Tap That
Author: Justin Wang MD, Editor: Jeffery Greco MD
Ultrasound Guided Lumbar Puncture
Point of care ultrasound now considered standard of care for many bedside procedures. So why not utilize it for lumbar punctures, especially patients with difficult to appreciate landmarks?
Benefits of US Guidance
Can clearly identify anatomical landmarks/measurements1,2
Spinous processes (i.e. midline)
Interspinous spaces (desired target)
Distance from skin to ligamentum flavum (length of needle required to obtain CSF)
Decreased procedure time, attempts, failures, complications and pain during procedure1,2,3
Useful for patients with difficult/nonpalpable landmarks
Obese
Scoliosis
Hx of spinal surgery
Hx of difficult lumbar puncture
Traditional Technique (Transverse + Longitudinal Views)1,2,3
Can use linear probe in more thin/pediatric patients (better resolution) but will likely require curvilinear
Most usage of US in lumbar puncture in current clinical practice is merely to identify the ideal needle insertion site/angle and expected distance to subarachnoid space
Transverse view
Goal: Identify midline
Start by identifying sacrum
Sacrum: hyperechoic, serrated appearance due to fused bones
Slide probe superiorly identify L5-L2 sequentially by visualizing spinous processes
Spinous processes: Small, hyperechoic, crescent/rim shaped tips of the spine that casts a deep vertical shadow
If having trouble locating spinous process, look for the paraspinal muscles and tendons attaching to it on either side
Mark perpendicular to probe at each level at the location of the spinous process to denote midline
Longitudinal view
Goal: Identify the widest interspinous space (L3/L4 vs L4/L5) and measure the distance from skin to ligamentum flavum
Visualize the spinous processes, interspinous spaces, ligamentum flavum, and posterior longitudinal ligament (PLL)
Spinous processes: Hyperechoic tombstone appearance with shadowing deep
Ligamentum flavum/PLL: hyperechoic lines deep to interspinous spaces between spinous processes
Mark targeted interspinous spaces on either side of probe
Identify distance from skin to ligamentum flavum to estimate the length of needle required
Once views and markings are established, the patient must remain in the same position
Alternative techniques
Paramedian view/approach1,4
Paramedian view used instead to identify lamina and ligamentum flavum in the interlaminar space
Probe will be oriented longitudinally and laterally on either side of midline
Lamina will appear as round shaped hyperechoic humps with ligamentum flavum between each lamina
Erector spinae muscles can also be visualized above lamina
Mark off lamina on either side of probe as you would do on a traditional longitudinal view
After identifying desired target/interlaminal space, spinal needle should be angled 10-15° toward midline and 10-15° toward cephalad
Some studies show up to 30-40% higher success rate on first pass through paramedian approach4
Larger target
Avoids interspinous ligaments
Paramedian view may also be used to mark off lamina locations and combined with transverse view markings of midline for the traditional spinal needle approach
Real Time US Guidance
Described since 2001, but few studies evaluating use yet.1
Some studies propose using additional needle guided system to better visualize needle approach in US views5
Usually performed using an oblique, in-plane, paramedian approach1
Start with identifying the widest interspinous space between L3-L5 in paramedian view
Then rotate probe 45 degrees towards midline to obtain an oblique paramedian view
US view should be from the spinous process of the superior vertebra on one side of the probe to the lamina of the inferior vertebra on the other end of the probe
Slide probe 1-2 cm craniomedially to allow easier needle insertion underneath probe
Spinal needle should be inserted in plane with ultrasound beam
Typically will not be able to visualize needle tip as it penetrates the ligamentum flavum due to shadowing artifact of the spinous process
Insertion technique similar to paramedian approach but without real time ultrasound guidance