Isolated brainstem death: case presentation demonstrating preserved supratentorial perfusion on 99mTc-bicisate brain scintigraphy

The diagnosis of brain death (BD) is primarily clinical and usually straightforward when both supratentorial and infratentorial structures are irreversibly injured. In contrast, isolated catastrophic posterior fossa lesions—particularly those involving the brainstem—are uncommon and may demonstrate preserved supratentorial perfusion or cortical electrical activity on ancillary testing, even in the absence of brainstem function. This apparent dissociation is typically transient and invariably progresses to global cerebral circulatory arrest and death. Few reports have documented the natural evolution of this phenomenon, highlighting the rarity of such cases and their uniformly poor outcome. A 47-year-old woman with no known history of chronic seizure disorder presented in an obtunded state. On arrival, she experienced continuous seizures and the clinical status rapidly deteriorated. Initial head CT scan without contrast revealed basilar artery thrombosis. She received intravenous tissue plasminogen activator (tPA) and levetiracetam. She underwent mechanical thrombectomy with partial recanalization (TICI 2b). Despite intervention, neurologic examination remained poor with absent spontaneous respiration and brain stem reflexes. Subsequent non contrast head CT scan demonstrated worsening brain stem edema and obstructive hydrocephalus. Due to poor clinical status, a 99m Tc-bicisate brain perfusion scan was performed which demonstrated absent posterior fossa perfusion with preserved supratentorial tracer uptake. Due to this preserved supratentorial perfusion, life support was continued. Follow-up head CT scan without contrast revealed progression to diffuse cerebral edema, and massive trans tentorial and tonsillar herniation. The patient was later clinically declared brain dead. Organ donation followed in accordance with her previously expressed wishes. This is a rare case of isolated posterior fossa injury with preserved supratentorial perfusion compatible with “brainstem death”. The case highlights the importance of ancillary testing in uncommon supra/infra tentorial dissociation to differentiate brain death from brainstem death.