Pulmonary sequestration

A pulmonary sequestration is a medical condition wherein a piece of tissue that ultimately develops into lung tissue is not attached to the pulmonary arterial blood supply, as is the case in normally developing lung. This sequestered tissue is therefore not connected to the normal bronchial airway architecture, and fails to function in, and contribute to, respiration of the organism.
This condition is usually diagnosed in children and is generally thought to be congenital in nature. More and more, these lesions are diagnosed "in utero" by prenatal ultrasound.
Presentation.
Symptoms can vary greatly, but they include a persistent dry cough.
Complications.
Failure to have a pulmonary sequestration removed can lead to a number of complications. These include:
Cause.
There is still much debate to whether pulmonary sequestration is a congenital problem or acquired through recurrent pulmonary infection. It is widely believed that extralobar pulmonary sequestrations are a result of prenatal pulmonary malformation while intralobar pulmonary sequestrations can develop due to recurrent pulmonary infections in adolescents and young adults. The most frequently supported theory of sequestration formation involves an accessory lung bud that develops from the ventral aspect of the primitive foregut. The pluripotential tissue from this additional lung bud migrates in a caudal direction with the normally developing lung. It receives its blood supply from vessels that connect to the aorta and cover the primitive foregut. These attachments to the aorta remain to form the systemic arterial supply of the sequestration. Early embryologic development of the accessory lung bud results in formation of the sequestration within normal lung tissue. The sequestration is encased within the same pleural covering. This is the intrapulmonary variant. In contrast, later
development of the accessory lung bud results in the extrapulmonary type that may give rise to communication with the GI tract. Both types of sequestration usually have arterial supply from the thoracic or abdominal aorta. Rarely, the celiac axis, internal mammary, subclavian, or renal artery may be involved. Intrapulmonary sequestration occurs within the visceral pleura of normal lung tissue. Usually, no communication with the tracheobronchial tree occurs. The most common location is in the posterior basal segment, and nearly two thirds of pulmonary sequestrations appear in the left lung. Venous drainage is usually via the pulmonary veins. Foregut communication is very rare, and associated anomalies are uncommon. Extrapulmonary sequestration is completely enclosed in its own pleural sac. It may occur above, within, or below the diaphragm, and nearly all appear on the left side. No communication with the tracheobronchial tree occurs. Venous drainage is usually via the systemic venous system. Foregut communication and associated anomalies, such as diaphragmatic hernia, are more common.
Diagnosis.
Bronchopulmonary sequestration (BPS) is a rare congenital malformation of the lower respiratory tract.It consists of a nonfunctioning mass of normal lung tissue that lacks normal communication with the tracheobronchial tree, and that receives its arterial blood supply from the systemic circulation.
BPS is estimated to comprise one to six percent of all congenital pulmonary malformations, making it an extremely rare disorder.
Sequestrations are classified anatomically.Intralobar sequestration (ILS) in which the lesion is located within a normal lobe and lacks its own visceral pleura.Extralobar sequestration (ELS) in which the mass is located outside the normal lung and has its own visceral pleuraThe blood supply of 75% of pulmonary sequestrations is derived from the thoracic or abdominal aorta.The remaining 25% of sequestrations receive their blood flow from the subclavian, intercostal, pulmonary, pericardiophrenic, innominate, internal mammary, celiac, splenic, or renal arteries.
Treatment.
Usually the sequestration is removed after birth via surgery. In most cases this surgery is safe and effective; the child will grow up to have normal lung function.
In a few instances, fetuses with sequestrations develop problematic fluid collections in the chest cavity. In these situations a Harrison catheter shunt can be used to drain the chest fluid into the amniotic fluid.
In rare instances where the fetus has a very large lesion, resuscitation after delivery can be dangerous. In these situations a specialized delivery for management of the airway compression can be planned called the EXIT procedure, or a fetal laser ablation procedure can be performed. During this minimally invasive fetal intervention, a small needle is inserted into the sequestration, and a laser fiber is targeted at the abnormal blood vessel going to the sequestration. The goal of the operation is to use laser energy to stop the blood flow to the sequestration, causing it to stop growing. Ideally, after the surgery, the sequestration steals less blood flow from the fetus, and the heart and lungs start growing more normally as the sequestration shrinks in size and the pleural effusion goes away.
The treatment for this is a wedge resection, segmentectomy, or lobectomy via a VATS procedure or thoracotomy.
Pulmonary sequestrations usually get their blood supply from the thoracic aorta.