Clinical Anatomy 9860-62 (1996)

Thoracic Outlet: An Anatomical Redefinition That Makes Clinical Sense

DON RANNEY Schoo/ of Anatomy, Unfvmity of Watcfoo, Waterloo, Ontario, Canada

The diagnosis of syndrome (TOS) is intrinsically difficult, and the literature about it is full of confusing terminology. Symptoms may arise due to compression of neural andlor vascular elements in one or more of three different locations. A number of tests were developed during the early part of this century, and a variety of syndromes have been described that relate to these tests. all of which are now considered to be subtypes of the . Yet anatomists and clinicians fail to agree on even the definition of the thoracic out- let. It is proposed that anatomists not use the term as a synonym for the superior thoracic aperture, nor thoracic outlet for the inferior thoracic aperture. What many clinicians call the thoracic outlet should be called the scalene triangle by both anatomists and clinicians, divisible into a lower portion to be called the thoracic outlet (for subclavian vessels and nerve roots C.8 and T. I) and an upper portion, the cervical outlet (for nerve roots C.5, C.6, and nor- mally C.7). What is currently called thoracic outlet syndrome should be renamed the cervico- arillary syndrome (CAS), divisible into three subtypes: thoracic outlet, costoclavicular, and pectoralis minor syndromes. Compression of the upper roots of the brachial plexus between the anterior and middle should be recognized as cervical outlet syndrome, and all terms containing the word scalenus should be discarded. 0 1996 Wiky-~iss,Inc. Key words: brachial neuritis, cervical outlet, definition, scalene triangle, scalenus

Thoracic outlet syndrome (TOS) is a controversial outlet that would be agreed upon by all. This, in turn, subject with regard to both diagnosis and management would allow the various compression syndromes to be (Lederman, 1987; Cuetter and Bartoszek, 1989). The defined, or redefined, with a greater degree of anatom- situation is further confused by the lack of a generally ical precision. accepted anatomical definition of the thoracic outlet. Travel1 and Simons (1983) have defined the thoracic Standard anatomical textbooks (e.g., Moore, 1992) use outlet as the thin triangular space between the anterior the term thoracicoutletas a synonym for the inferior tho- and middle scalene muscles, whose base is the first . racic aperture, the opening into the abdominal area that Others (Mosely et al., 1991) have accepted this defini- is bounded by the lower costal elements. This is not at tion. But there are problems with this definition, both all what clinicians have in mind when they talk about semantic and practical, which add unnecessary confu- the 's exit from the by passing sion to the diagnosis and management of thoracic out- over the first rib between the anterior and middle sca- let syndrome. Other authors (Berger and Kleinert, lene muscles. Anatomists might think of such an area 1991; Press and Young, 1994) call this space between as a part of the thoracic inlet. The superior thoracic aperture is the space bounded Received for publication November 15,1994; revised April 11,1995. by the left and right first rib together with the first tho- Address reprint requests to Dr. Don Ranney, Head, School of racic and manubrium of the . Some- Anatomy, Department of Kinesiology, University of Waterloo, Wlx- times anatomists refer to this opening as the thoracic rerloo, Ontario N2L 3G1, Canada. inlet and call the inferior thoracic aperture the thoracic This article is an updated version of a rough draft entitled "The outlet. Yet several structures pass out of the inlet or into Thoracic Outlet: An Anatomical Re-definition That Makes Clinical Sense" by the same author previously printed in Excerpta Medica the outlet, as thus defined. It seems reasonable, there- International Congress Series (ICS), Current Trends in Hand fore, to standardize the terminology of these anatomi- Surgery (1995), M. Vastamaki (ed.). Amsterdam, Netherlands: El- cal apertures, and to develop a definition of the thoracic sevier Science B.V., pp. 331-334.

0 1996 Wiley-Liss, Inc. Thoracic Outlet: Anatomical Redefinition 61 the anterior and middle scalene muscles the sca/ene tri- angle. This is not a new term, but its use by all may help reduce diagnostic confusion.

THORACIC OUTLET SYNDROME The constellation of symptoms now attributed to this condition was described by Sir Astley Cooper in 1818, but it was Peet et al. (1956) who first published and apparently coined the term that is in current use.' However, thoracic outlet syndrome is not a single clin- ical entity, and the nerve compression may be at one of three locations. Mackinnon and Dellon (1988) have suggested there may be compression at more than one site. The clinical presentation is that of pain, tingling, and possibly numbness along the post-axial border of the upper limb, with or without vascular symptoms. The precise symptomatology varies according to the extent of arterial, venous, or nerve compression. Phys- ical signs vary according to site. Three sites of compression are possible.

The subclavian artery and lower roots of the brachial plexus may be compressed where they cross the first Fig. 1. Thnc possible sites of compression within the cervico- rib (or a cervical rib) between the anterior and mid- axillary canal (Reproduced by permission from Berger and Kleinert, dle scalene muscles. About this level the two lowest 1991). roots usually combine to form the lower trunk. The subclavian artery and vein and/or lower trunk of the brachial plexus may be compressed behind ing the etiologic factors and clinical features of all sub- the in the costoclavicular space. sets of TOCS" (thoracic outlet compression syndrome). The axillary artery and/or vein and/or one of the This paper has been written to help meet that need. cords of the brachial plexus may be trapped in the angle between the pectoralis minor tendon and REDEFINING THE THORACIC OUTLET the coracoid process on which it inserts. This is apt to occur with hyperabduction of the arm and has The terms thoracic inlet and thoracic outlet as they ap- been called the hyperabduction syndrome or pectoralis pear in current anatomy texts are not of any great func- minor syndrome (see Fig. 1). tional significance. The terms superior thoracic aperttm and inferior thoracic aperture are preferable anatomical At all three sites the nerves and vessels are enclosed terms. The space most clinicians call the thoracic out- within a fascia1 tube, the cervicoaxillary canal (Anson, let is in fact the scalene triangle. We may consider this 1966). Hence, the term cere,icoaxillary syndrome (CAS) divisible into a lower part, the thoracic outlet, and an would be a better diagnostic term than thorack outlet upper pan, the cervical o~tlet.~The upper roots of the syndrome, to be applied in clinical situations until fur- brachial plexus were never in the.thorax and by defin- ther investigation could identify the precise location of ition therefore cannot pass into the arm through a tho- the compression site. racic outlet. They arise in the and, passing from Cuetter and Bartoszek (1989) have stated: "The the neck into the upper limb, must pass out through a confusions and contradictions in the literature empha- cervical outlet. But inferior to these upper roots the size the poor understanding of the syndrome and the subclavian artery does pass out of the thorax, changing urgent need for a more efficient nomenclature describ- its name to axi/lary as it crosses the lower border of the

'Rob and Standeren (1958) quickly accepted it. Lord and Rosati (1958) initially rejected it. But when, in a revision of the same mono- 2Theentire scalene triangle is, of course, in the neck. The division graph, they did accept the term, they erroneously credited it to Rob of this triangle into cervical and thoracic components is with refer- and Standeren (Lord and Rosati, 1971). ence to its contents, and hence its clinical significance. first rib. With it normally pass the eighth cervical and Cooper, A. 1818 On exostosis. In Surgical Essays, 3rd etll. first thoracic nerve roots andlor the inferior trunk of the (reprinted in 1821 as 1st American Edition). Cooper, A. and brachial plexus that these form (generally at the lateral B. Travers (eds.). London: Cox and Son, pp. 135-165. border of the anterior scalene muscle). When there is a Cuetter, A.C. and M.D. Bartoszek 1989The thoracic outlet syn- cervical rib or band, their exit from the thorax is at a drome: Controversies, overdiagnosis, overtreatment and rec- ommendations for management. Muscle Nerve, 12410419. higher level and the seventh cervical nerve root, while Lederman, R.J. 1987 Thoracic outlet syndrome: Review of the not actually passing out of the thorax, may be deemed controversies and a report of 17 instrumental musicians. to have done so. Med. Probl. Perform. Art., 287-91. Terminology used in clinical diagnoses should also Lord, J.W. and L.M. Rosati 1958 Neurovascular compression be amended. The constellation of symptoms now called syndromes of the upper extremity. Clin, Symp., 10:35-62. thoracic outlet syndrome should be renamed cmico- Lord, J.W. and L.M. Rosati 1971 Thoracic outlet syndromes. axillary syndrome (CAS). When the specific site of com- Clin, Symp., 231-32. pression has been determined, a more precise term- Mackinnon, S.E. and A.L. Dellon 1988 Multiple crush syn- drome. In Surgery of the Peripheral Nerve. New York: thoracic outlet, cosfoclavicular or pectoralis minor--can be Thieme Medical, p. 360. applied as appropriate. Clearly distinguished from any Moore, K.L. 1992 Clinically Oriented Anatomy, 3rd ed. Balti- , of these would be compression of the upper roots of the more, MD: Williams & Wilkins, p. 49. brachial plexus, with pre-axial border sensory distur- Mosely. L.H., R.M. Kalafut, P.D. Levinson, and S.A. Mokris bance and nothing to suggest vascular compression. 1991 Cumulative trauma disorders and compression neu- This would be a newly named condition, cervical outlet ropathies of the upper extremities. In Occupational Hand syndrome. In the past this may have been called by and Upper Extremity Injuries & Diseases. Kasdan, M. L. (ed.). Philadelphia: Hanley & Belfus, pp. 353-402. some scalenus syndrome or scalenus anticus syndrome. But Peet, R.M., J.D. Henrikson, T.P. Anderson, and G.M. Martin the terms scalenussyndrome and scalenus anticus syndrome 1956 Thoracic outlet syndrome. Evaluation of a therapeutic are better left in the history books. exercise program. Staff Meet Mayo Chi., 31:281-287. Press, J.M. and J.L. Young 1994 Vague upper-extremity symp- toms? Consider thoracic outlet syndrome. Physician Sports REFERENCES Med. 2257-64. Anson, B.J. 1966 Morris' Human Anatomy, 12th ed. New York: Rob, C.G. and A. Standeren 1958 Arterial occlusion compli- McGraw-Hill, p. 46. cating thoracic outlet compression syndrome. Br. Med. J., 2: Berger, A.C. and J.M. Kleinert 1991 Work-related vascular in- 709-712. juries and diseases. In Occupational Hand and Upper Ex- Travell, J.G. and D.G. Simons 1983 Myofascial Pain and Dys,- tremity Injuries and Diseases. Kasden, M.L.(ed.). Philadel- function: The Trigger Point Manual, Vol. 1. Baltimore, MD: phia: Hanley & Belfus, pp. 319-339. Williams and Wilkins, p. 355.