3100 · 3 Motor System

Plexus Syndromes

The cervical plexus is formed by nerve roots C2­C4, the brachial plexus by nerve roots C5­T1, and the lumbosacral plexus by nerve roots L1­S3.

Lesions of the Cervical Plexus

The cervical plexus (Fig. 3.31) occupies a relatively sheltered position and is thus rarely injured. Unilateral or bilateral phrenic nerve dysfunction (C3, C4, and C5) is more commonly caused by a mediastinal process than by a cervical plexus lesion.

Suboccipital n.

Greater occipital n.

Lesser occipital n.

Great auricular n.

Transverse cervical n.

Supraclavicular nn.

To the brachial plexus

Fig. 3.31 The cervical plexus

C1

Hypoglossal n. (CN XII)

C2

Superior cervical ganglion

C3

C4

Ansa cervicalis

C5

Phrenic n.

(schematic drawing)

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Complex Clinical Syndromes due to Lesions of Specific Components of the Nervous System · 101 3

Lesions of the Brachial Plexus

Brachial plexus lesions are classified into two types, upper and lower, on clinical and pragmatic grounds. The anatomy of the brachial plexus is shown in Fig. 3.32.

In upper brachial plexus palsy (Duchenne­Erb palsy), due to a lesion of the C5 and C6 nerve roots, the deltoid, biceps, brachialis, and brachioradialis muscles are paretic. There is a sensory deficit overlying the deltoid muscle and on the radial side of the arm and hand.

Dorsal scapular n.

Suprascapular n.

Lateralcord (C5–7)

Posterior cord (C5–T1)

Medialcord (C8–T1)

Musculocutaneous n.

Median n.

Radial n.

Axillary n.

Ulnar n.

Fig. 3.32 The brachial plexus (schematic drawing)

C4

C5

C6

C7

C8

T1

Phrenic n.

Subclavius n.

Lateral pectoral n.

Medial pectoral n.

Long thoracic n.

Subscapular n.

Thoracodorsal n.

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3 102 · 3 Motor System

		Fig. 3.33 Scalene syndrome
	C5	(thoracic outlet syndrome) due to a
		cervical rib.
Anterior
scalene m.	C6
Cervical rib
Fibrous band	C7

Brachial plexus

T1

Subclavian a.

1st rib

In lower brachial plexus palsy (Klumpke palsy), due to a lesion of the C8 and T1 nerve roots, the wrist and finger flexors and the intrinsic muscles of the hand are paretic. Occasionally, Horner syndrome is present in addition. There are prominent trophic abnormalities of the hand and fingers.

Causes of Brachial Plexus Lesions

Trauma, usually due to road accidents or sporting injuries, is by far the most common cause of damage to the brachial plexus. Men are much more frequently affected than women. Most patients are between 20 and 30 years old.

Brachial plexus damage also has many etiologies other than trauma: compression syndromes in the area of the shoulder (scalene syndrome; compression by safety belts, rucksack straps, etc.; costoclavicular syndrome; hyperabduction syndrome); tumors (e. g., apical lung tumor with Pancoast syndrome); inflammatory-allergic lesions (neuralgic shoulder amyotrophy); and birth injuries.

Scalene syndrome (Fig. 3.33). The cords of the brachial plexus pass through the so-called scalene hiatus, which is delimited by the anterior and middle scalene muscles and the first rib. The hiatus normally has enough room for the cords of the brachial plexus and the subclavian artery, which accompanies them, but pathological abnormalities such as those associated with a cervical rib can critically narrow the hiatus. In such cases, the cords of the brachial plexus and

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Complex Clinical Syndromes due to Lesions of Specific Components of the Nervous System · 103	3

the subclavian artery must pass over the attachment of the cervical rib to the first (thoracic) rib and are vulnerable to compression at this site. The most prominent symptom of scalene syndrome (a type of thoracic outlet syndrome) is position-dependent pain radiating into the upper limb. Paresthesia and hypesthesia are often present, especially on the ulnar side of the hand. In severe, longstanding cases, there may be weakness of Klumpke type (see above). Damage to the sympathetic nerve fibers traveling with the subclavian artery frequently causes vasomotor disturbances as well.

Lesions of the Lumbosacral Plexus

Here, too, lesions may be classified into two types: lumbar plexus lesions and sacral plexus lesions. The anatomy of the lumbosacral plexus is shown in Fig. 3.34.

Lumbar plexus lesions (L1, L2, and L3) are less common than brachial plexus lesions, because of the sheltered location of the lumbar plexus. The causes of damage to both plexuses are largely the same. There are, however, practically no cases of inflammatory-allergic dysfunction of the lumbar plexus (which would be analogous to neuralgic shoulder amyotrophy). On the other hand, metabolic disturbances such as diabetes mellitus are more likely to affect the lumbar plexus than the brachial plexus.

Sacral plexus lesions. The sacral plexus is formed by nerve roots L4, L5, and S1 through S3. The most important nerves emerging from the sacral plexus are the common peroneal and tibial nerves, which are joined together as the sciatic nerve in its course down the posterior thigh. The two nerves separate from one another just above the knee and then follow their individual paths further down the leg (Fig. 3.35).

The common peroneal nerve mainly innervates the extensors of the foot and toe, while the tibial nerve innervates the plantar flexors and most of the intrinsic muscles of the foot. A lesion of the common peroneal nerve, or of the common peroneal portion of the sciatic nerve, weakens the extensors, causing a foot drop (steppage gait); a lesion of the tibial nerve weakens the plantar flexors, making toe-walking impossible. Peroneal nerve palsy is more frequent than tibial nerve palsy, because the course of the tibial nerve is relatively sheltered. Peroneal nerve palsy impairs sensation on the lateral surface of the leg and the dorsum of the foot, while tibial nerve palsy impairs sensation on the sole.

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3104 · 3 Motor System

	Iliohypogastric n.
Lumbar plexus	Ilioinguinal n.
	Genitofemoral n.
	Lateral femoral cutaneous n.

Obturator n.

Femoral n.

Superior gluteal n.

plexus

Inferior gluteal n.

Sciatic n.

Sacral

Common peroneal (common fibular) n.

Tibial n.

Posterior femoral cutaneous n.

Pudendal n.

Fig. 3.34 The lumbosacral plexus (schematic drawing)

L1

L2

L3

L4

L5

S1

S2

S3

S4

S5

Coccygeal n.

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Complex Clinical Syndromes due to Lesions of Specific Components of the Nervous System · 105	3

Musculocutaneous n.

Median n.

Posterior cord

Axillary n.

Radial n.

Ulnar n.

Superior and inferior gluteal nn.

Femoral n.

Sciatic n.

Obturator n.

Saphenous n.

Tibial n.

Peroneal n.

Ulnar n.

Fig. 3.35 The course of selected important peripheral nerves

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