Outcome Prediction of Third Ventriculostomy: A Proposed Hydrocephalus Grading System

Abstract

An important factor in making a recommendation for different treatment modalities in hydrocephalus patients (VP shunt versus endoscopic third ventriculostomy) is the definition of the underlying pathology which determines the prognosis/outcome of the surgical procedure. Third ventriculostomies (3rd VS) are successful mainly in obstructive hydrocephalus but also in some subtypes of communicating hydrocephalus. A simple, easily applicable grading system that is designed to predict the outcome of 3rd VS is proposed. The hydrocephalus is graded on the basis of the extent of downward bulging of the floor of the third ventricle, which reflects the pressure gradient between the 3rd ventricle and the basal cisterns, presence of directly visualised CSF pathway obstruction in MRI, and the progression of the clinical symptoms resulting in five different grades. In this proposed grading system, grade 1 hydrocephalus subtype shows no downward bulged floor of the 3rd ventricle, no obstruction of the CSF pathway, and no progressive symptoms of hydrocephalus. There is no indication for 3rd VS. Grades 2 to 4 show different combinations of the described parameters. Grade 5 subtype shows a markedly downward bulged floor of the 3rd ventricle and direct detection of the CSF pathway obstruction (i.e., aqueductal stenosis) with progressive clinical deterioration. Retrospective application of this grading scheme to a series of 72 3rd VS has demonstrated a high correlation with the outcome: The success rate in grade 3 reached 40%, in grade 4: 58%, and in grade 5: 95%. This standardised grading system predicts the outcome of 3rd VS and helps in decision making for 3rd VS versus VP shunting.

Phase-Contrast MR Imaging Support for the Diagnosis of Aqueductal Stenosis

“…5,6 Furthermore, a recent study tried to define predictors of good outcomes of ETV and proposed an objective grading system, independent of clinical and etiologic data, based on morphologic MR imaging criteria. 7 However, we think that the first step should be to provide a reliable diagnosis of obstructive hydrocephalus to select the appropriate surgical treatment. In 1967, a study used radiologic features on ventriculography to define signs and different shapes of AS.…”

“…However, idiopathic AS is frequent, and checking for indirect signs of obstruction is usually recommended. 7 Downward bulging of the floor of the 3rd V, underneath the line from the chiasma to the mamillary bodies, has been proposed as a sign of a raised pressure gradient between the 3rd V and the prepontine cistern and, thus, as an indirect sign of AS. 7 In our population, this sign was absent in 7 patients with AS.…”

“…7 Downward bulging of the floor of the 3rd V, underneath the line from the chiasma to the mamillary bodies, has been proposed as a sign of a raised pressure gradient between the 3rd V and the prepontine cistern and, thus, as an indirect sign of AS. 7 In our population, this sign was absent in 7 patients with AS. Because it depends on both the pressure difference between the 2 compartments and on its duration, the downward bulging may be slight if the pressure gradient is low or of a short duration.…”

“…Besides, the bulging may be difficult to measure in this region, because it may be hindered in posthemorrhagic or postmeningitic AS. 7 All of these direct or indirect signs are operator-dependent, difficult to reproduce, and lack validated cutoff values. On the other hand, PC-MR imaging can be used for neurologic and neurosurgical features to assess intracerebral and cervical CSF flows in qualitative and quantitative evaluations.…”

“…5,6 Conventional MR imaging provides useful information in AS, because it may show triventricular dilation, CSF pathway obstruction at the aqueductal level on sagittal T2 sequences, downward bulging of the floor of the third ventricle (3rd V), anterior bulging of the 3rd V, etc. 7 Nevertheless, these criteria depend on a subjective evaluation by the neuroradiologist, may be difficult to assess in some patients, and thus are hardly comparable in postsurgical outcome studies. 6,8 Phase-contrast MR imaging (PC-MR imaging) is a rapid, simple, and noninvading technique, which is sensitive to CSF flows.…”