The ideal candidates are younger patients with full MCA distribution stroke. One issue to be mindful of is that the “watch” part should be focused on watching to confirm the radiographic size of the stroke and the presence of cerebral edema. I would caution against watching for clinical deterioration or failure of medical therapy because, by the time this happens, secondary injury may already have occurred. If a patient is a good candidate for a craniectomy and has a stroke of sufficient size with the presence of cerebral edema, it's best to discuss early with the patient’s decision-makers and surgeons and act earlier rather than later.
If the infarct is >2/3 of MCA territory and the patient is <60 years of age, they should be considered for decompressive hemi-craniectomy (DHC) within 48 hours of the ischemic event. This criterion is based on a meta-analysis of three RCTs of Destiny, Decimal, and Hamlet (Vahedi et al., PMID 17303527). In my practice, if the infarct is 2/3 MCA territory, and there is decreased arousal/somnolence on the exam, I request a DHC assessment. If the infarct is the entire MCA territory or both MCA/ACA territories, I immediately request a DHC assessment. I do not wait for pupillary changes or midline shifts to worsen, by then it's typically too late.