Conjoined nerve root

A conjoined root is a type of developmental anomaly involving a nerve root.

It is the most common nerve root developmental anomaly of the cauda equina being twice as common as two roots in the same foramen, the next most common anomaly 1.

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 malformations 3, which may cause low back pain. The nerve root anomaly itself does not cause symptoms, but may be confused with disc hernias or lead to complications, if overlooked prior to spinal surgery.

The term conjoined nerve root actually refers to the roots of two 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 anomalies 3, such as:

May show associated vertebral anomalies or malformations.

May show the anomaly, but often fails to do so, if confined to the intervertebral disc 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 anomaly 5.

Imaging differential considerations include:

  • disk hernia
  • post-arachnoiditic adhesions of the cauda
  • other congenital root anomalies
Neuroanatomy
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Article information

rID: 16025
Section: Anatomy
Synonyms or Alternate Spellings:
  • Conjoined root

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Cases and figures

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    Case 1: right L5 and S1
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    Case 2: left S1 and S2
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    Case 3
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    Case 4: right L5-S1 with S1 hemilumbarisation
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