Studies on the thyroid and thymic arteries of Japanese adults and fetuses

The arterial system of the thyroid gland and the thymus was reinvestigated in 43 fetuses and 77 adults. The textbook-type was low in frequency, being 2.3% in fetuses and 20.8% in adults. It is largely due to the existence of many abnormalities in constant arteries and of the anomalous arteries. Most of them were more abundant in fetuses than in adults with a few exceptions. Among the anomalous arteries, the middle thymothyroid artery showed the highest frequency of 44.2% in fetuses and of 27.3% in adults. The superior thymic artery and the middle thymic artery were also abundant, being 33.7%, 18.8% and 32.6%, 14.3% in fetuses and adults respectively. On the other hand, the supreme thymic artery and the thyroid ima artery arising from the internal thoracic artery were extremely rare. From these results, the basic arterial pattern of both glands and its transition to the textbook-type were discussed. It is suggested that if the thyroid and thymic arteries arising from the aortic arch or brachiocephalic artery are considered to be almost constant, the frequencies of the textbook-type increase to 14% in fetuses and 41.6% in adults respectively.