Title : “No kicking in the body bag”: Determination of brain death with the aid of nuclear medicine scintigraphy
Abstract:
Background: The gold standard of ancillary imaging in determining brain death is Digital Subtraction Angiography (DSA) of the four cerebral vessels, which boasts a near 100% sensitivity and specificity. However, its use is limited due to its time-intensive nature, need for transfer to an angiography suite, and operator skill level. Scintigraphy involves the administration of radio-pharmaceuticals and the detection of gamma rays emitted by their decay within the brain. In the context of brain death, the radio-pharmaceutical used is typically technetium-99m hexamethylpropyleneamine oxime (Tc-99m HMPAO). Upon intravenous injection, Tc-99m HMPAO is absorbed by viable brain tissue, and scintigraphy images show perfusion to these regions, highlighting areas with preserved blood flow. In brain death, images obtained at timed intervals during the perfusion scan will show absent intracranial uptake, known as the "empty light bulb sign" as demonstrated in Figure 1. There is also corresponding uptake in the external carotid arteries. The absent or reduced flow to the internal carotid arteries is theorized to lead to shunting to the external carotid arteries, also appreciated in Figure 1 in the sagittal planes.
Learning Objectives: Brain death, the irreversible cessation of all brain functions, is a critical determination with profound implications for patient care, organ transplantation, and ethical considerations. Traditionally, brain death diagnosis varies across the world relying on clinical criteria, mechanism of injury, and a variety of ancillary imaging modalities. Nuclear medicine scintigraphy has emerged as a valuable ancillary tool in confirming brain death. The main advantage of nuclear medicine scintigraphy in brain death diagnosis is its objectivity. Unlike clinical criteria, which can be confounded by factors such as sedation, paralysis, or the presence of pharmacological agents, scintigraphy provides an objective visualization of cerebral perfusion.
Conclusion: Nuclear medicine scintigraphy can complement clinical testing in complex cases where clinical assessment alone may not suffice. In cases of severe head trauma, drug overdose, or hypothermia, the presence of neurological reflexes can create diagnostic uncertainty. Scintigraphy can serve as a confirmatory tool in such scenarios, while remaining cost and time sensitive.
