Arachnoid granulations may control heat exchange between intracranial dural sinuses and cerebrospinal fluid

Selective brain cooling is a system in a human that protects the brain from hyperthermia. Cool venous blood from head skin and upper respiratory tract drains into intracranial dural sinuses. In that region, cool blood in the dural sinuses decreases the temperature of the cerebrospinal fluid. Cerebrospinal fluid provides brain cooling. All cortical arteries to the brain pass the cerebrospinal fluid compartment. Also cerebrospinal fluid washes cortical nervous tissue. To provide optimal temperature for the brain cortex, heat exchange between cerebrospinal fluid and venous blood in dural sinuses should be well controlled. Head skin is in direct contact with the outside, and significant heat exchanges may occur within dural sinuses. A barrier made of dura mater and arachnoid mater has been proposed to transmit heat from dural sinuses to the cerebrospinal fluid. However, this barrier is a mechanical barrier and can't optimize the temperature of cerebrospinal fluid. Also it has two laminas (dura mater and arachnoid mater) and dura mater has a high vascularization. Therefore, this barrier may obstruct heat exchange. In this hypothetical paper, I offer arachnoid granulations as a functional barrier for heat exchange between blood in dural sinuses and cerebrospinal fluid. Arachnoid granulations are invaginations of arachnoid mater to the dural sinuses. Cerebrospinal fluid passes to the dural sinuses via arachnoid granulations. An arachnoid granulation provides a very thin wall between two compartments and may transmit heat effectively. Also arachnoid granulations may control cerebrospinal fluid flow to the dural sinuses according to temperature differences between two compartments. It is worth researching whether there are any functional or histological differences of the arachnoid granulations between people living in cold and hot places. There may also be an association between pathologies such as migraine and pseudotumor cerebri and this possible control mechanism. Cells and tissues need optimal heat for best enzymatic activity. Body temperature is well controlled by hypothalamic nuclei. However, there is an extra control mechanism for brain temperature identified in a number of animal species called " carotid rete " [1]. Arterial blood supply to the brain is being cooled by venous blood within carotid rete. This mechanism is referred to as " selective brain cooling ". Humans have no carotid rete. However, there are some anatomic features that are supposed to correspond to selective brain cooling [2-4]. Cool venous blood from head skin drains to intracranial dural sinuses [Fig.1]. Venous blood of nasal mucosa and paranasal …