The recent event with the Titan submersible reminded me of this case.
33 year old female with a ruptured aneurysm that ultimately caused a large left-sided stroke with massive brain swelling. This necessitated a decompressive craniectomy to release the pressure and placement of a ventricular shunt.
2 months later, she presented with a sunken appearance where the craniectomy was done and new seizures.
CT shows new sunken appearance of the brain at the craniectomy site and a paradoxical, left-to-right midline shift away from the craniectomy.
Sunken skin flap syndrome (also known as trephine syndrome) is caused by atmospheric pressure pushing against the brain, with risk factor being ventricular shunt or drain (which will reduce intracranial pressure). It is a known complication of craniectomies, and the treatment is cranioplasty (place the missing skull back on). She had already been planned to get the cranioplasty, but this problem developed a little earlier than anticipated. Note: a depressed appearance by itself is not a major issue (aside from cosmetic) - it is the presence of seizure or other neurologic symptoms that necessitate more urgent management.
