HSAS (hydrocephalus with stenosis of the aqueduct of Sylvius)

What it is

HSAS stands for hydrocephalus with stenosis of the aqueduct of Sylvius — hydrocephalus resulting from narrowing of the cerebral aqueduct. It is a recognized part of the L1 syndrome spectrum associated with L1CAM gene changes.

Understanding HSAS (hydrocephalus with stenosis of the aqueduct of Sylvius)

In HSAS, narrowing of the cerebral aqueduct obstructs CSF flow between the third and fourth ventricles, causing hydrocephalus with the characteristic triventricular pattern. As part of the L1 syndrome spectrum (which overlaps with X-linked hydrocephalus and Bickers-Adams syndrome), HSAS is associated with L1CAM gene changes and affects mainly boys. It can occur alongside other features of the spectrum. Because it is genetic, genetic counseling is important, and the hydrocephalus is treated with CSF diversion or, given the aqueductal level of obstruction, sometimes ETV, depending on the individual situation.

Why it matters

Understanding HSAS helps families see how aqueductal stenosis fits within the inherited L1 syndrome spectrum, and why genetic counseling and individualized treatment are part of care.