Shunt over drainage is a well-known complication of ventriculoperitoneal shunting. It leads to intracranial hypotension with classic MRI appearance (cerebellar tonsils caudal displacement, subdural fluid collections, venous congestion with dural sinuses and veins enlargement, etc), as in this case.

In chronic intracranial hypotension, skull remodeling changes (hyperostosis, paranasal sinuses enlargement, etc.) may be seen, like in this case.  These changes develop as a compensatory mechanism for reducing an intracranial compartment volume [2].

The pathophysiology of CSF over drainage after shunting is very complex and is not completely understood.  Different theories have been developed [3], where the siphon mechanism plays a central role.

Because of the displacement of the cerebellar tonsils, this case should be differentiated from acquired Chiari I malformation. But, unlike this case, there are no signs of intracranial hypotension in acquired Chiari I [1].