overdrainage

Overdrainage refers to excessive drainage of cerebrospinal fluid (CSF) from the intracranial space, most commonly as a complication of hydrocephalus management with CSF shunts or external drains. It results when CSF removal exceeds production or when drainage is amplified by posture or device mechanics, leading to intracranial hypotension and secondary brain sagging.

Causes and mechanisms include shunt systems, especially those without anti-siphon features or with settings that allow low opening pressure, which can siphon CSF when the patient stands. Programmable valves set too low, failure of anti-siphon devices, or external drains configured for high drainage can produce overdrainage. Diurnal or positional changes can also influence drainage in susceptible systems.

Clinical features commonly include orthostatic headaches that worsen when upright, along with nausea, vomiting, cognitive changes, and neck stiffness. In infants, irritability, poor feeding, and delayed development may be observed. Imaging typically shows reduced ventricular size or slit ventricles, with subdural hygromas or hematomas and signs of brain sagging on MRI.

Management involves reducing CSF drainage by adjusting valve settings or temporarily clamping or removing drains. Treat subdural collections if present, usually by observation or surgical drainage. If overdrainage recurs, shunt revision or the addition of anti-siphon/gravitational devices may be required; in children, monitoring head growth is important.

Prevention and prognosis emphasize the use of anti-siphon devices and appropriately calibrated programmable valves to minimize risk. Regular postoperative monitoring and imaging help detect early signs of overdrainage. When promptly managed, outcomes are generally favorable, though chronic subdural collections and repeat revisions can occur in some patients.