Locate the intervertebral space, skin to interspace, ligamentum flavum, epidural space
Use 7-9 mHz probe
Place probe in longitudinal just paramedian
Measure from skin to interspace
then do transverse
Probe orientation: In lumbar spinal imaging, two main probe orientations are used: the transverse and the longitudinal views. The goal of the transverse view is to determine an accurate anatomic midline by identification of the hyperechoic spinous process. This view is obtained by placing the probe perpendicular to the long axis of the spine (pic2). The purpose of this cross-sectional image is to identify the lumbar spinous process and center it on the image display. The bony spinous process will appear as a “hyperechoic” white convex rim with an anechoic shadow. We recommend looking for a solitary anechoic shadow if the hyperechoic rim is not seen, as this may be the only landmark visualized.
Often, paired hyperechoic structures (transverse processes, facet joints, or laminae) may be visualized surrounding the spinous process, adding support for midline confirmation (pic3).
Once the midline is localized, it should be marked and labeled as described in the next section.
Once the midline landmarks are identified, the longitudinal view should be obtained, always maintaining reference to the midline located in the transverse view. The goal of the longitudinal view is to determine the spinal interspace while placing the probe’s long axis parallel to the long axis of the spine (pic4). Again, the key structure to identify is the spinous process, which will appear as a hyperechoic convexity with a deep anechoic shadow (pic5). The spinous process should be the most superficial hyperechoic structure, and we recommend moving the probe in a lateral direction in an attempt to confirm that the structure is, in fact, the superficial spinous process and not a similar-appearing deeper and lateral structure.
Once the spinous process is identified, the probe should be moved cephalad and caudad, always maintaining the previously identified midline. If midline position is not maintained, inadvertent imaging of the similar-appearing lateral transverse processes may occur, leading to improper pre-puncture localization. The goal is to identify a contiguous spinous process and then center the probe and image between the contiguous spinous processes over the hypoechoic grey interspace (pic5). This interspace is the optimal location for needle insertion for lumbar puncture.
Physicians more experienced with identification of spinal anatomy may be able to locate deeper structures through this visualized interspace, such as the ligamentum flavum, which is the fibrous structure that lies just superficial to the epidural space, dura, and subarachnoid space. Ultrasound imaging can be used to measure the depth from the skin to this ligament and can be an accurate adjunct to guide spinal needle introduction.10 Once the interspace is identified, it should be marked and labeled as described below.
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- Lin M, Washington C. Tricks of the Trade: Ultrasound-Guided Lumbar Puncture. ACEP News 2007 2007(February):23.
Above from ACEP NEWS Sept 2007
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