Case report

During the routine undergraduate dissections on the upper limbs of a 50-yearold female cadaver, it was observed that on both the sides, the third part of the AA after giving the subscapular artery bifurcated into a SBA and a deep brachial artery. The SBA descended superficial to the lateral root of the median nerve; did not give any branch in the arm and continued as the brachial artery proper. Finally, on reaching the cubital fossa it terminated by dividing into radial and ulnar arteries. The deep brachial artery passed deep to the medial root of the median nerve and gave anterior and posterior circumflex humeral branches of AA and profunda brachii branch of brachial artery. Then it terminated by giving twigs to the muscles of arm (Fig. 1).

M Khullar

Assistant ProfessorDept. of AnatomyGuru Gobind Singh Medical CollegeFaridkot, Punjab

Meenakshi Khullar

Assistant ProfessorDept. of AnatomyGuru Gobind Singh Medical CollegeFaridkot, Punjab

Discussion

Variations in the arterial pattern of the upper limb are common and have been reported by several investigators.1 The presence of a SBA and the usual pattern of its branching in the upper arm or forearm have also been reported.4-6 The definition of the SBA was set for the first time by Adachi in 1928 and runs as follows: “The SBA is the one that runs superficial to the median nerve.”7 It may replace the main trunk or may be accompanied by an equally important, less important or more important trunk running deep to median nerve. Table 1 shows the prevalence of SBA as observed by different authors from time-to-time.

Ontogeny

The embryological background of these variations in the vasculature of the upper limb may be explained as abnormal deviations in the normal vascular patterns. Arey and Jurjus mentioned six explanations for the variations observed:8,9

1. The choice of unusual paths in the primitive vascular plexus
2. The persistence of vessels which are normally obliterated
3. The disappearance of vessels which are normally retained
4. An incomplete development
5. The fusion and absorption of parts which are normally distinct
6. A combination of factors leading to an atypical pattern normally encountered.
7. Ontogenic basis of the present case can be easily made out if we look at Singer’s
8. five stages of development of the brachial artery (Fig. 2):10

Stage I: Originally the subclavian artery extends to the wrist, where it terminates by dividing into terminal branches for the fingers. The distal portion of the artery becomes the interosseous artery of the adult.

Stage II: The median artery arises from the interosseous artery and becomes larger while interosseous artery subsequently undergoes retrogression. During this process, the median artery fuses with the lower portion of interosseous artery and ultimately forms the main channel for the digital branches becoming the principle artery of the forearm.

Stage III: In embryos of 18 mm, the ulnar artery arises from brachial artery and unites distally with the median artery to form superficial palmar arch.Digital branches arise from this arch.

Stage IV: In embryo of 21 mm length, the SBA develops in the axillary region and traverses the medial surface of the arm and runs diagonally from the ulnar to the radial side of the forearm to the posterior surface of the wrist. There it divides over the carpus into branches for the dorsum of the thumb and index finger.

Stage V: Finally three changes occur. When the embryo reaches the length of 23 mm the median artery undergoes retrogression becoming a small slender structure, now known as ‘arteria nervi mediani’. The SBA gives off a distal branch, which anastomoses with the superficial palmar arch already present. At the elbow an anastomotic branch between brachial artery and SBA becomes enlarged sufficiently to form with the distal portion of the latter, the radial artery, as a major artery of the forearm; the proximal portion of the SBA atrophies correspondingly.10 In the present case, it seems that in Stage III of Singer, ulnar artery came from brachial artery as usual.10 SBA continued as radial artery and anastomosis between SBA and brachial artery developed normally (See Fig. 3). However, brachial artery between origin of SBA and ulnar artery (‘A’ in Fig. 3) retrogressed and lost its communication with common interosseous artery. The SBA failed to retrogress and continued to supply radial artery. The anastomosis between SBA and brachial artery (‘B’ in Fig. 3), which usually forms proximal part of radial artery now formed proximal part of ulnar artery, thus giving appearance that ulnar artery and radial artery are terminal branches of SBA and common interosseous artery (‘C’ in Fig. 3) came as a branch of ulnar artery.

Clinical Significance

Gonzalez-Compta highlighted the diagnostic, interventional and surgical significance of such a vascular variation.11 Diagnostically, it may disturb the evaluation of angiographic images. Interventionally, accidental puncture of superficially placed arteries may occur while attempting venipuncture. Surgically, it is vulnerable in both orthopedic and plastic surgery operations.

Hence, the anatomic knowledge of the vascular patterns of upper limb is of crucial importance not only for neurosurgeons, but for all those involved in radiodiagnostics, particularly in cases involving traumatic injuries, as improved knowledge would allow more accurate diagnostic interpretation and surgical treatment.

References

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