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Figure 1: Axial scan of median nerve (arrow) at mid forearm; note the Figure 2: Axial scan of ulnar nerve (arrow) and ulnar artery (*) at forearm;
fascicular texture of the nerve and the homogeneous echogenicity of the in live scans pulsating arteries are a good landmark to be recognized
surrounding muscles
conflicts, abnormal muscles or muscle insertions, synovial
to 400 μm in axial resolution, which is higher than that cysts, nerve subluxation, postfracture fibrosis, and bone
achieved by a common MRI. There is increasing evidence formation.
[26]
in the literature on the helpfulness of HRU, in particular in
cases with equivocal clinical and neurophysiological data; Neurophysiological and clinical parameters are good
[27]
HRU may be diagnostic in a significant percentage of such predictors of postsurgical recovery, but HRU has also
patients. Its advantages include a bedside, painless study demonstrated its usefulness when correlated with clinical
[28]
of the nerve along the entire limb, with color‑Doppler neurophysiology in several nerve pathologies: (1) in
analysis integration and dynamic scans. In addition, it patients with a history of trauma, it can reveal neuromas
can be utilized in the presence of metal implants and and neurotmesis; (2) in cases of postsurgical neuropathy
orthopedic screws, and therefore is preferable to a of an iatrogenic origin, uncommon sites of injury can
high‑cost, single segment MRI study. be localized; (3) in severe diseases with unevocable
nerve potentials on neurophysiological examination,
Sonographic criteria for nerve identification are based on fascicular the site of injury can be easily showed by ultrasound;
echotexture detection. The cross‑sectional area (CSA) of (4) in patients with diffuse preexisting (and confounding)
[26]
the nerve is one of the most studied parameters and is neurophysiological alterations and clinical signs of a
examined in each nerve along the length of the limb in an new neuropathy, the nerve lesions can be delineated;
axial scan. CSA measurements are performed at the inner
border of the thin hyperechoic rim of the nerve, across the (5) in entrapment neuropathies, for screening purposes
[29]
site of entrapment or trauma to calculate the distal‑proximal (e.g. concomitant tenosynovitis is seen in 21.7% of carpal
CSA ratio. The nerve CSA is significantly related to the tunnel syndromes, and dynamic ulnar nerve subluxation
neurodiagnostic data and, when performed side by side is seen at the elbow in 28.5% of cubital grooves); (6) in
with a comprehensive neurodiagnostic exam, it increases its all brachial plexus pathologies, to identify multiple sites
diagnostic sensitivity. [30,31] of injury are common; (7) for early selection of surgical
candidates; [33,34] and (8) for detection of postsurgical
Echogenicity of the nerve should be reported; an improvement or complications. [35]
increased CSA of the entire nerve or of a few fascicles,
proximal to the site of entrapment or trauma, can be HRU does have some limitations, high frequency probes
associated with fibrosis of the fascicles or epineurium. provide optimal spatial resolution for superficial nerve
A few nerve pathologies, such as Schwannomas, will imaging while the deeper nerve course may remain
[36]
initially spare the nerve’s conduction and sensory‑motor unexplored. The sciatic nerve trunk cannot be
functions, manifesting only with inconstant signs of investigated over the horizontal gluteal fold, and the tibial
irritation. Fiber sparing and dislocation can be recognized and common peroneal nerves cannot be easily examined
by an experienced HRU examiner. in the mid leg behind the calf. Both the deep nerve
segments and nerve roots emerging from the spine should
Finally, nerve continuity can be assessed based on the be explored by MRI. Expert HRU investigation can be used
analysis of the epi‑perineurium and on the presence of a to visualize the cervical roots of the brachial plexus (the
partial neuroma or transection. [32] anterior branches of the spinal nerves as they emerge
Imaging will also uncover any predisposing anatomic from the intervertebral foramen) as well as the trunks in
abnormalities (i.e. bifid median nerve or persistent the interscalene area and the cords in the supraclavicular
median artery) or other concurrent diseases in the and infraclavicular and axillary regions. A similar guide
surrounding tissues which may require a different is helpful in interventional procedures to reach target
therapeutic approach. Examples include space‑occupying nerves, such as in regional anesthesia or during steroid
lesions, tumors, tenosynovitis, osteophytes, neurovascular infiltrations, thus minimizing the risk of complications.
Plast Aesthet Res || Vol 2 || Issue 4 || Jul 15, 2015 153