Patients that undergo decompressive craniectomy are at risk of delayed changes in brain function known as "Sunken Flap Syndrome" or "Syndrome of the Trephined." The goal of this clinical trial is to see if placing a prosthetic over patients' skull defects can prevent "Sunken Flap Syndrome."

The main questions are:

1. Can placing a prosthetic device over patients' skull defects prevent Sunken Flap Syndrome?
2. Can placing a prosthetic device over patients' skull defects decrease healthcare costs?
3. Can placing a prosthetic device over patients' skull defects improve recovery and return of brain function after decompressive craniectomy?

Patients that experience traumatic brain injuries, brain bleeds, and large strokes can build up high levels of pressure in the skull. When this pressure can't be controlled with medications, a life-saving surgery called a decompressive hemicraniectomy (DC) is often performed. In this surgery, a large portion of the patient's skull is removed to decrease pressure on the brain and decrease permanent damage.

After this surgery, many patients experience sinking of the brain in the skull as the pressure inside the head improves. The skull normally protects the brain from the outside environment. When large parts of the skull are removed, the brain is not able to regulate itself normally. This can lead to a number of problems, such as headaches, weakness, seizures, and even coma and permanent brain damage. This is referred to as "Sunken Flap Syndrome" (SFS) or "Syndrome of the Trephined" (SoT). After 3-6 months, patients can have the missing skull surgically repaired, which improves and sometimes fixes SFS, but the damage is sometimes too severe to be reversed.

There are reports of patients with SFS treated with custom-made prosthetics that cover the missing piece of skull. In this study, the researchers want to see if wearing a custom-made prosthetic can prevent patients from experiencing SFS. Patients will also receive additional non-invasive measurement to see if the prosthetic can improve brain function and recovery. Finally, the researchers want to know if the prosthetic is cost-effective by decreasing the frequency that patients see doctors or receive care to treat SFS.

Patients or the patient's medical decision makers will be asked if the patient wants to participate in the study after DC. If the patient or decision maker agrees to participate, the patient will be also asked if the patient wants to wear the prosthetic. The prosthetic is made of a common material used in other facial prosthetics. Patients that agree to wear the prosthetic will have a custom plate made for the participant.

All patients will receive the same post-operative care and appointments whether or not the prosthetic is worn. The participant will go to the normally scheduled post-operative doctor's appointments at 2 and 4 weeks after initial DC surgery. Patient's that agree to wear the prosthetic will receive it at the 4-week post-DC appointment. The participant will then be asked to wear it as much as possible, but to let the researchers know if the participant experiences any pain, itching, discomfort or other problems.

All patients will also be seen by the patient's physician before and after and after skull repair. At all appointments, patients will receive non-invasive testing of brain function. Recovery and rate of SFS will be compared between patients that do and do not wear the prosthetic.

Participants will:

• Go to the normally scheduled 2 and 4 week post-DC appointments
• Go to the normally scheduled pre- and post-skull repair appointments
• Receive additional non-invasive brain health testing at each appointment

Participants that agree to wear a prosthetic will:

• Receive the custom prosthetic at the 4-week post-DC appointment
• Wear the prosthetic as much as possible, including at night
• Take a brief survey about the prosthetic at the post-skull repair appointment

Inclusion Criteria:

• Age > 18
• Patients must be admitted to Johns Hopkins Hospital or Johns Hopkins Bayview Medical Center
• Patients must have undergone decompressive hemicraniectomy within 2 weeks of consent for inclusion in the study (before the initial 2 week post-craniectomy assessment)

Exclusion Criteria:

• Patients that undergo bilateral decompressive hemicraniectomy
• Patients that undergo suboccipital decompressive craniectomy
• Patients with pre-existing diagnosis of hydrocephalus
• Patients with a ventriculoperitoneal, ventriculoatrial, or other permanent cerebrospinal fluid shunt
• Patients with an open external ventricular drain at the time of their 2 week post-craniectomy assessment