Neuroradiological characteristics of hydrocephalus due to idiopathic extraventricular CSF pathways obstruction

Abstract

The development of research on CSF flow disorders made it possible initially to divide hydrocephalus into «communicating» and «non-communicating», and subsequently to distinguish the concepts of «intraventricular» and «extraventricular» obstruction. Improvement of radiological imaging technologies has allowed determining the exact level of CSF obstruction. In some cases, CSF flow disorders combine signs of different forms of hydrocephalus. Their correct classification allows selecting the type of surgical treatment, which reduces the rate of complications and patient»s dependence on the doctor. Purpose of the research: To study the radiological signs of hydrocephalus in idiopathic obstruction at the level of the posterior cranial fossa cisterns. Materials and methods. This study included adult patients (18 years old and over) whose disease was idiopathic in nature. From 2007 to 2020, 289 patients diagnosed with idiopathic hydrocephalus were treated at the N. N. Burdenko National Medical Research Center of Neurosurgery. Of these, 65 patients (18.7 %) had clinical and radiological signs of extraventricular obstruction. The male to female ratio was 25 and 40 (38.5 % and 61.5 %), respectively. A variety of radiological signs were assessed and their origin and occurrence in various forms of idiopathic hydrocephalus were determined. Results. FOHR was the highest (compared with other forms of idiopathic hydrocephalus (mean 0.52)). Other ventricular indices were also high. None of them correlated with the patient»s condition. Ventral dislocation of the premamillary membrane was detected in 89.2 %. Turkish saddle was of normal size in 51 (78.4 %) patients, while its enlargement was found in 13 (20 %) patients. A change in the periventricular signal was noted in 18.4 %. Aqueduct and IV ventricle outlets were patent in all cases as evidenced by CSF pulsation artifacts in T2 3D CUBE. The cerebral aqueduct was dilated in 63 (96.9 %) patients. Enlargement of the cisterna magna associated with hypotrophy of the caudal cerebellum was noted in 90.7 %, and this sign was significant for extraventricular cisternal obstruction (p <0.001). In addition to the T2 mode, the presence of sagittal sections in cisternography modes (FIESTA or CISS) was a prerequisite. By means of these modes, the ventral dislocation of the premamillary membrane was more clearly visualized, the presence of obstacles to the CSF flow in the cerebral aqueduct was excluded, and, most importantly, it was possible to determine the presence of additional membranes in the subarachnoid spaces between the ventral surface of the brain stem and the clivus. These were found in 100 % of the patients, which was also a significant pathognomonic sign (p < 0.001). Conclusion. The MRI picture of hydrocephalus with obstruction at the level of the posterior cranial fossa cisterns has specific signs. It combines the signs of other forms of hydrocephalus, chronic disease in combination with symptoms of the CSF pathways obstruction. It can be classified into a separate form and both endoscopic and shunt surgery can be used for treatment.