Macrocystic lymphatic malformation (macrocystic LM) is a type of lymphatic malformation, which means it is an abnormal cluster of lymph vessels and fluid-filled spaces that develops before birth. It is benign (not cancer), but it can grow large and press on nearby organs. In a macrocystic lesion, the cysts are big, usually more than 1–2 cm, and filled with clear lymph fluid. These cysts form soft, smooth, often lobulated lumps under the skin.Radiopaedia+2ScienceDirect+2
Lymphatic malformations are slow-flow vascular malformations in the ISSVA (International Society for the Study of Vascular Anomalies) classification. They are not tumors that grow because of fast cell division, but instead are structural errors in how the lymph system formed in the embryo. Most macrocystic lymphatic malformations are present at birth or appear in early childhood, especially in the neck, face, armpit, chest or mediastinum, but they can also occur in the abdomen, limbs, or other body areas.ISSVA+2Radiopaedia+2
A macrocystic lymphatic malformation is a non-cancer (benign) birth condition made of abnormal lymph vessels that form large, fluid-filled pockets (cysts), often in the neck, armpit, chest, face, tongue, or body wall. “Macro” means the cyst spaces are usually big enough to see on imaging and often to feel, and they can slowly grow, swell fast during illness, or press on nearby parts like the airway. Many experts also call it cystic hygroma (especially in the neck). ISSVA+2PMC+2
Why it happens
MLM happens when the lymph “drain pipes” do not form normally before birth, so lymph fluid collects inside cysts instead of moving through normal channels. Some cases are linked to genetic pathway changes (often the PI3K/AKT/mTOR pathway), which can make lymph vessel cells grow or behave abnormally. This is why “targeted medicines” are sometimes used for difficult cases in specialist centers. ScienceDirect+2Neurointervention+2
Although macrocystic LM is benign, it can cause serious problems if it compresses the airway, swallowing tube, major blood vessels, or nerves. The swelling may suddenly enlarge if it bleeds or becomes infected, which may turn a quiet lesion into an emergency situation. Because of this, early recognition, careful monitoring, and proper imaging are very important.DermNet®+2Cincinnati Children’s Hospital+2
Other names
Doctors and older textbooks use several different names for macrocystic lymphatic malformation. Common synonyms include:
Cystic hygroma
Cystic lymphangioma
Macrocystic lymphangioma
Cystic lymphatic malformation
Lymphangioma cysticum
Cystic lymphatic tumor (older, less preferred term)
Today, experts prefer the term lymphatic malformation rather than lymphangioma or cystic hygroma, because it better reflects that this is a malformation of vessels rather than a true tumor.DermNet®+2Wikipedia+2
Types of lymphatic malformations related to macrocystic LM
Although this article focuses on macrocystic LM, it helps to see where it fits among related types:
Macrocystic lymphatic malformation – large, well-defined cysts filled with lymph fluid; often in neck, axilla, chest, or abdomen.
Microcystic lymphatic malformation – many tiny cysts like a sponge; often seen on skin and mucosa, such as mouth or limbs.
Mixed macro- and microcystic LM – a combination of large and small cysts in the same lesion.
Isolated LM – lymphatic malformation alone without other vessel problems.
Combined LM – LM mixed with other vascular malformations (such as venous malformation) in the same area.LGD Alliance+3Cincinnati Children’s Hospital+3Compendium Vascular Anomalies+3
Causes of macrocystic lymphatic malformation
Each “cause” below is really a factor or mechanism that may contribute. In many babies, no clear single cause is found.
Abnormal lymphatic development in the embryo
The main cause is a structural error when the lymphatic system forms in early pregnancy. Some lymph sacs or channels do not connect properly to the main lymph network. Trapped sacs slowly expand into cysts and become a macrocystic lymphatic malformation.PMC+2ScienceDirect+2Failure of lymphatic sacs to join the central system
Normally, primitive lymph sacs connect to larger veins and lymph trunks. If this connection does not happen, the isolated sacs keep collecting lymph fluid. Over time they enlarge and form one or several big cysts in the neck, chest or abdomen.PMC+1Sporadic (random) developmental error
Most macrocystic LMs occur sporadically, meaning they happen by chance with no family history. A random error during tissue development can affect just one small area, while the rest of the baby develops normally.Dr. Bastidas+1Genetic changes in growth pathways (e.g., PIK3CA, VEGFR3)
Research has found mutations in genes like PIK3CA and VEGFR3 (FLT4) in some lymphatic malformations. These genes control lymph vessel growth and signaling. When they are altered, lymphatic cells may form abnormal, enlarged channels and cysts.MDPI+1Turner syndrome
Cystic hygroma (macrocystic LM) is frequently seen in fetuses with Turner syndrome (45,X or related karyotypes). The abnormal sex chromosome pattern appears to disturb lymphatic development in the neck and upper body, leading to large cystic neck swellings.Cleveland Clinic+1Down syndrome (trisomy 21)
Some babies with macrocystic lymphatic malformations also have Down syndrome. The extra chromosome 21 may be linked to changes in lymphatic and vascular development, although the exact mechanism is still under study.Cleveland Clinic+1Noonan syndrome
Noonan syndrome is another genetic condition associated with neck cystic hygromas in the fetus. Mutations in RAS-MAPK pathway genes can affect lymphatic vessel formation, leading to large cystic malformations.Wikipedia+1Other genetic / syndromic conditions
Rare syndromes such as Hennekam lymphangiectasia syndrome or certain complex vascular anomaly syndromes can include lymphatic malformations as part of their picture. In these cases, LM is one feature of a broader genetic disorder.RSNA Publications+1Family history of vascular or lymphatic malformations
Most cases are not inherited, but occasional families show more than one member with lymphatic or related vascular malformations. This suggests that inherited variants in genes controlling vessel development can increase risk in some families.MDPI+1Chromosomal imbalance detected on prenatal testing
Some fetuses with macrocystic neck lesions show chromosomal deletions, duplications, or other imbalances on karyotype or chromosomal microarray. These changes may interfere with normal lymphatic and vascular development.Wikipedia+1General problems in fetal fluid handling (hydrops, severe edema)
When a fetus has hydrops (severe body swelling and fluid buildup), the overloaded lymphatic system may not drain properly. This situation can be associated with or worsen large cystic lymphatic malformations in the neck or chest.Wikipedia+1Localized venous outflow problems in the neck or chest
If venous blood drainage from a region is abnormal, it can increase pressure around lymph vessels. Over time, this may promote dilation of lymph channels and enlargement of pre-existing small malformations into macrocystic lesions.Cosmoderma+1Trauma or bleeding inside a pre-existing small LM
A minor injury, birth trauma, or internal bleeding into a small, unrecognized lymphatic malformation can suddenly expand the cystic spaces. This can transform a subtle lesion into a large macrocystic swelling.PMC+1Infection of lymphatic channels (lymphangitis)
Infection in or near a lymphatic malformation can cause inflammation, fluid accumulation, and clotting inside lymph spaces. The inflamed lesion may enlarge, and repeated episodes can remodel small channels into larger cysts.DermNet®+1Rapid growth during childhood
As a child grows, the macrocystic lymphatic malformation can grow as well. Growth spurts may make a previously small lesion more obvious or symptomatic, even though the basic malformation has been present since birth.KidsHealth+1Hormonal changes during puberty
Puberty brings hormonal and body-size changes that can alter blood and lymph flow. Some macrocystic LMs become larger, softer, or more symptomatic during adolescence for this reason.Dr. Bastidas+1Pregnancy in adults with pre-existing LM
In adults who still have lymphatic malformations, pregnancy increases blood volume and fluid shifts. This may enlarge cysts or make symptoms worse, especially in the neck, chest, or extremities.ScienceDirect+1Previous surgery or radiation near lymph drainage pathways
In rare acquired cases, surgical removal of lymph nodes or radiation therapy may disrupt lymph flow and lead to abnormal lymphatic channels and cysts in nearby tissues. This is more often linked with lymphatic obstruction, but macrocystic changes can occur.ScienceDirect+1Co-existing venous or arteriovenous malformations
Combined vascular malformations (for example, capillary-lymphatic-venous malformations) can disturb local pressure and flow, causing some lymphatic components to dilate into macrocystic spaces.ISSVA+2Radiopaedia+2Unknown / idiopathic factors
Even with modern genetics and imaging, many macrocystic lymphatic malformations have no identifiable trigger beyond “developmental error.” For many families, the most accurate explanation is that it happened by chance during early fetal development.ScienceDirect+1
Symptoms and signs of macrocystic lymphatic malformation
Soft, painless lump under the skin
The most common early sign is a soft, squishy swelling that feels like a water-filled bag. It usually does not hurt and may change slightly in size from day to day. Parents often notice it in the neck, armpit, chest, or face.DermNet®+2Cincinnati Children’s Hospital+2Visible swelling in the neck or face
Macrocystic LMs often appear in the side or back of the neck or around the jaw. The swelling can distort the outline of the neck or face, sometimes causing visible asymmetry even in a newborn.Cleveland Clinic+1Skin color changes over the mass
The skin over the lesion may look normal, slightly bluish, or reddish-blue. Because the cysts are filled with clear lymph and sometimes a bit of blood, they can give the skin a translucent or “transparent” look.DermNet®+1Sudden increase in size
The mass can suddenly enlarge if there is bleeding into a cyst or if the lesion becomes infected. This rapid change often brings the child to urgent medical attention, especially if it affects breathing or swallowing.PMC+1Pain or tenderness in the swelling
Most of the time, macrocystic LMs are painless. However, pain and tenderness can appear if the cysts are inflamed, infected, or under high tension from rapid fluid build-up.DermNet®+1Redness and warmth over the lesion
If infection occurs, the skin on top of the lesion may become red, warm, and slightly firm. The child may also feel unwell, with fever or irritability. This is a warning sign that needs quick medical review.DermNet®+1Breathing difficulty (airway obstruction)
A large neck or chest macrocystic LM can press on the airway and make it hard for the baby to breathe. Signs include noisy breathing, fast breathing, chest retractions, or episodes of turning blue. In severe cases this is an emergency.Cleveland Clinic+2Cincinnati Children’s Hospital+2Noisy breathing or stridor
Stridor is a high-pitched noise when air passes through a narrowed airway. A mass that pushes on the windpipe or voice box can cause this sound, especially when the child is crying or lying down.Cincinnati Children’s Hospital+1Trouble swallowing or feeding
If the lesion presses on the esophagus or mouth, the baby may have trouble sucking, swallowing, or moving food through the throat. This can lead to gagging, choking, poor feeding, or weight gain problems.Cincinnati Children’s Hospital+1Drooling and gagging during feeds
Some babies drool a lot or cough and gag while feeding because the mass narrows the space in the mouth and throat. This difficulty may be worse when the child is lying flat.Snoring or disturbed sleep
Older children may snore or sleep with their neck in unusual positions to keep the airway open. Large neck or facial lesions can contribute to sleep-disordered breathing or pauses in breathing at night.Recurrent respiratory infections
If airway clearance is poor or if the mass causes partial blockage, the child may get frequent chest infections, wheezing, or bronchitis. Infections of the LM itself can also trigger fevers and malaise.Cincinnati Children’s Hospital+1Limited movement of nearby joint or limb
Macrocystic LMs in the armpit, chest wall, or limb can restrict range of motion. The child may avoid lifting the arm fully or may limp if the lesion is in the thigh or groin.ScienceDirect+1Bleeding into the cyst (hemorrhage)
Sometimes small blood vessels inside the lesion break and bleed into the lymph cysts. The swelling becomes suddenly larger, firmer, and painful, and the overlying skin may turn darker or bruised.DermNet®+1Cosmetic and emotional impact
Visible deformities of the face or neck can cause distress, shyness, or bullying, especially for school-age children and teenagers. Even when the lesion is medically stable, its appearance can strongly affect quality of life and self-esteem.KidsHealth+1
Diagnostic tests for macrocystic lymphatic malformation
Doctors combine the story (history), physical exam, and targeted tests to confirm a macrocystic lymphatic malformation and plan treatment.
Physical examination tests
Visual inspection of the swelling
The doctor looks at the size, shape, borders, and skin changes of the swelling. Macrocystic LM often appears as a soft, lobulated mass with normal, bluish, or reddish skin. The doctor also checks for signs of infection or rapid growth.DermNet®+2Cincinnati Children’s Hospital+2Palpation (feeling the mass with the hands)
By gently pressing the swelling, the doctor can tell if it feels soft, cystic, compressible, or firm. Macrocystic LMs usually feel like soft, fluid-filled sacs and may partly flatten under gentle pressure, helping to distinguish them from solid tumors.Radiopaedia+1Transillumination test with a light
A bright light is shone through the mass in a dark room. Clear fluid-filled cysts transmit light and look like a glowing balloon, supporting the diagnosis of a cystic lesion such as macrocystic LM. Solid masses or those full of thick blood do not transilluminate as well.DermNet®+1Airway and breathing assessment
The doctor listens to breathing sounds, looks for chest retractions, and checks oxygen level. If the mass is near the airway, they watch for stridor, noisy breathing, or signs of respiratory distress, which helps decide how urgent the situation is.Cincinnati Children’s Hospital+1
Manual tests
Manual compression test
The doctor presses gently but firmly on the swelling to see if it compresses and refills. A macrocystic LM often compresses easily and slowly refills with fluid, while a solid tumor or stiff malformation will not change as much.Posture and position change observation
The lesion is observed when the child is lying down, sitting, or standing. Some lymphatic malformations change size slightly with gravity or pressure changes, and this can give clues about their nature and how they affect breathing or swallowing.Range of motion testing of nearby joints
If the LM is near a shoulder, hip, or limb, the doctor gently moves the joint to see whether the mass restricts movement or causes discomfort. This helps assess functional impact and guides decisions about timing and type of treatment.Swallowing and feeding evaluation
For neck or oropharyngeal lesions, the clinician watches the child feed or swallow water. They look for coughing, gagging, or difficulty moving food. This simple manual observation test helps identify risk of aspiration and the need for more detailed studies.Cincinnati Children’s Hospital+1
Lab and pathological tests
Complete blood count (CBC)
A CBC checks red and white blood cells and platelets. It does not diagnose LM directly, but can show signs of infection (raised white cells) or anemia from bleeding into the lesion. It is also important before surgery or invasive procedures.Inflammatory markers (CRP, ESR)
Blood tests such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) rise when there is inflammation or infection. These markers support the diagnosis of an infected LM if the child has fever, redness, or pain in the lesion.Coagulation profile (clotting tests)
Tests like PT, aPTT, and fibrinogen measure how well the blood clots. They help assess surgical risk and screen for consumption of clotting factors in very large or complex vascular malformations.Genetic and chromosomal studies
In fetuses or infants with large neck LMs, doctors may suggest karyotype or chromosomal microarray to look for Turner syndrome, Down syndrome, Noonan syndrome, or other genetic changes. In some centers, targeted gene panels for vascular anomalies are also used.Wikipedia+2MDPI+2Histopathology of the lesion (tissue examination)
When the lesion is surgically removed or biopsied, a pathologist examines it under a microscope. Classic features include dilated lymphatic spaces lined by endothelial cells, separated by fibrous tissue and sometimes smooth muscle. This confirms that the mass is a lymphatic malformation and not another tumor.ScienceDirect+1
Electrodiagnostic tests
Nerve conduction studies
If a large LM lies near major nerves and the child has weakness, numbness, or tingling, nerve conduction studies may be used. These tests send small electrical impulses through nerves to see how well signals travel, helping assess nerve compression.Electromyography (EMG)
EMG measures the electrical activity of muscles. If the LM compresses nerves supplying a limb or facial muscles, EMG can show signs of nerve injury or chronic denervation, which may influence the need for decompressive surgery.
Imaging tests
Ultrasound of the lesion
Ultrasound is usually the first imaging test. It uses sound waves to show cystic spaces, their size, number, and depth. Macrocystic LMs appear as large, clear, fluid-filled areas often with thin internal walls (septa). Ultrasound also guides needle drainage or sclerotherapy.Compendium Vascular Anomalies+2Medscape+2Prenatal obstetric ultrasound
Many macrocystic LMs are first discovered on routine pregnancy scans, especially in the second trimester. A large, cystic neck mass or nuchal cystic hygroma can be seen, prompting further genetic testing and planning for delivery at a specialized center.Wikipedia+1Magnetic resonance imaging (MRI)
MRI provides detailed pictures of soft tissues and is considered the gold standard for defining the full extent of lymphatic malformations, especially in the head and neck. It shows multiloculated cystic masses, their relation to airway, blood vessels, nerves, and spine, and helps plan surgery or sclerotherapy.Medscape+2Ej Radiology+2Computed tomography (CT) scan
CT uses X-rays to create cross-sectional images. It is less commonly needed in children because of radiation, but may be used in urgent situations or to evaluate chest, abdominal, or bone involvement. CT shows low-density cystic areas and their effect on nearby structures.Medscape+1Lymphoscintigraphy or MR lymphangiography
These specialized imaging tests trace the flow of lymph fluid using contrast agents. They are mainly used in complex or widespread disease to understand how lymph drains, to map connections to normal lymphatics, and sometimes to guide interventional procedures or surgery.Compendium Vascular Anomalies+2AJR American Journal of Roentgenology+2

