Use of Intraoperative Ultrasonography in Spinal Surgery

by Beatrix Nanai, DVM and Ronald Lyman, DVM, DACVIM

abstract from The Journal of Veterinary Internal Medicine.

The purpose of this retrospective study was to 1) describe the intraoperative appearance of various canine pathological spinal conditions, and 2) to investigate how intraoperative ultrasonography assisted in modification of surgical and postoperative treatment plans.

Twenty five dogs undergoing spinal surgery received intraoperative ultrasound examination. Presenting neurological signs included spinal pain, ataxia. paraparesis. paraplegia, tetraparesis and root signature. The surgical procedures included continuous dorsal laminectomies (10), hemilaminec-tomies (20). and one dorsal laminectomy. Final neurological diagnoses were Hansen type II discs (8), Hansen type I disc (7), caudal cervical vertebral instability and malformation (9), spinal cord neoplasia (astrocytoma in one dog and anaplastic neoplasia in another dog), discospondylitis (1), granulomatous meningoencephalitis (1) and a nerve sheath mass (1). There was one normal lumbar spine imaged. A Phillips® 5000 HDI ultrasound unit (Ultrasource®. Grand Rapids, Michigan) was used with a linear 12-5 MHz broad band transducer and a sterile transducer cover. Longitudinal images were obtained.

The detectability of the lesions were 100%. All intervertebral disc lesions were hyperechoic. the GME and the nerve sheath mass were isoechoic, and the tumors were mixed hyper and hypoechoic. Power Doppler imaging technique enabled visualization of the spinal cord microcirculation in all patients. The signal intensity, vessel size and pulsatility were examined following decompression. The normal lumbar and the decompressed cervical spinal cord had orange-red flow on Power Doppler imaging, with large pulsating vessels. The decompressed lumbar cord had either orange>red flow with large pulsating vessels (5), or red>orange flow with medium pulsating vessels (1), and red flow with small pulsating vessels (4). Direct change in the treatment plans were in two IVD protrusions by extending the HL cranially and caudally, in one of the IVD extrusions by extending the HL site dorsally to retrieve the disc material from the opposite side, and in the GME patient, where the intramedullary spinal pathology was discovered by the ultrasound and aspirated under ultrasonographic guidance.

This study suggests that intraoperative spinal cord imaging by ultrasound is a useful and viable technique in the diagnosis and management of spinal cord lesions. Treatment plans were directly changed due to the sonographic findings in 4 of the 25 patients (16%). More studies are currently underway to examine the usefulness of this technique in the quantitative assessment of the spinal microcirculation and its relationship to prognosis following spinal surgeries.

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