A pulmonary sequestration (also known as a bronchopulmonary sequestration or cystic lung lesion), 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. As a result, this sequestered tissue is not connected to the normal bronchial airway architecture, and as a result, 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 prenatalultrasound.
Since it is enveloped in its own pleural sac, it rarely gets infected so almost always presents as a homogeneous soft tissue mass.
The mass may be closely associated with the esophagus, and fistulae may develop.
An arteriogram has been considered vital in documenting the systemic blood supply, allowing definitive diagnosis as well as preoperative planning.
The advent of new noninvasive imaging techniques has changed this thinking.
Sequestrations typically appear as a uniformly dense mass within the thoracic cavity or pulmonary parenchyma.
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 lesions have a cystic or more complex appearance.
Doppler studies are helpful to identify the characteristic aberrant systemic artery that arises from the aorta and to delineate venous drainage.
Chest CT showing pulmonary sequestration
CT scans have 90% accuracy in the diagnosis of pulmonary sequestration.
The most common appearance is a solid mass that may be homogeneous or heterogeneous, sometimes with cystic changes.
Less frequent findings include 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.
Emphysematous changes at the margin of the lesion are characteristic and may not be visible on the chest radiograph.
CT technique for optimal depiction of lesions by using state-of-the-art volumetric scanning requires a fast intravenous (IV) contrast injection rate and appropriate volume and delay based upon size.
Multiplanar and 3D reconstructions are helpful.
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.
In addition, MRA may demonstrate venous drainage of the mass and may obviate more invasive investigations.
However, CT allows sharper delineation of thin-walled cysts and emphysematous changes than MRI.
Failure to have a pulmonary sequestration removed can leads to a number of complications. These include:
Hemorrhage that can be fatal.
The creation of a left-right shunt, where blood flows in a shortcut through the feed off the aorta.
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.