Transverse subisthmic course of the innominate artery in an adult: detailed anatomy and additional variation

Abstract

A rare morphology of an aberrant innominate artery (IA) is reported here, together
with additional arterial variation encountered in the respective specimen.
The IA originated in the aortic arch on the left side of the trachea, coursed
on that side of the trachea to reach the left thyroid lobe, turned in at a right
angle to pass anterior to the trachea and immediately inferior and parallel to
the thyroid isthmus, and finally it divided inferior to the right thyroid lobe into
the right subclavian and common carotid arteries. The right common carotid
artery immediately turned at a right angle to ascend in the neck. Thus the
terminal branches of the IA had origins in a higher position than is usually
expected. This aberrant course of the IA determined a step-like morphology in
the sagittal plane of the left common carotid artery. Additional variations were
also encountered: (a) a lateralised right external carotid artery with the superior
thyroid artery initially coursing over the internal carotid artery; (b) the right
vertebral artery coursing over the inferior thyroid artery and entering the transverse
process of the fifth cervical vertebra; (c) the left subclavian and vertebral
arteries were tortuous. Knowledge of the presence of this IA variant, with
a transverse subisthmic segment, appears to be important in various surgical
approaches, such as tracheostomies, thyroidectomies, and mediastinoscopies;
in addition, the variations of the IA and the vertebral arteries are relevant for
lower cervical spine approaches. Nevertheless, the lateralised external carotid
artery may lead, if unidentified, to hemorrhagic complications during carotid
space approaches. It is important for surgeons to be aware that if an aberrant IA
is identified it may not be the only variation in that patient. (Folia Morphol 2010;
69, 4: 261-266)