The characteristic cerebellar tonsil herniation at the foramen magnum may either cause raised ICP by disturbing CSF flow (as observed in idiopathic CM1) or may itself be the effect of raised ICP (as observed in acquired CM1).
RESULTS No significant differences were observed between patients with symptomatic and asymptomatic CM-I related to tentorium length (50.3 vs 51.0 mm; p = 0.537), supraoccipital length (39.4 vs 42.6 mm; p = 0.055), clivus-tentorium distance (52.0 vs 52.1 mm; p = 0.964), clivus-torcula distance (81.5 vs 83.3 mm; p = 0.257), total posterior fossa volume (PFV; 183.4 vs 190.6 ml; p = 0.250), caudal PFV (152.5 vs 159.8 ml; p = 0.256), fourth ventricle volume to caudal PFV ratio (0.0140 vs 0.0136; p = 0.649), or CSF volume to caudal PFV ratio (0.071 vs 0.061; p = 0.138).
Therefore, the authors sought to identify, characterize, and examine the intradural pathology and CSF flow pathophysiology in the posterior fossa and at the level of the foramen magnum that occurs in the setting of CM-I.
The characteristic cerebellar tonsil herniation at the foramen magnum may either cause raised ICP by disturbing CSF flow (as observed in idiopathic CM1) or may itself be the effect of raised ICP (as observed in acquired CM1).
In the case of IIH and Chiari I malformation, children who have recurrent symptoms despite adequate posterior fossa decompression surgery (failed Chiari), there is a strong role for intracranial pressure monitoring as raised intracranial pressure may indicate long-term CSF diversion.
A "complex" hypothesis, on the other hand, can explain the occurrence of hydrocephalus and CIM because of the venous engorgement resulting from the hypoplasia of the posterior cranial fossa (PCF) and the occlusion of the jugular foramina, leading to cerebellar edema (CIM) and CSF hypo-resorption (hydrocephalus).
METHODS A semiautomated segmentation program was developed, and used to compare the pre- and postoperative volumes of the posterior cranial fossa (PCF) and the CSF spaces (cisterna magna, prepontine cistern, and fourth ventricle) in a cohort of pediatric patients with CM-I.