Standardization of postmortem human brainstem along the rostrocaudal axis to accommodate for inter-specimen structural heterogeneity

There is increasing recognition of the critical need for postmortem studies of human brainstem tissues for elucidating the pathophysiology of neurological disorders. While the brainstem is critical for a myriad of functions it is relatively small with a complex organization of tracts and nuclei. So, interindividual heterogeneity in brainstem structure that can derive from tissue procurement or be related to anthropometric features like height or weight can greatly impact studies of brainstem structure and function. In the absence of explicit approaches to account for these sources of heterogeneity drawing inferences from interindividual comparisons can be challenging. This study used postmortem brainstem samples from well-characterized older decedents to systematically assess factors contributing to heterogeneity in the length of whole brainstem samples. These findings led to a standardized approach to reproducibly assign rostrocaudal levels, with standardization relying upon readily identifiable internal anatomic landmarks. We validated this approach using postmortem MRI imaging. Standardized brainstem length correlated positively with subject height and brain weight but not age of death. By providing a reference series, this study will facilitate the assignment of reproducible levels to individual histological sections or MRI images when full brainstem specimens are not available, promoting reproducibility within and across different studies.