Figure 6 presents a morphological diagram of the BCB (Figure 6). The increase in BCB permeability occurs as a result of the slowing of the flow rate of the cerebrospinal fluid. This results in an increase in total protein concentration, including albumin, in the cerebrospinal fluid and an increase in the albumin quotient (QAlb) [12,15,56,57,58]. Neurological diseases leading to the slowing of the flow of cerebrospinal fluid include, among others: purulent bacterial meningitis, CNS leukemia, Froin syndrome, meningeal carcinoma, Guillain–Barré syndrome, and multiple sclerosis [56]. Here, ALB is linked to central nervous system leukemia.