Observational study to investigate the natural course of intracranial pressure (ICP) after decompressive craniectomy (DC) using long-term telemetric ICP monitoring. Patients will have continuous ICP measurement performed during the admission to the neuro-intensive care unit (NICU) and after discharge weekly measurements sessions will be performed before and after cranioplasty.

Several studies have investigated and documented the effect of DC in lowering ICP in intracranial hypertension following acute brain injuries, e.g. severe traumatic brain injury. But the natural course of ICP in these patients after the acute phase in the NICU has never been investigated. Clinical experience suggests that a DC affects cerebrospinal fluid circulation and ICP, e.g. causing hydrocephalus or subdural hygromas.

The aim of this observational study is to document the natural course of ICP following DC and to investigate the effect of cranioplasty on ICP. This is done by implantation of a telemetric ICP sensor and weekly follow-up monitoring sessions after discharge from the NICU until 1 month after cranioplasty. The monitoring sessions will include standardized body positions to investigate postural ICP changes before and after cranioplasty. The project will also provide experience with telemetric ICP monitoring during the acute phase in a NICU setting.

Inclusion Criteria:

• age > 18 years
• scheduled for a decompressive hemicraniectomy for elevated ICP or signs of intracranial herniation

Exclusion Criteria:

• skin damage in the frontal area where the telemetric ICP sensor is implanted
• lack of informed consent from next-of-kin or the patient's general practitioner

Adult patients scheduled for a decompressive hemicraniectomy for elevated ICP (e.g. following severe traumatic brain injury) or signs of intracranial herniation (e.g. following cerebral edema in patients with middle cerebral artery infarction).