Self-Assessment Questions: Text

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Appendix 1 Self-Assessment Questions: Text

1. Why do peripheral nerves often appear more echogenic after injection of anechoic local anesthetic?

A. The connective tissue content of the nerves has increased.
B. Nonattenuating fluid has been injected into an attenuating sound field.
C. The number of fascicles has increased.
D. Local anesthetic has entered the nerve and increased reflection.

2. Which of the following statements regarding peripheral nerve anatomy is most correct?

A. Polyfascicular nerves have a low connective tissue content compared with monofascicular nerves.
B. The cervical ventral rami have a high connective tissue content.
C. The number of fascicles and the connective tissue content of peripheral nerves are directly related.
D. Nerve fascicles are made exclusively of connective tissue.

3. Which of the following is most accurate?

A. Ultrasound frequencies of 10 MHz or higher are necessary to distinguish peripheral nerves from tendons based on echotexture alone.
B. Peripheral nerves can only be imaged with ultrasound frequencies of 10 MHz or higher.
C. Peripheral nerves can only be imaged with ultrasound frequencies of 20 MHz or higher.
D. Peripheral nerves and tendons cannot be distinguished with ultrasound imaging.

4. Which of the following statements regarding probe compression is most correct?

A. Nerves do not move in response to probe compression.
B. Arteries cannot be compressed by the ultrasound probe.
C. Veins are easier to compress than arteries.
D. Nerves are easily compressed by the ultrasound probe.

5. What term describes the fact that the received echoes from peripheral nerves vary with the angle of insonation?

A. Acoustic emission
B. Anisotropy
C. Power Doppler imaging
D. None of the above

6. Which of the following statements is most accurate?

A. Nerves are more anisotropic than tendons.
B. The anisotropy of peripheral nerves is thought to be related to their myelin content rather than their collagen content.
C. The amplitude of the received echoes from peripheral nerves is usually largest when the sound beam is perpendicular to the nerve.
D. Nerves and tendons do not exhibit anisotropy.

7. Which of the following influences needle tip visibility? (Select all that apply.)

A. The angle of insonation
B. The gauge of the needle
C. The bevel orientation
D. The bevel angle

8. Which of the following is associated with comet-tail artifact?

A. First rib
B. Pneumothorax
C. Normal pleura
D. Brachial plexus

9. Select the best answer.

A. Bone is a strong absorber of sound waves.
B. Pleura is a strong reflector of sound waves.
C. Both of the above statements are true.

10. Which of the following statements regarding interscalene block is true?

A. The phrenic nerve lies medial to the brachial plexus within the middle scalene muscle.
B. The phrenic nerve crosses over the anterior scalene muscle medial to the brachial plexus.
C. The dorsal scapular nerve is often seen within the anterior scalene muscle.
D. The spinal accessory nerve arises from the brachial plexus.

11. Which of the following statements regarding the first rib and pleura is true?

A. Only the first rib produces comet-tail artifact.
B. Comet-tail artifact signifies the presence of pneumothorax.
C. The pleura produces a bright reflection and comet-tail artifact.
D. The first rib does not produce reflection of sound waves.

12. What is the most common anatomic variation in the interscalene region?

A. Cervical rib
B. Cervical ventral rami that pass over or through the anterior scalene muscle
C. Phrenic nerve passing through the middle scalene muscle
D. Phrenic nerve passing through the subclavian artery

13. The phrenic nerve lies on which muscle in the neck?

14. The cords of the brachial plexus are named with respect to what structure?

15. What branches leave the brachial plexus sheath under the pectoralis minor at the coracoid process?

16. At the level of an axillary block, the musculocutaneous nerve typically lies in what muscle?

17. Regarding the anatomy of the axilla, pick one nerve (MCN, RAD, MED, ULN) for each:

The nerve that passes though the coracobrachialis muscle: _______
The nerve that passes between the axillary artery and vein: _______
The nerve that follows the profunda brachii artery into the triceps muscle and spiral groove of the humerus: _______
The nerve that passes from lateral to medial over the surface of the axillary artery and can be displaced to either side of the artery with probe compression: _______

18. True or False? In most subjects, the lateral femoral cutaneous nerve travels over (superficial to) the sartorius muscle near its insertion on the anterior superior iliac spine.

19. Which of the following statements regarding the femoral nerve are true? (Select all that apply.)

A. The femoral nerve is always oval in shape.
B. The femoral nerve is never triangular in shape.
C. The femoral nerve can be triangular in shape, especially when imaged proximal to the inguinal ligament.

20. The femoral nerve lies deep to which of the following structure(s)? (Select all that apply.)

A. Fascia lata
B. Fascia iliaca
C. Iliopsoas muscle

21. True or False? The saphenous nerve travels with the infrapatellar nerve and the nerve to the vastus medialis throughout most of its course in the thigh.

22. The saphenous nerve follows the course of what major structure as it descends the medial leg?

23. Which muscle separates the anterior and posterior divisions of the obturator nerve?

A. Adductor longus
B. Adductor magnus
C. Adductor brevis
D. Obturator internus
E. Pectineus

24. Which adductor muscles are not innervated by the obturator nerve?

25. Name the blood vessel most closely associated with the following nerves:

Saphenous nerve: _________________________
Tibial nerve: _________________________
Sural nerve: _________________________
Superficial peroneal nerve: _________________________
Deep peroneal nerve: _________________________

Answers to Text Questions

Answer 1: B

CLINICAL SIGNIFICANCE: Injection of a nonattenuating fluid into an attenuating sound field can cause enhancement of echoes deep to the fluid. This phenomenon is often seen during clinical blocks. Although this occurs after successful injections, fluid injected anywhere between the nerve and the skin surface will cause this effect.

REFERENCE: Filly RA, Sommer FG, Minton MJ. Characterization of biological fluids by ultrasound and computed tomography. Radiology 1980;134:167–71.

Answer 2: C

CLINICAL SIGNIFICANCE: Monofascicular nerves are more vulnerable to stretching and compression injury because they have a low connective tissue content.

REFERENCES: Sunderland S. The connective tissues of peripheral nerves. Brain 1965;88:841–54.

Sunderland S, Bradley KC. The cross-sectional area of peripheral nerve trunks devoted to nerve fibers. Brain 1949;72:428–49.

Sunderland S, Bradley KC. The perineurium of peripheral nerves. Anat Rec 1952;113:125–41.

Answer 3: A

CLINICAL SIGNIFICANCE: Nerves can be imaged at low frequencies (<10 MHz), but they appear as cordlike structures without internal fascicular architecture.

REFERENCE: Giovagnorio F, Martinoli C. Sonography of the cervical vagus nerve: normal appearance and abnormal findings. AJR Am J Roentgenol 2001;176:745–9.

Answer 4: C

CLINICAL SIGNIFICANCE: Probe compression is usually a quick and easy way to identify vascular structures. Compression tests are often useful for peripheral imaging.

Answer 5: B

CLINICAL SIGNIFICANCE: Anisotropy is a well-described property of many anatomic structures, including nerves and tendons.

REFERENCES: Connolly DJ, Berman L, McNally EG. The use of beam angulation to overcome anisotropy when viewing human tendon with high-frequency linear array ultrasound. Br J Radiol 2001;74:183–5.

Soong J, Schafhalter-Zoppoth I, Gray AT. The importance of transducer angle to ultrasound visibility of the femoral nerve. Reg Anesth Pain Med 2005;30:505.

Answer 6: C

CLINICAL SIGNIFICANCE: With experience, practitioners learn to manipulate the ultrasound transducer to enhance the received echoes from peripheral nerves.

REFERENCE: Crass JR, van de Vegte GL, Harkavy LA. Tendon echogenicity: ex vivo study. Radiology 1988;167:499–501.

Answer 7: A, B, C

CLINICAL SIGNIFICANCE: Needle tip visibility is crucial to real-time ultrasound guidance of all interventional procedures. Note that the cut of the bevel angle (D) has been studied and shown not to influence needle tip visibility.

REFERENCES: Bondestam S, Kreula J. Needle tip echogenicity: a study with real-time ultrasound. Invest Radiol 1989;24:555–60.

Hopkins RE, Bradley M: In vitro visualization of biopsy needles with ultrasound: a comparative study of standard and echogenic needles using an ultrasound phantom. Clin Radiol 2001;56:499–502.

Schafhalter-Zoppoth I, McCulloch CE, Gray AT. Ultrasound visibility of needles used for regional nerve block: an in vitro study. Reg Anesth Pain Med 2004;29:480–8.

Answer 8: C

CLINICAL SIGNIFICANCE: Distinguishing pleura from other nearby structures is crucial for interventional procedures in the supraclavicular region.

REFERENCES: Ziskin MC, Thickman DI, Goldenberg NJ, et al. The comet tail artifact. J Ultrasound Med 1982;1:1–7.

Thickman DI, Ziskin MC, Goldenberg NJ, et al. Clinical manifestations of the comet tail artifact. J Ultrasound Med 1983;2:225–30.

Answer 9: C

REFERENCE: Han S, Medige J, Davis J, et al. Ultrasound velocity and broadband attenuation as predictors of load-bearing capacities of human calcanei. Calcif Tissue Int 1997;60:21–5.

Answer 10: B

CLINICAL SIGNIFICANCE: Phrenic nerve block is often observed after brachial plexus block procedures in the neck. The phrenic nerve and the brachial plexus lie under the prevertebral fascia, which promotes the distribution of local anesthetic to both.

REFERENCE: Kessler J, Schafhalter-Zoppoth I, Gray AT. An ultrasound study of the phrenic nerve in the posterior cervical triangle: implications for the interscalene brachial plexus block. Reg Anesth Pain Med 2008;33:545–50.

Answer 11: C

CLINICAL SIGNIFICANCE: Distinguishing the first rib and pleura is critical during supraclavicular blocks. Like other bones, the first rib efficiently absorbs sound waves. Lung sliding and comet-tail artifact from reverberation are characteristics of the pleural line.

REFERENCE: Thickman DI, Ziskin MC, Goldenberg NJ, et al. Clinical manifestations of the comet tail artifact. J Ultrasound Med 1983;2:225–30.

Answer 12: B

CLINICAL SIGNIFICANCE: The C5 and C6 ventral rami often travel over or through the anterior scalene muscle (5%-15% incidence). A cervical rib is an anatomic variant that occurs in 0.5% of the general population.

REFERENCES: Harry WG, Bennett JD, Guha SC. Scalene muscles and the brachial plexus: anatomical variations and their clinical significance. Clin Anat 1997;10:250–2.

Mangrulkar VH, Cohen HL, Dougherty D. Sonography for diagnosis of cervical ribs in children. J Ultrasound Med 2008;27:1083–6.

Answer 13: The anterior scalene muscle

CLINICAL SIGNIFICANCE: (1) Diaphragmatic paralysis is an expected consequence of interscalene block (>99%). (2) Diaphragmatic contraction during electrolocation indicates anterior placement of the needle in relation to the brachial plexus.

REFERENCE: Kessler J, Schafhalter-Zoppoth I, Gray AT. An ultrasound study of the phrenic nerve in the posterior cervical triangle: implications for the interscalene brachial plexus block. Reg Anesth Pain Med 2008;33:545–50.

Answer 14: The second part of the axillary artery (under the pectoralis minor muscle)

CLINICAL SIGNIFICANCE: This is the anatomic position of the brachial plexus for infraclavicular block (posterior cord gives rise to the radial nerve, axillary nerve; medial cord gives rise to the median, ulnar, medial cutaneous nerves; lateral cord gives rise to the musculocutaneous, median).

Answer 15: Axillary and musculocutaneous nerves

CLINICAL SIGNIFICANCE: These nerves must be separately blocked when brachial plexus block is performed distal to the infraclavicular region.

Answer 16: The coracobrachialis

CLINICAL SIGNIFICANCE: The musculocutaneous nerve is not part of the neurovascular bundle in the axilla and therefore is frequently not anesthetized during conventional axillary blockade.

Answer 17

The nerve that passes though the coracobrachialis muscle: MCN

The nerve that passes between the axillary artery and vein: ULN

The nerve that follows the profunda brachii artery into the triceps: RAD

The nerve that passes from lateral to medial over the surface of the axillary artery and can be displaced to either side of the artery with probe compression: MED

CLINICAL SIGNIFICANCE: These characteristic features distinguish these peripheral nerves in the axilla.

Answer 18: True

CLINICAL SIGNIFICANCE: Ultrasound landmarks for regional block

Answer 19: C

CLINICAL SIGNIFICANCE: Identification of the femoral nerve is critical to block success. The femoral nerve typically lies in the groove between the iliacus and psoas muscles.

REFERENCE: Gruber H, Peer S, Kovacs P, et al. The ultrasonographic appearance of the femoral nerve and cases of iatrogenic impairment. J Ultrasound Med 2003;22:163–72.

Answer 20: A and B

CLINICAL SIGNIFICANCE: Needle tip placement in the correct layer is essential to femoral nerve block success.

REFERENCE: Dalens B, Vanneuville G, Tanguy A. Comparison of the fascia iliaca compartment block with the 3-in-1 block in children. Anesth Analg 1989;69:705–13.

Answer 21: True

CLINICAL SIGNIFICANCE: Concomitant block is likely. The infrapatellar nerve is usually considered a branch of the saphenous nerve.

REFERENCE: Lundblad M, Kapral S, Marhofer P, et al. Ultrasound-guided infrapatellar nerve block in human volunteers: description of a novel technique. Br J Anaesth 2006;97:710–14.

Answer 22: Saphenous vein

CLINICAL SIGNIFICANCE: The saphenous nerve is a sensory branch of the femoral nerve. It innervates the medial leg. In most patients, the sensory block extends to the medial malleolus and medial foot, and in some patients, it extends to the great toe.

REFERENCE: Benzon HT, Sharma S, Calimaran A. Comparison of the different approaches to saphenous nerve block. Anesthesiology 2005;102:633–8.

Answer 23: C

CLINICAL SIGNIFICANCE: The adductor brevis is an important landmark for ultrasound-guided obturator nerve block.

REFERENCE: Soong J, Schafhalter-Zoppoth I, Gray AT. Sonographic imaging of the obturator nerve for regional block. Reg Anesth Pain Med 2007;32:146–51.

Answer 24: The pectineus (femoral nerve) and part of the adductor magnus (partially innervated by the sciatic nerve)

CLINICAL SIGNIFICANCE: Complete obturator block reduces adduction strength (but not entirely).

REFERENCE: Bouaziz H, Vial F, Jochum D, et al. An evaluation of the cutaneous distribution after obturator nerve block. Anesth Analg 2002;94:445–9.

Answer 25

Saphenous nerve—saphenous vein

Tibial nerve—posterior tibial artery

Sural nerve—small saphenous vein

Superficial peroneal nerve—no major vessel is commonly associated (a small fibular artery is sometimes present)

Deep peroneal nerve—anterior tibial artery and dorsalis pedis artery

CLINICAL SIGNIFICANCE: Vascular landmarks often help identify peripheral nerves.

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