Anatomic study of the filum terminale and its correlations with the tethered cord syndrome

To evaluate the intradural anatomic features of the filum terminale (FT) in fresh human cadavers, analyzing morphological parameters relevant for the diagnosis of the tethered cord syndrome.

Forty-one fresh cadavers were dissected, and the following parameters were evaluated: cadaver height, weight, and age, FT length, FT diameters at the initial point and midpoint, and topographic relationships of the initial and fusion points of the FT to the adjacent vertebrae.

The mean FT length was 156.44 mm (range, 112.8-211.1 mm), the mean initial diameter was 1.38 mm (range, 0.4-2.5 mm), and the mean midpoint diameter was 0.76 mm (range, 0.1-1.55 mm). Four specimens (9.76%) exhibited FT thicknesses of more than 2 mm at their initial points. The FT most frequently started at the middle L1 level (19.51%) and fused with the dura mater at the upper S2 level (31.71%). Two fila (4.88%) started below the L2 level. Statistically significant correlations were observed (Pearson correlation, P < 0.05) between specimen weight and height (P = 0.019), initial point and midpoint diameters of the FT (P < 0.001), initial vertebral level and specimen height (P = 0.012), and initial and fusion vertebral levels (P = 0.004).

Variation ranges were large for almost all anatomic parameters of the FT. Six cadavers (14.63%) in our study fulfilled one of the anatomic diagnostic criteria for tethered cord syndrome. Neurosurgeons must remember the normal variations in the anatomic features of this region when establishing the diagnosis of tethered cord syndrome or performing surgical procedures involving the caudal part of the dural sac.