Found on: webinfo@chiroviewpresents.com
3-7-02

Pitfalls in Diagnostic Imaging
Spondylolisthesis: The subtle radiographic findings

Ian McLean, DC, DACBR - Department Head
Diagnostic Imaging - imcleandc@aol.com

In a previous document, I broadly discussed the classification and 
classical features of spondylolisthesis.  In clinical practice 
however, subtle cases of  L5 isthmic spondylolisthesis at are 
relatively common with minimal radiographic findings that can be 
easily missed.

Here is what to look for:

On the AP radiograph, subtle radiographic findings include mild 
dysplasia of the posterior arch, which might include spina bifida 
occulta, and asymmetrical presentation of the pedicles.  Further, 
spondylolisthesis creates anterior subluxation of the vertebral body 
and posterior subluxation of the neural arch that will cause the L5 
transverse processes to overlap the sacral alae.  In advanced cases, 
this may create the classical „inverted Napoleons hatū.  I have found 
this to be a particularly helpful radiographic finding in picking up 
spondylolisthesis on the AP radiograph.

On the lateral projection of the lumbar spine, a mild degree of 
retrolisthesis is usually expected.  Spondylolisthesis should be 
considered even if there is a minute degree of anterior displacement 
of L5 in respect to S1.  As a side note, I am not a fan of Ullmannžs 
line, which is not as sensitive as Georgežs line.    The posterior arch 
should also be evaluated for mild dysplasia and osseous defects in 
the region of the pars interarticularis.

Follow-up evaluation can include oblique radiographs, although a 
collimated AP radiograph with 30 degrees of cephalic tube tilt is 
often a superior image.  Axial CT or MRI images spondylolisthesis 
can at times be a diagnostic dilemma.  On occasion, the presence of a 
spondylolisthesis can be recognized by virtue of a widened spinal 
canal secondary to the anterior displacement of the vertebral body 
and posterior displacement of the neural arch.   Subsequent close 
inspection should then reveal the pars defects.

Images relating to this description can be found at 
http://mcleanradiology.com/