Left anterior inferior cerebellar artery supplied by an anomalous branch arising from the right vertebral artery: a case diagnosed by magnetic resonance angiography

Inside the human head, a complex network of blood vessels delivers oxygen to the brain, much like a city's water mains supply a neighborhood. Among these vessels are the vertebral arteries, which travel up the neck to join together and form the basilar artery, a central pipeline that feeds the lower brain and the cerebellum, the part of the brain responsible for balance and coordination. From this main pipeline, smaller branches split off to nourish specific areas. One such branch, the anterior inferior cerebellar artery, usually springs from the basilar artery to feed the front and bottom of the cerebellum. While most people have a standard layout for these vessels, nature occasionally draws a different map. When these vessels are missing or take an unusual path, it can complicate the diagnosis of strokes or make surgical planning difficult. Understanding these rare variations is crucial for doctors who need to know exactly where blood is flowing and where it might be blocked.

A recent case report from Japan highlights one of the most unusual maps ever documented. An 88-year-old woman arrived at Saitama Sekishinkai Hospital with vomiting, a symptom that often signals a problem in the back of the brain. Doctors used a powerful magnetic resonance scanner to look inside her skull. The images revealed that she had suffered a stroke in the area usually supplied by the left posterior inferior cerebellar artery, a vessel that had become blocked. However, the most striking discovery came when the team examined the blood vessels themselves. Standard imaging showed that the left vertebral artery, which should have been on the left side of her neck, was completely missing from the view. Even more surprisingly, the artery that should have been feeding the front of her left cerebellum was not coming from the usual central pipeline. Instead, it was being fed by a strange, detouring branch that originated from the right vertebral artery on the opposite side of her body.

To understand how this was possible, the researchers had to look closer than standard scans allow. They used a specialized technique called MR cisternography, which creates detailed images of the fluid-filled spaces around the brain. This method acted like a high-resolution map of the tunnels where the arteries run. It revealed that the missing left vertebral artery was actually there, but it was blocked and hidden within the fluid. The anomalous branch supplying the left cerebellum was not a random error; it appeared to be a connecting vessel that had formed between the right and left sides, bridging the gap where the left artery was occluded. The researchers concluded that this unusual vessel likely developed as a variation of the spinal artery system, a network that normally connects the two main arteries in the neck, but in this patient, it had taken on a new role to keep blood flowing to the brain.

This case is significant because it describes a configuration that had never been reported in the English medical literature before. While doctors know that arteries can sometimes branch from unexpected places, finding a left-sided vessel supplied entirely by a branch from the right side, specifically to replace a blocked artery, is a unique occurrence. The study emphasizes that standard imaging can sometimes miss these hidden connections, leading to an incomplete picture of a patient's vascular health. By combining standard magnetic resonance angiography with the fluid-focused cisternography and creating partial three-dimensional images, the team was able to trace the full path of the blood flow. The patient was treated without surgery and recovered well, but the discovery serves as a reminder that the human body can adapt its internal plumbing in ways that are both rare and vital to recognize.