To the Editor: Intracranial pressure (ICP) monitoring is crucial in the management of various neurological and neurosurgical diseases such as traumatic brain injury (TBI), hydrocephalus, and intracerebral hemorrhage. However, pathological ICP (not only above, but also under reference ranges) may persist beyond the admission to the neurointensive care unit (NICU).1 Currently, the gold standard for the measurement of ICP in TBI patients remains the external ventricular catheter. Most ICP monitoring devices in current clinical use require a physical connection between the brain and the external environment. The placement of these devices carries a significant morbidity, particularly infection, which limits the duration of monitoring. Therefore, patients undergoing repeated monitoring require multiple surgical procedures.2 Several telemetric monitoring devices, in which data are in some way transmitted transcutaneously, have been developed over the last 30 yr. The possibility of intracranial continuous monitoring for several weeks in patients is a novel concept. The emergence of telemetric evaluation using sensors for short- and long-term monitoring is part of a new era.3 This technique offers to neurosurgeons an overview of the changes within the cranial vault in relation to ICP and allows measurements in the patient's everyday life. Telemetric ICP monitoring is useful in patients with complicated cerebrospinal fluid (CSF) dynamic disturbances who would, otherwise, require repeated invasive pressure monitoring.4 We all know decompressive craniectomy (DC) is being widely used to manage refractory intracranial pressure; however, the issues related to long-term sequel and morbidity are not well addressed as well as understood. Lilja-Cyron et al3 present an interesting study on the long-term potential of the evaluation by telemetry of ICP in patients undergoing DC and aimed at helping to define the best time for cranioplasty. Changes in the level of hydrodynamics of the CSF are a complex phenomenon, and this type of studies stimulates research in this field. The study offers us evidence confirming that ICP values continue to decrease gradually after NICU discharge from 7.8 ± 2.0 mm Hg to –1.8 ± 3.3 mm Hg (P = .02), reaching negative values after the third week of discharge. The most pronounced decrease occurred during the first month. DC abolishes normal intracranial fluid dynamics, ie, there was no difference between the ICP in supine and the ICP in the sitting position (P = .67). Pulsatile wave amplitude (PWA) was markedly reduced from initial 1.2 ± 0.7 mm Hg to 0.4 ± 0.3 mm Hg (P = .05). Intracranial PWA largely depends on intracranial compliance,5 and due to the disruption of the brain's rigid enclosing following DC, it is not surprising that PWA is diminished after DC. Pulse wave propagation is believed to be an important driver of CSF flow, and emerging evidence also supports its role in other intracranial fluid movements, such as glymphatic flow.6-8 Hence, the reduced intracranial PWA may contribute to the development of complications related to CSF flow (hygroma, hydrocephalus, and “syndrome of the trephined”) occurring after DC. “Pressure unloading” of the brain through postural ICP changes is absent following DC and that PWA, considered to be a prime driver of intracranial fluid movements, is severely diminished. These abnormalities appear very early in the postcraniectomy period and may potentially cause or worsen CSF-related complications observed after DC or directly affect the brain function. All this leads to the concerns that neurosurgeons have after DC is performed: When is the best time to perform cranioplasty? Lilja-Cyron et al3 have marked the lack of subgroup analyses by etiology of brain edema. That is why further investigations and studies are needed to define the right time for cranioplasty, specifically in patients with TBI, and also to determine if there is a difference in ICP change in different diseases requiring DC (TBI, acute middle cerebral artery infarct, etc). Carrying out the cranioplasty after DC has a positive impact not only at the aesthetic level but also on the cerebral metabolism and the hydrodynamics of the CSF.9,10 Cranioplasty remarkably improves neurological and cognitive outcomes supported by an improvement in cerebral blood perfusion.11 Performing it early between 15 and 30 d after initial craniectomy may also minimize infection, seizure, and bone flap resorption, whereas waiting for >90 d may minimize hydrocephalus but may increase the risk of seizure.12 Absence of postural ICP change and reduced PWA in the postcraniectomy period support an early cranioplasty strategy, but the surgical timing must be based on an overall assessment of individual patients.3 The correction of the cranial defect after DC will allow us as physicians to reduce the development of complications such as trephination syndrome, hygromas, hydrocephalus, and ischemic events, all of which are a consequence of disturbances of intracranial fluid movements (CSF and/or glymphatic flow). The telemetric ICP monitoring in the NICU and after discharge of patients with neurotrauma will most likely become a technique for comprehensive management. Disclosures The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.