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SPINE
Kummell, in 1891, reported a delayed post-traumatic
vertebral collapse that occurred weeks or even months after
an injury. Many underlying mechanisms have been suggested,
however, at the present time the most widely accepted mechanism
is osteonecrosis. Affected patients generally are middle-aged
or elderly men or women with the interval between the acute
traumatic episode and the vertebral collapse varying from
days to years. While Kummell's disease may be asymptomatic,
progressive angular kyphotic deformity accompanied by local
pain and sometimes even spinal cord compression are clinical
hallmarks. The typical location is the lower thoracic and
upper lumbar vertebral bodies. The classic radiographic finding
of collapse and a vacuum cleft within the vertebral body appearing
as a transverse radiolucent line in the center of the vertebral
body or adjacent to one of its endplates, was not described
in the initial case study, however. This vacuum cleft is exaggerated
with extension views and is seen on CT scans as well as on
MR imaging, on the former as low signal intensity on all pulse
sequences. Typically, however, the prolonged supine positioning
leads to replacement of the gas by fluid resulting in high
signal intensity within the cleft on T2-weighted images. Gas
within the vertebral body is not diagnostic of osteonecrosis
and rarely gas formation from spinal infection and focal collections
of gas within the vertebral body reflecting the presence of
Schmorl's nodes, can also be present.
Osteonecrosis due to Sickle Cell Disease
Unlike other etiologies of avascular necrosis, sickle cell
disease may cause ischemia where there is abundant vascularity,
for example, of the vertebral bodies. The reason for this
is due to the altered, "sickle", shaped red blood
cells. As they traverse the capillaries, they have a propensity
to get "clogged". As with hair in the sink, once
a number of sickled cells get hung up in the capillary system,
it is easier for more and more to get clogged until an ischemic
event occurs. The process results in osteonecrosis of the
central portion of the vertebral body endplates. Collapse
will eventually occur from the loading forces of weight bearing
giving rise to the classic "H-Shaped" vertebral
body.
AVN of the vertebral bodies due to sickle cell disease
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