Craniotomy – Opening the Top of the Skull.

To operate on the brain, the neurosurgeon must open up the skull, which is known as a craniotomy.

A trauma flap craniotomy can be used to open up one entire side of the head, from the frontal to the occipital lobe. For this purpose, a standardized skin incision is made from front to back and then curved to end in front of the ear. The temporal muscle must be incised and removed, after which a large frontotemporoparietal craniotomy can be performed. This kind of decompressive craniectomy can be performed within a few minutes as an emergency procedure, whereas complex interventions on the base of the skull take several hours. A two-stage procedure may be necessary here: in the first operation, access is created, and in the second operation the tumor is removed. Particularly in the case of complex tumors found at the base of the skull, a procedure lasting several hours is required to create access. This is done by milling away the basal bone and performing careful microsurgical dissection. Since further tumor resection can take several hours, a second procedure is carried out to ensure the patient’s safety. In principle, a craniotomy can be performed directly over the pathology using anatomical landmarks or a navigation system.

After a craniotomy, the bone flap that was removed should be reimplanted. The procedure and its associated risks are explained in more detail below.

How is the top of the skull opened up?

To surgically treat brain diseases, the skull must first be opened up. These operations are performed in a neurosurgery clinic, and the extent and location of the procedure depend on the underlying pathology.

The brain is surrounded by rigid protective bone. A hole is drilled into this bone after the skin is pulled back and, if necessary, the muscles and overlying periosteum are cut through. Such a hole can be drilled using a burr or a perforator, such as the evoDrill from evonos. An advantage of this tool is that it stops automatically when there is no more bony resistance, which is a particularly safe method when opening the skull via vessels located in the dura. The evoDrill is available in different diameters, allowing you to select the appropriate size and perform the primary opening with minimal effort. For very large craniotomies, multiple drill holes can be created and connected using a craniotome. The sawn-out bone flap is then levered out and removed. This reveals the dura, which contains large venous vessels. Milling requires both knowledge of the position of these structures and careful manual handling.

Many craniotomies are performed according to anatomical standards. For instance, there are predefined access routes to reach pathologies in the posterior, middle, and anterior cranial fossae. The anterior skull base can be accessed via a pterional approach, which involves opening the skull frontotemporally. Some of the bony protrusions at the base may need to be removed.

In addition to theoretical learning methods, there are cadaver courses available that help neurosurgeons learn and practice these sometimes very complex access routes, giving them the opportunity to improve their anatomical understanding and manual skills on the base of the skull.

Navigation systems are now available that can be used to access areas not limited by anatomical landmarks. These systems can read previously created thin-layer images from an MRI or CT and reference them to the patient’s fixed head. This makes it possible to plan access to a tumor as well as the extent and exact localization of the craniotomy before opening the skull. Navigation also helps to identify possible tumor borders that are not visible under the microscope.

When is the cranial bone reimplanted after a craniotomy?

If a craniotomy is performed to remove a tumor or other pathology, the skull bone is reimplanted during the same operation.

After a microsurgical procedure, such as tumor removal or vascular malformation elimination, the dura mater is first closed. This is done by suturing it watertight, or inserting an artificial replacement or a separate muscle or fascia. Then, the previously removed bone flap is refitted and fixed to the skull with at least three small plates. There are various plate models with different lengths and shapes to ensure a perfect fit, such as those available in the evoFix from evonos. The surgeon can select the right models from a wide range of options and fixate them with self-tapping screws.

In cases of brain swelling due, for example, to traumatic brain injury or a heart attack, the primary surgical objective is to create space for the brain. This procedure is called a craniectomy. In these cases, the initial plan is to leave the bone flap detached to allow the brain to expand.The patient’s head is turned to one side, and the largest possible trephination is performed. The surgeon may need to secure the head with a clamp to remove a large flap. The bone flap is cleaned and cryopreserved until the brain has sufficiently swollen and reimplantation can be planned. Alternatively, the autologous bone flap can be implanted in a subcutaneous pocket in the abdominal wall. However, this prolongs operating time and involves additional risks. There are no strict time specifications for this procedure. The brain swelling and the patient’s overall state must be considered on a case-by-case basis. A distinction is made between early and late reimplantation. Early reimplantation occurs within the first three months after the primary procedure, while a late reimplantation occurs after more than three months.

When reimplanting the removed bone flap secondarily, the old scar must be opened, and the bone edges must be carefully dissected so that the flap, or PEEK or titanium implant, can be precisely implanted. Manipulation of the brain should be avoided to prevent injury.

What are the risks associated with reattaching the top of the skull?

One of the risks associated with reinserting the top of the skull is postoperative bleeding.

Cranioplasty, or the reinsertion of an autologous bone flap or a custom-made implant, generally has a high rate of complications. The risk of complications such as infection, bleeding, and hydrocephalus is around 30%, with post-operative bleeding being the most common complication.

Sinking skin flap syndrome (SSFS) is a problematic situation. This occurs when the brain has sunk well below the level of the skull, creating a large space into which bleeding can occur after the bone flap is reimplanted. Neither drains nor sutures can significantly reduce the risk.

For patients with a permanent cerebrospinal fluid drain, such as a ventriculoperitoneal shunt, raising the valve pressure level can reduce the flow of cerebrospinal fluid out of the body and into the cavity.

Overall, the patient benefits from the reimplantation of the bone flap, on the one hand, for cosmetic reasons, and, more importantly, because it protects the brain. During reimplantation, care must be taken to ensure direct contact between the bones in prominent areas like the forehead. Patients at risk of falling or with seizure disorders require mechanical protection, such as a skullcap, in particular. While waiting for reimplantation, patients can wear a customized helmet while moving around to minimize the risk of injury.

Moreover, a patient’s neurological condition often benefits from rehabilitation, probably due in most part to improved blood circulation, atmospheric pressure, and cerebral glucose metabolism.

Other possible complications following bone flap reimplantation include seizures, hydrocephalus and infection. If an infection occurs, the flap must be removed again and followed up with a long course of antibiotics. Then, an artificial lid made of titanium or PEEK must be produced for a new cranioplasty. The evoShape from evonos, for example, can be used for this procedure. It is adapted to the patient based on a CT scan, providing a perfect fit and making the operation quicker and safer while ensuring an aesthetically pleasing result.

Several studies and articles address risk minimization during bone flap reinsertion, noting a slight advantage of the manufactured preparations with regard to infection.

How do the bones of the skull grow together?

The bones of the skull typically grow together during childhood through the ossification of the cranial sutures.

In an infant, the individual skull plates are flexibly connected to each other via soft cranial sutures, which allow the skull to expand as the brain grows. By the end of the first year of life, 90% of skull growth is complete, but the skull can become deformed during this time, especially during the first few months of life. If the deformation is caused by the baby lying on one side of the head, consistently turning the infant’s head to the other side can help compensate for the asymmetry.

Craniosynostosis resulting from a closed suture must be treated surgically. Apart from skull asymmetry, it can lead to increased intracranial pressure and brain damage. After surgery, a special helmet is worn to restore a normal head shape.

In adults, the bone cannot deform. In this case, trauma results in a skull fracture. If there are fragments, they must be removed and placed correctly, and screwed together if necessary. If there are no fragments or if there is a comminuted fracture, a bone replacement can be made and inserted.

If a craniotomy is performed again after surgery to access a tumor, the bone flap may grow back together with the rest of the skull over time. In this case, a new craniotomy must be performed.

What are the long-term effects of a craniotomy?

The long-term effects of a craniotomy largely depend on the underlying disease. A direct craniotomy can mainly affect the patient’s appearance. If the bones are not directly adjacent to each other, a gap is created, which some patients find disturbing. The plates required for fixation may also be palpable, especially on the forehead or under thin skin.

In cases of autolysis, the reimplanted skull bone dissolves more and more at the edges, which can lead to cosmetic problems and loosening. If the patient is experiencing significant discomfort, a new cranioplasty procedure can be performed.

A patient’s neurological condition largely depends on the pathology and preoperative deficits. For example, if a tumor is causing neurological symptoms, such as weakness, due to its space-occupying effect, these symptoms can be alleviated by removing the tumor. However, tumor resection in the motor cortex, which controls movement, can lead to impaired mobility. Additionally, bleeding or circulatory disorders occurring in eloquent areas of the brain can exacerbate existing symptoms or cause new impairments, including paralysis or speech disorders. Neurological deficits can also occur if a vessel has to be coagulated, as in the case of a stroke. The extent of the damage depends on the size and supply area of the affected vessel.