Caudal Agenesis: Classification Based on the Pathoembryogenesis of the Spinal Cord

Caudal agenesis (CA) is a congenital disease characterized by lower vertebral bone defects. Previous classifications for CA were based on the levels of bony defects or the conus medullaris. We created a new pathoembryogenic classification that takes into account the level of conus, considering both its shape and filum. We evaluated its accuracy in reflecting the neurological status and the need for untethering.

Patients with radiologic studies available on our institute's electronic image view system between 1985 and 2019 were reviewed. Our classification categorized patients with CA into 3 groups: the failure of formation (a conus level > L1 or normal level conus with a blunt shape), the failure of regression (a conus level < L3 or normal level conus with a thickened filum or a filar lipoma), and the normal (a normal level conus without specific abnormalities). We analyzed which of the following 3 classifications better reflects the neurological status and the probability of recommending untethering: classifications based on (1) bony defect level, (2) conus level, and (3) pathoembryogenic mechanism.

A total of 89 patients were included in this study. The pathoembryogenic classification revealed more significant differences in motor or sensory deficits compared with other classifications (failure of formation: 42%; failure of regression: 16%; and normal: 0%, P = .039). In addition, the pathoembryogenic classification emerged as a significant or suggestive predictive factor for motor and sensory deficits (motor: odds ratio 11.66, P = .007; sensory: odds ratio 5.44, P = .066). Notably, only the pathoembryogenic classification exhibited a significant difference in the probabilities of recommending untethering between groups (failure of formation: 42%; failure of regression: 81%; and normal 12%, P < .001).

The correlation between bony classification and spinal cord abnormalities was exaggerated. Our new pathoembryogenic classification was valuable in prognosticating neurological status and identifying the patient group more likely to require untethering among patients with CA.