A conjoined root is a type of developmental anomaly involving a nerve root.
It is the commonest nerve root developmental anomaly of the cauda equina being twice as common as two roots in the same foramen, the next most common anomaly1.
The incidence in cadaveric studies is about 8%. In a recent prospective MRI study, it was 6%2. In retrospective studies, the incidence is reported much lower.
There seems to be an association with vertebral malformations3, which may cause low back pain. The nerve root anomaly itself does not cause symptoms, but may be confused with disk hernias or lead to complications, if overlooked prior to spinal surgery.
The term conjoined nerve root actually refers to the roots of 2 adjacent segments, arising at the same level from the thecal sac, enveloped by a common root sleeve.
The L5 and S1 are most frequently involved.
Vertebral anomalies3, such as
- vertebral arch defects
- spina bifida
- absence of the ipsilateral facet joints
May show associated vertebral anomalies or malformations
May show the anomaly, but often fails to do so, if confined to the intervertebral disk spaces.
The most accurate non-invasive imaging study.
Axial slices should be contiguous over several segments, and coronal slices should be included. Typical signs include 4:
- asymmetry of the anterolateral corners of the dural sac
- excess extradural fat between the asymmetric dura and the nerve root (fat crescent)
- parallel course of the affected nerve roots at the disc level
Myelography, post-myelographic MSCT
Probably the most accurate imaging study in this type of anomaly5.
Imaging differential considerations include
- disk hernia
- post-arachnoiditic adhesions of the cauda
- other congenital root anomalies
- 1. Neidre A, Macnab I. Anomalies of the lumbosacral nerve roots. Review of 16 cases and classification. Spine. 1983;8 (3): 294-9. - Pubmed citation
- 2. Böttcher J, Petrovitch A, Sörös P et-al. Conjoined lumbosacral nerve roots: current aspects of diagnosis. Eur Spine J. 2004;13 (2): 147-51. doi:10.1007/s00586-003-0634-8 - Pubmed citation
- 3. Yoshioka S, Sairyo K, Sakai T et-al. Congenital absence of lumbosacral articular facet joint associated with conjoined nerve root: a case report. J Orthop Traumatol. 2010;11 (3): 183-7. doi:10.1007/s10195-010-0100-4 - Free text at pubmed - Pubmed citation
- 4. Song SJ, Lee JW, Choi JY et-al. Imaging features suggestive of a conjoined nerve root on routine axial MRI. Skeletal Radiol. 2008;37 (2): 133-8. doi:10.1007/s00256-007-0403-6 - Pubmed citation
- 5. Mccormick CC. Developmental asymmetry of roots of the cauda equina at metrizamide myelography: report of seven cases with a review of the literature. Clin Radiol. 1982;33 (4): 427-34. - Pubmed citation
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|