Decompressive craniotomy is a procedure used in severe intracranial hypertension unresponsive to other measures.
Patients with traumatic brain injury,stroke or cerebral edema may undergo this procedure.
The removal of the bone flap may cause by itself neurological deterioration which follows an initial improvement.
Days or weeks after surgery, a marked concavity may develop at the craniectomy site associated with a midline shift to the opposite side.This changes are aggravated by the presence of a VP shunt,dehydration and position changes.
It has been theorized that this " syndrome of the sinking skin flap" 1 ,2 (SSSF) is caused by the direct transmission of the atmospheric pressure to the intracranial cavity aggravated by CSF hypovolemia.
The increased frequency of hydrocephalus in patients after decompressive craniotomy is explained by a disturbance of CSF flow around the convexities.
Severe CSF hypovolemia can produce an herniation syndrome which can be reversed by Trendelemburg position.
The definitive and most effective treatment of the SSSF is cranioplasty 3 .
Cranioplasty protects the brain,and provides cosmetic results but most importantly , improves the neurological deficits by a decrease of local intracranial pressure and correction of CSF dynamics. Also 4 the cranioplasty may affect postural blood regulation,cerebrovascular reserve capacity and cerebral glucose metabolism. Sakamoto 5 described a patient after decompressive craniotomy with a CBF measured in CT perfusion imaging of 23 ml/100g/min and 37 ml/100g/min in the contralateral side which increased to 31 and 41 ml/100g/min respectively after cranioplasty. From this data we learn that the CBF was abnormally low bilaterally and increased significantly after cranioplasty. Another conclusion may be that
any intervention which further reduces CBF like hypotension and hyperventilation has to be avoided .
The cranioplasty itself may result in complications due to brain dysfunction,risk of fluid collection and subdural or intracerebral hematoma.Chun Chih Liao 6and coworkers recommend that if there is a VP shunt ,it has to be occluded several days before the cranioplasty to allow the expansion of the depressed area,eliminating the dead space between the bone and the dura,lessening the risk of hematoma.
There is another complication after brain surgery described by Van Roost 7
This investigator described a severe and sometimes fatal complication after uneventful intracranial surgery.
A postoperative rapid, malignant ,diffuse brain swelling , with a maximum at the level of the basal ganglia and thalamus and symmetrical distribution. They called it "pseudohypoxic brain swelling" (PBS)
The clinical picture which started 30 to 400 min after the end of surgery,included signs of brain stem dysfunction in some patients , seizures, or persistent coma after the end of anesthesia.
The CT scans showed hypodensities which resembled an hypoxic incident (which was ruled out) or severe brain swelling.
TCD-In some patients was normal, other showed accelerated flow or a reberberating flow in fatal cases.
MRI confirmed the CT changes
SPECT- rCBF bilaterally reduced.
ICP- there was a negative correlation between ICP values and survival.
The hypothesis was that excessive CSF loss via wound drainage and subsequent low ICP possibly triggered PBS, due to a massive negative pressure on the brain. Since they stopped removing the vacuum from the suction bottles, and blocking the drains until the patient awakens, no new cases were observed.
Although they described one case of this pathology after cranioplasty, based in anecdotic evidence we think that pseudohypoxic brain swelling is more frequent after large cranioplasties .
Anesthetic implications
-Patient scheduled for cranioplasty after decompressive craniotomy and VP shunt should have a temporary occlusion of the shunt several days before surgery.
-Avoid hypotension and provide normoventilation or mild hypoventilation to avoid further decreases of CBF
-Do not open the drain until the patient is fully awake.
References
1 Han PY et al "Syndrome of the Sinking Skin Flap" Secondary to the ventriculoperitoneal shunt after craniectomy.J Korean Neurosurg Soc 43 51-53 2008
2 Yamamura A. et al : Cranioplasty following decompressive craniotomy. Analysis of 300 cases. No Shinkei Geka 5:345-353,1977
3 Segal DH et al Neurosurgical recovery after cranioplasty. Neurosurgery 34:729-731,1994.
4 Winkler PA et al Influence of cranioplasty on postural blood flow regulation, cerebrovascular reserve capacity and cerebral glucose metabolism. JNeurosurg 93:53-61,2000
5 Sakamoto S. et al CT perfusion imaging in the syndrome of the sinking skin flap before and after cranioplasty.Clin Neurol Neurosurg Sep;108(6):583-5
6 Dirk Van Roost et al Pseudohypoxic brain swelling: a newly defined complication after uneventful brain surgery,probably related to suction drainage. Neurosurgery 53:1315-1327,2003
