Idiopathic normal pressure hydrocephalus, secondary chronic hydrocephalus, and other cerebrospinal fluid (CSF) disorders are often challenging to diagnose. Since shunt surgery is usually the only therapeutic option and carries significant morbidity, optimal patient selection is crucial. The tap test is the most commonly used prognostic test to confirm the diagnosis but lacks sensitivity. The lumbar infusion test appears to be a better option, offering additional information on brain dynamics without increasing morbidity. However, this technique remains underused. In a narrative review, supported by the extensive experience of several European expert centers, Jannelli et al. detail the physiological basis, indications, and CSF dynamics parameters that can be measured. They also discuss technical modalities and variations, including one versus 2 needles, patient positioning, and the site of CSF measurement, as well as in vivo shunt testing. Finally, they discuss the limitations and morbidity associated with the LIT. This review aims to assist teams wishing to incorporate LIT into their screening tools for chronic hydrocephalus and other CSF disorders ¹⁾