Underdrainage

What it is

Underdrainage is the draining of too little cerebrospinal fluid by a shunt — less than needed to control pressure. It allows CSF to remain elevated, so symptoms of raised pressure persist or recur.

Understanding Underdrainage

When a shunt does not drain enough, intracranial pressure can stay high, causing ongoing or recurrent symptoms such as headache or, in babies, continued rapid head growth. Underdrainage can result from a valve setting that is too high (draining too little), a partial obstruction, or other factors. It is the opposite problem to overdrainage, and balancing the two is part of managing a shunt. Underdrainage can often be addressed by adjusting a programmable valve to a lower setting (draining more), or by identifying and treating a partial obstruction. Distinguishing underdrainage from overdrainage and from other causes of symptoms is part of the evaluation when a shunt is not controlling hydrocephalus well.

Why it matters

Understanding underdrainage helps families see that a shunt can also drain too little, leaving pressure high and symptoms persisting, and that adjusting the valve or addressing the cause can often correct it.