Devendra Kumar MBBS, MD, Presenter: Nothing to Disclose

Rakesh K Sheoran DMRD, MD, Abstract Co-Author: Nothing to Disclose

Zeev Vladimir Maizlin MD, Abstract Co-Author: Nothing to Disclose

Santosh D Patil MD, Abstract Co-Author: Nothing to Disclose

Shortening of anterior-posterior diameter of L5 with disproportionate excessive posterior wedging and invariable associated bilateral spondylolysis are hallmark of Hypoplastic L5. Fank Miller first described this in 1979 and coined the term psuedospondylolisthesis.Now Wilms et al described MR features and measurement criteria of L5 Hypoplasia, which are predictors of spondylolysis in MR imaging in AJNR, 2008.The purpose of our study is to explore the imaging characteristics of L5 Hypoplasia on CT and/or MRI and enforced the congenital hypothesis of L5 Hypoplasia.

We described the characteristic imaging findings of L5 Hypoplasia in 20 patients. We followed the Wilms et al’s criteria in measuring the AP diameter of L5 and compared it with AP diameter of L4 and S1 and degree of posterior wedging.CT was performed mostly to confirm the spondylolysis. Spondylolysis was described in term of nondisplaced linear defect, gap between the lysed segments and separated lysed fragments with presence or absence of thinning of pedicle and facet joints. Secondary degenerative findings in L4-L5 and L5-S1 discs, facet joint arthropathy, neural foramina narrowing and nerve root compression were described.

The mean difference between the AP diameters of L5 and L4 was 2.8 mm and L5-S1 was 3.9mm.The mean posterior wedging was 25.5%. We found posterior wedging is more reliable indicator of L5 Hypoplasia. Significant central canal widening was noted at L5 level as compared to L4 level. True anterolisthesis was seen in 14 patients, which were associated with significant adjacent disc disease, facet joint arthropathy, neural foramina narrowing and exiting nerve root compression.

Our result confirmed the invariably associated bilateral spondylolysis with L5 Hypoplasia in young and middle age group who presented with non specific low backache with or without radiation pain. Hypoplastic L5 is often overlooked in commonly performed MR examination of LS spine and considered as normal variation, thus bilateral spondylolysis.   Presence of L5 Hypoplasia in children support the congenital hypothesis as possible cause of L5 Hypoplasia.  

Hypoplastic L5 is often overlooked in routinly performed MR examination.CT plays an important role in identifying the spondylolysis with other feathers of L5 Hypoplasia.  

Kumar, D, Sheoran, R, Maizlin, Z, Patil, S, Diagnosis of Spondylolysis on MRI: Importance of Recognization of Hypoplastic L5 on MRI.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11007159.html