from preexisting lymphatic vessels/embryonic veins, is the main developmental mechanism underlying the formation and expansion of lymphatic vessel networks in an embryo. However, abnormal lymphangiogenesis could be observed in many pathological conditions and has a close relationship with the development and progression of various diseases. Mechanistic studies have revealed a set of lymphangiogenic factors and cascades that may serve as the potential targets for regulating abnormal lymphangiogenesis, to further modulate the progression of diseases. Actually, an increasing number of clinical trials have demonstrated the promising interventions and showed the feasibility of currently available treatments for future clinical translation. Targeting lymphangiogenic promoters or inhibitors not only directly regulates abnormal lymphangiogenesis, but improves the efficacy of diverse treatments. In conclusion, we present a comprehensive overview of lymphatic vessel development and physiological functions, and describe the critical involvement of abnormal lymphangiogenesis in multiple diseases. Moreover, we summarize the targeting therapeutic values of abnormal lymphangiogenesis, providing novel perspectives for treatment strategy of multiple human diseases.

The value of MRI in the diagnosis of pediatric head and neck lymphatic malformations: A study of 46 surgical cases

Objective To discuss the value of MRI in diagnosing and evaluating the pediatric head and neck lymphatic malformations (HNLMs). Methods We performed a retrospective review of 46 children who were referred to our hospital in the last decade for the treatment of HNLMs. Results About 34 cases confirmed with intralesional hemorrhage while the capsule contents were dark red or light bloody liquid. The remaining 12 pure HNLMs were filled with yellow clear or watery liquid. The multilocular HNLMs accounted for 95.7 % (44/46). The accuracy of contrast enhanced MRI (CE-MRI) diagnosis of HNLMs was 100 %. On MRI, the HNLMs appeared as irregular shape [95.7 % (44/46)], clear boundary [91.3 % (42/46)], infiltrative growth [91.3 % (42/46)] cystic masses. The cystic wall and septa were hyperintense on T1WI and hypointense on T2WI (100 %), and displayed enhancement. The capsule contents had hypointense on T1WI and hyperintense on T2WI in 18 cases (pure HNLMs,12; intracystic hemorrhage,6), while that of mixed signal in 28 cases (pure HNLMs,0; intracystic hemorrhage,28). Capsule contents were enhanced in 22 cases (pure HNLMs,1; intracystic hemorrhage,21), while the remaining 24 without enhancement (pure HNLMs,11; intracystic hemorrhage,13). Liquid-liquid levers were found in 21 cases (pure HNLMs,0; intracystic hemorrhage,21). There were statistical differences in capsule contents signal, enhancement, and liquid-liquid levels between the two groups (P < 0.05). Conclusions On MRI, HNLMs typically show a thin-walled, well-circumscribed, irregularly shaped, infiltrative, unenhanced, multilocular cystic mass with hypointense on T1WI and hyperintense on T2WI. The capsule wall and septa are hyperintense on T1WI, hypointense on T2WI, and display enhancement. Changes in the signal of capsule contents or appearance of liquid-liquid levels indicate intracystic hemorrhage.

Infectious complications of vascular anomalies treated with sirolimus: A systematic review

BACKGROUND AND OBJECTIVES

Initially developed as immunosuppressive agents, mammalian target of rapamycin (mTOR) inhibitors are currently used widely in the management of vascular malformations and tumors. The incidence of infectious complications in the vascular anomalies (VA) population is not well defined. The goal of this systematic review was to better define the types and severity of reported infectious complications in patients with VAs treated with mTOR inhibition.

METHODS

This was a systematic review conducted following PRISMA guidelines evaluating all research articles focused on infectious complications in patients with VAs treated with sirolimus or everolimus. Thirty articles including 1182 total patients and 316 infections (in 291 unique patients) were ultimately included.

RESULTS

The majority of infections were viral upper respiratory (n = 137, 54%), followed by pneumonia (n = 53, 20%), and cutaneous infections (n = 20, 8%). There were six total infection-related fatalities, which all occurred in patients younger than 2 years. Two cases of Pneumocystis jirovecii pneumonia (PJP) were reported. These were infants with kaposiform hemangioendothelioma (KHE) who were also treated with steroids and did not receive PJP prophylaxis. Almost one-third (n = 96, 32%) of infectious complications were graded 3-4 according to Common Terminology Criteria for Adverse Events (CTCAE) criteria. Details of patient age, subtype of VA, and timing of infection were lacking from many reports.

CONCLUSIONS

Most infectious complications reported in patients with VA on mTOR inhibitors were viral respiratory infections and non-severe. Bacteremia, infectious fatalities, and PJP are exceedingly rare. Future studies are needed to clarify the spectrum of infectious risks in VA patients and to provide guidance for infection prevention.

Complex lymphatic anomalies: Challenging diagnostic considerations

Diagnosis of complex lymphatic anomalies can be difficult, and biopsies can be associated with significant morbidity. Mediastinal masses with features such as osseous involvement warrant thorough noninvasive evaluation prior to biopsy.

Vasculature is getting Hip(po): Hippo signaling in vascular development and disease

The Hippo signaling pathway regulates developmental organ growth, regeneration, and cell fate decisions. Although the role of the Hippo pathway, and its transcriptional effectors YAP and TAZ, has been well documented in many cell types and species, only recently have the roles for this pathway come to light in vascular development and disease. Experiments in mice, zebrafish, and in vitro have uncovered roles for the Hippo pathway, YAP, and TAZ in vasculogenesis, angiogenesis, and lymphangiogenesis. In addition, the Hippo pathway has been implicated in vascular cancers and cardiovascular diseases, thus identifying it as a potential therapeutic target for the treatment of these conditions. However, despite recent advances, Hippo's role in the vasculature is still underappreciated compared with its role in epithelial tissues. In this review, we appraise our current understanding of the Hippo pathway in blood and lymphatic vessel development and highlight the current knowledge gaps and opportunities for further research.

Verification of the efficacy of topical sirolimus gel for systemic rare vascular malformations: a pilot study

Numerous clinical trials of sirolimus, an inhibitor of mechanistic/mammalian target of rapamycin complex 1, for the treatment of vascular malformations have been conducted. However, aside from lymphatic malformations, the efficacy of sirolimus for venous and capillary malformations has not been established. Moreover, no generalized venous or capillary malformations have been treated with topical sirolimus. To evaluate the safety and efficacy of topical sirolimus for venous and capillary malformations and to compare the efficacy of topical and systemic sirolimus therapy, an open-label single-arm pilot study with 0.2% sirolimus gel was conducted from July 19, 2019, to January 30, 2020, in four patients diagnosed with different vascular malformations (blue rubber bleb nevus syndrome, common venous malformation, phakomatosis pigmentovascularis type IVb, and angiokeratoma in Fabry disease). The primary endpoint was the safety evaluation of sirolimus gel. The main secondary endpoint was the improvement rate evaluated by the Central Judgment Committee at 12 weeks using photographs. No adverse events were observed. Blood sirolimus was not detected in any patient. Two patients (50%) had mild improvement, and the remaining two patients (50%) showed no change after 12 weeks of treatment. Blue rubber bleb nevus syndrome, a generalized venous malformation, showed the greatest response. In conclusion, 0.2% sirolimus gel was found to be as clinically effective as systemic sirolimus treatment in patients with venous and capillary malformations and more effective for early active lesions, even systemic venous malformations.

Lymphatic muscle cells are unique cells that undergo aging induced changes

Lymphatic muscle cells (LMCs) within the wall of collecting lymphatic vessels exhibit tonic and autonomous phasic contractions, which drive active lymph transport to maintain tissue-fluid homeostasis and support immune surveillance. Damage to LMCs disrupts lymphatic function and is related to various diseases. Despite their importance, knowledge of the transcriptional signatures in LMCs and how they relate to lymphatic function in normal and disease contexts is largely missing. We have generated a comprehensive transcriptional single-cell atlas-including LMCs-of collecting lymphatic vessels in mouse dermis at various ages. We identified genes that distinguish LMCs from other types of muscle cells, characterized the phenotypical and transcriptomic changes in LMCs in aged vessels, and uncovered a pro-inflammatory microenvironment that suppresses the contractile apparatus in advanced-aged LMCs. Our findings provide a valuable resource to accelerate future research for the identification of potential drug targets on LMCs to preserve lymphatic vessel function as well as supporting studies to identify genetic causes of primary lymphedema currently with unknown molecular explanation.

Differences in Efficacy and Safety of Sirolimus and Sildenafil in Pediatric Lymphatic Malformations

OBJECTIVES

To explore the differences in the efficacy and safety of oral sirolimus and sildenafil in the treatment of pediatric intractable lymphatic malformations (LMs).

METHODS

From January 2014 to May 2022, we retrospectively enrolled children with intractable LMs treated with oral drugs (sirolimus or sildenafil) and divided the patients into sirolimus and sildenafil groups from Beijing Children's Hospital (BCH). Clinical features, treatment, and follow-up data were collected and analyzed. The indicators were the ratio of reduction in lesion volume pre and posttreatment, the number of patients with improved clinical symptoms, and adverse reactions to the two drugs.

RESULTS

Twenty-four children in the sildenafil group and 31 children in the sirolimus group were included in the present study. The effective rate in the sildenafil group was 54.2% (13/24), with a median lesion volume reduction ratio of 0.32 (-0.23, 0.89) and clinical symptoms improved in 19 patients (79.2%). On the contrary, the effective rate in the sirolimus group was 93.5% (29/31), with a median lesion volume reduction ratio of 0.68 (0.34, 0.96), and clinical symptoms improved in 30 patients (96.8%). There were significant differences (p < 0.05) between the two groups. Regarding safety, four patients in the sildenafil group and 23 patients in the sirolimus group with mild adverse reactions were reported.

CONCLUSION

Both sildenafil and sirolimus can reduce the volume of LMs and improve clinical symptoms in partial patients with intractable LMs. Sirolimus is more effective than sildenafil and the adverse reactions associated with both drugs are mild and controllable.

LEVEL OF EVIDENCE

III Laryngoscope, 133:3192-3199, 2023.

Congenital Neck Masses

There are many possible causes of congenital neck masses, with the most common ones being thyroglossal duct cysts, branchial cleft anomalies, and vascular malformations. Most congenital neck masses are asymptomatic in the neonatal period, but depending on the location and the size, they can cause airway obstruction and serious complications at birth. Proper diagnosis is important for optimal treatment planning, and if the airway is compromised, multidisciplinary teamwork is critical for proper airway management. This review summarizes the clinical features, etiology, diagnosis, management, and prognosis of different types of congenital neck masses.

Widespread keratinocytic epidermal nevus with an associated chylous pericardial effusion

A 17-year-old male presented for review of a widespread keratinocytic epidermal nevus (KEN) in the setting of a chronic pericardial effusion. Biopsy of the epidermal nevus revealed a KRAS mutation. Pericardiocentesis revealed a chylous effusion and magnetic resonance lymphangiogram demonstrated an underlying lymphatic malformation. There are rare case reports of KEN with an associated KRAS mutation. This case highlights the importance of being alert to epidermal nevus syndrome, particularly in patients with a widespread nevus and seemingly unrelated pathology.

Rapid lymphatic malformation expansion: Imaging, association with asymptomatic Streptococcus infection, multidisciplinary management, and therapeutic approach

Lymphatic malformations are congenital anomalies of the lymphatic system that can occur anywhere in the body and typically present in early childhood. They are often painless, slow-growing, and asymptomatic, but may lead to a wide range of symptoms depending on their size and location. Rarely, congenital malformations may not be diagnosed until later in childhood or adolescence, despite being present from birth. In some individuals, lymphatic malformations can expand quickly, especially in the setting of an inflammatory process. We present the case of an 8-year-old boy who had a rapidly enlarging, nonpainful mass on his right neck and a positive streptococcus throat swab. After evaluation by multiple specialists and imaging studies, he was diagnosed with a multilocular, multicystic lymphatic malformation. He was treated with fluoroscopy-guided doxycycline sclerotherapy, and has had near total resolution of neck swelling. This case report is significant because it highlights the potential benefits of a multidisciplinary approach to the diagnosis and management of lymphatic malformations. Additionally, it emphasizes the importance of considering congenital malformations in the differential diagnosis of neck masses, even in older children. Finally, it also adds to the growing body of evidence that hypothesizes that strep throat infections may trigger the sudden expansion of previously asymptomatic congenital lymphatic malformations.

Somatic mutation spectrum of a Chinese cohort of pediatrics with vascular malformations

BACKGROUND

Somatic mutations of cancer driver genes are found to be responsible for vascular malformations with clinical manifestations ranging from cutaneous birthmarks to life-threatening systemic anomalies. Till now, only a limited number of cases and mutations were reported in Chinese population. The purpose of this study was to describe the somatic mutation spectrum of a cohort of Chinese pediatrics with vascular malformations.

METHODS

Pediatrics diagnosed with various vascular malformations were collected between May 2019 and October 2020 from Beijing Children's Hospital. Genomic DNA of skin lesion of each patient was extracted and sequenced by whole-exome sequencing to identify pathogenic somatic mutations. Mutations with variant allele frequency less than 5% were validated by ultra-deep sequencing.

RESULTS

A total of 67 pediatrics (33 males, 34 females, age range: 0.1-14.8 years) were analyzed. Exome sequencing identified somatic mutations of corresponding genes in 53 patients, yielding a molecular diagnosis rate of 79.1%. Among 29 PIK3CA mutations, 17 were well-known hotspot p.E542K, p.E545K and p.H1047R/L. Non-hotspot mutations were prevalent in patients with PIK3CA-related overgrowth spectrum, accounting for 50.0% (11/22) of detected mutations. The hotspot GNAQ p.R183Q and TEK p.L914F mutations were responsible for the majority of port-wine stain/Sturge-Weber syndrome and venous malformation, respectively. In addition, we identified a novel AKT1 p.Q79K mutation in Proteus syndrome and MAP3K3 p.E387D mutation in verrucous venous malformation.

CONCLUSIONS

The somatic mutation spectrum of vascular malformations in Chinese population is similar to that reported in other populations, but non-hotspot PIK3CA mutations may also be prevalent. Molecular diagnosis may help the clinical diagnosis, treatment and management of these pediatric patients with vascular malformations.

The emerging importance of lymphatics in health and disease: an NIH workshop report

The lymphatic system (LS) is composed of lymphoid organs and a network of vessels that transport interstitial fluid, antigens, lipids, cholesterol, immune cells, and other materials in the body. Abnormal development or malfunction of the LS has been shown to play a key role in the pathophysiology of many disease states. Thus, improved understanding of the anatomical and molecular characteristics of the LS may provide approaches for disease prevention or treatment. Recent advances harnessing single-cell technologies, clinical imaging, discovery of biomarkers, and computational tools have led to the development of strategies to study the LS. This Review summarizes the outcomes of the NIH workshop entitled "Yet to be Charted: Lymphatic System in Health and Disease," held in September 2022, with emphasis on major areas for advancement. International experts showcased the current state of knowledge regarding the LS and highlighted remaining challenges and opportunities to advance the field.

Surgical creation of lymphocutaneous fistulas for the management of infants with central lymphatic obstruction

PURPOSE

Central lymphatic obstructions are associated with anasarca and high mortality. We hypothesized that opening dilated cutaneous lymphatic channels by creating a lymphocutaneous fistula (LCF) would decompress the lymphatic circulation and improve anasarca.

METHODS

We reviewed all patients that had at least one LCF created between 9/2019 and 12/2022. LCF efficacy was determined by changes in weight, urine/diuresis, ventilation, and clinical status.

RESULTS

We created eleven LCFs in four infants. LCFs initially drained 108 cc/kg/d (IQR68-265 cc/kg/d). Weights significantly decreased after LCF creation (6.9 [IQR6.1-8.1] kg vs. 6.1 [IQR 4.9-7.6] kg, P = 0.042). Ventilatory support decreased significantly in all patients after at least one LCF was created, and 3/4 patients (75%) had significantly lower peak inspiratory pressures (28 [IQR 25-31] cmH2O vs. 22 [IQR 22-24] cmH2O, P = 0.005; 36 [IQR36-38] cmH2O vs. 33 [IQR 33-35] cmH2O, P = 0.002; 36 [IQR 34-47] cmH2O vs. 28 [28-31] cmH2O, P = 0.002). LCFs remained patent for 29d (IQR 16-49d). LCFs contracted over time, and 6/11 (54.5%) were eventually revised. There were no complications. Two patients died from overwhelming disease, one died from unrelated causes, and one remains alive 29 months after their initial LCF.

CONCLUSION

LCFs provide safe and effective temporary lymphatic decompression in patients with central lymphatic obstruction. While LCFs are not a cure, they can serve as a bridge to more definitive therapies or spontaneous lymphatic remodeling.

LEVEL OF EVIDENCE

IV.

Sirolimus treatment for paediatric head and neck lymphatic malformations: a systematic review

PURPOSE

This PRISMA-compliant systematic review aimed to assess risks and benefits of sirolimus treatment for paediatric lymphatic malformations by focusing not only on treatment efficacy but also on possible treatment-related adverse events, and treatment combinations with other techniques.

METHODS

Search criteria were applied to MEDLINE, Embase, Web of Science, Scopus, Cochrane Library, and ClinicalTrials.gov databases and included all studies published up to March 2022 reporting paediatric lymphatic malformations treated with sirolimus. We selected all original studies that included treatment outcomes. After the removal of duplicates, selection of abstracts and full-text articles, and quality assessment, we reviewed eligible articles for patient demographics, lymphatic malformation type, size or stage, site, clinical response rates, sirolimus administration route and dose, related adverse events, follow-up time, and concurrent treatments.

RESULTS

Among 153 unique citations, 19 studies were considered eligible, with reported treatment data for 97 paediatric patients. Most studies (n = 9) were case reports. Clinical response was described for 89 patients, in whom 94 mild-to-moderate adverse events were reported. The most frequently administered treatment regimen was oral sirolimus 0.8 mg/m2 twice a day, with the aim of achieving a blood concentration of 10-15 ng/mL.

CONCLUSION

Despite promising results for sirolimus treatment in lymphatic malformation, the efficacy and safety profile of remains unclear due to the lack of high-quality studies. Systematic reporting of known side effects, especially in younger children, should assist clinicians in minimising treatment-associated risks. At the same time, we advocate for prospective multicentre studies with minimum reporting standards to facilitate improved candidate selection.

Cardiac Lymphatic Insufficiency Leads to Diastolic Dysfunction Via Myocardial Morphologic Change

Although cardiac lymphatic vessels have received increasing attention in recent years, there is still a knowledge gap between cardiac lymphatics and heart homeostasis in a normal heart. In the present study, we established a mouse model of cardiac lymphatic insufficiency ablating cardiac lymphatic collector vessels to reveal the crucial role of cardiac lymphatic vessels in maintaining cardiac homeostasis and the impact on cardiac function both in physiological and pathologic settings. Furthermore, therapeutic lymphangiogenesis improved the adverse effect on cardiac morphologic changes and functions. These findings suggest that the cardiac lymphatic system would be a novel therapeutic target for heart disease.

Pathological angiogenesis: mechanisms and therapeutic strategies

In multicellular organisms, angiogenesis, the formation of new blood vessels from pre-existing ones, is an essential process for growth and development. Different mechanisms such as vasculogenesis, sprouting, intussusceptive, and coalescent angiogenesis, as well as vessel co-option, vasculogenic mimicry and lymphangiogenesis, underlie the formation of new vasculature. In many pathological conditions, such as cancer, atherosclerosis, arthritis, psoriasis, endometriosis, obesity and SARS-CoV-2(COVID-19), developmental angiogenic processes are recapitulated, but are often done so without the normal feedback mechanisms that regulate the ordinary spatial and temporal patterns of blood vessel formation. Thus, pathological angiogenesis presents new challenges yet new opportunities for the design of vascular-directed therapies. Here, we provide an overview of recent insights into blood vessel development and highlight novel therapeutic strategies that promote or inhibit the process of angiogenesis to stabilize, reverse, or even halt disease progression. In our review, we will also explore several additional aspects (the angiogenic switch, hypoxia, angiocrine signals, endothelial plasticity, vessel normalization, and endothelial cell anergy) that operate in parallel to canonical angiogenesis mechanisms and speculate how these processes may also be targeted with anti-angiogenic or vascular-directed therapies.

Splenic Lymphatic Malformation With Papillary Endothelial Proliferation: A Rare Histologic Variant or a Unique Entity?

Lymphatic malformations (LMs) are congenital anomalies of the lymphatic system due to abnormalities that occur during the development of the lymphovascular system. Also known as lymphangiomas, they are usually multifocal, affect multiple organ systems, and are seen in a variety of developmental or overgrowth syndromes. Splenic lymphangiomas are uncommon and usually occur in the context of multiorgan lymphangiomatosis. Within the spleen, 7 prior cases have been reported of LMs with unusual papillary endothelial proliferations (PEPs), which can mimic more aggressive splenic lymphovascular tumors. It is not currently known if splenic LM-PEP represents a unique entity, or is simply an unusual, site-specific, morphologic variant of LM. To address this question, we conducted a retrospective, single-institutional review of this rare entity and systematically evaluated its clinical, histologic, radiologic, electron microscopical, and molecular features. In all 3 splenic LM-PEPs, the clinical course was benign, imaging demonstrated subcapsular lesions with characteristic "spoke-and-wheel" appearance, histology showed distinctive PEPs within lymphatic microcysts, immunohistochemistry confirmed a lymphatic endothelial phenotype and electron microscopy demonstrated lesional endothelial cells, rich in mitochondria and intermediate filaments with prominent cytoplasmic lumina and vacuoles and lacking Weibel-Palade granules. Occasional lymphothelial cells were situated within the cytoplasm of another lesional cell, appearing to be engulfed. Next-generation sequencing identified a PIK3CA mutation in 1 patient, while in 2 others no molecular alterations were identified. We conclude with a summary of all prior published cases and discuss key diagnostic elements that distinguish this benign entity from its more aggressive mimickers.

Investigation into the genetics of fetal congenital lymphatic anomalies

OBJECTIVE

Congenital lymphatic anomalies (LAs) arise due to defects in lymphatic development and often present in utero as pleural effusion, chylothorax, nuchal and soft tissue edema, ascites, or hydrops. Many LAs are caused by single nucleotide variants, which are not detected on routine prenatal testing.

METHODS

Demographic data were compared between two subcohorts, those with clinically significant fetal edema (CSFE) and isolated fetal edema. A targeted variant analysis of LA genes was performed using American College of Medical Genetics criteria on whole exome sequencing (WES) data generated for 71 fetal edema cases who remained undiagnosed after standard workup.

RESULTS

CSFE cases had poor outcomes, including preterm delivery, demise, and maternal preeclampsia. Pathogenic and likely pathogenic variants were identified in 7% (5/71) of cases, including variants in RASopathy genes, RASA1, SOS1, PTPN11, and a novel PIEZO1 variant. Variants of uncertain significance (VOUS) were identified in 45% (32/71) of cases. In CSFEs, VOUS were found in CELSR1, EPHB4, TIE1, PIEZO1, ITGA9, RASopathy genes, SOS1, SOS2, and RAF1.

CONCLUSIONS

WES identified pathogenic and likely pathogenic variants and VOUS in LA genes in 51% of fetal edema cases, supporting WES and expanded hydrops panels in cases of idiopathic fetal hydrops and fluid collections.

Genomic profiling informs diagnoses and treatment in vascular anomalies

Vascular anomalies are malformations or tumors of the blood or lymphatic vasculature and can be life-threatening. Although molecularly targeted therapies can be life-saving, identification of the molecular etiology is often impeded by lack of accessibility to affected tissue samples, mosaicism or insufficient sequencing depth. In a cohort of 356 participants with vascular anomalies, including 104 with primary complex lymphatic anomalies (pCLAs), DNA from CD31+ cells isolated from lymphatic fluid or cell-free DNA from lymphatic fluid or plasma underwent ultra-deep sequencing thereby uncovering pathogenic somatic variants down to a variant allele fraction of 0.15%. A molecular diagnosis, including previously undescribed genetic causes, was obtained in 41% of participants with pCLAs and 72% of participants with other vascular malformations, leading to a new medical therapy for 63% (43/69) of participants and resulting in improvement in 63% (35/55) of participants on therapy. Taken together, these data support the development of liquid biopsy-based diagnostic techniques to identify previously undescribed genotype-phenotype associations and guide medical therapy in individuals with vascular anomalies.

Case report: Generalized lymphatic anomaly of multiple abdominal organs in a young dog

A 9-month-old, female Pomeranian dog presented with vomiting and lethargy. Ultrasonography revealed multilobulated anechoic round shape structures at the ovarian and uterine locations. Through computed tomography scan, an extensive non-contrast multilobulated fluid-filled mass suspected of originating from the walls of the ovary, uterus, urinary bladder and rectum was observed. Ovariohysterectomy and urinary bladder biopsy were performed. Histopathological examination revealed numerous cystic lesions lined by plump cuboidal cells believed to be of epithelial origin. Immunohistochemical staining showed that the cyst-like lesions lining cells were strongly positive for lymphatic vessel endothelial hyaluronan receptor 1. Based on these results, lesions were identified as generalized lymphatic anomaly (GLA), in which lymphangiomas develop in multiple organs. After 6 months follow-up, the size of the cysts remaining in the region of the bladder did not undergo much change. GLA should be included in the differential diagnosis when multiple cystic lesions are interspersed in multiple organs.

Svep1 is a binding ligand of Tie1 and affects specific aspects of facial lymphatic development in a Vegfc-independent manner

Multiple factors are required to form functional lymphatic vessels. Here, we uncover an essential role for the secreted protein Svep1 and the transmembrane receptor Tie1 during the development of subpopulations of the zebrafish facial lymphatic network. This specific aspect of the facial network forms independently of Vascular endothelial growth factor C (Vegfc) signalling, which otherwise is the most prominent signalling axis in all other lymphatic beds. Additionally, we find that multiple specific and newly uncovered phenotypic hallmarks of svep1 mutants are also present in tie1, but not in tie2 or vegfc mutants. These phenotypes are observed in the lymphatic vasculature of both head and trunk, as well as in the development of the dorsal longitudinal anastomotic vessel under reduced flow conditions. Therefore, our study demonstrates an important function for Tie1 signalling during lymphangiogenesis as well as blood vessel development in zebrafish. Furthermore, we show genetic interaction between svep1 and tie1 in vivo, during early steps of lymphangiogenesis, and demonstrate that zebrafish as well as human Svep1/SVEP1 protein bind to the respective Tie1/TIE1 receptors in vitro. Since compound heterozygous mutations for SVEP1 and TIE2 have recently been reported in human glaucoma patients, our data have clinical relevance in demonstrating a role for SVEP1 in TIE signalling in an in vivo setting.