7.4. Differential Diagnosis of Thoracic Outlet Syndromes
Anatomical Variations of the Thoracic Outlet
- Bone defects:
- Cervical rib
- Abnormal or rudimentary first rib
- Droopy shoulder syndrome
- Costoclavicular syndrome
- Congenital bands or ligaments
- Pectoralis minor (hyperabduction syndrome)
- Large subclavian muscle
- Tight thoracic inlet
- Scalene triangle congenital defects:
- Narrow scalene triangle
- Proximity of anterior and middle scalene muscles
- High emergence of roots from the triangle
- Interdigitated muscle fibers between the middle and anterior scalene muscles
- Adherence of nerve roots to the anterior scalene muscle
- Congenital narrowness of the costoclavicular space
- Clavicle (acromial head depression compresses the costoclavicular space)
- Tight pectoralis minor space (below the insertion of the pectoralis minor tendon into coracoid process): hyperabduction of arm closes the space
Anatomy of the Thoracic Outlet
- The major components of the thoracic outlet:
- Sternocostovertebral space:
- Most proximal part of the thoracic outlet tunnel
- Anatomy:
- Anteriorly demarcated by the sternum
- Posteriorly by the spine
- Laterally by the first rib
- Subclavian artery, subclavian vein C4–T1 roots of the plexus traverse this space
- Nerve roots have exited spine and have not formed trunks
- Associated structures:
- Apex of the lung and pleura
- Sympathetic trunk
- Jugular vein
- Lymphatics of the neck
- May rarely be congenitally narrowed
- Usual pathology of the sternocostovertebral space:
- Thyroid mass
- Thymus enlargement
- Parathyroid mass
- Lymph nodes
- Lung
- Pancoast tumor (squamous or adenocarcinoma of the lung)
- Scalene triangle:
- Anatomy:
- Bounded by the anterior scalene muscle anteriorly
- Middle scalene muscle posteriorly
- First rib forms the base
- Anterior scalene muscles:
- Origin is the transverse process of C3–C6
- Insertion on the scalene tubercle of the first rib varies; tubercle insertion is between the subclavian artery and vein and the pleural dome
- Variants of insertion:
- Behind the artery
- Between the artery and the brachial plexus
- Entire base of the scalene triangle (traps the neurovascular bundle)
- Anterior insertion may merge with insertion of the middle scalene muscle (20% of patients)
- C5–C6 roots may transverse the anterior scalene muscle rather than descend between the anterior and middle scalene muscles
- Middle scalene muscle:
- Origin is the transverse process of C2–C7
- Insertion (Chassaignac's) retroarterial tubercle of the first rib
- May insert on the fibrous septum of the pleural dome; lateral fibers insert on the second rib
- C8–T1 roots (individually or together as the lower trunk) compressed by more anterior or forward compression of the middle scalene muscle (sharp anterior edge); congenital fibromuscular bands noted along the anterior edge of the muscle may also compress the C8–T1 roots
- First rib:
- Floor of the scalene triangle
- T1 closest to the rib
- Congenital rib anomalies, bony ridges, hypoplasia or inward curvature may compress the neurovascular bundle
- Scalene triangle congenital variations:
- Base of the triangle 0.77 cm in men; 0.67 cm in women
- C5–C6–C7 emerge from the apex of the triangle; the fibers of the middle and anterior scalene muscles merge at the apex. Patients with C5, C6–C7 root involvement greater involvement incidence that have roots that emerge from the apex, inter digitation of anterior and middle scalene muscles. It occurs in 70% of symptomatic patients. Adherence of C5–C6 roots to the middle scalene muscles is another source of pathology
- Costoclavicular space (compresses the brachial plexus)
- Pectoralis minor space (compresses the brachial plexus)
Cervical Ribs
- Gruber classification of cervical ribs:
- Type I – < 2.5 cm:
- Protrudes slightly beyond transverse process, attaches to the first rib by a tight fibrous band
- Type II – 2.5 cm:
- Attaches to the first rib by a tight fibrous band
- Rib and band lie within or on the medial border of the middle scalene muscle
- Narrows the scalene triangle
- Type III:
- Complete rib with fibrous connection to the first rib
- Type IV:
- Complete rib with cartilaginous joint at the first rib
- Complete rib causes the neurovascular bundle to arch over the rib
- Compressed when the shoulder girdle is depressed
- General Features of Cervical Ribs
- Incidence 0.3% of patients
- Women 2:1 greater than men
- Approximately 10% of patients with cervical ribs are symptomatic; usually symptoms are initiated by trauma
- Arterial damage to subclavian artery (stenosis or aneurysmal dilatation) associated with bony defects
Ligaments and Fibrous Bands that Compress Cervical Nerve Roots
- Twelve different fibrous structures can compromise the thoracic outlet
- Most significant ligaments:
- Transverse process of C7 to first rib
- Tip of cervical rib that inserts on the first rib
- Ligaments are within the body or on the anterior surface of the middle scalene muscle; may affect C8 or T1 (or the lower trunk)
- Common anomalies; incomplete cervical rib or a long transverse process of C7 from which a tight band inserts on to the first rib
- Roo's congenital bands and ligaments:
- Type I: tip of an incomplete cervical rib inserts posteriorly to the scalene tubercle
- Type II: origin from transverse process of C7 inserts on the scalene tubercle
- Type III: originates and inserts on the first rib; origin is posterior and insertion is anterior
- Type IV:
- Originates within the middle scalene muscle (C2–C7)
- Courses on the anterior edge of the middle scalene
- Inserts with the muscle on the first rib
- Adjacent to C8, T1
- Type V:
- Scalene minimus muscle is the Vth band
- Origin is the anterior scalene muscle (lower fibers)
- Courses behind the subclavian artery in front of the plexus to insert on the first rib
- Type VI: scalene minimus insertion into Sibson's fascia over the cupula of the lung rather than the first rib
- Type VII:
- Fibrous cord coursing on the anterior surface of the anterior scalene
- Inserts on the costochondral junction or sternum
- Band lies behind the subclavian vein which it may compress
- Type VIII:
- Origin: middle scalene muscle
- Courses under the subclavian artery and vein
- Inserts on the costochondral junction
- Type IX: web of muscle and fascia that fills the posterior curve of the first rib
- Rib-band syndrome of Gilliat:
- Type II band
- Compresses the C8, T1 roots (lower cord)
- Paresthesias of the 4th, 5th fingers, medial forearm to medial humerus
- Atrophy and wasting of intrinsic hand muscles
- Thyroglossal duct cyst (involvement of C3–C4 roots)
- Branchial cleft cysts (involvement of C2–C5 roots)
- Short pedicle and block vertebral body:
- Entrapment of the nerve root under the pedicle and in the exit foramina
- Achondroplasia (at all cervical levels)
Neurogenic Thoracic Outlet Syndrome (Neuropraxic Injury)
- General features:
- Most frequent cause of TOS
- Traumatic in origin (MVA, repetitive movements, falls)
- High percentage of patients have an underlying anatomical variant:
- The four anatomical spaces of the thoracic outlet:
- Sternocostovertebral space
- Scalene triangle (most frequently involved)
- Costoclavicular space
- Pectoralis minor space
- Congenital bands (twelve types)
- Cervical ribs
- Long neck droopy shoulder
- Tight thoracic inlet
- Abnormal insertion of the anterior, middle or minimus scalene muscles
- Associated with injury to the cervical and brachial plexus
- A delayed and progressive lesion
- Later stages associated with CRPS II (may spread; "mirror" or generalize)
- Clinical features:
- Abnormal posture of the affected extremity; forward flexed and dropped shoulder as position of comfort (weakness of lower trapezius muscles and levator scapulae; associated ventral roots of C1–C4)
- Positive stretch maneuvers:
- Roos' abduction stress maneuver invariably positive in < 1 minute; Wright's maneuver frequently positive. Heaviness and paresthesias in specific plexus radiations within 1–2 minutes. Control patients can maintain posture for at least three minutes (abduction stress position)
- Positive Tinel's signs:
- Erb's point (supraclavicular plexus)
- Pectoralis minor space (lateral infraclavicular)
- Neurovascular bundle (proximal humerus)
- Cubital tunnel (ulnar nerve)
- Arcade of Frohse (dorsal radial sensory fibers)
- Pronator canal (median nerve)
- Occasionally the carpal tunnel and Guyon canal at the wrist are concomitantly positive
- Sensory loss in specific plexus distribution:
- Upper trunk:
- Lateral deltoid, forearm and thumb
- Trapezius ridge and medial scapular border (pain at its tip-Notalgia); the C4–C7 root radiations
- Lower trunk:
- Medial forearm (antebrachial cutaneous) and arm (brachial cutaneous) to the axilla
- Radiation into the complete 4th finger (ulnar splits the 4th finger)
- Proximal lesions may have Horner's syndrome (C8–T1 involvement)
- Middle trunk:
- Not as clearly defined
- The posterior upper arm (triceps)
- Dorsal forearm; dorsal hand; dorsal thumb; second and third finger
- Median sensory 2nd and 3rd fingers
- Lateral cord:
- Lateral forearm
- Thumb, index and radial side of the third finger
- Lateral antebrachial cutaneous nerve
- Medial cord:
- Medial forearm: medial antebrachial cutaneous nerve)
- Ulnar side of the third finger and complete 4th and 5th finger
- Frequent involvement of the Intercosticobrachial nerve: the anterior chest wall (T1–T3 primarily, lateral chest wall (anterior axillary line); radiate under the breast to the middle of the abdomen at xiphoid process)
- Posterior cord:
- Triceps muscle
- Dorsal forearm to base of the thumb (posterior antebrachial radial cutaneous nerve)
- Muscle weakness:
- Upper trunk:
- Musculocutaneous nerve (biceps)
- Middle trunk:
- Abduction, forward elevation and extension of the shoulders; internal and external arm rotation decreased forearm and finger extension
- Lower trunk:
- Ulnar innervated muscles of hand and forearm
- Median innervated intrinsic hand muscles
- Muscles innervated by anterior interosseous
- Extensor indices proprius
- Reflexes:
- Most often normoactive
- May be increased if CRPS II/RSD has supervened (sympathetic hyperactivity induces contraction of the intrafusal muscle fibers of the nuclear bag)
- Clinical signs and symptoms of CRPS II/RSD particularly if the lower trunk is damaged (carries the sympathetic of the arm)
Cervical Rib Band Syndrome
- Young to middle aged females
- C8–T1 primary rami or lower trunk stretched over cervical rib or band whose origin is the transverse process of C7 or a rudimentary cervical rib that inserts on the first rib
- Hand weakness and wasting:
- All intrinsic hand muscles affected
- Lateral thenar muscles most severely affected
- Medial forearm muscles wasted
- Patchy sensory loss of the medial forearm, third, fourth and fifth fingers
- X-ray reveals rudimentary cervical ribs or elongated inferiorly angulated transverse process of C7
Droopy Shoulder Syndrome
- Women > men
- Long neck with sloping shoulders
- Second thoracic vertebra noted above the clavicle on lateral chest X-ray
- Pain and paresthesias in upper trunk and lower trunk distributions
- Cervical plexus pain (face and back of the head)
- Positive Roos' abduction stress maneuver; positive Tinel's sign in the supra and infraclavicular fossa; neurovascular bundle, Arcade of Frohse and pronator canal
- Sensory deficit most often lower trunk distribution
- Slight weakness of intrinsic hand muscles
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