HMN 2026: How Skull microchannels reveal hidden route for brain immune defense

A study led by Rafael Gallareto-Sande, a predoctoral researcher at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), provides new insights into a network of tiny blood vessels within the cranial bones that play a key role in brain protection. The research, published in The Anatomical Record, reports for the first time the number and size of these microscopic channels, known as vascular microforamina, which connect the cranial bone with the intracranial space.

To conduct the study, the team used computed tomography on a sample of adult human crania. The results show marked interindividual variability: each cranium may contain from around 100 to 400 of these small channels, distributed across the inner surface of the cranial vault.

Most of these conduits are extremely small, with diameters below 0.5 mm. However, the larger channels, although fewer in number, contribute a comparable share of blood flow. These are mainly concentrated in specific regions of the skull, particularly in the posterior and central areas of the parietal bone, in association with major venous structures.

The observed distribution suggests a close relationship with the meningeal vascular system. It also indicates that the number of these channels—especially those of intermediate size—increases with the expansion of the diploë, the spongy bone tissue, particularly in the posterior regions of the cranium.

Brain defense

These microforamina were long thought to be primarily involved in brain thermoregulation. However, recent studies indicate that they also function as pathways for immune cell trafficking. In particular, bone marrow within the diploë can release molecules associated with neuroinflammatory processes through these channels, contributing to the brain’s defense against infection and injury.

“The microvessels are part of the so-called glymphatic system, a network responsible for the transport of solutes and the clearance of metabolic waste from the brain. Its proper functioning is essential and has been linked to conditions such as stroke and Alzheimer’s disease. This study therefore opens new avenues for research with implications for both anthropology and medicine,” says Gallareto-Sande.

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