Purpose: To establish normal values for lumbosacral dural sac dimensions with magnetic resonance (MR) imaging and to use these values to assess the sensitivity and specificity of dural ectasia as a marker for Marfan syndrome.
Materials and methods: MR imaging was performed to measure dural sac diameter (DSD) from L1 through S1 in 44 adult patients with Marfan syndrome and in 44 matched control subjects. DSD values were corrected for vertebral body size, yielding dural sac ratios (DSRs). The control subjects served to establish the upper limit of normal DSR values at the L1 through S1 levels.
Results: Cutoff values for normal DSRs for L1 through S1 were 0.64, 0.55, 0.47, 0.48, 0.48, and 0.57. Significant DSR differences were shown at all levels between patients with Marfan syndrome and control subjects (P <.001 at all levels). At L1 through S1, the sensitivity of dural ectasia as a marker for Marfan syndrome was 45%-77%, and the specificity was 95% or greater. By combining levels L3 and S1, dural ectasia as a marker for Marfan syndrome yielded a sensitivity of 95% (42 of 44 patients) and a specificity of 98% (43 of 44). The presence of dural ectasia excelled, compared with the presence of other Marfan syndrome manifestations in the patient population.
Conclusion: Abnormal DSR values at L3 or S1 can be used to identify Marfan syndrome with 95% sensitivity and 98% specificity.