Prepared by William Davenport, MD, William Woodard, MD,
Michael Couden, MD, from the Department of Radiology, Medical
University of South Carolina, Charleston, SC.
A 74-year-old female inpatient was referred for magnetic
resonance imaging (MRI) of the thoracolumbar spine after complaints
of chronic, unrelenting back pain (figure 1). The exact pain
history was sketchy, as the patient demonstrated some signs of
dementia. The patient's daughter reported no known trauma, and
there was no history of previous back surgery. Two days after the
MRI was obtained, the neurological surgery service requested a
myelogram of the thoracic spine (figure 2) for further elucidation
of the lesion that was demonstrated on MR imaging.
Ankylosing spondylitis with pseudarthrosis of the thoracic
T1- and T2-weighted sagittal images of the thoracolumbar spine
are shown in figure 1. A cross-table lateral plain radiograph
obtained as a myelogram scout image is shown in figure 2.
The MR imaging appearance of pseudarthrosis is characteristic.
In our case, the T1-weighted sagittal image (figure 1A) shows an
area of decreased signal intensity in the midthoracic spine
involving both the vertebral body and associated posterior
elements. Additional low signal intensity anterior to the affected
body is likely hematoma. Note that the low signal intensity area is
contiguous--apparent "bridging" of anterior and posterior spinal
elements. The T2-weighted sagittal image (figure 1B), shows an area
of low-intensity signal surrounding a central, "bridging"
high-intensity signal (representing the actual pseudarthrosis
The radiograph obtained as a scout image for a myelogram also
demonstrates typical bony ankylosis and exaggerated kyphosis
(figure 2). Note the well-defined midthoracic fracture, evident
anteriorly just superior to the diaphragm. This finding in a
clinical setting of chronic/subacute back pain would suggest
possible pseudarthrosis even if a trauma history were not
Pseudarthrosis is a potential complication of long-standing
ankylosing spondylitis. Thought to be an insufficiency lesion,
pseudarthrosis often causes back pain without known trauma or
several days after minimal trauma. It occurs most frequently at the
thoracolumbar junction, and the most common mechanism of injury
appears to be torsional strain. The pseudarthrosis represents
subacute or chronic fracture of both the vertebral body and
adjacent posterior elements of a given spinal segment. Sequelae
from this lesion can include neurologic deficit.
In patients with chronic ankylosing spondylitis with
long-standing back pain, infection must also be included in the
differential diagnosis. MRI can be useful in distinguishing
pseudarthrosis from infection. In infection, MR imaging shows
contrast enhancement in the adjacent discs and soft tissues, while
pseudarthrosis does not demonstrate increased enhancement of the
involved discs. In this case, notice the anterior bony changes
characteristic of ankylosing spondylitis in both MR views (figure