Decompressive craniectomies are craniectomies performed to relieve raised intracranial pressure, most commonly in the setting of florid cerebral oedema following cranial trauma or swelling following infarction 1.
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History
Craniectomies for the treatment of cranial trauma date back to at least 10,000 BC in the form of trephination, whereby a small circular craniectomy was performed with a stone 2. Evidence of similar procedures has been uncovered during many periods of human history, including ancient Egypt, Greece, and Rome 2.
The first modern description of large craniectomies performed for the treatment of elevated pressures in the setting of traumatic brain injury was published by Theodor Kocher in 1901. Soon thereafter, Harvey Cushing adopted the technique and performed it to control raised intracranial pressure from other causes, including incurable brain tumours 2.
Indications
The permanent removal of bone from the skull has numerous indications (see craniectomy). However, decompressive craniectomies are performed to manage raised intracranial pressure, most commonly secondary to traumatic brain injury or malignant ischaemic stroke. Occasionally, they may also be used in a variety of other clinical settings 1.
Indications include:
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malignant ischaemic stroke
in patients aged 60 years or younger, within 48 hours of stroke onset 8,9
Procedure
Decompressive craniectomies are performed similarly to routine craniotomies with the major difference being that the bone flap is not replaced at the end of the procedure. Instead, it is either discarded or frozen for later replacement 7.
Typically, a large question mark-shaped incision is performed extending from the ear, up towards the vertex and back down posteriorly; this allows much of the personal and parietal parts of the skull to be accessed while ensuring the facial nerve is preserved. Once the scalp flap is mobilised, a bone flap with a diameter of at least 12 cm is extracted. Additional removal of temporal bone may be necessary for further access to the middle cranial fossa 4.
An important step is opening the dura. The effectiveness of decompression merely from removal of the bone flap is limited as the dura is quite thick and inelastic allowing for minimal increase in the available intracranial volume 4. When the dura is opened necrotic parenchyma may be resected although this is generally not recommended 4. An intracranial pressure monitor can be introduced at this time 4. The dural defect is then closed using a dural patch (e.g. periosteum, fascia or artificial dural substitute) 4. Finally, the surrounding tissue and skin are repositioned and secured.
Complications
In addition to the usual complications of any surgical procedure, craniectomies have a number of specific sequelae 1.
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haemorrhage
ipsilateral or contralateral haematoma (subgaleal, extradural, subdural)
haemorrhagic contusion expansion
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CSF
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pressure-related
Outcomes
A decompressive craniectomy reduces intracranial pressure (by increasing the available volume into which the brain can expand - see Monro-Keillie hypothesis) and has been shown to improve survival rates in a number (but not all) of randomised control studies 3,5,6,8-10.
Complications are numerous and many of these survivors, however, have a significant permanent disability (modified Rankin scale (mRS) of 4 or 5). This is particularly common in older individuals (e.g. greater than 60 years) or those where raised intracranial pressure is the result of parenchymal pathology. Notably, in a meta-analysis of decompressive craniectomy in ischaemic stroke, decompression did also increase the number of patients with favourable outcomes (mRS 2 or 3) 9.
As such the use of decompressive craniectomy remains an area of controversy and careful individualised decision making must be taken when embarking upon its use 6.
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