The prevalence of isolated tentorial hypoplasia on magnetic resonance imaging

Introduction
The tent shape of the tentorium cerebelli helps preserve brain anatomy by providing cerebellum protection against pressure caused by the brain’s gravity effect. In the absence of this support structure of the tentorium, herniation occurs in the brain. Isolated tentorial hypoplasia (TH) is extremely rare. In this study, we aimed to calculate the prevalence of this entity, which is reported to be rare in the literature.

Material and methods
Magnetic resonance imaging (MRI) images of 5163 patients who applied to the training and research hospital for various reasons between 1 September 2020, and 31 August 2021, who underwent brain MRI, were reviewed retrospectively.

Results
The prevalence of TH among patients screened during a period of one year was calculated as 2.22%. Of these, 76.59% were female (n = 72) and 23.41% were male (n = 22). The rates of presentation of complaints among TH patients were 60.63% headache, 17.02% vertigo, 4.25% seizures, 3.19% tremor, 3.19% syncope, 7.44% forgetfulness, and 2.12% visual impairment. Five patients (11.76%) were admitted for metastasis investigation due to their primary malignancy; they did not have any complaints. Localization of TH: 18.08% (n = 17) were observed on the right side, 28.72% (n = 27) on the left side, and 53.19% (n = 50) on the bilateral tentorium leaf.

Conclusions
Being aware of TH during brain MRI evaluation will help prevent possible misdiagnoses. We hope that this study with a large number of patients will increase awareness about TH, because there are no studies other than cadaver studies and a few case reports.