What is "involucrum"

Involucre \In"vo*lu`cre\ (?; 277), n. [L. involucrum a covering, wrapper, fr. involvere to wrap up, envelop: cf. F. involucre. See Involve.] (Bot.)

1. A whorl or set of bracts around a flower, umbel, or head.

2. A continuous marginal covering of sporangia, in certain ferns, as in the common brake, or the cup-shaped processes of the filmy ferns.

3. The peridium or volva of certain fungi. Called also involucrum.

n. A sheath that covers or envelopes, especially one that forms around the sequestrum of new bone

An involucrum (plural involucra) is a layer of new bone growth outside existing bone seen in pyogenic osteomyelitis. It results from the stripping off of the periosteum by the accumulation of pus within the bone, and new bone growing from the periosteum.

It can be seen radiographically (i.e., with x-rays), although it is seen rarely in developed countries, given that osteomyelitis is rarely left untreated there.