at night, and progresses to urge incontinence and permanent incontinence. Pathogenesis Every day, the body makes roughly 600–700 ml of CSF, and about the same amount is reabsorbed into the bloodstream. Hydrocephalus is due to an imbalance between the amount of fluid produced and its absorption rate. Enlarged ventricles put increased pressure on the adjacent cortical tissue and cause myriad effects in the patient, including distortion of the fibers in the corona radiata. This leads to an increase in intracranial pressure (ICP). The ICP gradually falls, but still remains slightly elevated, and the CSF pressure reaches a high normal level of 150 to 200 mm H2O. Measurements of ICP, therefore, are not usually elevated. Because of this, patients do not exhibit the classic signs that accompany increased intracranial pressure such as headache, nausea, vomiting, or altered consciousness, although some studies have shown pressure elevations to occur intermittently. The exact pathogenesis is unknown, but consensus on some mechanisms include: An imbalance exists between production and resorption of CSF. The resistance to CSF outflow is often elevated. The disease is not caused by overproduction of CSF or obstruction of CSF flow at the ventricles. The syndrome is often divided into two groups, primary (also called idiopathic) and secondary, based on cause. The underlying etiology of primary NPH has not yet been identified. Primary NPH affects adults age 40 years or older, most commonly affecting the elderly. Secondary NPH can affect persons of any age and occurs due to conditions such as subarachnoid hemorrhage, meningitis, brain surgery, brain radiation, or traumatic brain injury. Diagnosis Patients with suspected NPH should have typical symptoms in addition to ventricular enlargement on neuroimaging. The international evidenced-based diagnostic criteria for primary NPH are: Gradual onset after age 40 years, symptoms duration of ≥ 3–6 months, clinical evidence of gait or balance impairment, and impairment of cognition or urinary incontinence Imaging from magnetic resonance imaging (MRI) or computed tomography (CT) is needed to demonstrate enlarged ventricles and no macroscopic obstruction to cerebrospinal fluid flow. Imaging should show an enlargement to at least one of the temporal horns of lateral ventricles, and impingement against the falx cerebri resulting in a callosal angle ≤ 90° on the coronal view, showing evidence of altered brain water content, or normal active flow (which is referred to as "flow void") at the cerebral aqueduct and fourth ventricle. MRI scans are the preferred imaging. The