Endoscopic third ventriculostomy through lamina terminalis: A feasible alternative to standard endoscopic third ventriculostomy
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.173655
Source of Support: None, Conflict of Interest: None
Context: Endoscopic third ventriculostomy (ETV), wherein a stoma is created in the floor of the third ventricle, has now become the standard procedure for noncommunicating hydrocephalus across the world. However, in certain situations, this procedure may pose technical difficulties. These include a narrow prepontine space, vascularized third ventricular floor, the presence of prominent blood vessels traversing within the prepontine space, significant basal exudates, thickened and ill-defined third ventricular floor, and distorted floor anatomy. In such situations, an endoscopic lamina terminalis opening may provide a safer and more effective alternative to the standard technique.
Keywords: Endoscopic third ventriculostomy; hydrocephalus; lamina terminalis fenestration; neuroendoscopy
Over the past 2 decades, endoscopic third ventriculostomy (ETV) has become a well established procedure of choice for obstructive hydrocephalus throughout the world. Although Sir Walter Dandy began treating hydrocephalus in the early 20th century, it was Michael R. Gaab's development of the universal neuroendoscopic system, in cooperation with Karl Storz Company, in the late 1980 and early 1990 that heralded the era of neuroendoscopy. The concept of opening of the lamina terminalis (LT) via a transventricular transforaminal route with the help of a rigid neuroendoscope for the treatment of hydrocephalus is not new. Oertel et al., performed an ETV-LT using a rigid endoscope in patients where ETV could not be performed in a standard fashion. However, utilization of a rigid endoscope always carried the risk of fornicial injury during this procedure. It has been observed that the safe opening of the LT via a transventricular route while preserving the anatomical structures, could be achieved with a flexible steerable endoscope via a routine precoronal burr hole., Endoscopic LT fenestration using a supraorbital minicraniotomy has also been described by some authors in human cadaveric specimens., On the other hand, open microsurgical fenestration of the LT is a widely practiced adjunct during the anterior circulation aneurysm surgery. The literature reporting the results of ETV-LT is very limited and thus very little is known about this potentially effective operative strategy. We wish to present our experience of utilizing the endoscopic transventricular transforaminal LT fenestration in a select group of patients.
Study design: A retrospective observational study
This study was a retrospective analysis of the clinical data, follow-up details, and video recordings of all our patients who underwent ETV via the trans-LT approach. There were eight cases from January 2007 to January 2014 who underwent this procedure. The total number of ETVs performed in the same period at our centre was 240.
All our 8 patients had undergone previous attempts at cerebrospinal fluid (CSF) diversion using a ventriculoperitoneal (VP) shunt or a standard ETV. These prior procedures either failed to function (in case of VP shunts) or were technical failures (in case of ETV). All patients underwent a detailed clinical evaluation, a developmental assessment using the Trivandrum Developmental Scale, and computed tomography (CT) scan or magnetic resonance imaging (MRI) of the brain. All patients were prospectively followed up.
A standard (Gaab's) rigid lens neuroendoscope with all standard accessories was used for the routine ETV procedure. In addition, we used the Karl Storz flexible neuroendoscope with a 2-mm working channel and accessories such as the perforating forceps, monopolar diathermy, and grasping forceps. The 2-mm working channel allowed for passage of a 3F (Fogarty) catheter for stoma dilatation.
Anterior wall of the third ventricle extends from the foramen of Monro above to the optic chiasma below. LT, which effectively forms this anterior third ventricular wall, actually is a thin sheet of gray matter covered by pia mater/ventricular ependyma, stretching between the anterior commissure and the optic chiasma. When viewed from within, the structures forming the anterior wall of the third ventricle are (from above downwards) rostrum of the corpus callosum, anterior commissure, LT, optic nerve, and chiasma. The A1-anterior communicating artery (ACommA) complex with various perforating vessels are intimately related to this wall lying within the cisterna lamina terminalis. The ideal stoma is created within the LT by communicating the third ventricle with the suprachiasmatic region.
The initial step during endoscopy includes identification of the floor of the third ventricle including the mammillary bodies and the infundibulum with its recess [Figure 1]a. We bent the tip of the flexible neuroendoscope anteriorly, and the following structures were identified: Optic chiasma and LT [Figure 1]b. The LT is seen as a thin, transparent, triangular sheet of gray matter between the anterior commissure and the optic chiasma.
In all these cases, the decision to open up the LT was taken intraoperatively when some difficulty in perforating the floor of the third ventricle was encountered.
All procedures were performed under general anesthesia in supine position with the patient's head being stabilized by either a jelly head ring or a horseshoe. Preoperative antibiotics were administered as per protocol. A standard precoronal burr hole, 1cm anterior to the coronal suture and 2 cm away from the midline (Kocher's point), was performed. The dura was incised and a working sheath with the obturator was introduced into the lateral ventricle. CSF was collected for routine analysis in all cases. Initially, third ventriculostomy through the floor was done/attempted. In selected cases, where the floor was not conducive for a ventriculostomy owing to scarring, hypervascularity, a narrow prepontine cistern, or in cases with significant basal exudates (as in tuberculous meningitis [TBM]), an alternative approach was attempted via the LT. The distal end of the sheath of the scope was stationed at the foramen of Monroe. A 4-mm flexible neuroendoscope (Karl Storz) was passed through the sheath, the end was maneuvered anteriorly to visualize the optic chiasma, and the LT was identified anterosuperior to it. The trajectory of the flexible endoscope is depicted in [Figure 2]. If the LT was thin, anterior cerebral arteries could also be visualized through it. Fenestration was done with low setting monopolar current passed through the endoscope, and then the stoma was dilated with the help of either the grasping forceps or a 3F Fogarty catheter [Figure 3]. Alternatively, in cases of a large foramen of Monro, after making the stoma, the flexible scope was removed, a 30° rigid scope was passed, and the stoma was dilated with a curved-tip Fogarty catheter (created by bending the same in vitro). Following this procedure, a flexible scope was introduced again to visualize the stoma and the LT. Unlike the standard third ventriculostomy through the floor, where the end point of surgery is the visualization of the basilar artery, in ETV-LT, the end point is the visualization of anterior cerebral arteries [Figure 4],[Figure 5],[Figure 6],[Figure 7],[Figure 8]. At the end of surgery, the scope was removed and the scalp wound closed after placing a reservoir. The latter is the standard practice at our place for controlled CSF tapping to prevent an early CSF leak through the wound.
Among the eight patients who underwent an ELTV, four had aqueductal stenosis, three had post-tuberculous meningitic hydrocephalus (confirmed on CSF evaluation), and one had a posterior fossa tumor.
In case 1 and 8, even though a stoma was created in the third ventricular floor (the standard ETV), the basilar artery was not clearly seen in case 1, and pulsations of the floor were reduced and unsatisfactory in case 8. The age, sex, presenting symptoms, imaging findings, reasons for LT fenestration, outcome, and follow-up of our patients are depicted in [Table 1].
Requirement of a subsequent diversionary procedure/s was considered as a failure of ETV through LT (ETV-LT). Using the above criteria, ETV-LT was successful in 6 of our patients at a 1.5 year follow-up. Two patients required a subsequent ventriculoperitoneal shunt. An intraoperative complication was seen in one patient in the form of minor contusion to the fornix.
A standard ETV through the floor of the third ventricle has become the standard of care in the management of obstructive hydrocephalus across the world. There are, however, situations where this seemingly easy procedure may not be feasible from a technical point of view. These subset of patients have either a narrow prepontine cistern, a vascularized third ventricular floor, prominent blood vessels coursing just beneath the premamillary membrane, thickened and ill-defined third ventricular floor, and distorted floor anatomy.
The alternative sites for a third ventriculostomy include the LT, the lateral recess in close proximity to the posterior cerebral artery, and the suprapineal recess. LT fenestration can be done through various routes, that is, endoscopic transventricular and transforaminal, endoscopic subfrontal, or the microscopic subfrontal or frontotemporal approach.
Oertel et al., described the risk of forniceal injury while maneuvering the rigid endoscope through the foramen of Monro to the LT region. The working sheath was guided anteriorly, passing over the infundibular recess to identify the optic chiasma and the anterior cerebral arteries. A blunt perforation was made between the anterior cerebral arteries, and the opening was further enlarged with the perforation forceps and a balloon catheter. The problem was that a rigid endoscope could be used only in cases of an enlarged foramen of Monro. Maneuvering the rigid scope through the foramen of Monro entailed a great deal of handling of the fornices with subsequent injury to them. To circumvent this unique issue, we used a flexible scope while following the same technique advocated by Oertel et al. Hence, the status of the foramen of Monro did not actually matter to us.
Rangel-Castilla et al., have shown a 76% rate of resolution of symptoms by the ETV-LT approach; a similar success rate (75%) was found in our case series. In the present series, the only complication that we encountered was a minor ependymal injury in proximity to the fornix which luckily did not result in any long-term sequelae.
In patients suffering from a chronic phase of inflammatory pathology such as tuberculous meningitis, the presence of thick basal exudates or post-inflammatory scarring often leads to the obliteration of the basal cisterns that limits the CSF flow through a standard third ventriculostomy. This has often been described as an extraventricular, intracisternal obstructive hydrocephalus. LT fenestration is more successful because the suprachiasmatic cisterns are infrequently involved by the basal exudates. This route, therefore, allows an unhindered passage of the third ventricular CSF through the supra chiasmatic cistern to the arachnoidal granulations and finally into the venous circulation. The overall success rate for an ETV in patients with TBM-associated hydrocephalus, as reported in large series, is approximately 70%.
The subfrontal supraciliary suprapineal approach has been described by various authors in cadavers as well as in live patients that also has a successful outcome.,,, The technique is feasible and is reliable in providing an alternative site for the ventriculostomy despite the presence of the prominent deep venous complex in this area. Chen et al., have advocated a post-coronal burr hole for a better approach to the LT region. A flexible scope allowed us to avoid a post-coronal burrhole (as the latter can lead to motor weakness on the contralateral side). The technique we described has the advantage that the decision to utilize this approach may be taken intraoperatively especially if the preoperative imaging does not suggest any obvious abnormality of the third ventricular floor. It also obviates excessive manipulation of the rigid scope at the foramen of Monroe which may cause injury to the fornix. Whenever required, the choroid plexus can also be simultaneously coagulated and a ventricular wash concomitantly performed under supervision.
The series we presented is the first report of an ETV-LT using a flexible endoscope via a precoronal burrhole. We would like to acknowledge certain limitations of this procedure. First, the learning curve for neuroendoscopy, particularly with the flexible endoscope, is steep; and second, it is feasible only if the expertise and instruments are available. A larger study sample and further research would be required to delineate the success of transventricular transforaminal ETV via the LT approach.
ETV-LT is a feasible and safe alternative to a standard ETV and allows one to create an alternative, and yet a very effective, CSF egress route with minimal complications. It is useful when the third ventricular floor opening cannot be done owing to a narrow prepontine interval, vascularized third ventricular floor, presence of prominent blood vessels, significant basal exudates, thickened and ill-defined third ventricular floor, and distorted floor anatomy. The use of flexible neuroendoscope makes the procedure easy as well as safe by preventing the potential forniceal injury that can happen with the rigid endoscopes.
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There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]