Ultrasonographic quantification of spinal cord and dural pulsations during cervical laminoplasty in patients with compressive myelopathy

Abstract

Purpose: Pulsatile movements of the dura mater have been interpreted as a sign that the cord is free within the subarachnoid space, with no extrinsic compression. However, the association between restoration of pulsation and adequate decompression of the spinal cord has not been established. The present study investigated the relationship between the extent of spinal cord decompression and spinal cord and dural pulsations based on quantitative analysis of intraoperative ultrasonography (US).

Methods: Eighty-five consecutive patients (55 males, 30 females; mean age, 64 ± 13 years) who underwent cervical double-door laminoplasty to relieve compressive myelopathy were enrolled. Spinal cord decompression status was classified as: Type 1 (non-contact), the subarachnoid space was retained on the ventral side of the cord, Type 2 (contact and apart), the cord showed both contact with and separation from the anterior element of the cervical spine, or Type 3 (contact), the cord showed continuous contact with the anterior element of the cervical spine. Spinal cord and dura mater dynamics were quantitatively analyzed using automatic video-tracking software. Furthermore, the intensity of spinal and dural pulsation was compared with the recovery of motor function at 1 year after surgery as measured by increase in the Japanese Orthopaedic Association Cervical Myelopathy Evaluation Questionnaire (JOACMEQ).

Results: Spinal cord pulsation amplitude ranged from 0.01 to 0.84 mm (mean 0.30 ± 0.16 mm) and dural pulsation amplitude ranged from 0.01 to 0.38 mm (mean 0.14 ± 0.08 mm). Average spinal cord pulsation amplitude in Type 2 patients was significantly larger than that in the other groups, whereas, average dural pulsation amplitudes were similar for all three groups. There was a significant correlation between spinal cord and dural pulsation amplitudes in Type 1 patients, but not in Type 2 or Type 3 patients. Type 3 patients showed a particularly poor correlation between spinal cord and dural pulsations. Spinal cord pulsation amplitude was moderately correlated with the recovery of motor function evaluated by JOACMEQ.

Conclusion: The present results suggest that restoration of dural pulsation is not an adequate indicator of sufficient decompression of the spinal cord following a surgical procedure.

Fig. 1

Decompression status of the spinal cord was classified into three types. In Type 1 (noncontact), the subarachnoid space was retained on the ventral side of the spinal cord (a). In Type 2 (contact and apart), the spinal cord showed both contact with and separation from the anterior element of the cervical spine in synchrony with cord pulsations (b). In Type 3 (contact), the cord showed continuous contact with the anterior element of the cervical spine (c)

Fig. 2

Representative images of spinal cord and dural pulsations tracked on intraoperative US. Regions of interest were set at the central echo of the spinal cord, a constant feature of the normal cord, and on the dorsal midpoint of the dura mater (a). Pulsatile movements of the dura mater (b) and the spinal cord (c) were automatically traced on the intraoperative US. Each pulsation was synchronized with the heart beat

Fig. 3

Spinal cord and dural pulsation amplitudes for each type of decompression. Average spinal cord pulsation amplitudes were significantly larger in Type 2 patients than in patients with other types of decompression (a); (one-way ANOVA with Bonferroni’s post hoc test, *P < 0.05, **P < 0.001). However, there were no significant differences in dural pulsation amplitudes among the different decompression groups (b)

Fig. 4

Relationship between spinal cord and dural pulsations. A significant correlation was observed between spinal cord and dural pulsation amplitudes in Type 1 patients (a); (correlation coefficient = 0.487, P = 0.001). However, there was no correlation in Type 2 (b) and Type 3 patients (c)

Fig. 5

The dura mater can show obvious pulsations despite minimal spinal cord pulsations. This patient with Type 3 decompression showed dural pulsations that were synchronized with the heartbeat (arrows), even though the spinal cord demonstrated minimal pulsations. Note that the dural pulsations are combined with large slow waves with a frequency corresponding to the respiratory rate (arrowheads)