Type 1.5 Split Cord Malformations: An Uncommon Entity

BACKGROUND: Split cord malformations (SCMs) are among the rare congenital spinal anomalies. In 1992, Pang et al. proposed the unified theory of embryogenesis and explained the formation of SCM type 1 and 2. This theory has been widely accepted in the neurosurgical literature, backed by several studies. However, there have been reports in the literature that defy both the classification as well as the formation of SCMs, based on the unified theory of embryogenesis. We report a case of SCM that does not fit into this classification scheme and try to elucidate its embryologic basis, with review of the relevant literature. We also attempt to include this variety into the existing classification system of SCMs. CASE DESCRIPTION: An 11-year-old boy presented with low backache after trivial trauma. He was neurologically intact. Imaging showed low-lying tethered cord and a midline ventral bony spur (D12, L1) with a single dural sac encasing both the hemicords. Surgical exploration showed a ventral bony spur with 2 hemicords, enclosed in a single dural tube. Excision of the bony spur and detethering of the filum terminal were performed. The postoperative course was uneventful and the patient was discharged satisfactorily. CONCLUSIONS: SCMs possibly represent a continuum of changes beginning at the gestational age of days 20-30. Terminology such as mixed or intermediate type is used to denote SCMs that show features of both type 1 and type II. We prefer using type 1.5 SCMs for all such cases, thereby avoiding confusion and maintaining uniformity in the nomenclature. However, further experimental studies are required to substantiate our understanding of these complex embryologic anomalies on the basis of current hypotheses.