Intramedullary Cavitations in Osteonecrosis (NICO)
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Completely hollow mandible ("dry rot"), with alveolar nerve almost floating freely in cavitation.

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Cavitations Defined & Explained

Certainly, one of the most unique and fascinating features of ischemic osteonecrosis is the presence of hollow spaces or "cavitations" within the marrow spaces.  By definition these must be larger than 5 mm. in diameter to warrant the use of the term cavitation, but in reality many older persons have smaller hollow spaces scattered throughout their bone marrow, at least as determined by Graff-Radford's cadaver study of the jawbones.  An expression of the uniqueness of these lesions can be found in the fact that the the first (1930) and only application of the term to bone pathology was for ischemic osteonecrosis and its variants.  

These spaces essentially represent "dry rot" of the bone and fatty marrow, a process which can only be explained by slow and chronic strangulation of the bone's blood supply, i.e. ischemia. In persons with a generalized marrow ischemia, such as those taking estrogen or corticosteroids, alcoholics or those with autoimmune diseases such as lupus erythematosus, multiple cavitations are common. Any bone can have them, but those most susceptible are the hip, the jaws and the knees. They may be associated with increased medullary pressures and are often associated with local or referred pain.

Cavitation can occur in only one of two conditions, according to osteonecrosis authorities consulted by this Center: ischemic osteonecrosis and unicameral bone cyst (called traumatic bone cyst in the jaws). The necessary ischemia is apparently a part of several significant bone diseases, such as osteoporosis (subchondral bone cysts) and florid osseous dysplasia (with traumatic bone cysts) of the jaws.

Most cavitations in the jaws are found in the third molar regions, and in the maxilla this phenomenon is referred to as a "hollow tuberosity." The walls are usually irregular and are often discolored brown and black ("blowtorched" appearance), but a sizeable proportion of lesions have very smooth, very hard (marble-like) walls. The more smooth the walls, the less likely is the cavitation to have a pool of blood at its base and the less likely it is to bleed during surgery (some examples have presented with almost no hemorrhage until the damaged/altered bony wall is removed and the surgeon enters the surrounding fatty marrow).

While many health professionals refer to the disease of osteonecrosis, or the resulting pain, as cavitations, these hollow spaces are not, in fact, the real disease. They merely represent one manifestation or sign of ischemic osteonecrosis, a disease produced by chronically poor blood flow through bone marrow. It is true that curetting the walls of a cavitation seems to eliminate or greatly reduce the pain of osteonecrosis, but this probably results from a combination of: the elimination of local toxins from necrosis and inflammation (and maybe from bacteria); the release of fluid or gaseous pressures in the marrow; the stimulation of fresh hemorrhage into this dried out area. Treating the cavitation is, however, not treating the disease itself, it is only treating one sign and perhaps a few associated symptoms, such as pain, pressure and a burning sensation.

Bone Diseases Associated with Intramedullary Cavitations?

Although ischemic marrow damage can be produced by a large number of systemic diseases, they result in a surprisingly small number of bone diseases.  Many names have been given to ischemic osteonecrosis and bone marrow edema over the years (click for listing) but excluding these, the following table lists those few bone diseases capable of creating true, "air-filled" intramedullary cavitations or hollow spaces.