Idiopathic Intracranial Hypertension (IIH)
A “mass effect” is what happens when any additional mass exists inside the skull that takes up space (space-occupying mass). Examples of such masses include: cranial cysts/tumors, hydrocephalus, or any factor causing edema (such as trauma, infection, disease, or an adverse reaction to certain medications).
IIH was previously called such terms as “Pseudotumor Cerebri” (PTC) and “Benign Intracranial Hypertension” (BIH), because the increased pressure was such that it would suggest the presence of a tumor. These terms were inaccurate and misleading, as this disorder and what it can lead to (such as blindness and papilledema), pain and damage are not suggestive of something benign. Some medical professionals still use these outdated terms.
When it comes to someone with a Chiari Malformation, labeling it as “idiopathic” makes it somewhat of a misnomer, as the blocking of cerebrospinal fluid associated with a Chiari Malformation often elevates intracranial pressure (so it fails to be idiopathic).
Despite all the associated name changes, one thing remains clear and is somewhat indisputable, Intracranial Hypertension (IH) can cause a pushing effect on the cerebellar tonsils, causing a Chiari Malformation, AND the blockage of fluid associated with a Chiari Malformation increases Intracranial Hypertension, so it is an evolving circle until a successful treatment stops the pressure.