28 Endoscopic Magendie and Luschka Foraminoplasty

28.1 Introduction

Neuroendoscopy is a rapidly growing subspecialty in the field of neurosurgery. The flexible neuroendoscope has allowed us to familiarize ourselves with areas of the ventricular system as well as cerebrospinal fluid dynamics.1,2,3 Precise indications exist for some of these procedures, while others are still being determined.4,5,6,7,8,9,10,11,12,13,14,15

Hydrocephalus from fourth ventricular outlet obstruction (FVOO) is a clinical entity that has drawn our attention. There exist various procedures for the treatment of FVOO such as ventriculoperitoneal (VP) shunt placement, suboccipital craniectomy using microsurgical techniques, and endoscopic third ventriculostomy (ETV).16,17,18,19,20,21,22 Each of these procedures has shown different outcomes. Longatti et al19 first described a successful transventricular transaqueductal opening of the foramen of Magendie using a flexible neuroendoscope. Torres-Corzo et al23 recently reported their experience with endoscopic transventricular transaqueductal opening of the foramina of Magendie and Luschka.

Two etiologies have been described for FVOO: a primary (idiopathic) form and a secondary form. The primary form consists of a membranous occlusion and congenital atresia of the foramen of Magendie and/or the foramina of Luschka. These patients have a thin, firm, transparent membrane across the foramen of Magendie.16,23,24,25 Microscopic examinations of these membranes have shown gliosis and neural tissue with no active inflammation.17 The primary form is associated with posterior fossa abnormalities, such as Chiari malformations and basilar invagination.21,25,26 The secondary form involves underlying pathologies that may be responsible for inflammation and scarring of fourth ventricle outlet foramina. These include chronic inflammatory processes, infection, and/or hemorrhage. All these conditions foment an inflammatory process with subsequent meningitis and/or arachnoiditis. This leads to scar tissue formation leading to foraminal stenosis and obstruction.1,14,15,19,21,27,28,29,30 In this chapter, we will review the indications, operative technique, and potential complications of endoscopic transventricular transaqueductal Magendie and Luschka foraminoplasty.

28.2 Indications/Contraindications

Endoscopic transventricular transaqueductal Magendie and/or Luschka foraminoplasty is indicated in patients with tetraventricular hydrocephalus secondary to FVOO.7,23 It is true that tetraventricular hydrocephalus can be diagnosed with computed tomography (CT) or magnetic resonance imaging (MRI). However, an obstructive membrane or stenosis at the level of the foramen of Magendie is difficult to visualize and cannot always be observed on imaging.31 Neuroendoscopic exploration of the fourth ventricle is indicated whenever technically possible, because it is the only way to definitely diagnose FVOO while minimizing invasiveness but ensuring absolute sensitivity.1,2,9,13,15,19,22,27,29

Patients with ventriculoperitoneal (VP) shunt placement with obstruction or trapped fourth ventricle are also potential candidates for neuroendoscopic exploration.15,23 Patients who are being treated with an endoscopic procedure for hydrocephalus in which ETV could not be performed safely or was thought would have a low rate of success, based on intraoperative findings such as a thickened premammilary membrane, thickened or scarred membranes in the basal subarachnoid space, and/or nonpatent basal subarachnoid space, are candidates for fourth ventricle exploration with possible Luschka and Magendie foraminoplasty (Video 28.1).7,23,30,32

Patients with pathological entities of the craniocervical junction (Chiari type 1 and 2 malformations) with FVOO should be explored because of the possibility of atresia and membranous obstruction of the foramen of Magendie. Luschka foraminoplasty should be considered when it is not possible to perform Magendie foraminoplasty.7,9,22,23

Endoscopic transventricular, transaqueductal access to the fourth ventricle requires a dilated cerebral aqueduct to be able to maneuver the endoscope without causing injury to this structure as well as to the floor of the fourth ventricle. Due to the complexity of this procedure, other alternatives should be attempted first including ETV, lamina terminalis fenestration, etc.7,23

28.3 Operative Technique

28.3.1 Preoperative Preparation

Preoperative preparation is similar to other endoscopic procedures. The procedure is performed under general anesthesia. The patient is positioned supine with the head slightly inclined 20 to 30º. The right frontal area is prepped and draped in sterile fashion. The right-side ventricle is approached in most cases.7,19,23

**Video 28.1** Endoscopic Magendie and Luschka foraminoplasty (flexible neuroendoscope). The lateral and third ventricles are approached with a flexible neuroendoscope. The cerebral aqueduct is entered until the fourth ventricle is reached. The cerebellar vermis, choroid plexus, and floor of the fourth ventricle are identified. Advancing the endoscope along the midline reveals stenosis of the foramen of Magendie secondary to severe reactive inflammatory ventriculitis. The endoscope is aimed laterally, advanced along the choroid plexus, and passed under the cerebellar peduncle to reach the foramen of Luschka. A membrane veil covers the foramen of Luschka. Using grasping forceps, the membrane is carefully opened. After the fenestration is completed, the lower cranial nerves come into sight. Adequate CSF flow through the Luschka foramen is observed. The endoscope is withdrawn back into the midline of the fourth ventricle and a Magendie foraminoplasty is performed. At the end, the foramina of Luschka and Magendie are inspected again to confirm adequate CSF flow.

28.3.2 Description of the Procedure

The bur hole is made 1 cm in front of the coronal suture and 2 to 3 cm lateral to the midline. The endoscope is fixed to the supporting arm, and it is introduced into the right lateral ventricle. An inspection of the entire ventricular system is performed. If technically possible, an ETV is performed. The basal subarachnoid cisterns are inspected to ensure adequate space and to confirm the presence of membranes and/or adhesions. ETV efficacy is evaluated by the movement of the edges of the fenestration. These should move freely with CSF pulsations. This confirms appropriate communication between the ventricular system and the basal subarachnoid space. The opening of the foramina of Magendie and/or Luschka is always performed last, in addition to ETV, and is based on intraoperative assessment of ETV success.23,29,30

When ETV is not technically feasible or is thought to have a low success rate and the diagnosis of FVOO is made, opening of the foramina of Magendie and/or Luschka should be considered. The flexible neuroendoscope is advanced into the posterior portion of the third ventricle. The tip must be positioned in a neutral position, anteriorly and below the interthalamic adhesion looking at the entrance of the cerebral aqueduct (Video 28.1). The endoscope is rotated along its axis in a counterclockwise direction, and the tip is bent posteriorly along the midline to identify the aditus aqueducti. The aqueduct is dilated in most cases and the endoscope is passed through gently using slow maneuvers especially when passing the two natural aqueductal constrictions. After entering the fourth ventricle, the endoscope is advanced toward the center of the fourth ventricle (Fig. 28.1a,b). Anatomical landmarks to be identified are the facial colliculi, lateral striae medullares, hypoglossal triangle, and obex. These structures are seen in the lower half of the endoscopic image, while the choroid plexus and cerebellar vermix are seen superiorly. The endoscope is advanced along the midline bringing the foramen of Magendie into view (Fig. 28.1a–c). Magendie foraminoplasty is performed if this outlet is occluded (Fig. 28.1c,d). Initially a blunt perforation is made and then enlarged with grasping forceps. The neurosurgeon must be careful to avoid injury to the posterior inferior cerebellar arteries (PICAs) (Fig. 28.1e–g). Coagulation must never be used to extend the initial opening. Furthermore, the endoscope is passed through the foramen to confirm communication with the cisterna magna (Fig. 28.1h). The endoscope is then drawn back into the fourth ventricle. If the surgeon must localize the foramen of Luschka, the choroid plexus is identified and followed into the lateral recess (Fig. 28.2a). The endoscope must then be advanced below the inferior cerebellar peduncle to identify the semipermeable membrane, just below which lies the foramen of Luschka (Fig. 28.2b,c). If feasible, this membrane is opened (Video 28.1). The same technique is used for Luschka foraminoplasty: an initial blunt perforation is performed followed by enlargement with grasping forceps. Care must be taken not to injure cranial nerves VII and VIII (Fig. 28.2e,f). These structures come into view once the arachnoid mater has been removed. Again, the endoscope is passed through the foramen to ensure communication with the cerebellopontine cistern (Video 28.1).7,19,22,23