Is a filum terminale with a normal appearance really normal?

Tethered spinal cord is defined as a condition in which the conus medullaris ends at a level below the L1-2 intervertebral space. The spinal cord is considered to be tethered when there is a thick filum terminale or low-lying conus medullaris. It has also been reported that a normal level of the conus medullaris and normal thickness of the filum terminale do not mean that there is no cord tethering. In this investigation, we examined 21 fila terminalia; 5 of them were taken from cadavers, and these were used as a control group (group 1; n/n), 8 from patients with a normal appearance of the filum terminale but with clinical symptoms (incontinence) and pathologic results of a urodynamic study (group 2; n/ab), and 8 from patients with an abnormal appearance of the filum terminale and with clinical symptoms (group 3; ab/ab). Interestingly, we found that while fila terminalia in the control group were made up mainly of collagen fibers, more connective tissue with dense collagen fibers, some hyalinization and dilated capillaries were noticed in the fila from group 2. Our results suggest that these histological features may reflect a decreased elasticity within the filum terminale, resulting in a tethering effect on the lower conus in otherwise normal physiological conditions. These findings lead us to reconsider sectioning of the filum terminale in incontinent patients with normal results in radiological studies, whose condition is called "nonneurogenic neurogenic bladder."