Pulmonary hypoplasia
Encyclopedia
Pulmonary hypoplasia is incomplete development of the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s, resulting in an abnormally low number or size of bronchopulmonary segment
Bronchopulmonary segment
Each of the tertiary bronchi serves a specific bronchopulmonary segment. These segments each have their own artery. Thus, each bronchopulmonary segment is supplied by a bronchus, and two arteries, a pulmonary artery and a bronchial artery which run together through the center of the segment...

s or alveoli
Pulmonary alveolus
An alveolus is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well...

. A congenital malformation, it most often occurs secondary to other fetal
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

 abnormalities that interfere with normal development of the lungs. Primary (idiopathic
Idiopathic
Idiopathic is an adjective used primarily in medicine meaning arising spontaneously or from an obscure or unknown cause. From Greek ἴδιος, idios + πάθος, pathos , it means approximately "a disease of its own kind". It is technically a term from nosology, the classification of disease...

) pulmonary hypoplasia is rare and usually not associated with other maternal or fetal abnormalities.

Incidence of pulmonary hypoplasia ranges from 9–11 per 10,000 live birth
Live birth
In human reproduction, a live birth occurs when a fetus, whatever its gestational age, exits the maternal body and subsequently shows any sign of life, such as voluntary movement, heartbeat, or pulsation of the umbilical cord, for however brief a time and regardless of whether the umbilical cord or...

s and 14 per 10,000 births. Pulmonary hypoplasia is a common cause of neonatal death. It also is a common finding in stillbirth
Stillbirth
A stillbirth occurs when a fetus has died in the uterus. The Australian definition specifies that fetal death is termed a stillbirth after 20 weeks gestation or the fetus weighs more than . Once the fetus has died the mother still has contractions and remains undelivered. The term is often used in...

s, although not regarded as a cause of these.

Causes

Causes of pulmonary hypoplasia include a wide variety of congenital malformations and other conditions in which pulmonary hypoplasia is a complication. These include congenital diaphragmatic hernia
Congenital diaphragmatic hernia
Congenital diaphragmatic hernia is a congenital malformation of the diaphragm. The most common type of CDH is a Bochdalek hernia; other types include Morgagni's hernia, diaphragm eventration and central tendon defects of the diaphragm...

, congenital cystic adenomatoid malformation
Congenital cystic adenomatoid malformation
Congenital cystic adenomatoid malformation is a congenital disorder similar to bronchopulmonary sequestration. In CCAM, usually an entire lobe of lung is replaced by a non-working cystic piece of abnormal lung tissue. This abnormal tissue will never function as normal lung tissue.In most cases the...

, fetal hydronephrosis
Hydronephrosis
Hydronephrosis is distension and dilation of the renal pelvis calyces, usually caused by obstruction of the free flow of urine from the kidney, leading to progressive atrophy of the kidney...

, caudal regression syndrome
Caudal regression syndrome
Caudal regression syndrome or sacral agenesis is a little-known and rare congenital disorder in which there is abnormal fetal development of the lower spine—the caudal partition of the spine....

, mediastinal tumor, and sacrococcygeal teratoma
Sacrococcygeal teratoma
Sacrococcygeal teratoma is a teratoma located at the base of the coccyx . It is thought to be a derivative of the primitive streak.-Natural history:...

 with a large component inside the fetus. Large masses of the neck (such as cervical teratoma
Teratoma
A teratoma is an encapsulated tumor with tissue or organ components resembling normal derivatives of all three germ layers. There are rare occasions when not all three germ layers are identifiable...

) also can cause pulmonary hypoplasia, presumably by interfering with the fetus's ability to fill its lungs. In the presence of pulmonary hypoplasia, the EXIT procedure
EXIT procedure
The EXIT procedure, or ex utero intrapartum treatment procedure, is a specialized surgical delivery procedure used to deliver babies who have airway compression...

 to rescue a baby with a neck mass is not likely to succeed.

Fetal hydrops
Hydrops
-Medicine:* In general, hydrops is another name for edema.** Endolymphatic hydrops - a pathological feature present in Ménière's disease.** Hydrops fetalis is edema in a fetus.-Zoology:* Hydrops, a colubrid snake genus....

 can be a cause, or conversely a complication.

Pulmonary hypoplasia is associated with oligohydramnios
Oligohydramnios
Oligohydramnios is a condition in pregnancy characterized by a deficiency of amniotic fluid. It is the opposite of polyhydramnios.-Diagnosis:Diagnosis is made by ultrasound measurement of the amniotic fluid index...

 through multiple mechanisms. Both conditions can result from blockage of the urinary bladder
Urinary bladder
The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor...

. Blockage prevents the bladder from emptying, and the bladder becomes very large and full. The large volume of the full bladder interferes with normal development of other organs, including the lungs. Pressure within the bladder becomes abnormally high, causing abnormal function in the kidneys hence abnormally high pressure in the vascular system entering the kidneys. This high pressure also interferes with normal development of other organs. An experiment in rabbits showed that PH also can be caused directly by oligohydramnios.

Pulmonary hypoplasia is associated with dextrocardia of embryonic arrest
Dextrocardia
Dextrocardia is a congenital defect in which the heart is situated on the right side of the body. There are two main types of dextrocardia: dextrocardia of embryonic arrest and dextrocardia situs inversus...

 in that both conditions can result from early errors of development, resulting in congenital cardiac disease.

PH is a common direct cause of neonatal death resulting from pregnancy induced hypertension.

Diagnosis

Medical diagnosis
Medical diagnosis
Medical diagnosis refers both to the process of attempting to determine or identify a possible disease or disorder , and to the opinion reached by this process...

 of pulmonary hypoplasia in utero
In utero
In utero is a Latin term literally meaning "in the womb". In biology, the phrase describes the state of an embryo or fetus. In legal contexts, the phrase is used to refer to unborn children. Under common law, unborn children are still considered to exist for property transfer purposes.-See also:*...

 may use imaging, usually ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...

 or MRI
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...

. The extent of hypoplasia is a very important prognostic factor. One study of 147 fetuses (49 normal, 98 with abnormalities) found that a simple measurement, the ratio of chest
Chest
The chest is a part of the anatomy of humans and various other animals. It is sometimes referred to as the thorax or the bosom.-Chest anatomy - Humans and other hominids:...

 length to trunk (torso
Torso
Trunk or torso is an anatomical term for the central part of the many animal bodies from which extend the neck and limbs. The trunk includes the thorax and abdomen.-Major organs:...

) length, was a useful predictor of postnatal respiratory distress
Respiratory distress
Respiratory distress may refer to either/both:* Labored breathing, the physical presentation of respiratory distress*Shortness of breath or dyspnea - a sensation of respiratory distress-See also:*List of terms of lung size and activity...

. In a study of 23 fetuses, subtle differences seen on MRIs of the lungs were informative. In a study of 29 fetuses with suspected pulmonary hypoplasia, the group that responded to maternal oxygenation had a more favorable outcome.

Pulmonary hypoplasia is diagnosed also clinically.

Management

Management has three components: interventions before delivery, timing and place of delivery, and therapy after delivery.

In some cases, fetal therapy is available for the underlying condition; this may help to limit the severity of pulmonary hypoplasia. In exceptional cases, fetal therapy may include fetal surgery
Fetal surgery
Fetal surgery is any of a broad range of surgical techniques that are used to treat birth defects in fetuses who are still in the pregnant uterus.* Open fetal surgery involves completely opening the uterus to operate on the fetus....

.

A 1992 case report of a baby with a sacrococcygeal teratoma (SCT) reported that the SCT had obstructed the outlet of the urinary bladder causing the bladder to rupture in utero and fill the baby's abdomen with urine (a form of ascites
Ascites
Ascites is a gastroenterological term for an accumulation of fluid in the peritoneal cavity.The medical condition is also known as peritoneal cavity fluid, peritoneal fluid excess, hydroperitoneum or more archaically as abdominal dropsy. Although most commonly due to cirrhosis and severe liver...

). The outcome was good. The baby had normal kidneys and lungs, leading the authors to conclude that obstruction occurred late in the pregnancy and to suggest that the rupture may have protected the baby from the usual complications of such an obstruction. Subsequent to this report, use of a vesicoamniotic shunting
Shunt (medical)
In medicine, a shunt is a hole or a small passage which moves, or allows movement of fluid from one part of the body to another. The term may describe either congenital or acquired shunts; and acquired shunts may be either biological or mechanical.* Cardiac shunts may be described as...

 procedure (VASP) has been attempted, with limited success.

Often, a baby with a high risk of pulmonary hypoplasia will have a planned delivery in a specialty hospital such as (in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

) a tertiary referral hospital
Tertiary referral hospital
A tertiary hospital, tertiary referral center or tertiary care center is a term without a formal definition which in the United States generally refers to:...

 with a level 3 neonatal intensive-care unit. The baby may require immediate advanced resuscitation and therapy.

Early delivery may be required in order to rescue the fetus from an underlying condition that is causing pulmonary hypoplasia. However, pulmonary hypoplasia increases the risks associated with preterm birth, because once delivered the baby requires adequate lung capacity to sustain life. The decision whether to deliver early includes a careful assessment of the extent to which delaying delivery may increase or decrease the pulmonary hypoplasia. It is a choice between expectant management and active management
Active management
Active management refers to a portfolio management strategy where the manager makes specific investments with the goal of outperforming an investment benchmark index...

. An example is congenital cystic adenomatoid malformation
Congenital cystic adenomatoid malformation
Congenital cystic adenomatoid malformation is a congenital disorder similar to bronchopulmonary sequestration. In CCAM, usually an entire lobe of lung is replaced by a non-working cystic piece of abnormal lung tissue. This abnormal tissue will never function as normal lung tissue.In most cases the...

 with hydrops
Hydrops
-Medicine:* In general, hydrops is another name for edema.** Endolymphatic hydrops - a pathological feature present in Ménière's disease.** Hydrops fetalis is edema in a fetus.-Zoology:* Hydrops, a colubrid snake genus....

; impending heart failure may require a preterm delivery. Severe oligohydramnios
Oligohydramnios
Oligohydramnios is a condition in pregnancy characterized by a deficiency of amniotic fluid. It is the opposite of polyhydramnios.-Diagnosis:Diagnosis is made by ultrasound measurement of the amniotic fluid index...

 of early onset and long duration, as can occur with early preterm rupture of membranes
Rupture of membranes
Rupture of membranes or amniorrhexis is a term used during pregnancy to describe a rupture of the amniotic sac. Normally, or "spontaneously", it occurs at full term at the onset of, or during, labor...

, can cause increasingly severe PH; if delivery is postponed by many weeks, PH can become so severe that it results in neonatal death.

After delivery, most affected babies will require supplemental oxygen. Some severely affected babies may be salvaged with extracorporeal membrane oxygenation
Extracorporeal membrane oxygenation
In intensive care medicine, extracorporeal membrane oxygenation is an extracorporeal technique of providing both cardiac and respiratory support oxygen to patients whose heart and lungs are so severely diseased or damaged that they can no longer serve their function...

 (ECMO). Not all specialty hospitals have ECMO, and ECMO is considered the therapy of last resort for pulmonary insufficiency. An alternative to ECMO is high-frequency oscillatory ventilation.

History

In 1908, Maude Abbott
Maude Abbott
Maude Elizabeth Seymour Abbott was a Canadian doctor and was one of Canada's earliest female medical graduates and an expert on congenital heart disease....

 documented pulmonary hypoplasia occurring with certain defects of the heart. In 1915, Abbott and J. C. Meakins showed that pulmonary hypoplasia was part of the differential diagnosis of dextrocardia
Dextrocardia
Dextrocardia is a congenital defect in which the heart is situated on the right side of the body. There are two main types of dextrocardia: dextrocardia of embryonic arrest and dextrocardia situs inversus...

. In 1920, decades before the advent of prenatal imaging, the presence of pulmonary hypoplasia was taken as evidence that diaphragmatic hernia
Diaphragmatic hernia
Diaphragmatic hernia is a defect or hole in the diaphragm that allows the abdominal contents to move into the chest cavity. Treatment is usually surgical.The following types of diaphragmatic hernia exist:* Congenital diaphragmatic hernia** Morgagni's hernia...

s in babies were congenital, not acquired.
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