Presentation
Headache, worse in vertical position. Prior ventriculoperitoneal and cysto-peritoneal shunting 6 years ago.
Patient Data
There is cerebellar tonsils displacement into the upper cervical canal through the foramen magnum, bilateral subdural fluid collections. Dural sinuses are enlarged and round-shaped. In addition, there is calvarium thickening and sphenoid sinus hyperpneumatisation. Enlargement of the central canal of the spinal cord (at C5-Th2 levels) with syrinx formation is also seen.
There is a Y-shaped ventriculoperitoneal and cysto-peritoneal shunt.
Features are consistent with chronic intracranial hypotension due to CSF overdrainage.
There is skull hyperostosis with laminated thickening of the calvarium, as well as sphenoid sinus hyperpneumatization and sella turcica shrinkage.
Previous MRI (6 years ago)
MRI right after ventriculoperitoneal and cysto-peritoneal shunting. There is a large suprasellar arachnoid cyst with brainstem displacement. No cerebellar tonsils displacement. No other signs of intracranial hypotension.
Case Discussion
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].