Figure 1

Image segmentation for volume determination. Image segmentation of cranial compartments and their parenchymal contents. The delineation of the metencephalic volume and the cerebral volume (or caudal cranial fossa volume and rostral and middle cranial fossa volume respectively) was set along the contour of the rostral aspect of the cerebellum and a line connecting the touching point of the cerebellum with the brainstem to the rostral border of the pons (A-C). The caudal boundary of the caudal cranial fossa volume and the metencephalic volume was a line between the intercondylar incisures and the most caudal point of the foramen magnum (A, B, white line). The caudal cranial fossa volume was measured by adding the volume of the cerebellum and brainstem (A: marked in red) to the CSF subarachnoid space that surrounds it (B: marked in red) in this defined compartment. The rostral and middle cranial fossa volume and cerebral volume were measured in the same manner using the first contour as a caudal end (C, D). The total brain volume was calculated as the sum of metencephalic volume and cerebral volume, the total endocranial volume was calculated as the sum of the total brain volume and subarachnoid space.