Real-time ultrasonography of the spinal cord: intraoperative and postoperative imaging

Use of Intraoperative Ultrasound During Spinal Surgery

STUDY DESIGN

Review and technical report.

OBJECTIVE

Intraoperative ultrasound has been used by spine surgeons since the early 1980s. Since that time, more advanced modes of intraoperative imaging and navigation have become widely available. Although the use of ultrasound during spine surgery has fallen out of favor, it remains the only true real-time imaging modality that allows surgeons to visualize soft tissue anatomy instantly and continuously while operating. It is our objective to demonstrate that for this reason, ultrasound is a useful adjunctive technique for spine surgeons, especially when approaching intradural lesions or when addressing pathology in the ventral spinal canal via a posterior approach.

METHODS

Using PubMed, the existing literature regarding the use of intraoperative ultrasound during spinal surgery was evaluated. Also, surgical case logs were reviewed to identify spinal operations during which intraoperative ultrasound was used. Illustrative cases were selected and reviewed in detail.

RESULTS

This article provides a brief review of the history of intraoperative ultrasound in spine surgery and describes certain surgical scenarios during which this technique might be useful. Several illustrative cases are provided from our own experience.

CONCLUSIONS

Surgeons should consider the use of intraoperative ultrasound when approaching intradural lesions or when addressing pathology ventral to the thecal sac via a posterior approach.

Percutaneous ultrasonographic evaluation of the spinal cord after cervical laminoplasty

STUDY DESIGN

Prospective cohort study.

OBJECTIVE

To investigate the dynamic changes of cervical spinal cord with postural change after cervical laminoplasty by means of postoperative percutaneous ultrasonography.

SUMMARY OF BACKGROUND DATA

Many reports have been published about intraoperative ultrasonographic evaluation of the spinal cord. Few reports have described postoperative diagnostic ultrasonographic findings of the spinal cord after a previous laminectomy. To date, there are no studies that have examined the changes in pulsation pattern and intensity of the spinal cord at different body positions with percutaneous ultrasonography.

METHODS

Thirty-three patients after cervical laminoplasty were evaluated postoperatively by percutaneous ultrasonography of the cervical spinal cord. Ultrasonographic images were obtained from 5 different body positions sitting with neck neutral, sitting with neck flexion, sitting with neck extension, prone, and supine position.

RESULTS

The pattern and intensity of cervical spinal cord pulsation and the anteroposterior position of the cervical spinal cord changed according to posture. Pulsation of the cervical spinal cord was more common in sitting position, whereas wave motion was more common in supine position.Supine, prone, sitting with neck extension, sitting with neck neutral, and sitting with neck flexion position were ranked in descending order of spinal cord pulsating intensity. Subarachnoidal space ventral to the cervical spinal cord was more likely to appear in the supine position.

CONCLUSION

Assuming that good spinal cord pulsation represents good spinal circulation, these results suggest that the supine position will provide the most favorable condition for recovery of the cervical spinal cord.

The value of intraoperative ultrasonography in cervical corpectomy: assessment by postoperative computed tomography

OBJECTIVE

We assessed the value of intraoperative ultrasonography (IUS) in cervical corpectomy by using postoperative computed tomography (CT) for comparison.

METHODS

Twenty patients underwent a one-, two-, or three-level cervical corpectomy. The decompression was performed in a stepwise fashion, guided in each case by IUS findings until considered adequate. Each patient underwent postoperative CT to evaluate the accuracy of the IUS in guiding the decompression.

RESULTS

In the 20 patients who underwent corpectomy, IUS guided a complete lateral gutter decompression. No evidence of asymmetry and excessive bone removal was identified by IUS at the end of the procedure. IUS was not useful in assessing the adequacy of longitudinal decompression because of the absence of neural landmarks in the sagittal plane. Postoperative CT confirmed adequate decompression in all patients. The width of decompression at the posterior margin of the vertebral body ranged from 18 to 20 mm, with a mean of 19.2 mm.

CONCLUSION

We conclude that IUS is helpful and reliable in performing a properly centered, thorough, lateral decompression in cervical corpectomy. A limited corpectomy can be started under visual guidance and then enlarged after IUS findings until complete decompression of the neural elements has been achieved. This approach avoids the problems of asymmetry, inadequate decompression, and excessive bony removal that could lead to endangerment of the vertebral artery and possible failure of the reconstruction. The accuracy of the IUS was confirmed in this study by postoperative CT.

Intraoperative ultrasound imaging in lumbar disc herniation surgery

The diagnosis of lumbar disc herniation has improved with metrizamide rhizography and CT. Also, visualization of the operative site has been enhanced with use of the operating microscope. However, evaluation of the completeness of herniated disc removal can be difficult, especially in the case of medially located lesions. Also, intradural extension of the herniation can be impossible to rule out in some cases without intradural exploration. Intraoperative ultrasound imaging is safe, rapid and readily available in most hospitals. Its application to real-time imaging control of 10 selected cases of herniated lumbar disc showed that the herniated material could be visualized in relation to the interspace and dural sac in all cases. The effect of removal of the herniation on nerve root compression could also be evaluated. Especially in cases involving extension of the herniation to the medial region under the dura, or into the intradural space, the removal of herniated material could be adequately confirmed without the need for further manipulation with surgical instruments. With appropriate transducer design and frequency, the method can be applied to microsurgical technique to rule out sequestration outside of the surgical exposure.

Equipment Considerations for Intraoperative Ultrasound

For most ultrasound sections and especially for those who are just beginning intraoperative ultrasound, it will be necessary to perform these studies with scanners brought from the general ultrasound section. The purpose of this article is to familiarize sonographers with the preparation of equipment for intraoperative ultrasound: choosing and sterilizing the most appropriate transducer, and ensuring that the scanner is clean and electrically safe for operating room use.