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The role of high-resolution ultrasound and MRI in the evaluation of peripheral nerves in the lower extremity

Steven Kyungho Lee
Steven Kyungho Lee
, 
Ali Mostafa Serhal
Ali Mostafa Serhal
, 
Muhamad Serhal
Muhamad Serhal
, 
Julia Michalek
Julia Michalek
 e 
Imran Muhammad Omar
Imran Muhammad Omar
   | 23 nov 2023
Journal of Ultrasonography's Cover Image
INFORMAZIONI SU QUESTO ARTICOLO
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Article Category: Review Paper
Pubblicato online: 23 nov 2023
Pagine: e328 - e346
Ricevuto: 07 ago 2023
Accettato: 22 ago 2023
DOI: https://doi.org/10.15557/jou.2023.0038
Parole chiave
© 2023 Steven Kyungho Lee et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Fig. 1.

Illustrations of the major lower extremity peripheral nerves from anterior (A) and posterior (B) perspectives. Areas of potential peripheral nerve compression are in italicized type
Illustrations of the major lower extremity peripheral nerves from anterior (A) and posterior (B) perspectives. Areas of potential peripheral nerve compression are in italicized type

Fig. 2.

A 19-year-old male patient with motor vehicle accident and right lower extremity traction injury. A. Axial proton density (PD) fat-suppressed (FS) magnetic resonance (MR) image of the right knee at the distal femoral metaphyseal level shows moderate thickening and edema-like signal of the common peroneal nerve (CPN) (arrow). For comparison, the tibial nerve (arrowhead) is normal in caliber and signal. Linear pre-quadriceps edema (asterisk) is related to a cutaneous wound. B. Grayscale long axis ultrasound (US) image of the CPN demonstrates the typical sonographic findings of intrinsic neuropathy, including hypoechoic nerve thickening and loss of the expected fascicular echotexture (arrow). C. Microvascular Doppler long axis US image of the CPN shows mild intraneural vascularity (arrowheads), which can be a subtle sign of peripheral neuropathy. This technique is more sensitive to slow flow than color or power Doppler imaging and can detect milder cases of hyperemia. However, it is susceptible to subtle transducer movements, which can cause extensive color artifacts (arrows). To distinguish between true vascularity and artifact, the transducer should be held still in position for a few seconds. True vascularity will persist in the same place and be pulsatile
A 19-year-old male patient with motor vehicle accident and right lower extremity traction injury. A. Axial proton density (PD) fat-suppressed (FS) magnetic resonance (MR) image of the right knee at the distal femoral metaphyseal level shows moderate thickening and edema-like signal of the common peroneal nerve (CPN) (arrow). For comparison, the tibial nerve (arrowhead) is normal in caliber and signal. Linear pre-quadriceps edema (asterisk) is related to a cutaneous wound. B. Grayscale long axis ultrasound (US) image of the CPN demonstrates the typical sonographic findings of intrinsic neuropathy, including hypoechoic nerve thickening and loss of the expected fascicular echotexture (arrow). C. Microvascular Doppler long axis US image of the CPN shows mild intraneural vascularity (arrowheads), which can be a subtle sign of peripheral neuropathy. This technique is more sensitive to slow flow than color or power Doppler imaging and can detect milder cases of hyperemia. However, it is susceptible to subtle transducer movements, which can cause extensive color artifacts (arrows). To distinguish between true vascularity and artifact, the transducer should be held still in position for a few seconds. True vascularity will persist in the same place and be pulsatile

Fig. 3.

Frontal diagram of the lumbosacral plexus shows nerve roots extending from the lumbosacral spine
Frontal diagram of the lumbosacral plexus shows nerve roots extending from the lumbosacral spine

Fig. 4.

Sciatic nerve variations that can contribute to piriformis syndrome. A. A 34-year-old female patient with pain in the right lower extremity. Axial STIR SPACE post contrast imaging of the pelvis through the piriformis muscles demonstrates a type A sciatic nerve in relation to the piriformis muscle (arrowhead). The main sciatic nerve (long arrow) and S2 nerve root (short arrow), which joins with the sciatic nerve more distally, are ventral to the piriformis muscle belly. B. A 58-year-old female patient with right lower extremity pain and weakness. Axial STIR SPACE post contrast imaging of the pelvis through the piriformis muscles demonstrates a type B sciatic nerve in relation to the piriformis muscle (arrowhead). The main sciatic nerve (long arrow) is ventral to the piriformis muscle. However, there is a slip of the piriformis muscle (arrowhead) that crosses ventral to the S2 nerve root (short arrow), and this nerve root is focally completely encased by the muscle. However, the type A variant is the most commonly seen (80% of cases), and the type B variant is the most common variant that has been associated with piriformis impingement (seen in 8% of cases). Several additional variants have been described. However, these are much less commonly seen
Sciatic nerve variations that can contribute to piriformis syndrome. A. A 34-year-old female patient with pain in the right lower extremity. Axial STIR SPACE post contrast imaging of the pelvis through the piriformis muscles demonstrates a type A sciatic nerve in relation to the piriformis muscle (arrowhead). The main sciatic nerve (long arrow) and S2 nerve root (short arrow), which joins with the sciatic nerve more distally, are ventral to the piriformis muscle belly. B. A 58-year-old female patient with right lower extremity pain and weakness. Axial STIR SPACE post contrast imaging of the pelvis through the piriformis muscles demonstrates a type B sciatic nerve in relation to the piriformis muscle (arrowhead). The main sciatic nerve (long arrow) is ventral to the piriformis muscle. However, there is a slip of the piriformis muscle (arrowhead) that crosses ventral to the S2 nerve root (short arrow), and this nerve root is focally completely encased by the muscle. However, the type A variant is the most commonly seen (80% of cases), and the type B variant is the most common variant that has been associated with piriformis impingement (seen in 8% of cases). Several additional variants have been described. However, these are much less commonly seen

Fig. 5.

Coronal short tau inversion recovery (STIR) three-dimensional (3D) sampling perfection with application-optimized contrasts using different flip angle evolution (SPACE) maximal intensity projection (MIP) postcontrast magnetic resonance (MR) image through the lumbosacral plexus. A 14-year-old male with a history of pelvic fracture after dirt bike accident shows post-traumatic pseudomeningocele formation involving the left L4–S1 neural foramina secondary to nerve root avulsions (arrow). There is associated asymmetric thickening and increased STIR signal within the intra-pelvic course of the left sciatic nerve (arrowhead). This sequence is often performed after contrast administration to suppress vascular signal and make the adjacent nerves more conspicuous
Coronal short tau inversion recovery (STIR) three-dimensional (3D) sampling perfection with application-optimized contrasts using different flip angle evolution (SPACE) maximal intensity projection (MIP) postcontrast magnetic resonance (MR) image through the lumbosacral plexus. A 14-year-old male with a history of pelvic fracture after dirt bike accident shows post-traumatic pseudomeningocele formation involving the left L4–S1 neural foramina secondary to nerve root avulsions (arrow). There is associated asymmetric thickening and increased STIR signal within the intra-pelvic course of the left sciatic nerve (arrowhead). This sequence is often performed after contrast administration to suppress vascular signal and make the adjacent nerves more conspicuous

Fig. 6.

Normal grayscale sonographic appearance of the sciatic nerve in short axis (arrowhead) as it exits the pelvis deep to the piriformis and gluteus maximus muscles (arrow). Note that the echogenicity of the nerve is similar to the overlying muscles, which can make evaluation of the nerve challenging in this region
Normal grayscale sonographic appearance of the sciatic nerve in short axis (arrowhead) as it exits the pelvis deep to the piriformis and gluteus maximus muscles (arrow). Note that the echogenicity of the nerve is similar to the overlying muscles, which can make evaluation of the nerve challenging in this region

Fig. 7.

A 31-year-old male with clinical symptoms of left-sided piriformis syndrome. A. Coronal T1-weighted (T1W) non-fat suppressed (NFS) MR image of the pelvis prior to steroid injection demonstrates symmetric appearance of the piriformis muscles (arrowheads). Coronal (B) and axial (C) T1W NFS MR images of the pelvis after steroid injection demonstrate marked atrophy of the left piriformis muscle as compared to the right (arrowhead), with the left sciatic nerve running through the greater sciatic notch (arrow)
A 31-year-old male with clinical symptoms of left-sided piriformis syndrome. A. Coronal T1-weighted (T1W) non-fat suppressed (NFS) MR image of the pelvis prior to steroid injection demonstrates symmetric appearance of the piriformis muscles (arrowheads). Coronal (B) and axial (C) T1W NFS MR images of the pelvis after steroid injection demonstrate marked atrophy of the left piriformis muscle as compared to the right (arrowhead), with the left sciatic nerve running through the greater sciatic notch (arrow)

Fig. 8.

A 36-year-old female with a clinical history of meralgia paresthetica. Axial 3D STIR SPACE MIP image demonstrates asymmetric thickening and increased signal of the right lateral femoral cutaneous nerve at the anterior superior iliac spine (arrowhead)
A 36-year-old female with a clinical history of meralgia paresthetica. Axial 3D STIR SPACE MIP image demonstrates asymmetric thickening and increased signal of the right lateral femoral cutaneous nerve at the anterior superior iliac spine (arrowhead)

Fig. 9.

An 18-year-old male with a history of deep lacerations of the medial aspect of the right mid-to-distal thigh after an accident through a glass door resulting in transection of the femoral artery and nerve. Axial STIR MR image through the mid-to-distal right thigh demonstrates marked denervation edema within the vastus medialis (arrow), vastus intermedius (asterisk), vastus lateralis (arrowhead), and rectus femoris (curved arrow) muscles
An 18-year-old male with a history of deep lacerations of the medial aspect of the right mid-to-distal thigh after an accident through a glass door resulting in transection of the femoral artery and nerve. Axial STIR MR image through the mid-to-distal right thigh demonstrates marked denervation edema within the vastus medialis (arrow), vastus intermedius (asterisk), vastus lateralis (arrowhead), and rectus femoris (curved arrow) muscles

Fig. 10.

A 21-year-old female with a history of multiple gunshot wounds to the left thigh. Transverse grayscale ultrasound (US) image through the medial mid-thigh demonstrates the normal “honeycomb” appearance of the saphenous nerve (arrowhead) within the adductor (Hunter’s) canal as it runs adjacent to the femoral artery and deep to the sartorius muscle. The fascicles of this nerve are similar size in cross-sectional area
A 21-year-old female with a history of multiple gunshot wounds to the left thigh. Transverse grayscale ultrasound (US) image through the medial mid-thigh demonstrates the normal “honeycomb” appearance of the saphenous nerve (arrowhead) within the adductor (Hunter’s) canal as it runs adjacent to the femoral artery and deep to the sartorius muscle. The fascicles of this nerve are similar size in cross-sectional area

Fig. 11.

A 54-year-old female patient with medial ankle laceration with a glass shard 7 months prior. A–C. T2-weighted (T2W) axial FS MR images of the distal tibial metaphysis on a routine ankle MRI from proximal to distal show a thickened, edematous saphenous nerve proximal to the site of laceration (arrow) in A. B. At the site of the laceration, the nerve is not seen. However, it is unclear whether this represents nerve discontinuity or focal fibrosis. C. Distal to the site of laceration, the nerve is again thickened and edematous (arrow). D. Long axis panoramic image of the saphenous nerve shows the complementary information provided by ultrasound. There is a complete transection with a nearly 2 cm gap in the nerve (arrows) that was difficult to see on MRI. The medial distal tibial metaphyseal cortex deep to the proximal tendon stump is irregular (arrowhead), likely related to the laceration. E. Long axis color Doppler image of the proximal nerve stump shows mild, bulbous thickening of the nerve (between calipers), indicating a developing stump neuroma. The patient had more focal tenderness over this area. No intraneural hyperemia was seen
A 54-year-old female patient with medial ankle laceration with a glass shard 7 months prior. A–C. T2-weighted (T2W) axial FS MR images of the distal tibial metaphysis on a routine ankle MRI from proximal to distal show a thickened, edematous saphenous nerve proximal to the site of laceration (arrow) in A. B. At the site of the laceration, the nerve is not seen. However, it is unclear whether this represents nerve discontinuity or focal fibrosis. C. Distal to the site of laceration, the nerve is again thickened and edematous (arrow). D. Long axis panoramic image of the saphenous nerve shows the complementary information provided by ultrasound. There is a complete transection with a nearly 2 cm gap in the nerve (arrows) that was difficult to see on MRI. The medial distal tibial metaphyseal cortex deep to the proximal tendon stump is irregular (arrowhead), likely related to the laceration. E. Long axis color Doppler image of the proximal nerve stump shows mild, bulbous thickening of the nerve (between calipers), indicating a developing stump neuroma. The patient had more focal tenderness over this area. No intraneural hyperemia was seen

Fig. 12.

Diagram of the tibial nerve branching. TN – tibial nerve; MCN – medial calcaneal nerve; ICN – inferior calcaneal nerve; LPN – lateral plantar nerve; MPN – medial plantar nerve
Diagram of the tibial nerve branching. TN – tibial nerve; MCN – medial calcaneal nerve; ICN – inferior calcaneal nerve; LPN – lateral plantar nerve; MPN – medial plantar nerve

Fig. 13.

A 73-year-old female with a clinical history of tarsal tunnel syndrome who presented for US-guided percutaneous local anesthetic and steroid injection of the tarsal tunnel. A. Short-axis grayscale US image of the tarsal tunnel parallel with the malleolar-calcaneal axis demonstrates the normal anatomy of the contained structures including the posterior tibialis tendon (arrow), flexor digitorum longus tendon (curved arrow), flexor hallucis longus tendon (asterisk), and the tibial nerve (arrowhead). B. Short-axis grayscale US image demonstrates the tip of a 25-gauge needle (arrowhead) within the tarsal tunnel between the posterior tibialis tendon (arrow) and the flexor digitorum longus tendon (curved arrow)
A 73-year-old female with a clinical history of tarsal tunnel syndrome who presented for US-guided percutaneous local anesthetic and steroid injection of the tarsal tunnel. A. Short-axis grayscale US image of the tarsal tunnel parallel with the malleolar-calcaneal axis demonstrates the normal anatomy of the contained structures including the posterior tibialis tendon (arrow), flexor digitorum longus tendon (curved arrow), flexor hallucis longus tendon (asterisk), and the tibial nerve (arrowhead). B. Short-axis grayscale US image demonstrates the tip of a 25-gauge needle (arrowhead) within the tarsal tunnel between the posterior tibialis tendon (arrow) and the flexor digitorum longus tendon (curved arrow)

Fig. 14.

Diagram of the soleal sling between the medial and lateral gastrocnemius heads. TN – tibial nerve, CPN – common peroneal nerve; SM – semimembranosus muscle; BF – biceps femoris muscle; MG – medial gastrocnemius muscle; LG – lateral gastrocnemius muscle
Diagram of the soleal sling between the medial and lateral gastrocnemius heads. TN – tibial nerve, CPN – common peroneal nerve; SM – semimembranosus muscle; BF – biceps femoris muscle; MG – medial gastrocnemius muscle; LG – lateral gastrocnemius muscle

Fig. 15.

A. Axial T1W NFS MR image of the left leg at the level of the soleal sling in a 31-year-old female patient with chronic ankle pain with concern for tibial neuropathy at the soleal sling demonstrates flattening of the tibial nerve (arrowhead) with effacement of the intervening fat plane between it and the fascial soleal sling (arrows). B. Axial T1W NFS image at the level of the soleal sling in a different patient demonstrates a normal tibial nerve (arrowhead) with preservation of the intervening fat between it and the soleal sling
A. Axial T1W NFS MR image of the left leg at the level of the soleal sling in a 31-year-old female patient with chronic ankle pain with concern for tibial neuropathy at the soleal sling demonstrates flattening of the tibial nerve (arrowhead) with effacement of the intervening fat plane between it and the fascial soleal sling (arrows). B. Axial T1W NFS image at the level of the soleal sling in a different patient demonstrates a normal tibial nerve (arrowhead) with preservation of the intervening fat between it and the soleal sling

Fig. 16.

A 48-year-old female with injury to the left ankle after a motor vehicle accident, who presented with numbness to the plantar medial aspect of the distal forefoot. Axial grayscale US image of the inframalleolar ankle demonstrates an anechoic ganglion cyst (arrow) adjacent to and causing mass effect on a thickened and hypoechoic medial plantar nerve (arrowhead). FDL – flexor digitorum longus
A 48-year-old female with injury to the left ankle after a motor vehicle accident, who presented with numbness to the plantar medial aspect of the distal forefoot. Axial grayscale US image of the inframalleolar ankle demonstrates an anechoic ganglion cyst (arrow) adjacent to and causing mass effect on a thickened and hypoechoic medial plantar nerve (arrowhead). FDL – flexor digitorum longus

Fig. 17.

A 43-year-old female with medial sided ankle pain. A. Coronal T2-weighted (T2W) fat-suppressed (FS) MR image through the ankle demonstrates thickening and increased signal within the medial plantar nerve (arrowhead), which can be seen in the setting of Jogger’s foot. B. Short-axis T2W FS MR image of the forefoot at the level of the metatarsal bases demonstrates denervation edema within the abductor hallucis muscle (arrowhead)
A 43-year-old female with medial sided ankle pain. A. Coronal T2-weighted (T2W) fat-suppressed (FS) MR image through the ankle demonstrates thickening and increased signal within the medial plantar nerve (arrowhead), which can be seen in the setting of Jogger’s foot. B. Short-axis T2W FS MR image of the forefoot at the level of the metatarsal bases demonstrates denervation edema within the abductor hallucis muscle (arrowhead)

Fig. 18.

A 61-year-old female with left foot metatarsalgia and clinical concern for Morton’s neuroma. A. Short-axis grayscale US image of the left plantar forefoot at the level of the metatarsal heads without compression demonstrates a hypoechoic lesion within the third intermetatarsal web space compatible with a Morton’s neuroma (arrowhead). B. Dynamic compression of the metatarsals on an US image in the same position demonstrates a positive sonographic Mulder sign with plantar displacement of the neuroma (arrowhead) (Video 2)
A 61-year-old female with left foot metatarsalgia and clinical concern for Morton’s neuroma. A. Short-axis grayscale US image of the left plantar forefoot at the level of the metatarsal heads without compression demonstrates a hypoechoic lesion within the third intermetatarsal web space compatible with a Morton’s neuroma (arrowhead). B. Dynamic compression of the metatarsals on an US image in the same position demonstrates a positive sonographic Mulder sign with plantar displacement of the neuroma (arrowhead) (Video 2)

Fig. 19.

A 46-year-old male with a 1-year history of forefoot pain between the third and fourth toes. Short-axis (A) and horizontal long-axis (B) T1W NFS MR images demonstrate a tear-drop shaped isointense lesion in the third intermetatarsal web space (arrowheads) compatible with a Morton’s neuroma. T1W NFS sequences are often the most useful for detecting Morton’s neuromas on MRI since they use the fat as a natural contrast to outline the abnormality
A 46-year-old male with a 1-year history of forefoot pain between the third and fourth toes. Short-axis (A) and horizontal long-axis (B) T1W NFS MR images demonstrate a tear-drop shaped isointense lesion in the third intermetatarsal web space (arrowheads) compatible with a Morton’s neuroma. T1W NFS sequences are often the most useful for detecting Morton’s neuromas on MRI since they use the fat as a natural contrast to outline the abnormality

Fig. 20.

A 64-year-old female with lateral ankle pain while walking. Coronal T1W NFS MR image of the hindfoot demonstrates severe fatty atrophy of the abductor digiti quinti muscle (arrowhead) that is often seen in the setting of inferior calcaneal neuropathy
A 64-year-old female with lateral ankle pain while walking. Coronal T1W NFS MR image of the hindfoot demonstrates severe fatty atrophy of the abductor digiti quinti muscle (arrowhead) that is often seen in the setting of inferior calcaneal neuropathy

Fig. 21.

A 62-year-old male with foot drop. Axial PD FS MR image of the knee at the level of the proximal tibial metaphysis shows a lobulated cystlike lesion anterior to the fibular neck (arrowhead). There is a thinner neck arising from the proximal tibiofibular joint (arrow), indicating that the ganglion likely arises from the proximal tibiofibular joint and may extend along the articular branch of the CPN. Finally, there is mild, diffuse anterior tibialis muscle edema (asterisk), which is compatible with peroneal neuropathy
A 62-year-old male with foot drop. Axial PD FS MR image of the knee at the level of the proximal tibial metaphysis shows a lobulated cystlike lesion anterior to the fibular neck (arrowhead). There is a thinner neck arising from the proximal tibiofibular joint (arrow), indicating that the ganglion likely arises from the proximal tibiofibular joint and may extend along the articular branch of the CPN. Finally, there is mild, diffuse anterior tibialis muscle edema (asterisk), which is compatible with peroneal neuropathy

Fig. 22.

A 68-year-old female with pain and swelling of the left knee and foot drop. Axial (A) and coronal (B) T2W FS MR images of the left knee demonstrate thickening and increased signal within the common peroneal nerve as it curves along the fibular neck (arrowhead). C. Short-axis grayscale US image at the fibular head in an 18-year-old female presenting with foot drop demonstrates marked thickening of a hypoechoic common peroneal nerve with loss of the normal fascicular architecture (arrowhead)
A 68-year-old female with pain and swelling of the left knee and foot drop. Axial (A) and coronal (B) T2W FS MR images of the left knee demonstrate thickening and increased signal within the common peroneal nerve as it curves along the fibular neck (arrowhead). C. Short-axis grayscale US image at the fibular head in an 18-year-old female presenting with foot drop demonstrates marked thickening of a hypoechoic common peroneal nerve with loss of the normal fascicular architecture (arrowhead)

Fig. 23.

A 72-year-old female with a palpable abnormality in the lateral mid to distal lower leg. Palpation of this area causes paresthesias over the anterolateral distal lower leg radiating to the foot. A. Coronal T2W FS image of the distal lower leg shows a 1.1 cm mass (arrow) immediately deep to a vitamin E capsule indicating the location of the palpable abnormality. The mass is continuous proximally and distally with the superficial peroneal nerve (SPN) (arrowheads). The lesion avidly enhanced following intravenous contrast administration (not shown). B. Long axis grayscale US image of the same lesion shows a 1.2 cm nodule (arrow) corresponding to the palpable abnormality and the MRI finding that is continuous with the SPN. The nerve has a typical fasciculated appearance proximally and distally (arrowheads). The majority of the nerve fibers are displaced superficially and the lesion appeared to arise eccentrically from the deeper fibers of the nerve, suggesting it represents a schwannoma. However, the diagnosis should be confirmed histologically
A 72-year-old female with a palpable abnormality in the lateral mid to distal lower leg. Palpation of this area causes paresthesias over the anterolateral distal lower leg radiating to the foot. A. Coronal T2W FS image of the distal lower leg shows a 1.1 cm mass (arrow) immediately deep to a vitamin E capsule indicating the location of the palpable abnormality. The mass is continuous proximally and distally with the superficial peroneal nerve (SPN) (arrowheads). The lesion avidly enhanced following intravenous contrast administration (not shown). B. Long axis grayscale US image of the same lesion shows a 1.2 cm nodule (arrow) corresponding to the palpable abnormality and the MRI finding that is continuous with the SPN. The nerve has a typical fasciculated appearance proximally and distally (arrowheads). The majority of the nerve fibers are displaced superficially and the lesion appeared to arise eccentrically from the deeper fibers of the nerve, suggesting it represents a schwannoma. However, the diagnosis should be confirmed histologically

Fig. 24.

A 22-year-old female with a history of traumatic right ankle inversion injury and clinical concern for superficial peroneal nerve injury. Long-axis grayscale US images of the lateral distal calves (right side on top, left side on bottom for comparison) demonstrate markedly hypoechoic and thickened right SPN (arrowhead) as compared to the contralateral side (arrow)
A 22-year-old female with a history of traumatic right ankle inversion injury and clinical concern for superficial peroneal nerve injury. Long-axis grayscale US images of the lateral distal calves (right side on top, left side on bottom for comparison) demonstrate markedly hypoechoic and thickened right SPN (arrowhead) as compared to the contralateral side (arrow)

Fig. 25.

A 36-year-old asymptomatic female imaged to assess the deep peroneal nerve (DPN). A. Transverse grayscale US image of the proximal lower leg shows the DPN (arrow). Proximally, the CPN is usually well seen dividing into the DPN and SPN. However, there is a small, hypoechoic structure just anterior to the nerve, which can be mistakenly identified as the nerve. B. Transverse color Doppler imaging can be helpful to identify the adjacent anterior tibial artery and appropriately localize the nerve. The nerve dives deeply into the anterolateral lower leg and can be difficult to see at and distal to this location. C. Transverse grayscale US image of the distal lower leg shows the DPN more distally (arrow). Although the nerve has a typical honeycomb appearance in the short axis, the hypoechoic nerve fibers are very thin, and the nerve may be difficult to distinguish from other tissues at this level. D. Transverse color Doppler US image of the distal tibial metaphysis at the same level shows internal pulsatile vascular color flow in the dorsalis pedis artery adjacent to the nerve (between calipers), which may help to localize the nerve
A 36-year-old asymptomatic female imaged to assess the deep peroneal nerve (DPN). A. Transverse grayscale US image of the proximal lower leg shows the DPN (arrow). Proximally, the CPN is usually well seen dividing into the DPN and SPN. However, there is a small, hypoechoic structure just anterior to the nerve, which can be mistakenly identified as the nerve. B. Transverse color Doppler imaging can be helpful to identify the adjacent anterior tibial artery and appropriately localize the nerve. The nerve dives deeply into the anterolateral lower leg and can be difficult to see at and distal to this location. C. Transverse grayscale US image of the distal lower leg shows the DPN more distally (arrow). Although the nerve has a typical honeycomb appearance in the short axis, the hypoechoic nerve fibers are very thin, and the nerve may be difficult to distinguish from other tissues at this level. D. Transverse color Doppler US image of the distal tibial metaphysis at the same level shows internal pulsatile vascular color flow in the dorsalis pedis artery adjacent to the nerve (between calipers), which may help to localize the nerve

Fig. 26.

A 63-year-old female with a history of gunshot wounds to the left lower extremity. Grayscale long-axis (top) and short-axis (bottom) US images of the sural nerve at the level of the posterior lateral ankle demonstrate post-traumatic architectural distortion of the deep soft tissues (curved arrow) with a thickened and hypoechoic sural nerve (arrowhead) and a focal nodular area of thickening along its course compatible with a neuroma-in-continuity (arrows)
A 63-year-old female with a history of gunshot wounds to the left lower extremity. Grayscale long-axis (top) and short-axis (bottom) US images of the sural nerve at the level of the posterior lateral ankle demonstrate post-traumatic architectural distortion of the deep soft tissues (curved arrow) with a thickened and hypoechoic sural nerve (arrowhead) and a focal nodular area of thickening along its course compatible with a neuroma-in-continuity (arrows)

Sample MR neurography protocol used for lumbosacral plexus evaluation. Imaging is performed from L2 through the femoral greater trochanters, and anterior abdominal wall and inguinal region imaging should be included to assess the femoral nerves as they extend to the thighs as well as some of the smaller nerves, such as the ilioinguinal and iliohypogastric nerves. Postcontrast imaging is performed primarily to achieve vascular suppression on the STIR SPACE sequence rather than to assess for nerve enhancement. Coronal oblique imaging can be optional to assess the L5 and sacral nerve roots, is performed to be en face with the sacrum and is planned from a midsagittal localizer image. TE – echo time. TR – repetition time

Sequence TE (msec) TR (msec) Slice thickness Flip angle Acquisition matrix
Axial T1 10 600–700 3 mm 140 352 × 352
Axial STIR 60 4000 3 mm 140 320× 320
Coronal STIR 60 4000 3 mm 140 384 × 384
Coronal T1 NFS 10 600–800 3 mm 150 512× 512
Coronal Oblique T1 NFS 10 600–700 3 mm 140 320× 320
Axial T1 FS precontrast 12 650 5 mm 160 320× 320
Axial T1 FS postcontrast 12 650 5 mm 160 320× 320
Coronal T1 FS postcontrast 12 650–1150 3 mm 150 320× 320
Coronal STIR SPACE 3D post contrast 250 2500–3000 isotropic variable 384 × 384
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