Hydrocephalus
Hydrocephalus may be communicating or noncommunicating. In communicating hydrocephalus, the lumbar subarachnoid space shares the increased pressure with the ventricular space. In noncommunicating hydrocephalus, the increased pressure of the ventricular space is not accompanied by increased pressure of the lumbar subarachnoid space.
Communicating hydrocephalus occurs secondary to: (1) an obstruction in the subarachnoid space in the convexity of the cranium that prevents the cerebrospinal fluid from reaching corpuscles of Pachioni; (2) an obstruction at the level of the corpuscle of Pachioni that blocks the absorption of cerebrospinal fluid; or (3) an anatomical or functional obstruction at the level of the sinuses that prevents drainage of cerebrospinal fluid. A functional obstruction of the sinus results from increased venous pressure inside the sinus that raises the threshold of intracranial pressure needed to open the “valves” of the corpuscles of Pachioni. The most common cause of communicating hydrocephalus in the neonatal period is intraventricular hemorrhage. Intraventricular hemorrhage produces an obliterative arachnoiditis of the posterior fosa.
Noncommunicating hydrocephalus is due to an obstruction at the foramen of Monro, aqueduct of Sylvius, or at the foramina of Luschka and Magendie. Obstruction at any of these orifices may occur due to blood clot, tumor, congenital narrowing, or scar tissue proliferation.