Sequestration in medical terminology refers to the separation or isolation of a component—such as tissue, an organ segment, or a volume of blood—from the body’s normal systems. This detachment often occurs from the main circulatory or structural architecture, leading to localized problems or systemic emergencies. The specific meaning of sequestration changes dramatically depending on the context, applying to distinct clinical conditions involving the spleen, lungs, and bone.
Splenic Sequestration Crisis
Splenic sequestration describes a life-threatening complication most frequently observed in young children with sickle cell disease. The crisis occurs when a large volume of blood suddenly becomes trapped inside the spleen, the organ located in the upper left abdomen. This pooling happens because the abnormally shaped, stiff red blood cells characteristic of the disorder get stuck in the spleen’s narrow blood vessels.
The sickled cells block the outflow of blood, causing the organ to rapidly swell and become engorged. As blood pools in the spleen, it is removed from the body’s general circulation, causing a rapid decrease in total circulating blood volume. This sudden loss leads to profound anemia and hypovolemia, potentially causing shock.
The crisis presents with signs such as a fast heart rate, paleness, extreme fatigue, and severe pain or swelling in the left abdomen. Since a significant portion of oxygen-carrying red blood cells is suddenly unavailable, a swift medical response is necessary to stabilize the patient. This condition is most common in infants and children between six months and five years old, before the spleen scars down and loses function due to repeated sickling episodes.
Pulmonary Sequestration
Pulmonary sequestration is a congenital anatomical anomaly, meaning it is a structural defect present from birth. It involves a piece of lung tissue that has separated from the normal bronchial and circulatory systems, rendering it non-functional. This separated tissue receives its blood supply from the systemic circulation, typically a branch of the aorta, rather than the pulmonary artery like normal lung tissue.
The sequestered lung tissue does not connect to the tracheobronchial tree, meaning air cannot enter or leave through normal airways. This anomaly is classified into two main types based on its location relative to the rest of the lung. Intralobar sequestration is encased within the same pleural covering as the adjacent lung tissue and accounts for the majority of cases.
Extralobar sequestration, which is less common, is completely separate from the surrounding lung and has its own distinct pleural sac. Venous drainage differs between the two types: intralobar lesions usually drain into the pulmonary veins, while extralobar lesions drain into the systemic veins. Intralobar types often present later in life with recurrent infections, whereas extralobar types are more likely to cause respiratory distress in newborns. Diagnosis relies on imaging studies that identify the abnormal systemic blood vessel feeding the isolated tissue. The definitive treatment for symptomatic or recurrently infected sequestration is surgical removal of the non-functioning segment.
Bone Sequestrum
The term sequestration also applies to a specific condition within bone pathology, where the separated element is referred to as a sequestrum. A sequestrum is a fragment of dead, necrotic bone tissue that has become detached from the surrounding healthy bone structure. This process is a common outcome of chronic osteomyelitis, a persistent bacterial infection of the bone.
The infection causes inflammation and swelling within the rigid bone structure, compromising the blood supply to a bone segment. When the blood supply is lost, the affected tissue dies and separates from the healthy bone, forming the sequestrum. This dead bone is isolated from the body’s defenses, including bloodstream antibiotics, allowing the infection to persist.
The body often attempts to wall off this area by forming a layer of new bone around the sequestrum, called an involucrum. Despite this encapsulation, the sequestrum acts as a continuous source for bacterial growth and chronic infection. To resolve the underlying osteomyelitis, the dead bone must be surgically removed in a procedure known as sequestrectomy.