Entrapment at the elbow (cubital tunnel syndrome) results from compression of the ulnar nerve as it courses in the elbow joint under the aponeurosis connecting the two heads of the flexor carpi ulnaris. It may result from acute trauma, repeated movements, inflammation, nerve compression, traction, or friction (e.g., leaning on the elbow, or intraoperative malpositioning). It may result from virtually any insult leading to deformity of the elbow joint, including elbow fracture, arthritis, ganglion cysts, lipomas, and neuropathic (Charcot) joints. “Tardy ulnar palsy” is an ulnar neuropathy that evolves years after an injury to the elbow.

Symptoms of ulnar neuropathy at the elbow include elbow pain, sensory loss and paresthesias of the fifth and ulnar half of the fourth digits and ulnar aspect of the hand, and wasting of the hypothenar and intrinsic hand muscles. Marked weakness of the flexor carpi ulnaris suggests that the lesion is above the elbow. There may be claw hand deformity as well as tenderness or enlargement of the ulnar nerve (palpable in the epicondylar groove); Tinel sign may be present at the elbow.

Differential diagnosis includes C8 or T1 radiculopathy, syringomyelia, amyotrophic lateral sclerosis (ALS), lower brachial plexopathy (Pancoast syndrome), and peripheral polyneuropathy. Nerve conduction studies may show conduction block or slowing across the elbow; electromyography (EMG) may show denervation.

Treatment options include conservative measures (removing exacerbating factors, padding the elbow/armchair rests, nerve gliding exercises, splints) and surgery (decompression, nerve transposition, epicondylectomy). There is little evidence regarding choosing between conservative and operative management. Decompression and transposition appear to be equally effective; transposition, however, is associated with more wound infections. Generally, conservative measures are attempted first, and surgery is indicated if they fail or in patients with moderate-severe neuropathy (prominent weakness/sensory deficits, significant axon loss on EMG) caused by trauma or structural abnormality.

Entrapment at the wrist or hand (Guyon canal) presents with hand weakness and atrophy, and variable sensory involvement. Motor findings are the same as with more proximal lesions, except that the flexor carpi ulnaris and flexor digitorum III and IV are spared. Sensory findings depend on the location of the lesion with respect to the origin of the palmar and dorsal cutaneous branches. The most common causes are compression by ganglia from carpal joints, carpal bone fracture, repeated blunt trauma, and ulnar artery disease (i.e., aneurysm, thrombosis). Typically, EMG and nerve conduction studies demonstrate involvement of the hand ulnar motor fibers with sparing of sensory function to the dorsal hand. Treatment options include conservative measures (above-mentioned) and decompression of the ulnar tunnel (Guyon canal).

Vascular ultrasound has been used extensively for decades. Newer uses of ultrasonography include imaging of peripheral nerves, and as an aid to invasive procedures and new applications in neurotherapeutics.

The carotid and vertebral arteries and their branches can be evaluated with ultrasound—that is, sound with frequency higher than 20,000 Hz. B-mode (brightness modulation) is based on the transmission of ultrasound through tissues and reflection from tissue interfaces. This imaging technique produces a real-time two-dimensional picture of examined extracranial vessels in longitudinal or transverse view. It allows measurement of vessel diameter and reveals the presence of stenosis or occlusion. High-resolution scans can also determine plaque morphology including ulceration, calcification, or hemorrhage. In Doppler ultrasonography, the ultrasound is reflected off moving targets (erythrocytes). Increased blood flow velocity in a narrowed segment of arterial lumen (stenosis) is associated with higher frequency shift, which correlates with flow velocities. The best result in vascular ultrasonography can be obtained by combination of these two techniques in duplex ultrasonography, which combines the advantages of B-mode with exact sampling of the site, and systolic, diastolic, and mean velocities measured in Doppler mode.

Carotid duplex ultrasonography has an excellent accuracy for detection of stenotic areas compared with angiography. For arteries with more than 50% stenosis, sensitivity is approximately greater than 90%; for occlusions, sensitivity is 80% to 96% and specificity is 95%. However, these results vary considerably with the experience of the ultrasonography technician. Examination of vertebral arteries allows determination of flow direction (for example, subclavian steal syndrome), but morphologic evaluation is not always possible.

Blood flow velocities in the major intracranial arteries can be examined by transcranial Doppler (TCD). TCD has established value in detection of stenosis greater than 65% in the major basal intracranial arteries, assessing collateral flow, evaluating and monitoring vasospasm after subarachnoid hemorrhage, detecting arteriovascular malformations, and assessing patients with brain death. The accuracy of TCD also depends highly on operator skill and experience. TCD may also be used for intraoperative monitoring during carotid endarterectomy and cardiac surgery and in testing cerebrovascular reactivity and hemodynamic reserve (see section on “Transcranial Doppler”).

Ultrasound is now gaining wider use in evaluation of the peripheral nervous system and musculoskeletal system. It can delineate the anatomy of nerve entrapment syndromes and detect foreign bodies impinging on nerves after penetrating trauma. Reports of intrinsic nerve lesions such as hamartomas and neuromas have been described. Ultrasound can efficiently guide biopsies, lumbar puncture, and nerve blocks, leading to more successful outcomes.

Ultrasound of cranial nerves is a developing field. Four cranial nerves can be reliably imaged—optic, facial, vagus, and spinal accessory nerves. Many reports have highlighted the detection of optic nerve anomalies and lesions with ultrasound. Another area under development is applications of ultrasound as therapy including Parkinson disease, essential tremor, and occipital neuralgia.