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Object: Neuroendoscopists often note pulsatility or flabbiness of the floor of the third ventricle during endoscopic third ventriculostomy (ETV) and believe that either is a good indication of the procedure's success. Note, however, that this belief has never been objectively measured or proven in a prospective study. The authors report on a simple test—the hydrostatic test—to assess the mobility of the floor of the third ventricle and confirm adequate ventricular flow. They also analyzed the relationship between a mobile floor (a positive hydrostatic test) and prospective success of ETV.
Methods: During a period of 3 years between July 2001 and July 2004, 30 ETVs for obstructive hydrocephalus were performed in 22 male and eight female patients. Once the stoma had been created, the irrigating Ringer lactate solution was set at a 30-cm height from the external auditory meatus, and the irrigation valve was opened while the other ports on the endoscope were closed. The ventricular floor ballooned downward and stabilized. The irrigation valve was then closed and ports of the endoscope were opened. The magnitude of the upward displacement of the floor was then assessed. Funneling of the stoma was deemed to be a good indicator of floor mobility, adequate flow, and a positive hydrostatic test. All endoscopic procedures were recorded using digital video and recordings were subsequently assessed separately by two blinded experienced neuroendoscopists. Patients underwent prospective clinical follow up during a mean period of 11.2 months (range 1 month–3 years), computerized tomography and/or magnetic resonance imaging studies of the brain, and measurements of cerebrospinal fluid pressure through a ventricular reservoir when present. Failure of ETV was defined as the subsequent need for shunt implantation. The overall success rate of the ETV was 70% and varied from 86.9% in patients with a mobile stoma and a positive hydrostatic test to only 14.2% in patients with a poorly mobile floor and a negative test (p < 0.05). The positive predictive value of the hydrostatic test was 86.9%, negative predictive value 85.7%, sensitivity 95.2%, and specificity 66.6%.
Conclusions: The authors concluded that the hydrostatic test is an easy, brief test. A positive test result confirms a mobile ventricular floor and adequate flow through the created ventriculostomy. Mobility of the stoma is an important predictor of ETV success provided that there is no obstruction at the level of the arachnoid granulations or venous outflow. A thin, redundant, mobile third ventricle floor indicates a longstanding pressure differential between the third ventricle and the basal cisterns, which is a crucial factor for ETV success. A positive hydrostatic test may avert the need to insert a ventricular reservoir, thus avoiding associated risks of infection.
The recent resurgence of interest in ETV has arisen out of a dissatisfaction with the complications and long-term outcomes of conventional CSF shunt systems. Third ventriculostomy is designed to treat noncommunicating hydrocephalus with patent subarachnoid spaces and adequate CSF absorption. Results of ETV are most closely associated with the origin of hydrocephalus encountered as well as with the clinical and neuroimaging features in an individual.
Patients with acquired aqueductal stenosis or tumors obstructing third ventricular outflow have demonstrated the highest success rates following ETV, exceeding 75% in carefully selected series of patients. Among those who have undergone shunt placement, patients with or without myelomeningocele, tumors, or cystic abnormalities leading to fourth ventricular outflow obstruction (for example, arachnoid cysts or Dandy–Walker malformations) and patients with congenital aqueductal stenosis have shownan intermediate response. Infants suffering from hydrocephalus after hemorrhage or infection or with associated myelomeningocele (without a previously inserted shunt) have demonstrated a poor response to ETV. Clinical presentations indicative of elevated intracranial pressure have been associated with the highest rate of ETV success (83%). Patients with other presentations (memory disturbances, incontinence, and focal deficits with associated tumors) have exhibited success rates of approximately 50% or less. Neuroimaging criteria include clear evidence of ventricular noncommunication, favorable third ventricle anatomy with a wide foramen of Monro sufficient to accommodate the endoscope, and a wide, thin, downward bulging floor draped over the clivus. According to data from multiple pediatric studies, there seems to be a significant association between increasing patient age and a more favorable ETV outcome. Results of several studies show success rates at or below 50% in patients younger than 2 years or 1 year of age, regardless of disease origin.
Traditional neuroimaging techniques have several limitations in assessing the success of the procedure, mostly in the early postoperative period. Indeed, a decrease in ventricle size is often minimal and not visible before 3 to 4 weeks post-ETV. Magnetic resonance imaging studies obtained to detect the presence of a flow void signal through the third ventricle floor reportedly have a significantly high incidence of false positives.
All previous studies have been focused on the preoperative prognostic factors or on postoperative neuroimaging data, but how can a surgeon know if the ETV will work intraoperatively? In this report we assessed the intraoperative predictors of ETV success including mobility of the stoma and flow through it by using a simple, objective intraoperative test.
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