Cervical and intracranial MRI findings in tetralogy of Fallot: Association with a persistent hypoglossal artery.

Dear Sir,

Persistent primitive hypoglossal artery (PHA) is a rare embryonic carotid-basilar artery anastomosis, demonstrated in about 0.027–0.26% of cerebral angiograms.[12] Furthermore, the PHA is often functionally a single artery or the most prominent supply to the brainstem and cerebellum.[1]

Tetralogy of Fallot (TOF) is the most common cyanotic cardiac defect, with a classic tetrad of manifestations: Pulmonary outflow tract stenosis or atresia, ventricular septal defect, aortic override, and right ventricular hypertrophy.[3]

We describe an extremely rare combination of TOF associated with a right aortic arch with a mirror–image branching, and a persistent hypoglossal artery.

A 2-year-old boy was admitted at our radiological department with visual impairment after being submitted to an elective surgical repair with Goretex graft interposed between the pulmonary artery and the brachiocephalic trunk. He was diagnosed with TOF at 25 gestational weeks and undergone surgical repair at day 7 of life. The deletion 22q11 was negative. His daily activity and neurological development were fair, but he presented with hypotonia and was speechless.

Brain magnetic resonance imaging (MRI) showed small dot-like lesions supra- and infratentorial with hyposignal on T2 gradient eco-weighted images [Figure 1] suggesting microbleeds due to microemboli. Contrast enhanced MRA demonstrated a right aortic arch with mirror–image branching and an anomalous vessel arising from the right internal carotid at the C2-C3 level and leading to the basilar artery [Figure 2]. Imaging of the time of flights revealed that this vessel entered the skull through the hypoglossal canal [Figure 3]. Bilateral vertebral arteries were hypoplastic, but the right posterior communicating artery was present.

Figure 1

Axial T2* gradient eco-weighted images showing brain microbleeds, appearing as small dots-like foci with hyposignal

Figure 2

Coronal and sagital imaging in contrast enhanced MRA showing an anomalous vessel arising from the right internal carotid artery to the basilar artery. In addition, a right aortic arch with a mirror–image branching is also demonstrated

Figure 3

Axial source image from 3D-TOF MRA demonstrating an anomalous artery coursing through the right hypoglossal canal to form the basilar artery with hypoplastic vertebral arteries

The patient condition slowly improved, and was discharged from the hospital with regular follow-ups at our pediatric cardiology department.

Neurological and developmental deficits are common in children with congenital heart disease due to multiple factors that include the etiology of the congenital heart disease, the effects of abnormal cardiovascular function, and the possible sequelae of open-heart surgery. Perioperative neurological complications include diffuse hypoxic-ischemic injury, cerebral hemorrhage, focal infarction due to macroemboli, but a leading cause of neurocognitive defects associated with open cardiac surgery is the production and circulation of microemboli.[4] The major types of microemboli are gas emboli, foreign material, and emboli generated from blood elements.

The PHA is a vestige of the embryonic carotid-vertebrobasilar anastomoses present during the 4–5 mm embryo stage. The embryological explanation begins with the description of two cerebral arterial systems present in the early development. The anterior one gives rise to the carotid artery which develops as a cranial extension of the paired dorsal aorta, and the posterior is the longitudinal neural artery. At the 3–4 mm stage, anastomotic vessels between the internal carotid artery and the longitudinal neural artery compensate for the absence of the vertebral arteries. These vessels are later known as carotid-vertebrobasilar anastomoses and are named after the cranial nerves with which they run. The hypoglossal arteries are formed by the second pair of segmental arteries. The anastomosis between the longitudinal neural arteries gives rise to the basilar artery. This artery then joins the internal carotid artery via the posterior communicating artery. At this time (5–6 mm stage) the otic, hypoglossal, and trigeminal arteries start to regress.[5]

Developmental anomalies of the aortic arch vessels are well known. About 25% of patients with TOF have a right aortic arch, most often with mirror–image branching.[2] The aortic arch anomalies can be understood by their embryologic origins. Development of the aortic arch can be described by the appearance and persistence or dissolution of the six paired vessels connecting the truncoaortic sac of the embryonic heart tube with the paired dorsal aortae.[6] When the right dorsal aorta remains patent and either the left fourth arch or the left dorsal aorta regresses abnormally, the right aortic arch is formed. If the distal portion of the left aortic arch, adjacent to the descending aorta, disappears, the subsequent developmental process results in a mirror image of the normal process.[7]

With the exception of atrial septal defect previously described in two case reports,[89] however, anomalies of the heart and aortic arch vessels in combination with PHA have never been reported. Our case, which illustrates the coexistence of a TOF and PHA, is to our knowledge the first reported case in the English language literature.

The coexistence of these vascular anomalies in the patient raises the question of a common etiologic factor or factors in their pathogenesis. One possible explanation for the persistent hypoglossal artery being frequently associated with hypoplastic vertebral arteries is the less need of vertebral arteries to supply the posterior circulation and the brainstem. It is difficult to relate the TOF and the right aortic arch associated with mirror–image branching with a persistent hypoglossal artery, but we can presume a common embryonic insult at the 3–10 mm fetal stage.