Entrapment Neuropathies in the Upper and Lower Limbs: Anatomy and MRI Features

Nevner viktige steder nerver kommer i klem.

http://www.hindawi.com/journals/rrp/2012/230679/

Although nerves may be injured anywhere along their course, peripheral nerve compression or entrapment occurs more at specific locations, such as sites where a nerve courses through fibroosseous or fibromuscular tunnels or penetrates muscles [2, 3].

Figure 1: The drawing shows anatomy of the suprascapular nerve from the posterior view. Note the nerve courses through the suprascapular notch (open arrow) and spinoglenoid notch (curved arrow). SSN: suprascapular nerve, SS: supraspinatus muscle, IS: infraspinatus muscle.

Suprascapular nerve compression or entrapment, known as suprascapular nerve syndrome, can occur as a result of trauma, an anomalous or thickened transverse scapular ligament, or extrinsic compression by a space-occupying lesion [7, 8], commonly a ganglia cyst or soft tissue tumor. Compression or entrapment at the suprascapular notch leads to supraspinatus and infraspinatus muscle denervation (Figure 2), whereas more distal entrapment at the spinoglenoid notch may present with isolated involvement of the infraspinatus muscle (Figure 3). Patients may present with poorly localized pain and discomfort at the back of the shoulder or the upper back, as well as weakness when raising the arm.


Figure 4: The drawing shows the axillary nerve within the quadrilateral space from a posterior view. AN: axillary nerve, Tm: teres minor muscle, Tr: long head of the triceps, TM: teres major muscle, H: humerus, D: deltoid muscle.

Clinical manifestations include poorly localized shoulder pain and paresthesias in the affected arm in a nondermatomal distribution. The diagnosis can be difficult since clinical symptoms may be confused with rotator cuff pathology or other shoulder joint-related abnormalities [9].


Figure 6: The drawing provides an anterior view of the course of the radial nerve at the elbow. Posterior interosseous nerve (PIN) entrapment may occur due to prominent radial recurrent artery (RRA), medial edge of the extensor carpi radialis brevis (ECRB), and proximal edge of the supinator muscle (SP) (arcade of Frohse). RN: radial nerve, SRN: superficial radial nerve.

The radial nerve is predisposed to injury and entrapment at several locations along its course, which include the radial nerve in the spiral groove of the humerus (spiral groove syndrome) above the elbow joint, where the PIN travels through the radial tunnel, and the superficial branch of the radial nerve where it crosses over the first dorsal wrist compartment (Wartenberg’s syndrome).

Compression or entrapment of the PIN in the radial tunnel may yield two different clinical presentations: posterior interosseous nerve syndrome and radial tunnel syndrome.
In patients with posterior interosseous nerve syndrome, the clinical presentation includes motor deficits of the extensor muscle group without significant sensory loss.
Patients with radial tunnel syndrome, on the other hand, typically present with pain over the proximal lateral forearm [12, 13], which can be caused by acute trauma, masses, and compression from adjacent structures.


Figure 8: The drawing demonstrates the course of the ulnar nerve from posterior view at the elbow. Note the nerve travels deep to the flexor carpi ulnaris muscle (FCU) beneath the arcuate ligament (AL).

Compressive or entrapped ulnar nerve neuropathies include cubital tunnel syndrome and Guyon’s canal syndrome.

Cubital tunnel syndrome is the second most common peripheral neuropathy of the upper extremity. It may be caused by abnormal fascial bands, subluxation, or dislocation of the ulnar nerve over the medial epicondyle, trauma, or direct compression by soft tissue masses. Clinical symptoms include a sensory abnormality of the ulnar hand and weakness of the flexor carpi muscle group of the 4th and 5th fingers.


Figure 12: The drawing of the median nerve shows that it courses along the anterior elbow, through the two heads of the pronator teres muscle (stars), and into the forearm beneath the edge of the fibrous arch of the flexor digitorum sublimis (open arrow).

Median nerve compression or entrapment neuropathies include pronator syndrome, anterior interosseous syndrome, and carpal tunnel syndrome.

Clinical findings include pain and numbness of the volar aspect of the elbow, forearm, and wrist without muscle weakness.


Figure 14: The drawing shows the proximal course the sciatic nerve passing inferior to the piriformis muscle (PS). SG: superior gemellus muscle.

Sciatic nerve entrapment may occur in the hip region and less commonly in the thigh, and clinical presentations are based upon the level of injury [3]. Sciatic neuropathy may result from conditions such as fibrous or muscular entrapment, vascular compression, scarring related to trauma (Figure 15) or radiation, tumors (Figure 16), and hypertrophic neuropathy [3, 17, 18].


Figure 17: Sagittal oblique projection of the knee illustrates the common peroneal nerve (CPN) arising from the sciatic nerve (SN) at the level of popliteal fossa. It travels around the fibular head deep to the origin of the peroneus longus muscle (PL). TN: tibial nerve.

The etiologies of common peroneal neuropathy may include idiopathic mononeuritis, intrinsic and extrinsic space-occupying lesions including an intraneural ganglion cyst (Figure 18) [21], or traumatic injury of the nerve, especially related to proximal fibular fractures [22]. Clinically, patients may experience pain at the site of entrapment with foot drop and a slapping gait [17, 23].


Figure 19: The drawing of the medial aspect of the ankle showing the course of the tibial nerve (TN) and its branches, the medial calcaneal nerve (MCN), and medial and lateral plantar nerves (MPN and LPN), passing through the tarsal tunnel. FR: flexor retinaculum.

Common etiologies include posttraumatic fibrosis due to fracture, tenosynovitis, ganglion cysts (Figure 20), space-occupying lesions, and dilated or tortuous veins. Most patients with tarsal tunnel syndrome have burning pain and paresthesia along the plantar foot and toes.

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