A standard lumbar puncture may be impossible for many anatomic or technical reasons. Previous accounts of caudal epidural anesthesia and other procedures via the sacral hiatus prompted us to test if image‐guided percutaneous trans‐sacral hiatus access to the lumbosacral subarachnoid cistern would be anatomically feasible. To study vertebral canal morphometry and curvature, we analyzed midsagittal computed tomography‐myelogram images of 40 normal subjects and digitally measured sacral curvatures between S1 to S5 and S2 to S4 using two methods whereby a lower angle signifies a straighter sacrum. We measured midsagittal vertebral canal area, hiatus width, dural sac termination levels, and distance from sacral hiatus to the dural sac tip (needle distance). Subjects were F:M = 25:15, with a mean age of 44.9 years. The two S1–S5 full sacral curvature mean angles were 57.3° and 60.4°. Almost all sacral hiatuses were at S4, and dural sac terminations were at S1–S2. The mean S2–S4 sacral curvature was 25.1°, and the mean needle distance was 57.7 mm. Using two‐way analysis of variance, there were significant sex differences for needle distances (p = .001), and full and limited sacral curvatures (p = .02, and p = .046, respectively). There were no significant linear regression correlations between age and sacral curvature, needle distance, canal area, or hiatus width. Therefore, despite a frequently prominent full sacral curvature, the combination of S1–S2 dural sac termination plus a relatively straight trajectory of the lower vertebral canal between S2 and S4 support the theoretical feasibility of percutaneous trans‐sacral hiatus and vertebral canal access to the lumbosacral cistern using a standard spinal needle.
Introduction/Aims
Standard fluoroscopic lumbar puncture (LP) can be impossible in patients with severe spinal deformities from spinal muscular atrophy (SMA) who require intrathecal nusinersen therapy. There usually exists a straight trajectory in the lower sacral canal (SC) that could allow image‐guided percutaneous transsacral hiatus puncture of the lumbosacral dural sac. In this study we determine whether sacra are comparatively straighter in SMA patients (SMAps) vs healthy controls (HCs), which may facilitate unhindered transsacral hiatus spinal needle insertion for intrathecal nusinersen therapy.
Methods
We retrospectively analyzed lumbosacral spine computed tomograms (CTs) or CT‐myelogram images of 38 SMAps and age‐ and sex‐matched HCs. We digitally measured ventrodorsal sacral curvatures, SC surface areas, dural sac termination levels, and distances from sacral hiatus to the most caudad aspects of dural sacs (“needle distance”).
Results
Mean ages of HCs and SMAps were 32.7 and 31.7 years, respectively, with dural sacs terminating at similar levels. Mean values for morphometrics were: (a) midsagittal SC surface area for HCs = 701.2 mm2, and for SMAps = 601.5 mm2 (not statistically significant [ns]); (b) using a “line method,” sacral curvature for HCs = 61.9°, and SMAp = 35.7° (P = .0009), and was similar when using an “angle summation method”; (c) width of sacral hiatus for HCs = 14.9 mm, and SMAps = 15.0 mm (ns); and (d) “needle distance” for HCs = 54.7 mm, and SMAps = 49.9 mm (ns).
Discussion
SMAps have significantly straighter sacra compared with HCs, which theoretically renders them more amenable to percutaneous transsacral hiatus puncture of the dural sac.
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