Congenital absence of the internal carotid artery: case reports and review of the collateral circulation

Abstract

Absence of the internal carotid artery (ICA) is a rare congenital anomaly. The embryology of the ICA and the common collateral pathways associated with its congenital absence are reviewed, with four new cases provided for illustration. While collateral blood flow may allow these patients to remain asymptomatic, two of our patients presented with transient ischemic attacks. Recognition of this anomaly has important implications during planned carotid or transsphenoidal surgery, in thromboembolic disease, and in the surveillance and detection of associated cerebral aneurysms.

fig 1.

Case 1: Hypoplasia of the left ICA. A, Source image from a 3D time-of-flight MR angiogram shows diminished flow-related signal intensity within the petrous portions of the left ICA (arrow). B, Compressed image from the MR angiogram shows a tortuous, enlarged PCOM (arrow) extending forward to supply the left MCA. The left ACA is supplied via a patent ACOM (arrowhead). There is no perceivable flow-related signal intensity within the supraclinoid left ICA on the compressed image. C, Axial image from a CT angiogram at the level of the petrous ICA shows hypoplasia of the left carotid canal (arrowhead).

fig 2.

Case 2: Agenesis of the left ICA. A, Source image from a 3D time-of-flight MR angiogram reveals absence of flow-related signal within the left petrous ICA (arrow). B, Compressed view from the MR angiogram displays absence of flow-related signal intensity within the left ICA with collateral supply to the left hemisphere through a patent ACOM. Normal flow is present within the right ICA (arrowhead). Focal loss of flow-related signal intensity within the A1 segment of the right ACA (arrow) represents a clinically insignificant stenosis. C, Axial CT scan of the skull base shows absence of the left carotid canal and a normally developed right carotid canal (arrow). D, Collateral supply to the left cerebral hemisphere is provided through a patent ACOM, as demonstrated on the frontal view from the right carotid arteriogram. Stenosis of the A1 segment of the right ACA is revealed again (arrow).

fig 3.

Case 3: Absence of the right ICA. A and B, Frontal (A) and lateral (B) projections from a left CCA arteriogram show an anomalous communication between the cavernous portions of the ICAs (arrow). This anomalous communication courses through the sella turcica. The right ACA is supplied via a patent ACOM, with the right A1 segment either being aplastic or extremely hypoplastic. The right MCA is a continuation of the right supraclinoid ICA.

fig 4.

Case 4: Aplasia of the left ICA. A, Frontal view from a right CCA arteriogram shows collateral flow to the left ACA across a patent ACOM (arrow). B, Frontal view from a left vertebral arteriogram displays collateral flow to the left MCA (arrow) via forward flow through a patent PCOM (arrowhead). C, Axial CT scan through the skull base reveals a diminutive left carotid canal (arrow).

fig 5.

A and B, Illustrations of the developing embryo at 6 mm (A) and 11 mm (B). After Congdon, as reproduced in ; see text

fig 6.

Absence of the ICA: pathways of collateral blood flow. After Lie and Quint et al ; see text