THE ANATOMICAL RECORD 214239-95 (1986) Report of a Rare Human Variation: Absence of the Radial Artery WILLIAM L. POTEAT Department ofdnatomy, School of Medicine, University of South Carolina, Columbia, S C 29208 ABSTRACT A case of unilateral absence of the radial artery is reported. The arterial system of the specimen was developmentally primitive with the anterior interosseous artery the chief blood supply to the forearm and hand. A “superficial ulnar artery” of small caliber supplemented the supply of the hand. Three large branches of the anterior interosseous artery supplied the hand with the lateral terminal branch replacing the radial artery distal to the wrist. The superficial palmar arch was formed by an anastomosis of the media and lateral terminal branches of the anterior interosseous artery. No deep palmar arch was present, but three palmar metacarpal arteries arose from a perforating artery which branched from a large dorsal branch of the anterior interosseous artery. The median artery was of small caliber and could not be traced beyond the midforearm. Based on this specimen and a review of other forearm and hand arterial variations, it is postulated that the ulnar artery may developmentally precede the median artery. Variations and anomalies of the arterial pattern of the upper extremity of man are fairly common. McCormack et al. (1953) and Coleman and Anson (1961) have published detailed descriptions of the major and minor variations of the arteries of the upper limb and hand. However, a variation that is quite rare is the complete absence of the radial artery in the forearm. Such cases have been reported by Charles (1894) and Kadanoff and Balkansky (1966).A third has now been observed which differs significantly from the other two cases, may be the most primitive pattern ever reported, and has potential embryologic and surgical significance. The pattern to be described has not been previously reported and does not appear t o fit the description of the embryologic development of these arteries (Woollard, 1922; Singer, 1933). MATERIALS AND METHODS The specimen was from a Caucasian female. The axilla, arm, and part of the forearm had been dissected and several of the smaller branches had been sacrificed by the time the students brought the variation to the attention of the author. When the potential significance of the variation was recognized, the author completed the dissection of the forearm and hand. The variation was present on the left side and the right side exhibited an unremarkable pattern of arterial distribution. No scars or surgical incisions were observed in the skin. The nomenclature to be used will be the English version of the Paris Nomina Anatomica and is consistent with that of the 38th British edition of Gray’s Anatomy. RESULTS The branching pattern of the subclavian artery was not unusual, but the branches of the axillary artery exhibited some variability. The subscapular artery was 0 1986 ALAN R. LISS, INC. of large caliber, for it was the origin of the lateral thoracic and posterior humeral circumflex arteries. The anterior humeral circumflex artery appeared normal. The profunda brachii artery arose from the brachial artery 5.0 cm distal to the origin of the subscapular artery. Three centimeters distal t o the origin of the profunda brachii artery, a “superficial ulnar” artery arose and coursed distally on the medial surface of the brachialis muscle. This artery supplied the brachialis muscle via several small branches and passed anterior to the origin of the flexor muscles from the medial epicondyle (Fig. 1).In the middle of the forearm the superficial ulnar joined the ulnar nerve and continued distally with it just lateral to the tendon of the flexor carpi ulnaris muscle. The brachial artery continued distally with the median nerve to the cubital fossa where it could then be named the common interosseus artery as there was no bifurcation into radial and ulnar arteries. In the cubital fossa a radial recurrent artery arose and coursed superiorly adjacent to the radial nerve (Fig. 1).The posterior ulnar recurrent artery arose from the common interosseous 2.0 cm distal to the origin of the radial recurrent artery (Fig. 1).This vessel crossed the brachialis tendon, passed deep to the humeral head of the flexor digitorum superficialis muscle, and joined the ulnar nerve deep to the flexor carpi ulnaris muscle. A superior ulnar collateral artery was identified as it arose from the brachial artery between the profunda brachii artery and the superficial ulnar artery. It could be traced distally to a point very close to the posterior ulnar recurrent vessel. Neither an inferior ulnar collateral artery nor an ante- Received April 30, 1985; accepted July 1, 1985 90 W.L. POTEAT Fig. 1. Anterior view of left forearm. The pin at the left marks the position of the elbow joint. a, brachial artery; b, anterior interosseous a.; c, “superficial ulnar a,,”; d, medial terminal branch of anterior interosseous; e, flexor pollicis longus tendon; f, pronator teres muscle (reflected medially);g, median a,;h, lateral terminal branch of anterior interosseous; i, accessory muscle described i n text; J, posterior ulnar recurrent a.; k,radial recurrent a. Fig. 2. Anterior view of distal forearm and wrist. a, anterior interosseous a,; b, lateral terminal branch; c, medial terminal branch; d, lateral cut edge of‘ pronator quadratus muscle; e, approximate position of radiocarpal joint; f, radius: g, long flexor tendons of the digits reflected medially; h, tendon of flexor pollicis longus. rior ulnar recurrent artery were identified with certainty. The common interosseous artery continued distally from the cubital fossa, passing first deep to the pronator teres muscle, then deep to the flexor digitorum profundus muscle, and continued distally on the anterior surface of the interosseous membrane as the anterior interosseous artery (Fig. 1).The posterior interosseous artery arose from the common interosseous artery 3 cm distal to the origin of the posterior ulnar recurrent and deep to the pronator teres muscIe and was distributed normally. The anterior interosseous artery was of approximately the same caliber as the brachial artery and the common interosseous artery (Fig. 1).From the anterior interosseous artery a small branch arose that coursed distally in company with the median nerve and was presumed to be the median artery. It was small and could be traced only to the distal third of the forearm P i g . 1). No vessel was observed arising from the brachial artery in the cubital fossa that coursed distally with any resemblance of a radial artery, nor was any vessel ob- ABSENCE OF RADIAL ARTERY 91 Fig. 3. Anterior view of distal forearm and hand. a, medial terminal branch of anterior interosseous artery anastomosing with “superficial ulnar a,”; b, “superficial ulnar a.”; c, superficial palmar arch; d, lateral terminal branch of anterior interosseous a. served arising from the axillary or brachial that would have been a “superficial radial artery.” The muscles of the forearm were supplied by the superficial ulnar artery, the common interosseous artery, and the very large anterior interosseous artery. The anterior interosseous artery passed deep to the pronator quadratus muscle and divided into two terminal branches of equal caliber at the distal border of the muscle (Fig. 2). The medial terminal branch continued medially deep to the long flexor tendons, turned anteriorly between the long flexor tendons of the fifth digit and the flexor carpi ulnaris tendon, and joined the superficial ulnar 4 cm proximal to the pisiform bone by a direct anastomosis (Fig. 3). The medial terminal branch of the anterior interosseous artery was approximately four times the caliber of the superficial ulnar. After the two vessels anastomosed, the resulting single vessel continued into the hand lateral to the pisiform bone and anterior to the transverse carpal ligament. A fairly typical superficial palmar arch was formed by the anastomosis of the lateral and medial terminal branches of the anterior interosseous artery (Fig. 3). No deep ulnar branch was identified. The lateral terminal branch of the anterior interosseous artery continued distally for 1 cm and turned laterally across the distal end of the radius (Fig. 2.) At this point it was deep to the flexor pollicis longus tendon and the tendon of an anomalous muscle t o be described subsequently. The artery continued distally through the floor of the “anatomical snuff box” with relations identical to a normal radial artery. On the dorsum of the hand the lateral terminal branch pierced the first dorsal interosseous muscle and came t o lie between it and the adductor pollicis muscle. This artery was in contact with the first metacarpal bone after piercing the first dorsal interosseous muscle. It continued distally to the meta- carpophalangeal joint where the princeps pollicis artery arose. The lateral terminal branch then pierced the adductor pollicis muscle t o complete the superficial palmar arch with the medial terminal branch of the anterior interosseous artery. The vessel did not have any branches resembling a deep palmar arterial arch. A typical deep arch was not observed in this specimen but was replaced by an artery to be described. On the dorsum of the hand the lateral terminal branch was the origin of a small dorsal carpal branch and a typical first dorsal metacarpal branch. A third large branch arose 0.5 cm proximal to the termination of the anterior interosseous artery and deep to the pronator quadratus muscle (Fig. 5). This artery pierced the interosseous membrane and continued distally across the dorsal aspect of the radiocarpal joint to the proximal end of the third intermetacarpal space (Fig. 4).At this point the vessel continued distally as a dorsal metacarpal artery and was the origin of a very large proximal perforating artery which passed between the two heads of the third dorsal interosseous muscle and entered the palm where it was deep to the transverse head of the adductor pollicis muscle. The proximal perforating artery divided into three terminal branches which continued distally to the digits (Fig. 5). The lateral of these three branches continued distally deep to the transverse head of the adductor pollicis muscle until it reached the radial side of the index finger where it was distributed as a typical radialis indicis artery. A short branch of the superficial palmar arch anastomosed with this radialis indicis artery just proximal to the second MP joint. The medial branch of the large proximal perforating artery coursed medially between the muscles of the hypothenar eminence and the two long flexor tendons to the fifth digit where it was distributed as a typical proper palmar digital artery. This vessel 92 W.L. POTEAT Flg. 4. View of dorsal aspect of distal forearm, wrist, and hand. a , dorsal terminal branch of anterior interosseous artery; b, dorsal metacarpal a,: c, proximal perforating a.: d, distal end of ulnar. had no anastomotic connections with the superficial palmar arch. The third branch of the proximal perforating artery coursed distally resembling a palmar metacarpal artery. This artery passed deep to the flexor tendons to the fourth digit and joined the common palmar digital artery to the fourth and fifth digits just proximal to its division into proper palmar digital arteries. The medial side of the second digit, the entire third digit, and the lateral side of the fourth digit were supplied by the first and second common palmar digital arteries with no anastomotic connection with the deep vessels arising from the proximal perforating artery (Fig. 5). After the origin of the proximal perforating artery, the large dorsal metacarpal vessel continued distally and joined the second common palmar digital artery just proximal to its bifurcation. This anastomosis completed the major anastomotic connections in the hand of this specimen. Other than the anastomosis of the superficial ulnar artery with the medial terminal branch of the anterior interosseous, it should be emphasized that all other anastomoses were of branches of the anterior interosseous artery, making it essentially the sole blood supply to the hand (Fig. 5). Two muscle variations were also observed in this specimen. The flexor carpi radialis muscle inserted on the trapezium where it blended with the origin of the abductor pollicis brevis muscle. The other variation was a n extra muscle which arose from the radius distal to the origin of the flexor pollicis longus muscle. Its tendon passed deep to the origins of the thenar musculature and inserted at the base of the second metacarpal bone. The muscle would have acted as a n accessory flexor of the wrist. Another observed variation was the Dosterior interosseous nerve terminating on the dorsum of the second and third digits rather than at the wrist. DISCUSSION The arterial pattern of this specimen may be the most primitive ever reported in man because 1) the anterior interosseous artery was the dominant supply of the hand, 2) the median artery was very small, 3) the ulnar artery was represented by a “superficial ulnar artery,” 4)no deep palmar arch was present, and 5 ) no “superficial brachial” or “superficial radial” arteries were present. The anterior interosseous artery is the distal part of the axial vessel in the developing human forearm, as well as being phylogenetically the oldest of the limb vessels (Woollard, 1922; Singer, 1933). The arterial pattern described above differs significantly from other cases of absence of the radial artery reported by Charles (1894) and Kadanoff and Balkansky (1966). The chief difference is in the termination of the anterior interosseous artery. In the present case, the anterior interosseous terminated by bifurcating into medial and lateral terminal branches, whereas in the others it terminated as the lateral terminal branch only. In all three cases the lateral terminal branch entered the palm similar to a normal radial artery. However, in the Kadanoff and Balkansky case, the lateral terminal branch formed the deep palmar arch, instead of forming the superficial arch as it does in this case. Charles (1894) did not describe the distribution of the anterior interosseous arterv in the hand. The Dresence of the “suDerficia1 ulnar artkry” makes this case more primitive, fbr in the other two the brachial artery terminated by bifurcating in the cubital fossa, whereas in this case it simply continued ABSENCE OF RADIAL ARTERY Fig. 5. Diagrammatic representation of the arteries of the hand. Solid lines represent arteries on the palmar aspect of the hand. Dashed lines represent arteries on the dorsum. a, anterior interosseous a.; b, “superficial ulnar a,”;c, dorsal branch of anterior interosseous artery; d, medial terminal branch of anterior interosseous a,; e, proximal perforating a,; f, palmar metacarpal a,; g, common palmar digital aa.; h, dorsal metacarpal a,; i, radialis indicis a,; j, princeps pollicis a.; k, anastomotic connection of superficial palmar arch with radialis indicis a.; 1, lateral terminal branch of anterior interosseous artery. as the anterior interosseous artery. McCormack et al. (1953) reported a “superficial ulnar artery” in 2.26% of their series, but none anastomosed with a branch of the anterior interosseous artery as in the present case. A further difference is that in the Kadanoff-Balkansky case there was a large dorsal terminal branch of the anterior interosseous artery which they reported formed the dorsal carpal rete, instead of terminating as in this case. Fontana and Ghilardi (1973) reported a case of a small radial artery with large ulnar artery and anterior 93 interosseous artery, but in their case the ulnar artery supplied most of the hand. Therefore, the present case is quite different from other reported arterial variations of the upper extremity. The anterior interosseous artery in this case was almost the sole blood supply to the hand, being reinforced only by the small anastomotic connection from the superficial ulnar artery. Based on the embryologic development of these arteries (Keibel and Mall, 1910; Singer, 1933;Mrazkova, 1973) and reported adult anomalies, the sequence of arterial development may differ from the classical descriptions. Since a reasonable assumption is that the present case represents developmental arrest at one of the early stages, then stages 2 and 3 of the classical description may be reversed (Fig. 6). Instead of the median artery being the first vessel t o develop after the axial system, it may be that the ulnar artery develops prior to the median, making it the more primitive vessel and the second dominant vessel t o the hand after the anterior interosseous. In one of Muller’s (1903) illustrations of a human embryo the ulnar artery is depicted as being further developed than the median artery. Since 1)the arterial pattern in the present report is so primitive, 2) a superficial ulnar artery does reach the hand where it anastomoses with the anterior interosseous artery, and 3) a very small median artery is present in the proximal forearm, one is then led to the conclusion that the development of the arteries of the upper limb may follow the proposed arrangement shown in Figure 6. In this arrangement it would be postulated that the ulnar system was the second to develop and that it developed like the superficial brachial-radial system. A “superficial ulnar artery” would first develop and later an anastomotic connection would develop in the cubital fossa between the brachial and the superficial ulnar, after which the proximal part of the superficial ulnar would degenerate or atrophy. The distal part of the ulnar would be derived from the medial terminal branch of the anterior interosseous artery. It would follow that the median artery network would develop next and join the hand plexus, at which time the anterior interosseous artery would regress in size. Stages 4 and 5 of Singer’s description would then occur as described. The above postulate is, of course, based on the assumption that the present case represents developmental arrest. One is left with the conclusion that either the classical description cannot be used to explain the variation or that it occurred as a result of some chance variation in the hemodynamic factors causing the median artery to regress in size rather than, or prior to, the regression of the anterior interosseous artery. The anastomosis of the medial terminal branch of the anterior interosseous artery with the superficial ulnar artery resembles the described development of the superficial brachial and radial arteries, so that the ulnar system may developjust like the radial system (Senior, 1926; Manners-Smith, 1910).This would indicate that the lateral terminal branch of the anterior interosseous artery forms the distal part of the radial artery system and that the superficial brachial forms the proximal part and later joins the lateral terminal branch of the anterior interosseous artery. It is also possible that the medial and lateral terminal branches of the anterior interosseous artery regress in size and remain as the palmar carpal rete of a normal specimen. W.L. POTEAT 94 PRESENT CASE STAGE 2 STAGE I STAGE 3 U PROPOSED STAGE I DESCRIPTION 2 STAGE STAGE 3 S T A G E 4,5 m CLASSICAL DESCRIPTION Fig. 6. Diagrams of the proposed and classical descriptions of the sequence of arterial development of the human upper limb. The diagram of the classic description is modified after Singer (1933). a, axillary a,;ai, anterior interosseous a,; b, brachial a,; c, anastomotic connection; m, median a,; r, radial a,; sb, superficial brachial a.; su, superficial ulnar a.; u, ulnar a. Another point supporting the proposed development is that when the median artery persists as a major vessel to the hand, the ulnar artery and radial artery are always present in some size, but when the anterior interosseous artery persists as a major vessel only the ulnar artery is present in the hand. Manners-Smith (1910) cites several examples in lower primates of the anterior interosseous artery terminating in a cross connection between the radial artery and ulnar artery and points to the major dorsal continuation of the anterior interosseous artery in lower primates, which is similar to the present report. The author is aware of no reported cases of the anterior interosseous artery and median artery being the only ones represented in the anastomosis and plexus of the hand. If' Singer's (1955) description is correct, one would predict such cases. In the extensive series of cases reported by Coleman and Anson (1961) on the arterial pattern in the hand, none resembled the pattern exhibited by this specimen. This may indicate that the superficial palmar arch is the more primitive of the two arches and that the deep palmar arch develops later on either by forming an anastomotic connection with the deep palmar branch of the ulnar or by subsequent anastomosis of the perforating vessels of the dorsal metacarpal arteries as is seen in this specimen. Besides the developmental implica- ABSENCE OF RADIAL ARTERY tions, the clinical significance of potential vascular problems in this sort of specimen such as in operations for carpal tunnel syndrome must be noted. Other clinical points would be a n absence of a radial pulse available a t the normal site, although there would have been a possibility of taking the pulse in the “anatomical snuff box.” Also in this case there would undoubtedly have been a strong pulse over the dorsal aspect of the wrist joint, due to the large dorsal terminal branch of the anterior interosseous artery. Such arteries may also present a hazard to venipuncture, as do anomalous arteries in the cubital fossa (Hazlett, 1949).It is of further interest to note variations of the muscles and nerves that occurred in conjunction with the major arterial variation, reinforcing the concept that variations within one system of the limb frequently occur with those of other systems (Van Allen et al., 1982). The question of the interrelationships of these systems in limb development is beyond the scope of this report. Van Allen et al. (1982) reported the morphology of the radial artery in cases of radial aplasia in fetuses with many other profound anatomical defects. In some of their cases the radial artery was absent and they related this absence to other limb defects such as absence of the radius itself. Furthermore, these authors point out these variations of the radial artery are not known to occur in adults. Such a comment clearly indicates the rarity of a specimen such as the one described in the present report. Very abnormal vasculature has been related to other morphologic defects in the limb (Van Allen et al., 1982; Pettersen et al., 1979).The vasculogenesis of the limb is also thought to be a significant factor for mesenchyme differentiation into muscle and bone (Caplan and Koutroupas, 1973; Caplan, 1978). It is interesting to note that two muscular anomalies were also present in this specimen. ACKNOWLEDGMENTS The aid of Dr. Miller J. Sullivan and Dr. Marcia G. Welsh in preparation of the manuscript is gratefully acknowledged. 95 LITERATURE CITED Caplan, A.I. (1978) The molecular basis for limb morphogenesis. In: Birth Defects. Proc. Fifth Int. Conference. J.W. Littlefield and J. DeBrouchy, eds. Excerpta Medica, Amsterdam. Caplan, A.I., and S. Koutroupas (1973) The control of muscle and cartilage development in t h e chick limb: The role of differential vascularization. J. Embryol. 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