Surgical aspects of classification and neuroimaging characteristics of idiopathic hydrocephalus in adults

Background. Hydrocephalus can be developing by a traumatic brain injury, intracranial hemorrhage, tumor, meningitis of congenital malformation of the central nervous system. When the cause of the hydrocephalus is unclear it is supposed as idiopathic hydrocephalus. The most important classification features are the etiology and level of CSF obstruction. The classification was improved and developed with diagnostic and surgical methods simultaneously. Currently, the neurosurgeons have the possibility for usage of various methods and techniques of surgical treatment with their advantages and disadvantages. Systematization of radiological parameters is necessary to make a decision about the type of the surgery. Aim. To analyze and systematize the neuroimaging characteristics of various forms of idiopathic hydrocephalus in adults, to assess the possible classification of idiopathic hydrocephalus. Materials and methods. Between October 2011 and March 2021 290 patients with idiopathic adult hydrocephalus were operated at the N.N. Burdenko National Medical Research Center of Neurosurgery of the Ministry of Health of Russia: onset of symptoms in adulthood; no indications of the etiology of hydrocephalus and congenital hydrocephalus. The age of the patients was 50 ± 18.2 (18–85) years. The magnetic resonance images of patients were evaluated for the size of the ventricles, condition of convexital and basal subarachnoid spaces, obstruction of the CSF pathways, and changes in the position of the premamillary membrane, septum pellucidum, the roof of the 3rd ventricle and the tonsils of the cerebellum, the size of the sella turcica, the angle of the corpus callosum. The frequency of each of these parameters is statistically estimated for each form of idiopathic hydrocephalus. Results. Aqueduct stenosis has become the most frequent form of idiopathic hydrocephalus. Hydrocephalus in obstruction of the foramen of Monroe, aqueduct, foramen of Magendie, and cisterns of the posterior cranial fossa was significantly more characteristic of young people ( p <0.05). Hydrocephalus with obstruction of convexital CSF spaces can be called hydrocephalus of the elderly ( p <0.001). Hydrocephalus without verified signs of occlusion CSF pathways occurs equally in all age groups. The FOHR index was significantly more important, and only in case of cisternal obstruction. Enlargement one or both lateral ventricles and flattening of the roof of the 3rd ventricle is characterized for Monro’s foramen obstruction ( p <0.001). The membrane at the outlet of the 4th ventricle and the absence of the “flow void” was typically only for patients with obstruction of the foramen of Magendie ( p <0.001). Ventral dislocation of the premamillary membrane was characteristic of obstruction of the cerebral aqueduct, the foramen of Magendie, and cisterns of the posterior cranial fossa. Compression of the convexital CSF spaces occurred in case of obstruction of the aqueduct, the foramen of Magendie, but CSF spaces of the posterior cranial fossa – only with obstruction of the foramen of Magendie. Dilation of the 4th ventricle was significantly associated with obstruction of the foramen of Magendie and cisterns of the posterior cranial fossa ( p <0.05). DESH symptom was significantly associated with obstruction of convexital CSF spaces ( p <0.001). Additional membranes in the cisterns of the posterior fossa were found only in cases of cisternal obstruction ( p <0.001). Cerebellar tonsils herniation was observed with obstruction of the foramen of Monroe, cerebral aqueduct, and foramina of Magendie. Conclusion. Because of statistical analysis, general signs found in all types of hydrocephalus, and private ones, characterizing only specific signs of the type of the disease, both were found. The classification is logical and justified, it is well applicable in neurosurgical and radiological practice. It allows rational planning of diagnostic evaluation and treatment of patients. A modern magnetic resonance imaging protocol should include T2 scans (with “flow void”) and FIESTA/CISS scans in the required planes, axial FLAIR scans.