Sequestrum

SEQUESTERUM (from Latin sequestro-I separate), a name usually given to isolated parts of dead bone, for example, in osteomyelitis, as well as generally to any dead tissue that is being rejected. Sometimes in lobar pneumonias and especially in Friedländer's grippe, extensive areas of necrosis develop in the lung in the form of sequestra. The formation of sequestra is observed in the parotid gland in mumps, in typhoid fever during the period of necrosis of the lymphatic apparatus of the intestines, etc. The formation of sequestra from soft tissues is rarely encountered in practice. Usually such necrotic foci undergo resorption, organization, etc. (see Necrosis) without preliminary complete rejection. Such rejection of dead soft tissues is probably possible only when this necrosis belongs to the category of coagulative necrosis or when special conditions arise, as for example in the lungs, when rapidly developing necrosis occurs without the participation of putrefactive microorganisms. The basis of the process of separation of a sequestrum (the so-called sequestration) is reactive inflammation, which is called demarcation inflammation and as a rule develops around any necrotic focus under the conditions mentioned above and leads to the complete rejection of necrotic masses. The size of sequestra can vary greatly: from small grains to an entire diaphysis of a tubular bone, for example, the tibia or femur. The further fate of a sequestrum depends on its size, physical properties, and its location. Superficial sequestra from soft tissues are freely removed from the body as such. Bony sequestra due to their density can remain in the body for a very long time, but sooner or later they are removed through the fistulas that arise in such cases; this is often preceded by prolonged inflammation with abundant granulations growing around the sequestrum, which sometimes undergo ossification, forming the so-called sequestrum capsule, in which the sequestrum is located among pus (see Osteomyelitis). Pulmonary sequestra are usually not removed as such, but after being rejected, they are melted down and then partially absorbed or expectorated; as a result, cavities are formed that resemble cysts or cavities. Sequestration has a prototype in physiological life, for example, in the form of rejection of the tail of the tadpole.