Pulmonary sequestration

Refers to a mass of lung tissue without any connection to the airway system.

Bronchopulmonary 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.

Such sequestered tissue is not connected to the normal bronchial airway architecture, and fails to function in, and contribute to, respiration.

Bronchopulmonary sequestration 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.

This condition is usually diagnosed in children and is generally thought to be congenital.

These lesions are increasingly diagnosed in utero by prenatal ultrasound.

Symptoms can include a persistent dry cough.

Complications:

Potentially fatal hemorrhage

The creation of a left-right shunt, where blood flows in a shortcut through the feed off the aorta

Chronic infection with diseases such as Bronchiectasis Tuberculosis Aspergillosis Bronchial carcinoid Bronchogenic squamous cell carcinoma

It is 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.

A theory of sequestration formation involves an accessory lung bud that develops from the ventral aspect of the primitive foregut.

The pluripotential tissue of additional lung bud migrates in a caudal direction with the normally developing lung.

The accessory bud receives its blood supply from vessels that connect to the aorta and 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, and it is encased within the same pleural covering.

This is the intrapulmonary type variant, in contrast to the later development of the accessory lung bud resulting 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: the celiac axis, internal mammary, subclavian, or renal artery may be involved, rarely.

Intrapulmonary sequestration occurs within the visceral pleura of normal lung tissue.

The most common location is in the posterior basal segment of the lung.

Nearly two thirds of pulmonary sequestrations appear in the left lung.

Extrapulmonary sequestration is enclosed in its own pleural sac, and may occur above, within, or below the diaphragm.

Venous drainage is usually via the systemic venous system.

Foregut communication and associated anomalies, such as diaphragmatic hernia, are more common.

BPS is estimated to comprise one to six percent of all congenital pulmonary malformations.

Sequestrations are classified anatomically. Intralobar sequestration in which the lesion is located within a normal lobe and lacks its own visceral pleura.

Extralobar sequestration in which the mass is located outside the normal lung and has its own visceral pleura

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.

Intralobar variety accounts for 75 percent of all sequestrations.

Intralobar sequestration usually presents in adolescence or adulthood as recurrent pneumonias.

The lung tissue lies within the same visceral pleura as the lobe in which it occurs.

Males and females are equally affected.

The arterial supply is usually derived from the lower thoracic or upper abdominal aorta.

Venous drainage is usually to the left atrium via pulmonary veins establishing a left to left shunt.

Two thirds of the time, the sequestration is located in the paravertebral gutter in the posterior segment of the left lower lobe.

Unlike extralobar sequestration, it is rarely associated with other developmental abnormalities.

Patients present with signs and symptoms of pulmonary infection of a lower lobe mass.

It is believed that sequestrations become infected with bacteria.

The extralobar variety accounts for 25 percent of all sequestrations.

Onset usually in infancy with respiratory compromise.

The extralobar lesion, as an accessory lung is contained within its own pleura.

Male to female predominance of 3:1 to 4:1.

Related to the left hemidiaphragm in 90% of cases.

May present as a subdiaphragmatic or retroperitoneal mass.

The arterial supply of comes from an aberrant vessel from thoracic aorta.

It usually drains via the systemic venous system to the right atrium, vena cava, or azygous systems.

Congenital anomalies occur more frequently in patients with extralobar sequestration the intralobar sequestration.

Associated anomalies include congenital cystic adenomatoid malformation, congenital diaphragmatic hernia, vertebral anomalies, congenital heart disease, pulmonary hypoplasia, and colonic duplication.

The extralobar lesion is enveloped in its own pleural sac, it rarely gets infected so almost always presents as a homogeneous soft tissue mass.

It may be closely associated with the esophagus, and fistulae may develop.

An arteriogram can document the systemic blood supply, allowing definitive diagnosis as well as preoperative planning.

Sequestrations typically appear as a uniformly dense mass within the thoracic cavity or pulmonary parenchyma on chest x-ray.

Recurrent infection can lead to the development of cystic areas within the mass.

Air-fluid levels due to bronchial communication can be seen.

The typical sonographic appearance of BPS is an echogenic homogeneous mass that may be well defined or irregular.

Some masses have a cystic or more complex appearance.

Doppler studies help to identify the characteristic aberrant systemic artery that arises from the aorta and to delineate venous drainage.

CT scans have 90% accuracy in the diagnosis of pulmonary sequestration, with the most common appearance is a solid mass that may be homogeneous or heterogeneous, sometimes with cystic changes.

Less frequent findings a large cavitary lesion with an air-fluid level, a collection of many small cystic lesions containing air or fluid, or a well-defined cystic mass is seen.

Contrast-enhanced MRA or even conventional T1-weighted spin-echo (SE) images may help in the diagnosis of pulmonary sequestration by demonstrating a systemic blood supply, particularly from the aorta, to a basal lung mass.

CT allows sharper delineation of thin-walled cysts and emphysematous changes than MRI.

Treatment

Usually sequestration is removed after birth via surgery.

In most cases this surgery is safe and effective, with growth to have normal lung function.

In a few instances, fetuses with sequestrations develop problematic fluid collections in the chest cavity.

In rare instances where the fetus has a very large lesion, a specialized delivery for management of the airway compression can be planned or a fetal laser ablation procedure can be performed: a needle is inserted into the sequestration, and a laser fiber is targeted at the abnormal blood vessel going to the sequestration.

The laser energy to stop the blood flow to the sequestration, causing it to stop growing, and with 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.

Blood supply arises from the aorta or its branches.

Blood supply is usually from one or more aberrant arteries.

Pulmonary sequestration-can be extralobar, being external to the lung and can be found at any site in the thorax.

Extralobar lesions most commonly found in infants and may be associated with congenital abnormalities.

Intralobar sequestrations present as masses of lung parenchyma that share a contiguous pleural lining with the adjacent normal lung and drain via the pulmonary venous system. to the

Intralobar lesions are found within the lung and are associated with infections or bronchiectasis.

Patients present in late childhood and adolescence with recurrent cough or multiple episodes of pneumonia.

Intralobar sequestration more common in the left posteriorobasal region.

More than 90% of intralobar sequestrations are located in lung bases.

Extralobar sequestration have a distinct low surface separate from normal lung and their own ab2242ant venous drainage, and are commonly diagnosed in infancy due to respiratory failure or an incidental finding.

Extralobar sequestration commonly occurs in the left lung, but can be in any area of the lung.