Morphometric parameters and histological study of the filum terminale of adult human cadavers and magnetic resonance images

Abstract

Background: Morphology and histology of filum terminale (FT) has a role in the pathophysiology of tethered cord syndrome (TCS). This research was implemented to investigate the morphometric parameters and histological structure of normal FT in adult human cadavers and magnetic resonance imaging (MRI) scans to correlate them with the pathophysiology of TCS. Materials and methods: Twenty five adult human cadavers (15 males, 10 females) and 100 MRI echo scans of lumbosacral region (50 males and 50 females), were used in this study. MRI patients were divided into 21-40 and 41-60 age groups. The cadavers were dissected at the prone position to explore their fila. The length of FT, filum terminale internum (FTI), filum terminale externum (FTE), vertebral level of beginning, dural piercing and termination of FT, and the initial, midpoint, and mid-FTE diameters were determined. Four segments were excised from lower conus, upper, middle, and lower thirds of FT. The specimens were processed for light microscopic examination. Statistical analysis was done for these parameters. Results: MRI morphometrical parameters of FT, except FTI length, revealed no age effect or sex differences, where length of FTI, FTE, initial diameter, level of conus medullaris termination (CMT) and dural sac termination (DST) were 174.1 ± 16.8, 75.8 ± 9.5, 1.6 ± 0.21, L1-2 and S2U in males and 166.9 ± 18.9, 74.1 ± 9.3, 1.53 ± 0.25, L1-2 and S2M vertebrae in females, respectively. However, non-significant sex difference was observed in morphometric parameters of cadaveric FT, where length of FTI and FTE, initial diameter, CMT and DST levels were 164.2 ± 11.6, 76.7 ± 8.1, 1.7 ± 0.14, L1L and S2U vertebrae in males and 159.2 ± 10.1, 71.02 ± 7.3, 1.6 ± 0.29, L1L and S2U in females, respectively. Moreover, CMT below L2 vertebra was seen in 5% of MRI scans and 8% of cadavers. Also, the initial diameter of FT > 2 mm was recorded in 7% of MRI and 8% of cadaveric cases. Histologically, the structure of FT showed gradual reduction in nervous, glial, and vascular tissues with converse increase in collagen content in FTE compared with those of FTI. Conclusions: Knowledge of the morphometric parameters and the histological structure of FT are necessary for clinicians who dealing with diagnosis or treatment of tethered cord syndrome.