Scanning Technique

• Position the patient sitting, with the trunk flexed to widen the interspinous space.
• Palpate the iliac crest on each side and mark the intercristal line (approximately at the L3-4 level).
• Select a curved 2-5 MHz transducer and place the transducer in the transverse plane at the level of the L3 or L4 vertebra.
• Apply ample acoustic gel to ensure good transducer-to-skin contact and eliminate potential for air trapping (artifact).
• Adjust the appropriate depth of field (usually > 6-8 cm), focus range (usually > 5 cm) and gain.

Localization of the Epidural / Subarachnoid Space

• The transverse ultrasound image reveals a superficial midline hypoechoic bony shadow that represents the posterior contour of the spinous process.
• Each lamina is visualized as a hyperechoic line anterolateral to the spinous process).
• Each transverse process is often visualized as a hyperechoic line located more lateral and anterior to the lamina.

Transverse Scan of the Spinous Process

• The transverse ultrasound image reveals a superficial midline hypoechoic bony shadow that represents the posterior contour of the spinous
• Position the transducer so that the midpoint of the transducer is aligned with the midpoint of the spinous process.
• Mark the skin surface locations of the midline spinous process at several vertebral levels.
• Take note of the distance from the skin to:
  1. The spinous process
  2. The lamina
  3. The transverse process

Next, visualize the interspinous space by moving the transducer cephalad or caudad until the bony hypoechoic shadow of the spinous process disappears.

Transverse Scan of the Interspinous Space

• Assess the size (width) of the interspinous space by slowly moving the transducer cephalad and caudad in the transverse plane. Alternatively, slightly angle the transducer cephalad and caudad to determine the size of the interspinous space.
• A narrow space is suggested when the bony shadows from two contiguous spinous processes are visualized with minimal transducer angulation.
• Note the distance from the skin to the ligamentum flavum and the dura. It is not always possible to visualize the ligamentum flavum and the dura as two separate structures.
• It is common to see a single hyperechoic line representing the ligamentum flavum/dura complex.
• Finally, record the level of the interspinous space by placing a mark on each end of the transducer.

Anatomical Correlation

Transverse View of the Spine



Transverse View of the Interspinous Space

Nerve Localization

Coming Soon

Needle Insertion Approach

Coming Soon

Local Anesthetic Injection

Coming Soon

Clinical Pearls

Ultrasound imaging of the spine prior to the actual neuraxial block procedure offers the following advantages:

• Accurate determination of the spinal levels and the interspaces (counting cephalad from the sacrum).
• Accurate localization of the posterior midline (location of the spinous processes).
• Assessment of the best possible interspace available for needle insertion for neuraxial block.
• Determination of the skin to ligamentum flavum/dura distance prior to needle insertion.
• Assess anatomical abnormality and pathology in patients with scoliosis, previous laminectomy and instrumentation.

Nerve Localization

1. Counting the Spinal Levels

• Perform a paramedian longitudinal scan (figure) to visualize the sacrum and the interlaminar spaces individually. This is a more accurate method of determining the actual spinal levels rather than estimating the level of the L3-4 interspace using the iliac crest.
• The sacrum is identified as a continuous hyperechoic line caudally (white arrowheads in the figure below) and a bone shadow below.
• Once the interlaminar space between L5 and sacrum is identified, the L5 level can be marked on the skin.

2. The Longitudinal Paramedian Window

• If midline interspinous space access is limited as suggested by ultrasound, the paramedian approach is indicated.
• Place the curved transducer in the longitudinal plane lateral to the spinous processes.

Longitudinal Paramedian Scan of the Interlaminar Space

LF/dura = ligamentum flavum
PBVB = posterior border of vertebral body
PLL = posterior longitudinal ligament

• The laminae of two contiguous vertebrae are identified as hyperechoic bony outlines with corresponding bone shadows below (figure above).
• Within this longitudinal window between the two laminae, seek the hyperechoic ligamentum flavum and dura (more superficial and posterior) and the posterior longitudinal ligament and the posterior part of the vertebral body (more anterior).
• The size of the paramedian window (i.e., the length of the hyperechoic ligamentum flavum/dura complex) is a good indication of the ease of needle access to this space.
• More laterally, the adjoining facet joints (superior and inferior articular processes) form a continuous curved hyperechoic line (figure above). The ligamentum flavum, dura and posterior longitudinal ligament are no longer visualized in this view.

Longitudinal Paramedian Scan of the Facets

• When the transducer is moved more laterally, the transverse processes (TP) are visualized in the longitudinal view (figure).
• The psoas muscle is seen in between the transverse processes.

Longitudinal Paramedian Scan of the Transverse Processes

ESM = erector spinae muscle
PsMM = psoas major muscle
TP = transverse process

• Once the facets and/or transverse processes are visualized, this is an indication that the transducer has moved too laterally. The next step is to move and orient the transducer medially to capture the longitudinal view of the laminae and the interlaminar space.
• In young adult subjects, it is possible to see epidural vascular pulsations. Epidural pulsations are especially conspicuous in the epidural space of neonates and infants.
• Inspect the paramedian window on each side of the spine and select the side and the interlaminar space that is most accessible for needle entry.

PLL = posterior longitudinal ligament

D = dura
LF = ligamentum flavum
PLL = posterior longitudinal ligament
TP = transverse process

D = dura
LF = ligamentum flavum
PLL = posterior longitudinal ligament

PLL = posterior longitudinal ligament

Catheter Insertion

Coming Soon

Image Gallery

1. Characteristics of the L2-3 Interspinous Space

Transverse Scan at the L2 Spinous Process

Transverse Scan at the L2-3 Interspinous Space

PLL = posterior longitudinal ligament
TP = transverse process

Longitudinal Paramedian Scan at the L2-3 Interlaminar Space

LF/dura = ligamentum flavum
PBVB = posterior border of vertebral body
PLL = posterior longitudinal ligament

Distinguishing features:

1. The LF/dura and PLL are visualized in the interlaminar space.
2. The interlaminar space is lateral to the spinous process and medial to the facet joints.

Longitudinal Paramedian Scan at the L2-3 Facet Location

Distinguishing features:

1. The facet joints form a continuous curved hyperechoic line.
2. The LP and the dura are no longer visible.

Longitudinal Paramedian Scan at the L2-3

Transverse Process Location

Distinguishing features:

1. Each transverse process (TP) casts a hypoechoic bony shadow underneath a hyperechoic bony outline.
2. The psoas muscle (PsMM) is visualized between the transverse processes.

2. Characteristics of the L5-Sacrum Interspinous Space

Transverse Scan at the L5-S1 Interspinous Space

Transverse Scan at the Sacrum

Longitudinal Paramedian Scan at the L5-S1 Interspace

LF/dura = ligamentum flavum/dura complex

3. Post Laminectomy

Scan over the laminectomy scar to capture both the transverse and longitudinal view. Notice the absence of spinous processes.
Arrowheads = laminectomy scar

Longitudinal scan showing the hyperechoic dura sac which is pulsatile in real time scanning; the subarachnoid space is anechoic.

Transverse scan showing the circular dura sac (arrowheads); it is pulsatile in real time.

4. Lumbar Scoliosis (Convex to the Right)

A patient with severe scoliosis with an obvious convex curvature to the right. The midline interspinous space is difficult to define by palpation alone.

A. A transverse scan showing the midline spinous process (SP) and the lamina (L) on the right side. The lamina on the left side is not visualized. The transverse processes (TP) are visualized on both sides.

B. A transverse scan showing the midline interspinous space (note the absence of the bone shadow) and visualization of the ligamentum flavum/dura (LF/D) complex (a hyperechoic line) and the posterior longitudinal ligament/vertebral body (PLL/VB) complex (a hyperechoic line) deeper. Note the PLL/VB line is not midline but shifted to the right indicating the scoliotic spine is convex to the right.

Video Gallery

Selected References

Adult Neuraxial Blocks

• Arzola C, Davies S, Rofaeel A, Carvalho JC: Ultrasound using the transverse approach to the lumbar spine provides reliable landmarks for labor epidurals. Anesth.Analg. 2007; 104: 1188-92.
• Ferre RM, Sweeney TW: Emergency physicians can easily obtain ultrasound /images of anatomical landmarks relevant to lumbar puncture. Am.J.Emerg.Med. 2007; 25: 291-6.
• Whitty RJ, Maxwell CV, Carvalho JC: Complications of neuraxial anesthesia in an extreme morbidly obese patient for Cesarean section. Int.J.Obstet.Anesth. 2007; 16: 139-44.
• Druhan SM, Shiels WE, Kang DR, Elton SW, Koranyi K: Successful sonographically guided drainage of epidural abscess. AJR Am.J.Roentgenol. 2006; 187: W512-W514
• Yoon JS, Sim KH, Kim SJ, Kim WS, Koh SB, Kim BJ: The feasibility of color Doppler ultrasonography for caudal epidural steroid injection. Pain 2005; 118: 210-4
• Peng P W, Rofaeel A. Using ultrasound in a case of difficult epidural needle placement. Can J Anaesth 2006; 53: 325-326.
• Ali M E, Laurito C E. Ultrasound guidance for epidural catheter placement: a coming of age? J Clin Anesth 2005; (17): 235-236.
• McLeod A, Roche A, Fennelly M. Case series: Ultrasonography may assist epidural insertion in scoliosis patients. Can J Anaesth 2005; (52): 717-720.
• Marhofer P, Greher M, Kapral S. Ultrasound guidance in regional anaesthesia. Br J Anaesth 2005; (94): 7-17.
• Peterson M A, Abele J. Bedside ultrasound for difficult lumbar puncture. J Emerg Med 2005; (28): 197-200.
• Yoon J S, Sim K H, Kim S J, Kim W S, Koh S B, Kim B J. The feasibility of color Doppler ultrasonography for caudal epidural steroid injection. Pain 2005; 118: 210-214.
• Chen C P, Tang S F, Hsu T C, Tsai W C, Liu H P, Chen M J, Date E, Lew H L. Ultrasound guidance in caudal epidural needle placement. Anesthesiology 2004; 101: 181-184.
• Grau T, Leipold R W, Fatehi S, Martin E, Motsch J. Real-time ultrasonic observation of combined spinal-epidural anaesthesia. Eur J Anaesthesiol 2004; 21: 25-31.
• Grau T, Bartusseck E, Conradi R, Martin E, Motsch J. Ultrasound imaging improves learning curves in obstetric epidural anesthesia: a preliminary study. Can J Anaesth 2003; 50:1047-1050.
• Lang S A, Tsui B, Grau T. New avenues of epidural research. Anesth Analg 2003; 97: 292-293.
• Grau T, Leipold R W, Delorme S, Martin E, Motsch J. Ultrasound imaging of the thoracic epidural space. Reg Anesth Pain Med 2002; 27: 200-206.
• Grau T, Leipold R W, Conradi R, Martin E, Motsch J. Efficacy of ultrasound imaging in obstetric epidural anesthesia. J Clin Anesth 2002; 14: 169-175.
• Moon S H, Park M S, Suk K S, Suh J S, Lee S H, Kim N H, Lee H M. Feasibility of ultrasound examination in posterior ligament complex injury of thoracolumbar spine fracture. Spine 2002; 27:2154-2158.
• Grau T, Leipold R W, Horter J, Conradi R, Martin E O, Motsch J. Paramedian access to the epidural space: the optimum window for ultrasound imaging. J Clin Anesth 2001;13: 213-217.
• Grau T, Leipold R W, Conradi R, Martin E. Ultrasound control for presumed difficult epidural puncture. Acta Anaesthesiol Scand 2001; 45: 766-771.
• Grau T, Leipold R W, Horter J, Martin E, Motsch J. Colour Doppler imaging of the interspinous and epidural space. Eur J Anaesthesiol 2001; 18: 706-712.
• Grau T, Leipold R W, Horter J, Conradi R, Martin E, Motsch J. The lumbar epidural space in pregnancy: visualization by ultrasonography. Br J Anaesth 2001; 86: 798-804.
• Grau T, Leipold R W, Conradi R, Martin E, Motsch J. Ultrasound imaging facilitates localization of the epidural space during combined spinal and epidural anesthesia. Reg Anesth Pain Med 2001; 26: 64-67.
• Nader-Djalal N, Reedy R, Bacon D R. Doppler guidance for epidural catheter placement. Reg Anesth Pain Med 1998; 23: 326-328.
• Rhodes D W, Bishop P A. A review of diagnostic ultrasound of the spine and soft tissue. J Manipulative Physiol Ther 1997; 20:267-273.

Pediatric Neuraxial Blocks

• Kil HK, Cho JE, Kim WO, Koo BN, Han SW, Kim JY: Prepuncture ultrasound-measured distance: an accurate reflection of epidural depth in infants and small children. Reg Anesth Pain Med 2007; 32: 102-6.
• Willschke H, Bosenberg A, Marhofer P, Willschke J, Schwindt J, Weintraud M, Kapral S, Kettner S: Epidural catheter placement in neonates: sonoanatomy and feasibility of ultrasonographic guidance in term and preterm neonates. Reg Anesth Pain Med 2007; 32: 34-40.
• Park JH, Koo BN, Kim JY, Cho JE, Kim WO, Kil HK: Determination of the optimal angle for needle insertion during caudal block in children using ultrasound imaging. Anaesthesia 2006; 61: 946-9.
• Tsui BC: Innovative approaches to neuraxial blockade in children: the introduction of epidural nerve root stimulation and ultrasound guidance for epidural catheter placement. Pain Res Manag 2006; 11: 173-80.
• Willschke H, Marhofer P, Bosenberg A, Johnston S, Wanzel O, Sitzwohl C, Kettner S, Kapral S: Epidural catheter placement in children: comparing a novel approach using ultrasound guidance and a standard loss-of-resistance technique. Br J Anaesth. 2006; 97: 200-7.
• Huang J. Disadvantages of ultrasound guidance in caudal epidural needle placement. Anesthesiology 2005; 102: 693-694.
• Marhofer P, Bosenberg A, Sitzwohl C, Willschke H, Wanzel O, Kapral S. Pilot study of neuraxial imaging by ultrasound in infants and children. Paediatr Anaesth 2005; 15: 671-676.
• Ozer Y, Ozer T, Altunkaya H, Savranlar A. The posterior lumbar dural depth: an ultrasonographic study in children. Agri 2005; 17: 53-57.
• Rapp H J, Folger A, Grau T. Ultrasound-guided epidural catheter insertion in children. Anesth Analg 2005; 101: 333-9.
• Roberts S A, Galvez I. Ultrasound assessment of caudal catheter position in infants. Paediatr Anaesth 2005; 15: 429-432.
• Roberts S A, Guruswamy V, Galvez I. Caudal injectate can be reliably imaged using portable ultrasound--a preliminary study. Paediatr Anaesth 2005; 15: 948-952.
• Chawathe M S, Jones R M, Gildersleve C D, Harrison S K, Morris S J, Eickmann C. Detection of epidural catheters with ultrasound in children. Paediatr Anaesth 2003; 13: 681-684.
• Kiechl-Kohlendorfer U, Unsinn K M, Schlenck B, Trawoger R, Gassner I. Cerebrospinal fluid leakage after lumbar puncture in neonates: incidence and sonographic appearance. Am J Roentgenol 2003;181:231-234.