Sylvian aqueduct syndrome and global rostral midbrain dysfunction associated with shunt malfunction

Object. This study is a retrospective analysis of clinical data obtained in 28 patients affected by obstructive hydrocephalus who presented with signs of midbrain dysfunction during episodes of shunt malfunction. Methods. All patients presented with an upward gaze palsy, sometimes associ ated with other signs of oculomotor dysfunction. In seven cases the ocular signs remained isolated and resolved rapidly after shunt revision. In 21 ca ses the ocular signs were variably associated with other clinical manifesta tions such as pyramidal and extrapyramidal deficits, memory disturbances, m utism, or alterations in consciousness. Resolution of these symptoms after shunt revision was usually slow. In four cases a transient paradoxical aggr avation was observed at the time of shunt revision. In 11 cases ventriculoc isternostomy allowed resolution of the symptoms and withdrawal of the shunt . Simultaneous supratentorial and infratentorial intracranial pressure record ings performed in seven of the patients showed a pressure gradient between the supratentorial and infratentorial compartments, with a higher supratent orial pressure before shunt revision. In version of this pressure gradient was observed after shunt revision and resolution of the gradient was observ ed in one case after third ventriculostomy. In six recent cases, a focal mi dbrain hyperintensity was evidenced on T-2-weighted magnetic resonance imag ing sequences at the time of shunt malfunction. This rapidly resolved after the patient underwent third ventriculostomy. Conclusions. It is probable that in obstructive hydrocephalus, at the time of shunt malfunction, the development of a transtentorial pressure gradient could initially induce a functional impairment of the upper midbrain, indu cing upward gaze palsy. The persistence of the gradient could lead to a glo bal dysfunction of the upper midbrain. Third ventriculostomy contributes to equalization of cerebrospinal fluid pressure across the tentorium by resto ring free communication between the infratentorial and supratentorial compa rtments, resulting in resolution of the patient's clinical symptoms.