Gestation-related reduction in lumbar cerebrospinal fluid volume and dural sac surface area

Facilitation of the spread of neuraxial anesthesia in pregnant women may be attributable in part to compression of the dural sac by the engorged epidural venous plexus. In this study, we used magnetic resonance imaging to examine pregnancy-induced changes in the lumbosacral cerebrospinal fluid (CSF) volume and dural sac surface area.

Magnetic resonance images of 18 healthy women (mean age 29 yr, mean height 158 cm, and mean weight 58 kg) were obtained to measure lumbosacral CSF volume and dural sac surface area in the nonpregnant and pregnant states (median 36 wk gestation [31-39]) and the paired images were compared.

The mean lumbosacral CSF volume and dural sac surface area in the nonpregnant state were 39.6 +/- 5.8 mL and 11.0 +/- 0.8 cm(2), respectively. Pregnancy was associated with compression of the dural sac, resulting in a significantly reduced mean CSF volume (33.2 +/- 6.2 mL) and dural sac surface area (9.9 +/- 1.0 cm(2)) in all subjects (P < 0.001). The mean change in CSF volume and dural sac surface area was 16.7% +/- 0.8% and 10.0% +/- 0.5%, respectively. Gestational week (between 31 and 39 wk) correlated significantly with the reduction in CSF volume (rho = 0.74, P < 0.001) and dural sac surface area (rho = 0.66, P < 0.01).

These findings indicate an association between gestational week (Weeks 31-39) and a reduction in both CSF volume and dural sac surface area. These reductions may, at least in part, explain the facilitation of the spread of intrathecal anesthesia in pregnant women.