US of the Peripheral Nerves of the Lower Extremity: A Landmark Approach

Abstract

Ultrasonography (US) is commonly used to assess the peripheral nerves of the lower extremity because of its many advantages over magnetic resonance (MR) imaging. The most obvious advantages over MR imaging are superior soft-tissue resolution, low cost, portability, lack of magnetic susceptibility artifact, and the ability to image patients who cannot undergo MR imaging. US has been shown to have equal specificity and greater sensitivity than MR imaging in the evaluation of peripheral nerves. Additional benefits are the capability of real-time and dynamic imaging, and the ability to scan an entire extremity quickly without the need for a patient to lie motionless for long periods of time, as with MR imaging. Any abnormal findings can be easily compared against the contralateral side. Published literature has shown that US has clinical utility in patients suspected of having peripheral nerve disease: US can be used to guide diagnostic and therapeutic decisions, as well as help confirm electrodiagnostic findings. Common indications for lower extremity peripheral nerve US are the evaluation for injury due to penetrating trauma, entrapment by scar tissue, or tumor. To confidently perform US of the peripheral nerves of the lower extremity, it is important to gain a thorough knowledge of anatomic landmarks and the course of each nerve. Readers who may not be familiar with US will be introduced to the basics of scanning the peripheral nerves of the lower extremity. Important anatomic landmarks and common sites of injury and entrapment will be reviewed.

Assessment of Peripheral Nerves With Shear Wave Elastography in Type 1 Diabetic Adolescents Without Diabetic Peripheral Neuropathy

“…Ultrasound is the first‐line choice for in vivo imaging of peripheral nerve abnormalities and can show the cross‐sectional area, thickness, echogenicity, continuity, mass, vascularity, and mobility . Hypoechogenicity of the nerve and increases in the cross‐sectional area and thickness are commonly observed findings of entrapment neuropathies on US imaging . However, sufficient US criteria for defining DPN have not been established because of the wide variability of findings and operator dependency of the method .…”

Ultrasound and Anatomical Study of Accessing the Nerves in the Knee by Fascial Planes

“…High‐frequency ultrasound imaging (5 to 17 MHz) can identify the location of peripheral nerves and their adjacent structures without difficulty …”

“…However, it is important to note that there are hypoechogenic spaces between the paraneurium and epimysium, the most superficial layer of connective tissue covering the muscle, as well as between the epineurium and paraneurium . Thus, in the transverse axis, nerves appear in the ultrasound image as a honeycomb structure, with hypoechoic fascicles surrounded by connective tissue and collagen, which are hyperechoic . Meanwhile, in the longitudinal axis, nerves appear as broad hypoechoic parallel lines, enabling us to differentiate them from tendons, which are hyperechoic, compact, and fibrillar .…”

Ultrasound Imaging of Disorders of Small Nerves of the Extremities: Less Recognized Locations

“…Lateral femoral cutaneous nerve compression under the inguinal ligament is a commonly described neuropathy, known as meralgia paresthetica. It is usually related to constrictive belts, obesity, or anterior iliac spine entesopathy . Compression of the distal branches of the common fibular nerve are not infrequent in the knee region by intramuscular or neural ganglia .…”