What Is a Fetal Lung Mass?

A fetal lung mass is a lump that grows inside or next to an unborn baby's lung.

What Happens With a Fetal Lung Mass?

When an unborn baby's lungs form during pregnancy, they grow in parts called lobes. Each lobe connects to the airway so air can move in and out of it when the baby starts breathing after birth.

A fetal lung mass can cause problems before the baby is born if it gets big enough to put pressure on:

• other parts of the lung
• the baby's heart
• blood vessels

When a fetal lung mass pushes on the heart and blood vessels, the heart has trouble pumping blood. If the heart can't keep up with the baby's needs, fluid builds up around the lungs and in the belly, a condition called hydrops fetalis (HI-drops fee-TAL-iss).

After the baby is born, the fetal lung mass can cause problems because it can:

• get infected (pneumonia)
• take up room so that the healthy lung lobes can't fill with air

The two common types of fetal lung masses are:

• congenital pulmonary airway malformation (CPAM), also called congenital cystic adenomatoid malformation (CCAM)
• bronchopulmonary sequestration (BPS)

Fetal lung masses usually stop growing around the 26th week of pregnancy and may begin shrinking around the 30th week.

What Are the Signs & Symptoms of a Fetal Lung Mass?

Most fetal lung masses don't cause symptoms before the baby is born.

After the baby is born, the lung mass may cause serious symptoms, including:

• blue-tinted skin (cyanosis)
• a collapsed lung (pneumothorax)
• trouble breathing (tachypnea)

What Causes a Fetal Lung Mass?

Doctors don't know what causes fetal lung masses. There's nothing the baby's parents can do to prevent one.

Who Gets a Fetal Lung Mass?

Fetal lung masses happen randomly during pregnancy. They're not caused by a genetic disorder and are not part of a syndrome (a group of problems that are often seen together).

How Is a Fetal Lung Mass Diagnosed?

A routine ultrasound scan of an unborn baby usually will find a fetal lung mass. When viewing the mass, an imaging specialist (radiologist) will:

• study its location
• measure its size
• try to determine what type it is

The radiologist also looks at how the mass affects the surrounding lung and heart, and might recommend other tests, including:

• magnetic resonance imaging (MRI)
• an ultrasound scan of the baby's heart (fetal echocardiogram)

A mass that wasn't found before birth may cause symptoms after the baby is born and starts breathing. Doctors will use one or more of these imaging tests to see what is causing the symptoms:

• ultrasound
• computed tomography (CT) scan
• MRI scan

How Is a Fetal Lung Mass Treated?

Treatment Before Birth

When a prenatal ultrasound finds a fetal lung mass, doctors will check its growth using ultrasound scans. These are usually done:

• every 2 weeks for a mass that is growing or stable
• every 4 weeks for a mass that is shrinking

If the lung mass is large enough to threaten the life of the fetus, doctors treat it by giving the mother steroid medicines. If these don't work, doctors consider other options, such as:

• thoracentesis: inserting a needle under ultrasound guidance into the fetus' chest to withdraw fluid from the lung mass
• thoracoamniotic shunt: putting a tube into the baby's chest to let fluid drain from the lung mass into the amniotic sac (the fluid-filled bag in the uterus where the fetus grows)
• fetal surgery: open or minimally invasive surgery to remove the lung mass

Treatment After Birth

If the lung mass causes symptoms after the baby is born, doctors usually do surgery right away to remove it.

If the lung mass doesn't cause symptoms, doctors usually remove it when the baby is 3–12 months old to:

• prevent pneumonia
• lower the chance of the mass becoming cancerous later in life, which can happen in rare cases

If a fetal lung mass is not surgically removed, doctors will need to follow its growth carefully with imaging studies until the child reaches adulthood.