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Paper text:
a 30-year - old male was admitted to our hospital due to a midline anterior neck mass . on the enhanced ct images ,
the mass was located at the infrahyoid midline neck and it showed the imaging features of a thyroglossal duct cyst .
the enhanced oblique coronal multiplanar reconstruction ct images revealed a variation of the aortic arch as an aberrant right subclavian artery that was distal to the left subclavian artery ( fig .
the right vertebral artery had its origin from the right common carotid artery at the inferior border of the right thyroid gland , and it had an aberrant entrance to the c5 transverse foramen ( fig .
the prevertebral segment of the right vertebral artery was located in the retro - thyroid area and very close to the thyroid gland ( fig .
a 67-year - old female was admitted to our hospital for an operation for thyroid cancer .
the enhanced ct images revealed an aberrant right subclavian artery distal to the left subclavian artery ( fig .
in addition , the left vertebral artery originated from the aortic arch between the left common carotid artery and the left subclavian artery .
the right vertebral artery had an origin from the right common carotid artery and also an aberrant entrance to the c5 transverse foramen ( fig .
the prevertebral segment of the right vertebral artery was located in the retro - thyroid area and close to the thyroid gland ( fig .
a 30-year - old male was admitted to our hospital due to a midline anterior neck mass . on the enhanced ct images ,
the mass was located at the infrahyoid midline neck and it showed the imaging features of a thyroglossal duct cyst .
the enhanced oblique coronal multiplanar reconstruction ct images revealed a variation of the aortic arch as an aberrant right subclavian artery that was distal to the left subclavian artery ( fig .
the right vertebral artery had its origin from the right common carotid artery at the inferior border of the right thyroid gland , and it had an aberrant entrance to the c5 transverse foramen ( fig .
the prevertebral segment of the right vertebral artery was located in the retro - thyroid area and very close to the thyroid gland ( fig .
a 67-year - old female was admitted to our hospital for an operation for thyroid cancer .
the enhanced ct images revealed an aberrant right subclavian artery distal to the left subclavian artery ( fig .
in addition , the left vertebral artery originated from the aortic arch between the left common carotid artery and the left subclavian artery .
the right vertebral artery had an origin from the right common carotid artery and also an aberrant entrance to the c5 transverse foramen ( fig .
the prevertebral segment of the right vertebral artery was located in the retro - thyroid area and close to the thyroid gland ( fig .
the embryologic mechanism of arsca with a right va - cc has been explained in the several studies ( 2 , 4 , 8) . the normal vertebral artery ( va ) builds up due to the process of longitudinal anastomosis and obliteration of the horizontal parts of the cervical intersegment artery .
normally , the first to the sixth cervical intersegment arteries ( cias ) develop into the va and the seventh cia makes the subclavian artery ( sca ) .
if longitudinal anastomosis of the right cia stops between the 6th and 7th cia , and the right side of the dorsal aorta is obliterated proximal to the 7th cia , then the right side subclavian artery ( sca ) originates from the left side aorta distal to the left sca and the right va originates from the right common carotid artery ( fig .
aberrant right subclavian artery has been reported with the incidence of less than 1% ( 8) .
a combination of these two variations is rare , but the true incidence of right va - cc with underlying arsca is not known .
fifteen cases of arsca were confirmed by enhanced ct or ct angiography in our hospital during the recent three years . among these cases ,
only the two cases we present herein showed the right va - cc variation . also , only these two cases had an aberrant level of the entrance of the va into the transverse foramen of the cervical spine . based on our results ,
the right va - cc variation is not likely to frequently occur with an underlying arsca .
there have been many reports about the variation of the arsca with a right va - cc , but only three reports remarked about the aberrant entrance of the va into the transverse foramen of the cervical spine ( 3 , 7 , 10 ) .
the vertebral artery usually enters into the transverse foramen of the 6th cervical spine ( the c6 entrance ) .
those three reports revealed different entrance levels as c2 , c3 and c4 . in our two cases ,
there have been no reports describing the anatomical course of this type of va - cc . in our cases , this va - cc had a close spatial relation with the thyroid gland .
it was located in the retro - thyroid area and very close to the thyroid gland . during its course up to the transverse foramen
this anatomical characteristic of the va - cc bears watching during anterior cervical spine surgery , thyroid surgery or other interventions .
if this va - cc were overlocked , it may be pulled with the longus colli muscle , or it may become lacerated during the anterior crevical spine surgery . during thyroidectomy , the inferior thyroid artery is usually ligated .
as mentioned by one autopsy result ( 7 ) , the inferior thyroid artery may be near to the right va - cc , so meticulous care may be needed to avoid an inadvertent injury to the va - cc during thyroidectomy . during thyroid aspiration
, the needle occasionally penetrates the posterior surface of the thyroid gland and it reaches the vertebral body . if the va - cc is near to the thyroid gland , then there is a possibility to puncture the va during thyroid aspiration .
therefore , knowledge of this aberrant course of the va may be helpful to avoid injury of the va when performing these procedures .
we present here two patients that had an aberrant right subclavian artery and an anomalous origin of the right vertebral artery from the right common carotid artery . 
 we review the previous literature and discuss herein the embryologic mechanism and clinical implications of this variation .