Age / Sex : 77 / F

Chief complaint : Back pain with radiating pain to lower extremity

1) What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

(Quiz는 quiz일 뿐이오니 답안은 한개만 보내주시기 바라오며, 복수의 답안을 보내주시는 분은 정답이 포함되어 있더라도 부득이 semi-correct answer로 처리토록 하겠습니다.)

Courtesy :  류혜진(Yoo Hye Jin), 서울대학교병원(Seoul National University Hospital)

Conjoined nerve root

Discussion

Diagnosis:  Conjoined nerve root

Discussion:

•        Conjoined nerve root is composed of two adjacent nerve roots, which share a common dural envelope at some time during their coursing from the thecal sac. It is believed that the development of an anomalous nerve root is secondary to aberrant migration of the involved roots during embryologic development. This recognized congenital anomaly may produce symptoms of a radiculopathy even in the absence of mechanical impingement. Conjoined nerve roots associated with other spinal anomalies are quite rare but are more easily diagnosed owing to other associated findings. These associated findings may include defects in the neural arch, spondylolysis or spondylolisthesis, spina bifida occulta, or other bony anomalies. It is well recognized that the most common location of a conjoined nerve root is at the L5-S1 level.

•       There are several characteristic features of a conjoined nerve root noted on MRI. The density of a nerve root anomaly is almost identical to that of the thecal sac, and it is considerably less dense than that of disk material. Also, the location of the root anomaly is often above the intervertebral disk space at the level of pedicle, while herniated disk fragments are usually seen at the level of the disk space. Often, an asymmetry or pouching out of the subarachnoid space in the axial view suggests the presence of a conjoined nerve root. In the absence of a disk bulge, a conjoined nerve root anomaly is easier to diagnose on MRI because of change in signal intensity between the posterior aspect of the anulus and the nerve root sheath itself. Coronal plane imaging allows the viewer to follow the take-off of several nerve roots in the same plane of imaging and therefore is the optimal imaging plane to visualize these anomalies.

•       The prevalence of lumbosacral nerve root anomalies varies widely. In surgical studies, up to a 2% incidence has been reported. Myelography reports of patients with complaints of leg pain in the presence of a suspected disk herniation double the incidence of suspected nerve root anomalies (4%). Anatomic studies have demonstrated a much higher incidience.

•       The conjoined nerve root represents the most common nerve root anomaly. Unfortunately, the most common environment in which nerve abnormalities are diagnosed is the operating room, which dramatically increases the potential for an iatrogenic complication. It is technically more difficult to remove a herniated disk in the presence of a conjoined nerve root. A surgeon must always be congnizant of the fact that a nerve root anomaly may be present during any surgical exploration. This should minimize the potential of an intraoperative nerve root injury during nerve root manipulation in the presence of an unrecognized conjoined nerve root. The lack of a preoperative awareness of a nerve root abnormality may lead to overzealous retraction of the neural elements when attempting to find a herniated disk fragment. Overretraction of an anomalous nerve root may result in a dural tear, damage to the nerve rootlet, or nerve root avulsion. This may result in continued or worsening leg pain, that is, the battered nerve root syndrome. Additionally, a nerve root anomaly may be misidentified as a protruding or herniated disk and incised inadvertently. This obviously will result in a sympathetic iatrogenic neural injury.

References:

Conjoined lumbar nerve roots. A frequently underappreciated congenital abnormality. J Spinal Disord Tech 2004; 17: 86-93

Conjoined lumbosacral nerve roots: current aspects of diagnosis. Eur Spine J 2004; 13: 147-151