This has come up in Question 2 from the second paper of 2014. Apart from neurosurgical options the College wanted their candidates to discuss blood pressure management, therapeutic hypothermia, likely prognosis and quality of life issues. Judging from the model answer, some detailed knowledge of the published trial evidence was expected.
A section of Oh's manual is dedicated to this exact issue. Chapter 51 ("Acute cerebrovascular complications") by Bernard Riley and Thearina de Beer contains within it a few paragraphs on decompressive craniectomy, on page 571. It would be worth pointing out that the key issues raised in these paragraphs were also raised in the model answer, and one would be well advised to review this material in order to produce an answer which appeases the examiners. For all we know, Riley or de Beer wrote that SAQ.
Apart from the brief entry in Oh's, several excellent resources exist for this topic:
If one were to discuss or critically evaluate the use of decompressive craniectomy in stroke, one would go about it in a systematic fashion:
- MCA infarction has a substantial mortality and morbidity.
- Factors which produce this effect include:
- Large volume of infarcted brain tissue, leading to significantly increased ICP.
- Significant risk for haemorrhagic transformation.
- Significant midline shift, with pressure on medial cerebral structures .
- Temporal herniation, with compression of the posterior cerebral artery.
- Poor perfusion of the contralateral cerebral hemisphere due to raised intracranial pressure.
- Many of these factors are related to the increased intracranial pressure.
- Decompressive craniectomy can decrease intracranial pressure by increasing cranial compliance.
- Ergo, decompressive craniectomy should be able to improve mortality and morbidity from acute MMCAS by vastly improving the perfusion in the penumbra of the stroke shortly after the craniectomy.
The college model answer lists three landmark studies worth referencing, which form the three famous European hemicraniectomy trials. They were HAMLET, DESTINY and DECIMAL.
- Prospective, multicenter RCT in Germany
- 32 patients were enrolled; then a statistically significant mortality reduction was found, and the study was terminated. The projected sample size was calculated to 188 patients, but the steering committee decided to terminate this trial anyway because of the results of the three other European decompressive craniectomy trials.
- Raw data suggests improved survival for the craniectomy group: 88% vs 47%.
- Prospective, multicenter RCT in France
- After randomization of 38 patients, the data safety monitoring committee recommended stopping the trial because of slow recruitment.
- Absolute reduction of 52.8% in the death rate in the surgery group.
- Survival was 22% in the "conservative management" group, and ~ 75% in the surgery group
- Prospective, multicenter RCT in the Netherlands
- 64 patients were randomised
- Again, survival was better with surgery (absolute risk reduction was 38%)
Pooled analysis of the European studies
A pooled analysis of the first three studies, including 93 patient cases, came to a fairly positive conclusion:
"...after decompressive surgery the probability of survival increases from 28% to nearly 80% and the probability of survival with an mRS of ≤3 doubles."
(mRS here being the score of the modified Rankin scale, equating to a disability where one requires some help, some of the time, with some things - but is otherwise able to walk unassisted).
In addition to the above studies, the college mentions that people in the over-60s age group are also being investigated as potential candidates for decompressive craniectomy.
They were probably referring to the DESTINY II Trial (2014):
- 112 patients, older than 60 years (median age was 70)
- Primary outcome measure was survival without severe disability; this was improved: 38% in the hemicraniectomy group, as compared with 18% in the control group.
- Survival in general also had lower mortality in the surgery group (33% vs. 70%).
- However, in contrast to the young patients, practically none of the survivors has an outcome as good as an mRS score of 3. The vast majority of the post-operative survivors were severely disabled.
Progression of an MCA infarct to a "malignant" MCA infarct:
These are the findings from the three abovementioned European trials.
- MCA territory stroke of >50% on CT
- Perfusion deficit of >66% on CT
- Infarct volume >82 mL within 6 hours of onset (on MRI)
- Infarct volume of >145mL within 14 hours of onset (on MRI)
- Age <60 years.
- Within 48 hours of symptom onset.
- It seems the benefit of craniectomy was lost after 96 hours; presumably all the salvageable penumbra has died, and mass effect is maximal.
- Craniectomy has to be large enough to extend past the margins of the infarct.
- Well tolerated even after thrombolysis( though apparently antiplatelet drugs tend to increase the risk of bleeding).
- There is no difference in outcome whether dominant or non-dominant hemispheres are involved.
- If there is a haemorrhagic transformation, a craniectomy and evacuation of clot may be required even if the patient did not meet MMCAS criteria as above. This is particularly helpful for posterior fossa pathology, where space is anatomically limited.
Intracranial pressure monitoring
- Does not work. ICP monitoring has not been proven to change outcome.
- EVD insertion may still be required for drainage of secondary hydrocephalus resulting from haemorrhagic stroke
- NNT for survival is 2
- NNT for severe disability is 6.
- Malignant MCA infarct has a mortality of 70%
- Craniectomy reduces this to 30%, but with residual deficit.