E2125. Brain Death - Utility of Cerebral Scintigraphy, CT, MRI, and DSA: What Residents Want to Know About This Prime Medico-Legal Entity
Rush University Medical Center
Rush University Medical Center
Brain death is irreversible loss of function of brain. The American Academy of Neurology (AAN) gives three clinical findings to confirm diagnosis of brain death including coma (GCS 3), apnea, and absence of brainstem reflexes. When clinical criteria do not meet, ancillary tests are required to support diagnosis of brain death as recommended by AAN. Brain death imaging diagnosis is underrated in educational activities because these types of studies are rarely encountered routinely and have their own prime medico-legal importance. This educational exhibit mainly highlights the role of nuclear medicine cerebral scintigraphy, CT/MRI, and catheter angiography in diagnosis of brain death.
Educational Goals / Teaching Points
The goals of this exhibit are to learn imaging findings of nuclear medicine cerebral scintigraphy, MRI/CT angiography, catheter angiography, and MRI/CT perfusion studies in the diagnosis of brain death.
Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
CT is the most frequently used initial imaging in comatose unconscious patients. CT reveals intracranial hemorrhage and post-traumatic findings of primary brain insult. In addition to primary insult, CT findings demonstrate changes of hypoxic injury (diffuse cerebral edema with effaced sulci and ventricles, loss of gray and white matter differentiation, and “reversal cerebellum” sign). MRI demonstrates the same imaging features as CT with a low parenchymal apparent diffusion coefficient and absence of flow void on a T2-weighted sequence. Cerebral catheter angiography is considered the gold standard ancillary imaging test for diagnosis of brain death. It demonstrates absence of cerebral flow in intracranial arteries. In a hypotensive patient, the study will be a false positive, and in post craniotomy / post ventricular shunt placement, the study can be a false negative. MRI/CT angiography also demonstrates absence of cerebral flow in intracranial arteries. MRI angiography has high sensitivity and specificity; however, drawbacks with MRI angiography include susceptibility artifact and technical difficulty with placing patients on a scanner with life support. 99mTc HMPAO, 99mTc-DTPA, and 99mTc ECD are commonly used radiotracers for the cerebral scintigraphy. Normal cerebral perfusion demonstrates trident sign (simultaneous visualization of bilateral middle cerebral arteries and anterior cerebral arteries) on the angiographic phase and visualization of venous sinus on the blood pool phase. In patients with brain death, absence of normal trident sign, hollow skull/light bulb sign, hot nose sign, and absence of tracer activity in superior sagittal sinus helps to confirm the diagnosis. Cerebral scintigraphy is 100% sensitive and specific for the diagnosis of brain death.
Brain death imaging diagnosis is underrated in educational activities, because these types of studies are rarely encountered routinely and have their own prime medico-legal importance. Reviewing this educational exhibit will strengthen the knowledge of reading physicians and residents for establishing a diagnosis of brain death.