Traumatic Acute Subdural Hematoma — Should the Bone Flap Be Removed or Replaced?
Shankar Gopinath
N Engl J Med April 23, 2023
DOI: 10.1056/NEJMe2302936
Traumatic acute subdural hematomas often warrant emergency evacuation of the blood clot to avoid further cerebral compression and its sequelae. Once the subdural clot is removed, the million-dollar question in the mind of the neurosurgeon is to whether to replace the bone flap (craniotomy) or not (decompressive craniectomy). In some instances, the decision to leave the bone flap on or off is relatively straightforward, such as in older persons with atrophic brains who have a visually “relaxed” brain after clot evacuation (in whom the bone flap should be replaced) or in a patient with massively swollen brain (in whom the replacement of the bone flap is virtually impossible). For those cases that lie between these two extremes, the decision to choose one or the other approach is complicated and has been based on the discretion and experience of the neurosurgeon — in other words, anecdotally.
Retrospective studies comparing outcomes between replacing and removing the bone flap have consistently shown that patients who have had severe cranial trauma, poor neurologic status, or considerable brain damage on imaging were more likely to have had the bone left off by the surgeon.1-3The authors of these studies generally concluded that the bone should be left off in cases in which patients were expected to have clinically significant brain injuries.4 This is intuitive and not surprising, but data from randomized trials to guide the decision for the large middle ground — in which there were intermediate degrees of cranial trauma and damage on imaging — have been lacking. So the findings reported by Hutchinson and colleagues in this issue of the Journal are welcome.5 Before this trial, the decision not to replace a bone flap was based on the assumption that the swollen brain would have more room to expand, which would mitigate dangerously high intracranial pressure.3 If the bone flap were to be replaced, the patient may need further surgery for removal of bone to relieve high intracranial pressure, by which time the effect of serious secondary cerebral complications would have already occurred.
Part of the reason for the lack of data to inform the craniotomy-versus-craniectomy debate is the heterogenous selection criteria that have been used in studies. As a result, there has been a tendency in recent years to advocate for craniectomy as a primary treatment, with the full understanding of its many disadvantages — such as the development of ipsilateral and contralateral hematomas, expansion of hemorrhagic contusions, infections, cerebrospinal fluid disturbances,6 “syndrome of the trephined” (a sunken skin flap with neurologic deterioration due to intracranial tissue shifts) — and with recognition of the problems associated with cranioplasty. Further complicating matters, data from a national survey have suggested that mortality is substantial among patients who have undergone a craniectomy.7
Other factors can tilt the choice toward craniectomy, including intraoperative hemodynamic instability, coagulopathy, prolonged operative time to obtain satisfactory hemostasis, lack of an adequate number of trauma neurosurgeons and perioperative staff, and lack of practitioners to accommodate frequent unanticipated emergency surgical cases. In these scenarios, it is safer to leave the bone off and rapidly close the patient’s scalp, thus shortening the operating time.
Hutchinson et al. have now found in a prospective randomized trial involving patients with traumatic acute subdural hematoma that disability and quality of life were similar with either surgical approach. In the past decade, the majority of patients would undergo craniotomy, but for the past few years, craniectomy has been performed more often than craniotomy. With these results, I expect that surgeons will be reassured that it is relatively safe to perform the quicker procedure of removal of the bone, knowing that if the bone is left in place, compression of the brain under the hematoma and the need for reoperation can largely be prevented. Because the incidence of local infections was low in both trial groups but was admittedly higher with craniectomy, the trial also showed that the price paid for choosing the quicker procedure is medical complications, most of which are treatable, such as infection related to repairing or replacing the skull defect — a trade-off for fewer intracranial risks that might be considered satisfactory.
Brain swelling and other intracranial problems that lead surgeons to leave the bone off during an operation for an acute subdural hematoma are associated with a variety of factors that may portend a poor prognosis. However, prompt treatment and intensive medical care and rehabilitation can lead to a meaningful return to activities of daily life.
