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7 Advanced Imaging: Spinal Surgery

Stephanie Nykamp

Myelography medium has been associated with a higher risk of post‐myelographic
Although computed tomography (CT) and magnetic resonance seizures [10,11]. When fluoroscopy is unavailable or myelography
imaging (MRI) have replaced myelography in many institutions, is performed in the CT suite, the cervical technique is often used as
myelography remains an excellent modality for localizing spinal it is easier to perform than lumbar injection [12].
cord disease when other modalities are unavailable. Orthogonal In cases of severe spinal cord swelling, as is seen in most acute
survey and post‐myelogram images of the entire region of interest intervertebral disc extrusions, cervical injection frequently fails to
should be performed. Postcontrast ventrodorsal oblique views are fully outline the lesion because contrast medium will not flow cau­
frequently advantageous for the circumferential localization of dal to the affected spinal cord. Raising the head and neck can
extradural lesions [1,2]. encourage contrast medium to flow caudally but if unsuccessful a
Myelography is performed by injection of a nonionic iodinated lumbar puncture may be needed to outline the lesion [12].
contrast medium (0.3–0.45 mL/kg) into the subarachnoid space.
Iohexol (which contains 240 mg iodine per milliliter) and iopami­ Lumbar Technique
dol (200 mg of iodine per milliliter) are commonly used, safe, and This technique is often preferred because it is associated with a
effective contrast agents [3–5]. The ideal iodine concentration has lower risk and it provides higher‐quality myelograms for thora­
been reported to be 200 mg/mL but higher concentrations (up to columbar lesions [13]. Because the dural sac ends blindly in the
350 mg/mL) have been used with no increase in complication rate lumbar region it is possible to pressurize the injection, forcing con­
[6,7]. Myelography can be performed at either the cerebellomedul­ trast medium past the swollen area of spinal cord and helping to
lary cistern or in the caudal lumbar region. Myelography is always outline the entire lesion and aid accurate localization. Although
performed under general anesthesia using aseptic technique. A 22G fluoroscopy is not required, it is useful for aiding needle place­
spinal needle is commonly used and a spinal needle is preferred ment. Lumbar injection is most commonly performed between
because the short bevel minimizes concurrent injection into the L4–L5 and L6–L7 with L5–L6 being the preferred site. Previous
epidural space. work has shown that it can be performed at any lumbar site with­
out increased risk of complication but is not typically recom­
Cervical Technique mended [14]. If fluoroscopy is not available, a radiograph should
The technique for performing puncture of the cerebellomedullary be obtained after initial placement of the needle but prior to enter­
cistern has been well described previously [8]. Briefly, the head ing the vertebral canal to confirm the site of injection. Once the
should be flexed and the needle placed on the midline between the needle has been placed in the vertebral canal a small test injection
occipital protuberance and the wings of the atlas. The bevel should (0.5–1.0 mL) can be made to confirm appropriate placement prior
be directed caudally and the needle advanced slowly with the mye­ to injecting the full contrast dose.
lographer stopping frequently, withdrawing the stylet, and checking Needle placement can be achieved by a paramedian or median
for cerebrospinal fluid (CSF) flow as a distinctive “pop” when enter­ approach (Figure 7.1) using a 22G spinal needle of appropriate
ing the dura is not always encountered [3]. Once flow of CSF is length. For the paramedian approach the needle is placed lateral to
established contrast medium should be injected slowly. Raising the the spinous process and angled craniomedially, entering the suba­
head will aid the caudal flow of contrast medium. Once the injec­ rachnoid space at an oblique angle (approximately 45°). The skin is
tion is complete this can be achieved by tilting the radiographic entered at the level of the spinous process with the needle directed
table or by placing the patient in sternal recumbency with the head ventral until it rests on the lamina and then walked off the lamina in
elevated [9]. It should be noted that cervical injection of contrast a craniomedial direction into the vertebral canal. On fluoroscopy or

Current Techniques in Canine and Feline Neurosurgery, First Edition. Edited by Andy Shores and Brigitte A. Brisson.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/shores/neurosurgery

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