Primary Posterior Fossa Lesions and Preserved Supratentorial Cerebral Blood Flow: Implications for Brain Death Determination

Abstract

Patients with primary posterior fossa catastrophic lesions, who clinically seem to be brain-dead, evolve from retaining to losing supratentorial blood flow. If absent cerebral blood flow is used as an additional criterion for the declaration of death by neurological criteria, these patients are not different than those who become brain death due to supratentorial lesions.

Neurological determination of death in isolated brainstem lesions: A case report to highlight the issues involved

“…The outstanding question is how to confirm death using neurological criteria to satisfy both the whole death and brainstem death formulations in the presence of an isolated brain stem lesion. It is reassuring that supratentorial cerebral blood flow is lost over time in patients with isolated brain stem lesions, 5 and that our patient showed evidence of on-going ischaemic necrosis both infratentorially and supratentorial at post mortem examination. Some may therefore argue that ancillary tests are unnecessary even in this scenario.…”

“…An isolated brain stem lesion, or one limited to structures supplied by the posterior cerebral circulation, is an unusual diagnosis as a cause for the NDD, accounting for only 1.9% of all causes in a recent observational study. 5 Data from the UK potential donor audit (PDA) which records details of every death in each ICU and emergency department, suggest that many intensivists in the UK will never make the diagnosis in these circumstances. 6 The absolute number of patients tested, as well as the proportion of those suspected of meeting the criteria who were actually tested, have both increased slightly over the past 7 years (Table 1).…”

“… Note: The number of patients with an isolated brainstem/posterior circulation lesion is an estimate based on the findings of Varelas and colleagues. 5 NDD: Neurological determination of death.…”

“…Interestingly, a recent observational study identified four patients with posterior fossa lesions, who met the criteria for NDD but retained supratentorial blood flow on initial CT angiography; this flow was absent on repeat CT angiography in all patients. 5 Furthermore, some investigators question the relevance of persistent perfusion, arguing that opacification of larger supratentorial vessels results from stasis filling, since the loss of flow starts at capillary level. 11 This argument is supported by further work from the same authors demonstrating non-viable brain on CT perfusion scan despite the presence of flow on CT angiography.…”

How should we use imaging in the determination of brainstem death?

“…It has been suggested that the vast majority of cases of brainstem death are a result of catastrophic supratentorial pathology, with only around 2% being due to isolated brainstem lesions. 18 The most likely mechanism starts with cerebral oedema, which would lead to the posterior cerebro spinal fluid pathways being impeded. There would be subsequent development of obstructive hydrocephalus which would cause an increase in the intracranial pressure.…”