To prevent the head from moving during the operation, it must be fixed rigidly without interfering with the approach.
The most widely used system is the Mayfield frame as shown in the photograph on the right.
This frame is fixed to the head by 3 spikes which penetrate down to the bone and the frame is itself fixed to the operating table.
Mayfield head frame:
The Mayfield frame is a 3 point anchor system. The straight part with 2 points can tilt and rotate on its axis. Once the position has been chosen, it is locked (external dial).
Mayfield head frame:
The image above shows one of the spikes that dig into the frame. There are special tips for children with thinner bones.
A spring-loaded force transducer is part of this fastener, which allows the depth of penetration into the bone to be controlled.
The scalp is very vascularized and hemostasis is therefore very important.
The vessels are first coagulated by bipolar coagulation, then the scalp is compressed by clips (Raney) made of plastic or metal.
An old alternative to clips was to use multiple small metal clips (Dandy).
Exposure of the bone:
The skin flap (with the periosteum retracted) is wrapped in a wet compress and retracted by hooks tensioned with springs. This allows for better exposure of the bone and contributes to hemostasis.
Opening of the bone:
A trephine hole is made with an electric trephine (sometimes several depending on the location of the craniotomy), then the bone is cut with a craniotome starting from the trephine hole.
Historically, trephine holes were made with a kind of crankshaft and a wire saw was passed between the holes to cut the bone (Gigli's saw).
Opening of the dura mater:
Once the bony opening is made, the bony flap is separated from the underlying layer which is called dura mater. This dura is very strong and is incised and then folded back into a special wet compress (on the right of the picture).
Once the dura is folded back, there is a thin transparent layer called an arachnoid. This layer retains cerebrospinal fluid (CSF).
Opening of the cortex:
Depending on the operation performed, we will often open a groove, descend along it and open the last layer of the meninges (pia mater) which is adherent to the brain and enter the cortex.
There are many types of intervention (resection of a tumor, of a part of the brain creating epileptic seizures, of a vascular lesion, etc.). In the photo on the right, it was the resection of a tumor called glioblastoma.
In the skull, perfect hemostasis must be obtained, because a possible hematoma could not escape (the skull being closed) and would compress the brain. Multiple hemostatic products are available to complete hemostasis achieved with bipolar coagulation.
The bone flap is then replaced and fixed by titanium microplates. There are various shapes and specials available for covering bit holes.
In the past, the flap was suspended by strong, nonabsorbable threads and it was important to have the bone beveled to prevent the flap from sinking inside the skull.