Aqueductal stenosis

Narrowing of the aqueduct of Sylvius.

Because of its small size, the aqueduct is the most likely place for a blockage of CSF in the ventricular system. This blockage causes ventricle volume to increase because the CSF cannot flow out of the ventricles and cannot be effectively absorbed by the surrounding tissue of the ventricles. Increased volume of the ventricles will result in higher pressure within the ventricles, and cause higher pressure in the cortex from it being pushed into the skull.

Aqueductal stenosis classification.

Aqueductal stenosis (AS) includes a large variety of etiologies: posthemorrhagic or postmeningitic obstruction, compression of the aqueduct, or presence of a third ventricle mass 1).

1. a congenital malformation: may be associated with Chiari malformation or neurofibromatosis.

2. acquired

a) due to inflammation (following hemorrhage or infection,e.g.syphilis,T.B.)

b) neoplasm:especially brainstem astrocytomas—including tectal gliomas,lipomas

c) Quadrigeminal cistern arachnoid cysts

New theories have emerged about the pathogenesis of AS in adults, and venous hypertension has been suggested as the primary phenomenon responsible for ventricle dilation and aqueductal obstruction 2).

Late-onset idiopathic aqueductal stenosis may present with clinical features indistinct from idiopathic normal pressure hydrocephalus (NPH).

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. 3).

But aqueductal stenosis (AS) is not always detected by conventional magnetic resonance imaging (MRI).

One-third of NPH patients with AS presented Rout >12 mmHg/ml/min 4).

Narrowing of the aqueduct of Sylvius which blocks the cerebrospinal fluid motion in the ventricular system, can lead to hydrocephalus, specifically as a common cause of congenital hydrocephalus and/or obstructive hydrocephalus.

Treatment of aqueductal stenosis (AQS) has undergone several paradigm shifts during the past decades. Currently, endoscopic third ventriculostomy (ETV) is recommended as treatment of choice. Several authors have addressed the issue of variable ETV success rates depending on age and pathogenetic factors. However, success rates have usually been defined as “ETV non-failure.”

Closure of the stoma can be associated with symptom recurrence and need for further surgical intervention.

A study analyzed 103 adult patients with aqueductal stenosis who underwent ETV for obstructive hydrocephalus and evaluated the effect of previous shunt placement on post-ETV outcomes.

This study was a retrospective review of 151 consecutive patients who were treated between 2007 and 2013 with ETV for hydrocephalus. One hundred three (68.2%) patients with aqueductal stenosis causing obstructive hydrocephalus were included in the analysis.

Postoperative ETV patency and aqueductal and cisternal flow were assessed by high-resolution, gradient-echo MRI. Post-ETV Mini-Mental State Examination, Timed Up and Go, and Tinetti scores were compared with preoperative values. Univariate and multivariate analyses were performed comparing the post-ETV outcomes in patients who underwent a primary (no previous shunt) ETV (n = 64) versus secondary (previous shunt) ETV (n = 39).

The majority of patients showed significant improvement in symptoms after ETV; however, no significant differences were seen in any of the quantitative tests performed during follow-up. Symptom recurrence occurred in 29 (28.2%) patients after ETV, after a median of 3.0 (interquartile range 0.8-8.0) months post-ETV failure. Twenty-seven (26.2%) patients required surgical revision after their initial ETV. Patients who received a secondary ETV had higher rates of symptom recurrence (p = 0.003) and surgical revision (p = 0.003), particularly in regard to additional shunt placement/revision post-ETV (p = 0.005). These differences remained significant after multivariate analysis for both symptom recurrence (p = 0.030) and surgical revision (p = 0.043).

Patients with obstructive hydrocephalus due to aqueductal stenosis exhibit symptomatic improvement after ETV, with a relatively low failure rate. Patients with a primary history of shunt placement who undergo ETV as a secondary intervention are at increased risk of symptom recurrence and need for surgical revision post-ETV 5).

Little JR, Houser OW, MacCarty CS. Clinical manifestations of aqueductal stenosis in adults. J Neurosurg 1975;43:546 –52
Bateman GA. Magnetic resonance imaging quantification of compliance and collateral flow in late-onset idiopathic aqueductal stenosis: venous pathophysiology revisited. J Neurosurg 2007;107:951–58
Kehler U, Regelsberger J, Gliemroth J, et al. Outcome prediction of third ventriculostomy: a proposed hydrocephalus grading system. Minim Invasive Neurosurg 2006;49:238 –43
González-Martínez EL, Santamarta D. Does aqueductal stenosis influence the lumbar infusion test in normal-pressure hydrocephalus? Acta Neurochir (Wien). 2016 Oct 11. PubMed PMID: 27730385.
Sankey EW, Goodwin CR, Jusué-Torres I, Elder BD, Hoffberger J, Lu J, Blitz AM, Rigamonti D. Lower rates of symptom recurrence and surgical revision after primary compared with secondary endoscopic third ventriculostomy for obstructive hydrocephalus secondary to aqueductal stenosis in adults. J Neurosurg. 2015 Oct 30:1-8. [Epub ahead of print] PubMed PMID: 26517771.
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