Secondary Neurulation Defects-1 : Retained Medullary Cord

Abstract

Retained medullary cord (RMC) is a relatively recent term. Pang et al. newly defined the RMC as a late arrest of secondary neurulation leaving a non-functional vestigial portion at the tip of the conus medullaris. RMC, which belongs to the category of closed spinal dysraphism, is a cord-like structure that is elongated from the conus toward the cul-de-sac. Because intraoperative electrophysiological confirmation of a non-functional conus is essential for the diagnosis of RMC, only a tentative or an assumptive diagnosis is possible before surgery or in cases of limited surgical exposure. We suggest the term 'possible RMC' for these cases. An RMC may cause tethered cord syndrome and thus requires surgery. This article reviews the literature to elucidate the pathoembryogenesis, clinical significance and treatment of RMCs.

Two cases of retained medullary cord running parallel to a terminal lipoma

“…Although the exact anatomical relationship between RMC and the associated terminal lipoma was not demonstrated, Kim et al . [ 1 ] showed that, in a caudal lipoma, the tapered low-lying conus is commonly continuous with the distally enlarging lipoma. When the low-lying conus contains a nonfunctional part, it is considered an RMC, as was the case for patient 3 in the first description by Pang et al .…”

“…[ 9 ] Therefore, operative exposure with IONM of the critical region is necessary for a definitive diagnosis of RMC. [ 1 , 3 , 8 - 10 ]…”

“…As a nonfunctional RMC is indistinguishable from the functional conus on neuroimaging and in the intraoperative view, confirming the presence of a nonfunctional C-LS with intraoperative neurophysiological monitoring (IONM) is essential for the diagnosis of RMC. [ 1 , 3 , 8 - 10 ] The central feature in the histopathology of RMC is the predominant presence of a central canal-like ependyma-lined lumen with a surrounding glioneuronal core. [ 6 , 8 , 9 , 11 ]…”

“…Although RMCs are not considered very rare,[ 8 , 9 ] the number of RMC patients tends to be underdiagnosed. [ 1 ] This is probably because RMCs have been recently defined, and their pathophysiology is not been fully understood. [ 1 ] Another reason is that some RMCs contain varying amounts of lipomatous tissues[ 1 , 5 , 8 , 9 , 11 ] and need to be differentiated from spinal lipomas, such as filar and caudal lipomas (terminal lipomas),[ 1 ] which are also believed to be caused by secondary neurulation failure.…”

“…[ 1 ] This is probably because RMCs have been recently defined, and their pathophysiology is not been fully understood. [ 1 ] Another reason is that some RMCs contain varying amounts of lipomatous tissues[ 1 , 5 , 8 , 9 , 11 ] and need to be differentiated from spinal lipomas, such as filar and caudal lipomas (terminal lipomas),[ 1 ] which are also believed to be caused by secondary neurulation failure. [ 4 ] We surgically treated two patients who had a nonfunctional C-LS, with a predominant presence of central canal-like structure, running parallel to the terminal lipoma.…”