Surgical evacuation CSDH via burr hole craniostomy appears to be the most widely practiced treatment technique worldwide and outcomes are generally favorable.

In previous reports, bilateral CSDH was raised as a predictor of rapid deterioration and worse outcomes attributable to brain herniation, in comparison with unilateral ones. Nevertheless, the optimal surgical considerations in bilateral CSDH still remain controversial. Thus, this study principally aims to finding out whether consecutive removal of bilateral CSDH really poses a complication risk. The secondary objectives of the study were to obtain information about the one-year prognosis of bilateral CSDH and to find factors that affect the prognosis, if any.

Inclusion criteria Symptomatic adult (≥18 years-old) patients with bilateral hemispheric CSDH

Exclusion criteria Patients with hematoma thickness smaller than 10 mm on either side, and those who previously underwent any cranial surgery

Randomization Simple randomization, without blocking, will be used to divide patients into two groups simultaneous burr hole craniostomy (Group-1) and consecutive burr hole craniostomy (Group-2).

Clinical Evaluation Neurological examination and scoring systems (Glasgow coma scale and Markwalder Grading) will be used.

Radiological Evaluation Radiological evaluations will be made with CT and MR imaging.

Operation Patients in group-1 were fixed in supine position with their heads in neutral and flexion position. Bilateral burr holes were made one after another, the dural surfaces were exposed at the same time, then the outer membranes of both sides opened and hematomas evacuated simultaneously. All the patients underwent a drainage system, performed with the insertion of a silicone tube into the subdural space and tunneled under the scalp to the exit point. In group-2, hematoma with a greater thickness was removed first (if thickness was equal on both sides, first incision was made on the right side). The head in supine position was rotated to the side with a smaller hemorrhage thickness. Previously, burr holes were made, the dural surfaces were exposed, the outer membrane opened, and the hematoma was evacuated at one side. Then, drainage system inserted into the subdural space. After the procedure of the first side was completed, as a consecutive process, the head was rotated to the other side, and the same procedure was repeated. The contralateral hematoma was evacuated.

Follow-Up Depending on the subdural fluid collected, all drains will be removed within post-operative 36-48 hours.

Only the patients with epileptic history and on epileptic medication will receive postoperative antiepileptics.

In the postoperative period, a comprehensive evaluation encompassing neurological examinations and CT imaging will be performed.

This evaluation protocol will be executed immediately following the surgical procedure, after the removal of surgical drains (usually on the second postoperative day), and at designated intervals of the 1st, 3rd, 6th, and 12th months to monitor patient progress and recovery.

Chronic subdural hematoma (CSDH) arises at the dural border cell layer and is characterized by a pathological collection of blood, fibrin, and degradation products between the dura mater and the arachnoid mater with an insidious onset and progression. Surgical evacuation CSDH via burr hole craniostomy appears to be the most widely practiced treatment technique worldwide and outcomes are generally favorable.Although unilateral CSDH is seen in the majority of patients, bilateral involvement is not rare in neurosurgical practices.

In previous reports, bilateral CSDH was raised as a predictor of rapid deterioration and worse outcomes attributable to brain herniation, in comparison with unilateral ones. Nevertheless, the optimal surgical considerations in bilateral CSDH still remain controversial. Thus, this study principally aims to finding out whether consecutive removal of bilateral CSDH really poses a complication risk. The secondary objectives of the study were to obtain information about the one-year prognosis of bilateral CSDH and to find factors that affect the prognosis, if any.

The study is conducted as a prospective randomized controlled trial.

Inclusion criteria Symptomatic adult (≥18 years-old) patients with bilateral hemispheric CSDH

Exclusion criteria Patients with hematoma thickness smaller than 10 mm on either side, and those who previously underwent any cranial surgery will be excluded.

Randomization Simple randomization, without blocking, will be used to divide patients into two groups simultaneous burr hole craniostomy (Group-1) and consecutive burr hole craniostomy (Group-2). Written consent will be taken from each patient and/or patient's relatives for the surgery and the use of data for this study.

Clinical Evaluation Neurological examination and scoring systems (Glasgow coma scale and Markwalder Grading) will be used.

Radiological Evaluation Radiological evaluations will be made with CT and MR imaging.

Operation The patients were operated on either under general or local anesthesia based on the recommendations of anesthesiologists and the patient's general medical status. First-generation cephalosporins were used as preoperative prophylactic antibiotics (cefazolin). Patients in group-1 were fixed in supine position with their heads in neutral and flexion position. Bilateral burr holes were made one after another, the dural surfaces were exposed at the same time, then the outer membranes of both sides opened and hematomas evacuated simultaneously. All the patients underwent a drainage system, performed with the insertion of a silicone tube into the subdural space and tunneled under the scalp to the exit point. In group-2, hematoma with a greater thickness was removed first (if thickness was equal on both sides, first incision was made on the right side). The head in supine position was rotated to the side with a smaller hemorrhage thickness. Previously, burr holes were made, the dural surfaces were exposed, the outer membrane opened, and the hematoma was evacuated at one side. Then, drainage system inserted into the subdural space. After the procedure of the first side was completed, as a consecutive process, the head was rotated to the other side, and the same procedure was repeated. The contralateral hematoma was evacuated. 12-gauge soft drainage sets with secretion bags were used for postoperative drainage in both groups.

Follow-Up Depending on the subdural fluid collected, all drains will be removed within post-operative 36-48 hours.

Only the patients with epileptic history and on epileptic medication will receive postoperative antiepileptics.

In the postoperative period, a comprehensive evaluation encompassing neurological examinations and CT imaging will be performed.

This evaluation protocol will be executed immediately following the surgical procedure, after the removal of surgical drains (usually on the second postoperative day), and at designated intervals of the 1st, 3rd, 6th, and 12th months to monitor patient progress and recovery.

Inclusion Criteria:

- Symptomatic bilateral hemispheric CSDH

Exclusion Criteria:

• Hematoma thickness smaller than 10 mm on either side
• Previously underwent any cranial surgery

Since the International Clinical Trials Registration Platform (ICTRP) became operational in 2007 and we do not have such a clinical trial registry system at the national level, the registration was made retrospectively. The first surgery date of the last patient included in the study was January 2004, and the recruitment period lasted approximately 6.5 years. This policy applies to trials that began enrolling participants on or after January 1, 2019.