Gross and microscopic study of the filum terminale: does the filum contain functional neural elements?
OBJECTIVE
The filum terminale (FT) is considered a fibrous structure that extends from conus medullaris of the spinal cord to coccyx. Based on previous studies and from their own experience with intraoperative electrophysiological monitoring of the sacral nervous system, the authors postulate that the FT contains functional neural elements in some individuals.


METHODS
The FT was dissected from 13 fresh stillborn cadavers (7 male, 6 female; mean gestational age 36 weeks and 1 day). The gross anatomical features were recorded, and connections between the FT and the nerve roots of the cauda equina were noted. These connections, when present, were sectioned for histological studies. The fila (both interna and externa) were also sectioned for histological and immunohistochemical studies. In addition, FT specimens were obtained from 5 patients undergoing sectioning of the FT in an untethering surgical procedure.


RESULTS
There were 5 gross connections between the FT and nerve roots demonstrating nerve fibers that were positive for S100. The FT showed islands of cells that were positive for GFAP in 10 cases, synaptophysin in 3 cases, S100 in 11 cases, and nestin in 2 cases. The nerve fibers in the FT were myelinated in 2 cases. The conus ended at the L-1 or L-2 vertebral level in all 13 specimens. The dural sac terminated at the S-2 vertebral level in most of the specimens. The 5 FT specimens that were obtained from patients revealed nerve bundles that were positive for S100 in 4 cases and cells that were positive for GFAP in 3 cases.


CONCLUSIONS
There are gross anatomical connections between the FT and nerve roots that contain nerve fibers. Apart from fibrous stroma, the FT may contain nerve bundles and cells that stain positive for GFAP, synaptophysin, S100, and nestin. These microscopic findings and previous intraoperative electrophysiological studies suggest a probable functional role for the FT in some individuals. At birth, the conus ends at a higher vertebral level (lower L-1 or upper L-2) than L-3.
Department of Neurosurgery, Narayana Medical College, Nellore, India.
Samson Sujit Kumar
SS
Gaddam
Vissa
V
Santhi
Srinivasa
S
Babu
Geeta
G
Chacko
Ramakrishna Appala
RA
Baddukonda
Vedantam
V
Rajshekhar
D002420:Cauda Equina / Q000473:pathology*; D005904:Glial Fibrillary Acidic Protein / Q000032:analysis; D006801:Humans; D007231:Infant, Newborn; D007381:Intermediate Filament Proteins / Q000032:analysis; D009412:Nerve Fibers / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000032:analysis; D064231:Nestin; D009434:Neural Pathways / Q000473:pathology; D009436:Neural Tube Defects / Q000469:parasitology / Q000473:pathology / Q000601:surgery; D012016:Reference Values; D009418:S100 Proteins / Q000032:analysis; D013126:Spinal Nerve Roots / Q000473:pathology*; D050497:Stillbirth; D016708:Synaptophysin / Q000032:analysis
D005904:Glial Fibrillary Acidic Protein; D007381:Intermediate Filament Proteins; C577484:NES protein, human; D009419:Nerve Tissue Proteins; D064231:Nestin; D009418:S100 Proteins; D016708:Synaptophysin