Fetal-Type Variants of the Posterior Cerebral Artery and Concurrent Infarction in the Major Arterial Territories of the Cerebral Hemisphere

Abstract

Fetal-type or fetal posterior cerebral artery (FPCA) is a variant of cerebrovascular anatomy in which the distal posterior cerebral artery (PCA) territory is perfused by a branch of the internal carotid artery (ICA). In the presence of FPCA, thromboembolism in the anterior circulation may result in paradoxical PCA territory infarction with or without concomitant infarction in the territories of the middle (MCA) or the anterior (ACA) cerebral artery. We describe 2 cases of FPCA and concurrent acute infarction in the PCA and ICA territories-right PCA and MCA in Patient 1 and left PCA, MCA, and ACA in Patient 2. Noninvasive angiography detected a left FPCA in both patients. While FPCA was clearly the mechanism of paradoxical infarction in Patient 2, it turned out to be an incidental finding in Patient 1 when evidence of a classic right PCA was uncovered from an old computed tomography scan image. Differences in anatomical details of the FPCA in each patient suggest that the 2 FPCAs are developmentally different. The FPCA of Patient 1 appeared to be an extension of the embryonic left posterior communicating artery (PcomA). Patient 2 had 2 PCAs on the left (PCA duplication), classic bilateral PCAs, and PcomAs, and absent left anterior choroidal artery (AchoA), suggesting developmental AchoA-to-FPCA transformation on the left. These 2 cases underscore the variable anatomy, clinical significance, and embryological origins of FPCA variants.

Keywords: angiography; developmental; fetal variant; posterior cerebral artery; stroke.

Figure 1.

Patient 1 had acute infarcts in the right MCA and PCA territories (hyperintense DWI, low ADC). The 3D time-of-flight (TOF) MRA images show a left FPCA (long arrow), a remnant of the P1 segment (arrowhead) of the right PCA (the rest of it is absent), stenosis at the petrous segment of the right ICA (short arrow), stenosis of the basilar artery above and below the SCA origin (only right SCA is visible), and absent flow in the left vertebral artery. The CT scan image shown was taken 2½ years prior to admission and retrieved from her old records. It clearly shows an intact classic right PCA (arrowhead) and a left fetal-type PCA (long arrow).

Figure 2.

Patient 2 had acute infarcts in the left ACA, MCA, and PCA territories (hyperintense DWI, low ADC). The 3D time-of-flight (TOF) MRA images show 2 PCAs on the left (PCA duplication)—a dominant fetal-type PCA (arrows) and a small-caliber classic PCA (arrowheads). The left PCA and the right PCA (dark arrowheads) branch off the basilar artery. Two posterior communicating arteries and a right anterior choroidal artery (large dark arrow) are also present (middle MRA and CTA images). There is no evidence of flow-disrupting stenosis.

Figure 3.

Diagram of human embryo in the choroidal stage (~5 weeks gestational age); only the left side is shown. (A) Some of the primitive cerebral arteries that are present during this stage are shown. The internal carotid artery (ICA) bifurcates into a rostral branch (rICA) and a caudal branch (cICA); the latter is the precursor of the posterior communicating artery (PcomA). The anterior cerebral artery (ACA) is a primitive rICA branch. Two large choroidal arteries are present: the anterior choroidal artery (AchoA), a branch of the rICA, and the posterior choroidal artery (PchoA), a branch of the cICA. Also shown are the precursors of the superior cerebellar artery (SCA) and posterior inferior cerebellar artery (PICA). Note that the anterior circulation supplies blood to the telencephalon (T), diencephalon (D), midbrain (M), pons (P), cerebellum (C), and medulla oblongata (MO). (B) Later-stage arteries (approaching the adult pattern) are superimposed on the same choroidal-stage embryo to show how they evolve. The middle cerebral artery (MCA) and posterior cerebral artery (PCA) become dominant and the choroidal arteries and PcomA regress but do not disappear. (C) In the most common variant of the fetal-type PCA, the PCA is a continuation of the PcomA and the P1 segment of the PCA (P1) regresses and may or may not disappear (absent in the diagram). This is the case in Patient 1. (D) In the less common variant of the fetal-type PCA, there are 2 PCAs (PCA duplication)—one is derived from the AchoA (often dominant) and the other is a classic PCA (often small). This is the case in Patient 2. BA, basilar artery; D, dorsal aorta; CBA, carotid-basilar anastomoses; cp, choroid plexus; cc, central canal (later develops into the ventricular system).