two cases of abnormal origins of the left external and

Okajimas Folia Anat. Jpn., 58(4-6) : 1231-1240, March 1982

Two Cases of Abnormal Origins of the Left

External and Internal Carotid Arteries

in the Japanese Monkey

By

KUMIKO TANUMA, MOTOHARU SUZUKI and FUMIO KIKKAWA

The 2nd Department of Anatomy, Nippon Medical School, Bunkyo-ku, Tokyo 113, Japan (Director : Proof. F. Kikkawa)

Department of Anthropology, Gifu College of Dentistry, Motosu-gun, Gifu 501-02, Japan

-Received for Publication, January 20, 1982-

Key words: Anomalous case, Left external carotid artery, Left internal carotid artery, Aortic arch.

Summary : We encountered two cases of abnormal origins of branches arising from the arch of the aorta. That is to say, in the first case, the aortic arch gave di-rectly off the left external carotid artery as its second branch and the left internal carotid artery as its third branch. In the second case, the aortic arch gave directly off the left external carotid artery as its second branch and the left brachiocephalic trunk dividing into the left internal carotid and the left subclavian artery as its last branch. In both cases the right brachiocephalic trunk arose nor-mally as the first branch of the aortic arch. In the first case the left subclavian artery was the last branch of the aortic arch.

It is conjectured that those anomalies were caused by the disappearance of the left third aortic arch and the persistence of the left carotid duct during the embry-onic period.

Pref ace

Although anomalies of the branches of

the aortic arch have been reported by

many workers, almost all reports have been done in man. Few accounts of anomalies can be found in primates.

We encountered two extremely rare

specimens which involved unusual origins of the left external and internal carotid

arteries during an investigation of the modes of the arrangement of the branches

arising from the aortic arch in the

Japanese monkey. The present paper is intended to report these findings and to

give an embryological consideration to them These cases were found in cor-rosion cast specimens.

Findings

Case 1: The first case was found in a male specimen (Weight : 7.4 kg, C-R

Length : 39.0 cm) (Text-Fig. 3A, Fig. 1) The aortic arch lay in front of the ver-

tebral column between the inferior margin

1231

1232 K. Tanuma, M. Suzuki and F. Kikkawa

Fig. 1. This drawing indicates the

various components of the aortic arch system

in an early embryonic period. The dotted

lines show vanishing parts.

Fig. 2. This drawing indicates a more

advanced embryonic period as compared to

Fig. 1. The various components are indicated

by the same scheme of symbols as used in

Fig. 1.

Key to abbreviations in text-figures

1-VI: aortic arch I-VI

CD : carotid duct

RVAR : right ventral aortic root

LVAR : left ventral aortic root

DAR : dorsal aortic root

RVA : right vertebral artery

LVA : left vertebral artery

RSA : right subclavian artery

LSA : left subclavian artery

SDI : Seventh dorsal intersegment artery

3-10: dorsal aortic root (segment 3 to 10) RICA : right internal carotid artery LICA : left internal carotid artery

RECA : right external carotid artery LECA : left external carotid artery

BT : brachiocephalic trunk AA : assending aorta

DA: ductus arteriosus PT : purmonary trunk

LA: ligamentum arteriosus

Abnormal Origins of the Left External and Internal Carotid Arteries 1233

Fig. 3. This scheme shows the various components of the adult. The various components

are indicated by the same symbolic marks as in the preceding figures. A: case 1, B: case 2.

of the third thoracic vertebral body and

the first third part of the fourth thoracic vertebral body, from which originated

from the proximal to the distal portion

the following four arteries. That is to say, the first branch was

the right brachiocephalic trunk, which

divided into the right subclavian artery and the right common carotid artery at

the level of half of the first thoracic vertebral body. The second branch was

the left external carotid artery which

arose from the aortic arch in contact with the right brachiocephalic trunk.

The third branch was the left internal carotid artery, which arose from the

aortic arch about 1.0 mm distal to the

left external carotid artery. The last

branch was the left subclavian artery. It arose from the aortic arch in contact

with the left internal carotid artery.

Case 2: The second case was also found in a male specimen (Weight : 3.5 kg, C-R

Length : 42.0 cm) (Text-Fig. 3B, Fig. 2). The aortic arch lay in front of the

third thoracic vertebral body, from which originated from the proximal to the distal

portion the right brachiocephalic trunk as the first branch, the left external carotid artery as the second branch and the left brachiocephalic trunk as the last branch. The right brachiocephalic trunk bifurca- ted into the right subclavian and right common carotid arteries at the level of the superior margin of the first thoracic vertebral body. The left external carotid artery originated from the aortic arch about 1.0 mm away from the right bra-chiocephalic trunk. The left brachioce-

phalic trunk arose from the posterior about 2.0 mm away from the origin of the left external carotid artery. After


the left brachiocephalic trunk ran 3.5 mm, it divided into the left internal carotid and left subclavian arteries.

In both cases the left common carotid artery was not formed.

Considerations

Representative accounts of the arran-

gement of the aortic branches have been given by Holzapfel (1899), Poynter (1916), Adachi (1928), Williams et al (1932, 1935), Nakagawa (1939), Edwards (1948) and Nizankowski et al (1975) in man. Keith

(1894) and Parsons (1901) have reported the arrangement in many primates includ-ing man.

As far as we looked through their descriptions, few reports exist on ano-malous arrangements of branches arising from the aorta in mammals except man. In particular, two cases in the present

paper repesent extremely rare arrange-ments. Namely, a similar case to our first one has been reported only in a case of a man by Siegfried (1907). On the other hand, the second case has never been reported either in animals or in man. Incidentally our first case corres-

ponds to what Nizankowski et al (1975) have reported : their type XIII in the list of

possible combinations in the origin and position of the branches arising from the aortic arch. An embryological interpreta-tion has already been given to the first case by Siegfried. We agree with his conclusion. Although there is a slight

difference in the original position of the left internal carotid artery in the first

and second cases, it can be considered that they are caused by the same embryological process.

The embryonic schemes in the present

paper are based on Barry's figures (1951) (Text-Fig. 1, 2). Fig. 1 indicates the aortic arch system in an early embryonic

period (Text-Fig. 1). Dotted lines show

vanishing parts. In mammals the first, the second and the fifth aortic arch system on both sides, the sixth aortic arch on the right side and the bilateral carotid . duct which is the dorsal aortic root between the third and fourth aortic arches, disappear in a normal developmental process during the embryonic period. The left sixth aortic arch normally persists as a rudimentary part ie, the ligamentum arteriosus in adults. In addition the eighth segment of the dorsal aortic root on the right side also disappears during the embryonic period.

It is generally stated that malformation is apt to take place at the fourth aortic arch. But in the present cases these anomalies can be regarded as malforma-tions of the third aortic arch and the carotid duct on the left during an early embryonic period. Anomalies which appear in these parts are extremely rare in mammals. That is to say, It is con-

jectured that such anomalies are caused by the abnormal disappearance of the third aortic arch and the abnormal per-sistence of the carotid duct on the left side during an embryonic period. The per-sistence of the carotid duct on the left may have been secondarily caused by the vanishing of the third aortic arch on the left.

In normal patterns, the external carotid artery originates from the ventral aortic root of the cranial part from the third aortic arch, the internal carotid artery derives from the third aortic arch and the dorsal aortic root of the cranial

part from it, and the common carotid artery derives from the ventral aortic root between the third and the fourth aortic arch. But in the present cases the left external carotid artery is formed by a sequent ventral aortic root of the cranial part from the fourth aortic arch on the left side and the left internal carotid artery is formed by a sequent dorsal


aortic root of the cranial part from the fourth aortic arch on the left side (Text-Fig. 1-3). In consequence, the left common carotid artery is not formed in either case.

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PLATE


Explanation of Figures

Plate I

Fig. 1. Case 1, Fig. 2. Case 2. AA : Arch of the aorta, RBT : right brachiocephalic trunk, LBT left brachiocephalic trunk, RCC: right common carotid artery, LEC: left external carotid

artery, LIC : left internal carotid artery, RS : right subclavian artery, LS : left subclavian artery, LV : left vartebral artery.

K. Tamura, et al.

two cases of abnormal origins of the left external and

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