The Thyroidea Ima Artery: An Unusual Collateral Vessel

Abstract

Case Report In mid-1963 a 35-year-old electrician who had suffered from headaches for many years had a sudden unexplained episode of unconsciousness from which he recovered rather promptly. He had another sudden episode of unconsciousness in June 1965 and upon recovery complained of pain over one eye. On admission to a hospital, carotid angiography demonstrated an aneurysm at the junction of the anterior cerebral and anterior communicating arteries on the right side. Left carotid angiography showed only the left middle cerebral circulation. A Selverstone clamp was applied to the right common carotid artery and gradually occluded. The headaches persisted, however, and a bruit was heard over the neck. Early in September 1965, the carotid artery was again exposed, and operative angiography revealed incomplete closure of the clamp. The artery was then occluded with a ligature placed below the clamp, and the bruit disappeared. In November 1966, follow-up angiography showed persistence of the aneurysm. No treatment was carried out at that time, but in June 1967 the patient was admitted to the hospital for re-evaluation and treatment. No abnormal neurological signs were present on examination. Two days after admission the aortic arch was catheterized following a femoral puncture. Selected injections were made into the innominate, both the vertebral, and the left carotid arteries. The stump of the right carotid artery was also catheterized. The aneurysm, measuring 17 × 9 × 6 mm, was identified in the region of the anterior communicating artery and was seen to fill from the right vertebral artery by anterograde passage of contrast material through the posterior communicating artery and also by opacification of the right internal carotid artery via the occipitovertebral anastomosis (Fig. 1). The aneurysm was also opacified through an anastomosis between the thyroidea ima artery and the superior thyroid artery, with subsequent retrograde opacification of the external carotid artery and then filling of the internal carotid artery (Fig. 2). Neither the left vertebral nor the left carotid artery injections demonstrated the aneurysm. The aneurysm was coated with plastic resin, and the patient was discharged. Discussion We feel that the collateral artery represents a thyroidea ima artery. According to Adachi (as quoted by Blum, 1) any thyroid artery originating from the arch of the aorta, innominate artery, right common carotid, or internal mammary artery is a thyroidea ima artery. Adachi maintained that the artery never originates on the left side, but Gruber (as quoted by Blum) described in 1872 a thyroidea ima artery originating from the left side in a 12-year-old boy. The incidence of the thyroidea ima artery in normal people has been assessed in the anatomy books as 4 to 10 per cent (5).