The clinical-functional result after frontal and parietal burr-hole trepanation for the treatment of chronic subdural hematoma (cSDH) is effective with regards to control of the hematoma and regression of symptoms (headache, decreased vigilance and neurological deficits). However, in patients the treatment may leave visible depressions of the scalp, just above the trepanation sites, that typically develop gradually after weeks - months after the procedure. A considerable proportion of patients find this aesthetically, functionally and psychologically disturbing; the skin depressions may even cause pain or interfere with activities of daily living, such as combing, etc.

An effective method would exist to avoid this undesired treatment effect: Before the skin is closed, a permeable titanium burr-hole plate could be attached above the trepanation site in order to prevent the skin from sinking into the bony defect. However, this is rarely done today, likely because there is no evidence that this treatment modification is effective and safe. Moreover, as material is implanted, this causes additional costs.

The primary aim of this study is to evaluate whether the application of burr-hole plates on both the frontal and parietal burr-hole in the context of burr-hole trepanation for the treatment of cSDH can improve patient satisfaction with the aesthetic result of the surgery.

In addition, the study is intended to demonstrate that this additional measure will not result in poorer hematoma control, poorer clinical/neurological outcomes, or additional complications for the patient.

In a prospective, single-blind and controlled approach, we randomize 80 patients with uni- or bilateral cSDH into an intervention group (with burr-hole plates) or into a control group (without burr-hole plates).

The primary end result of the study is the patient's reported satisfaction with the aesthetic outcome of the surgical scar. Secondary results are pain, functionality, neurological status, health-related quality of life, residual hematoma volume, and complications (according to Clavien-Dindo scale; especially re-operation rate for recurring cSDH and infections).

The study corresponds to a modern approach, since today's patients not only expect favorable treatment results for their disease, but the therapy should also avoid permanent undesired side-effects, if possible.

Participants fulfilling all of the following inclusion criteria are eligible for the study:

• Patients with first-time cSDH (hypodense, isodense, hyperdense or mixed-type in CT-imaging), scheduled for uni- or bilateral double burr hole trepanation under general anesthesia
• Patient age ≥ 18 years
• Patient non-comatose at time of inclusion (GCS > 8 points)
• Patient able to communicate (in terms of ability to hear, see, speak and understand)

The presence of any one of the following exclusion criteria will lead to exclusion of the participant:

• Patient with recurrent cSDH or previous surgery for cSDH
• Patient with cSDH treated by craniotomy or by single burr hole trepanation
• Patient with cSDH treated in local anesthesia
• Patient unlikely to attend the follow-up (due to reasons of residency, dismal prognosis, etc.)
• Pregnancy
• Known allergy against or incompatibility with Titanium
• Known or suspected non-compliance
• Inability to follow the study procedures, e.g. due to psychological disorders, dementia, etc. of the participant

IPD will be made available on reasonable request, once the results are published and if approved by the institutional review board (KEK-ZH).

After the results are published.

IPD will be made available on reasonable request, once the results are published and if approved by the institutional review board (KEK-ZH).

Patients will be blinded for allocation to the study group/side, but surgeons will not be. Patients will not be aware of the study group/side, since the operation takes place under general anesthesia. After surgery, it is not possible to see through the skin, whether or not a burr hole cover has been placed.

The fact that patients are blinded for the study group allocation will be mentioned in the discharge letter (in order to inform the family physician), and the neurosurgical team of nurses and physicians will also be informed not to "unblind" the patient.

Unblinding (and revealing a participant's allocated intervention) towards the patient is permissible only if the trial is suspended, prematurely terminated due to security concerns or completed.