Segmental Spinal Dysgenesis-"Redefined"

Abstract

Study design: Retrospective single institutional observational study.

Purpose: Segmental spinal dysgenesis (SSD), a complex spinal dysraphic state caused by notochord malformation disorders, is named after its morphological presentation where a spine segment is dysgenetic, malformed or absent. This study's objective was to examine and reassess SSD imaging findings and correlate them with an embryological explanation.

Overview of literature: Scott and his colleagues defined SSD as segmental agenesis or dysgenesis of the lumbar or thoracolumbar vertebrae and underlying spinal cord. Tortori-Donati and his colleagues defined it as a morphologic continuum ranging from hypoplasia to an absent spinal cord segment.

Methods: Fifteen children, whose imaging findings and clinical features were consistent with SSD, were included in the study. Magnetic resonance imaging (MRI) was performed per institutional spine protocol.

Results: Five children (33.3%) presented with a high-ending bulbous cord with no caudal segment, six (40%) presented with a dorsal or lumbar segmental dysgenetic cord with a low-lying, bulky caudal cord but without significant spinal canal narrowing, and four (26.6%) presented with segmental caudal dysgenesis with severe kyphoscoliosis, gibbus deformity, and spinal canal narrowing with a normal distal segment (normal or low-lying).

Conclusions: SSD is a complex spinal anomaly in children requiring clinical-radiological assessment followed by multidisciplinary management based on the extent and severity of the dysgenetic cord and the type of SSD. MRI plays a crucial role in both diagnosing and classifying SSD prior to surgical treatment to prevent further impairment.

Keywords: Magnetic resonance imaging; Scoliosis; Segmental spinal dysgenesis; Spinal cord.

Fig. 1.

(A–C) Sequential T2 axial sections of the lumbar spine at the D10–D11, L1–L2, and L5–S1 levels. (A) and (C) show the normal cord lying in the spinal canal, whereas (B) shows intersegmental cord absence.

Fig. 2.

(A) MRI T2 whole spine sagittal section shows the abruptly ending dorsal cord at the D11 vertebral level, with segmental absence of the cord beyond it. (B) A close-up view of the segmental dysgenesis where the low-lying caudal cord is seen separately in the lower spinal canal from L5–S1 to S1–S2. Congenital cartilaginous fusion of the L3, L4 vertebral body is seen with absence of the lower sacrum and coccyx (coccygeal agenesis). (C) Coronal magnetic resonance myelogram shows an absent lumbosacral cord segment with a normal low -lying distal cord segment. Mild narrowing of spinal canal may be noted at the level of L3–L4. MRI, magnetic resonance imaging.

Fig. 3.

(A, B) T1 and T2 sagittal lumbar spine shows a blunt-ending spinal cord at the D12 vertebra, with conus seen separately in the lower spinal canal (S1–S2 level) without significant spinal canal narrowing (type 1 segmental spinal dysgenesis). Right S2 hemivertebra with mild scoliosis is seen with convexity toward the left (coronal not provided). (C) Magnetic resonance myelogram in the sagittal plane shows the absent cord segment from the D12 to L1 segment. Note the associated neurogenic bladder.

Fig. 4.

(A) Magnetic resonance sagittal myelogram shows a high bulbous-ending cord without a caudal cord (caudal regression syndrome). (B) T2 sagittal section of entire spine shows the same finding with mild prominence of the central canal in the lower dorsal level. Sacral agenesis, involving the lower sacrum and coccyx, is also seen. Multiple vertebral segmentation fusion anomalies in the cervical and upper dorsal spine with scoliosis and convexity to right are also present (difficult to appreciate in given image). (C) T2 sagittal section of entire spine of another patient, showing high bulbous-ending cord at the upper border of the D12 vertebrae level (distal spinal cord hypoplasia). L1 left hemi vertebrae, fusion of the L3–L4 vertebrae, and sacral agenesis involving the lower sacral vertebrae are seen. Complex lumbosacral vertebral formation and segmental anomaly are noted with mild dorsolumbar scoliosis (convexity to the left).

Fig. 5.

(A, B) T2 sagittal section of the spine shows bifocal involvement in both the cervical and dorsolumbar segments. There is cord interruption from the D8–L3 vertebra levels due to herniation of the mid lumbar vertebrae in to the lower thoracic spinal canal, causing severe spinal canal narrowing and gibbus deformity. The conus and lower dorsal cord appear normal. The conus ends at the L–S1 vertebra level, tethered by thick filum terminale lipoma (type 2 SSD). Complete spondyloptosis of C6 over C7 is seen with mild compression of the lower cervical cord. There is syringomyelia of the cord from the D1–D6 vertebral level with focal agenesis/dysgenesis in the lower dorsa lumbar vertebrae. (C) Lumbar spine of another type 2 SSD patient; there is acute kyphosis at the D12 vertebrae level with a small, disc-like D12 vertebral body and non-visualization of the cord from the D9 vertebrae to the upper border of the L1 vertebra. Conus ends at the upper border of the L4 vertebral level. SSD, segmental spinal dysgenesis.