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What are fetal lung lesions?

A fetal lung lesion is a mass or lump in the chest of a fetus. The main types of fetal lung lesions are congenital pulmonary airway malformations (CPAM) and bronchopulmonary sequestration (BPS).

CPAMs are the most common fetal lung lesion, occurring in 1 out of 12,000 live births. These masses usually appear on one lung and have equal chances of being on either the right or left lung. CPAMs are connected to the normal airways and blood vessels in the lungs.

Bronchopulmonary sequestrations are located outside the lung and get their blood supply from the aorta. BPS vary in size: larger ones can take up a lot of space, putting pressure on the lungs, heart, and blood vessels in the chest.

At Boston Children’s Hospital, our Maternal Fetal Care Center specializes in the evaluation and treatment of lung lesions and other complex fetal conditions.

Fetal Lung Lesions | Symptoms & Causes

What are the symptoms of fetal lung lesions?

A pregnant person often has no symptoms when their fetus has a lung lesion. Doctors can diagnose the condition using ultrasound and fetal magnetic resonance imaging (MRI). The pregnant person may notice decreased fetal movements, an increase in abdomen size due to polyhydramnios (excess amniotic fluid), or swelling (edema) from mirror syndrome.

What causes fetal lung lesions?

The cause of fetal lung lesions isn’t known. However, doctors and researchers have determined that both CPAMs and bronchopulmonary sequestrations are benign lung malformations that usually develop between seven and 16 weeks gestation.

CPAMs typically fall into three types:

  • type 1: one dominant cyst visible to the eye
  • type 2: multiple small cysts visible to the eye
  • type 3: microcystic masses composed of tiny cysts only visible under a microscope, which appear more solid on an ultrasound study

A BPS is a mass of lung tissue that isn’t properly connected to the airways in the fetal lung, but it receives its blood supply from the fetal aorta. The mass can be within a lobe of the lung or outside of a lobe. Rarely a sequestration will be in the fetal abdomen and not the chest.

Fetal Lung Lesions | Diagnosis & Treatments

How are fetal lung lesions diagnosed?

Lung lesions can be detected before birth using ultrasound. Doctors performing the ultrasound may see a mass in the fetal chest that doesn’t look like normal lung tissue. The mass may also push a fetus’ heart from its normal position, and the abnormal tissue appears bright on the ultrasound, often with dark fluid-filled areas. Sometimes, the mass may cause too much amniotic fluid to accumulate around the fetus (polyhydramnios). Other prenatal tests include fetal echocardiography of the fetus’ heart or an MRI of the fetus and the entire uterus to get a clearer picture of the mass and check for any other problems.

How are fetal lung lesions treated?

Most lung lesions are small, don’t cause problems during pregnancy, and can be followed with ultrasound over time to measure the lesion, amniotic fluid levels, and the fetus’ overall health. Most lung masses cause no complications at birth, and the baby can go to the newborn nursery. A pediatric surgeon may order a chest x-ray while the baby is in the hospital, and in most cases, the baby will go home in the first few days of life with a return visit in the first couple of months to meet with the surgeon and receive a chest CT scan. These chest masses are usually removed during a minimally invasive procedure with a small scope (within the first three to nine months of life.

Larger lesions may require fetal intervention or a planned delivery with all the specialists present so that they may take any steps needed to help the baby breathe well.

The size of a fetal lung lesion can help predict surgical outcomes. Doctors measure the lung mass and calculate its volume using the Congenital Pulmonary Airway Malformation Volume Ratio (CVR). A higher CVR indicates a bigger lung lesion and can suggest a greater risk of complications.

Prenatal treatment options for fetal lesions

  1. Steroid medication can be given to the pregnant person to slow the growth of the fetus lung lesion.
  2. Fluid can be removed from the cyst in the chest with either a needle or shunt tubing, which may remain in place for the duration of the pregnancy.
  3. Doctors may block some of the blood supply to the lung mass using a heated catheter. This is done using a minimally invasive approach through the uterus.
  4. Rarely, doctors may choose to perform open fetal surgery and operate on the fetus to remove the lung mass, and then return the fetus back to the womb.

Delivery options for the highest-risk lesions

  • Doctors may perform a cesarean delivery (C-section) with pediatric surgeons, who will then take the newborn to an adjacent operating room to carefully remove the lung mass, present.
  • Ex-utero intrapartum treatment (EXIT): An EXIT procedure is a technique similar to a cesarean delivery. With EXIT, however, doctors surgically remove the lesion while the fetus is still connected to the umbilical cord and placenta. EXIT is used for rare cases when a fetus has an extremely large lung mass or has very small or underdeveloped lungs (pulmonary hypoplasia), and doctors believe it’s best if the lung mass is removed before separating the fetus from the placenta.

What is the long-term outlook for fetal lung lesions?

Most fetal lung lesions are benign, and once it’s removed, the remaining lobe(s) of the unaffected lung slowly expands and develops normally.

The outlook for fetal lung lesions depends on the size and location of the mass and its impact on the surrounding lung. Overall, lung lesions diagnosed and treated by the specialists at Boston Children’s Maternal Fetal Care Center have an excellent outcome.

Fetal Lung Lesions | Programs & Services