Surgical histopathology of a filar anomaly as an additional tethering element associated with closed spinal dysraphism of primary neurulation failure

Abstract

Background: Closed spinal dysraphism of primary neurulation failure could be associated with filar anomalies, such as filar lipoma or thickened and tight filum terminale (TFT), resulting from impaired secondary neurulation. Retained medullary cord (RMC) is a remnant of the cavitary medullary cord originating from the secondary neurulation failure. Some filar lipomas are known to contain a central canal-like ependyma-lined lumen with surrounding neuroglial tissues (E-LC w/NGT), that is, a characteristic histopathology of RMC. To clarify the embryological background of these filar anomalies, we evaluated the histopathological findings. Methods: Among 41 patients with lesions of primary neurulation failure who underwent initial untethering surgery, the filum including cord-like structure (C-LS) was additionally resected in 10 patients (five dorsal and transitional lipomas; five limited dorsal myeloschisis). We retrospectively analyzed the clinical, neuroradiological, intraoperative, and histopathological findings. Results: Among 10 patients, two patients were diagnosed with RMC based on morphological features and intraoperative neurophysiological monitoring. The diagnosis of filar lipoma was made in six patients, since various amounts of fibroadipose tissue were histopathologically noted in the filum. Two patients were diagnosed with TFT, since the filum was composed solely of fibrocollagenous tissue. E-LC w/NGT was noted not only in both C-LSs of RMCs but also in two out of six fila both with filar lipomas and fila with TFTs. Conclusion: These findings provide further evidence for the idea that entities, such as filar lipoma, TFT, and RMC, can be considered consequences of a continuum of regression failure occurring during late secondary neurulation.

A Presenile Patient with Filar Lipoma Who Developed Tethered Spinal Cord Syndrome Triggered by Lumbar Canal Stenosis

“… 14 ) Recently, some studies reported that this histopathological finding was present frequently in filar and caudal lipomas, which are also believed to originate from the secondary neurulation failure. 18 , 19 ) Because central canal-like structures are not present from end to end of RMC tissue, 15 - 18 ) central canal-like structures were missing in this case whereas GFAP-positive neuroglial tissues were present. The present findings provided further evidence for the idea that RMC and filar lipomas can be considered consequences of the continuum of regression failure during secondary neurulation.…”

“…The present findings provided further evidence for the idea that RMC and filar lipomas can be considered consequences of the continuum of regression failure during secondary neurulation. 14 , 15 , 18 , 19 )…”

Retained medullary cord and caudal lipoma with histopathological presence of terminal myelocystocele in the epidural stalk

“…[17,18,20,21] RMC is thought to originate from the failed regression of the medullary cord, [2,17,20,24] and the characteristic histopathological feature is the presence of a central canal-like ependyma-lined lumen (CC-LELL) with surrounding neuroglial tissues (NGT), as a remnant of the medullary cord. [2,4,5,[9][10][11][12][14][15][16][17]20,23] e cyst within the RMC is histopathologically a cystic dilatation of the CC-LELL with NGT, and this pathology is called "cystic RMC. " [2][3][4]14,17,24] Although diagnostic criteria for RMC have not yet been fully established, the following three items are generally considered important: [11] (1) typical morphological features on neuroimaging and intraoperative view, [2,17,20,24] (2) the electrophysiological border between the conus and C-LS, [2,4,[9][10][11][12]17,20,21,24] and (3) CC-LELL with NGT on histopathological examination of C-LS.…”

Intramedullary abscess at thoracolumbar region transmitted from infected dermal sinus and dermoid through retained medullary cord

“…As nonfunctional RMC is indistinguishable from the functional conus on neuroimaging; moreover, in the intraoperative view, detecting the presence of a nonfunctional C-LS with intraoperative neurophysiological monitoring (IONM) is mandatory for the diagnosis of RMC. [ 4 , 6 , 9 , 11 , 12 , 14 , 17 , 18 , 20 ] The characteristic histopathological feature of RMC is the predominant presence of a central canal-like ependymal-lined lumen (CC-LELL) with surrounding glial fibrillary acidic protein (GFAP)-immunopositive neuroglial tissues, as a remnant of the medullary cord. [ 4 , 6 , 9 , 11 , 12 - 17 , 18 , 21 ] Some CC-LELLs show cystic dilatation, in which case, these are referred to as “cystic RMC” or “RMC of cystic type,”[ 4 - 6 , 14 , 18 ] though Pang et al .…”

“…[ 4 , 6 , 9 , 11 , 12 , 14 , 17 , 18 , 20 ] The characteristic histopathological feature of RMC is the predominant presence of a central canal-like ependymal-lined lumen (CC-LELL) with surrounding glial fibrillary acidic protein (GFAP)-immunopositive neuroglial tissues, as a remnant of the medullary cord. [ 4 , 6 , 9 , 11 , 12 - 17 , 18 , 21 ] Some CC-LELLs show cystic dilatation, in which case, these are referred to as “cystic RMC” or “RMC of cystic type,”[ 4 - 6 , 14 , 18 ] though Pang et al . [ 17 ] did not describe cystic RMCs in their initial article.…”