HOW I DO IT - NEUROSURGICALTECHNIQUES

Endoscopic treatment of adult idiopathic obstructionof the foramen of Monro

Waleed A. Azab1& Tarek M. Alsheikh1

& Tamer M. Elmansoury1,2 & Ehab A. Abdelnabi3

Received: 1 March 2017 /Accepted: 7 June 2017# Springer-Verlag GmbH Austria 2017

AbstractBackground Adult idiopathic membranous obstruction of theforamen of Monro is an extremely rare condition that can beeffectively treated with endoscopic foraminoplasty. A unilat-eral or bilateral foraminoplasty is performed if one or both ofthe foramina of Monro are obstructed, respectively.Endoscopic septum pellucidotomy is usually used in combi-nation with the foraminoplasty.Methods The operative chart and video of one of our patientsundergoing endoscopic treatment for adult idiopathic mem-branous obstruction of the foramen of Monro were retrievedfrom our database and reviewed. A description of the surgicaltechnique was then formulated.Conclusions The surgical technique of endoscopicforaminoplasty plus septum pellucidotomy for adult idiopath-ic membranous obstruction of the foramen of Monro isdescribed.

Keywords Adult . Endoscopic . Foramen ofMonro .

Foraminoplasty . Idiopathic . Membranous

AbbreviationsCISS Construction interference in steady stateCSF Cerebrospinal fluidCT Computed tomographyEVD External ventricular drainageFIESTA Fast imaging employing steady-state acquisitionMRI Magnetic resonance imaging

Relevant surgical anatomy

The foramen of Monro is located at the junction of the roofand the anterior wall of the third ventricle. It is a duct-likecanal that communicates between the lateral and third ventri-cles. The size and shape of the foramina of Monro depend onthe size of the ventricles. In normal-sized ventricles, each fo-ramen is a crescent-shaped opening bounded anteriorly by theconcave curve of the fornix and posteriorly by the convexanterior tubercle of the thalamus. As the ventricles enlarge,the foramen on each side becomes larger and more rounded[1]. Its dimensions may vary from 0.3 cm to 0.8 cm in itslongest diameter [2]. The structures passing through the fora-men are the choroid plexus, the distal branches of the medialposterior choroidal arteries, and the internal cerebral,thalamostriate, superior choroidal, and septal veins [1]. Thechoroidal fissure is a narrowC-shaped cleft between the fornixand thalamus along which the choroid plexus is attached. Thefissure is situated in the medial part of the body, atrium, andtemporal horn of the lateral ventricle. It is limited in the bodyof the ventricle by the body of the fornix superiorly and by thethalamus inferiorly. The choroid plexus from each lateralventricle extends through the foramen of Monro and iscontinuous with the two parallel strands of choroid plexusin the roof of the third ventricle. The choroidal fissure isformed at approximately 8 weeks of embryonic development

Electronic supplementary material The online version of this article(doi:10.1007/s00701-017-3246-5) contains supplementary material,which is available to authorized users.

* Waleed A. Azabwaleedazab@hotmail.com

1 Department of Neurosurgery, Ibn Sina Hospital, P.O. Box 25427,13115 Safat, Kuwait

2 Department of Neurosurgery, Ain Shams Faculty of Medicine,Cairo, Egypt

3 Department of Radiology, Ibn Sina Hospital, Kuwait City, Kuwait

Acta NeurochirDOI 10.1007/s00701-017-3246-5

when the vascular pia mater that forms the epithelial roof ofthe third ventricle invaginates into the medial wall of the ce-rebral hemisphere [3].

Surgical technique of endoscopic foraminotomy

Patient positioning and burr hole placement

A Lotta® endoscope (Karl Storz, Tuttlingen, Germany) isused. Under general anesthesia, the patient is positioned su-pine with the head in neutral position, elevated 15–20° abovethe level of the heart inMayfield® horseshoe headrest (IntegraLifeSciences Corporation, Cincinnati, OH, USA). A 3–4-cmlinear skin incision is made parallel to the midline and cen-tered over a point at which the burr hole is to be placed. Theburr hole is 4 cm off the midline just anterior to the coronalsuture (Fig. 1). The dural surface is bipolar-coagulated andincised in a cruciate fashion. Precise hemostasis at this stageis important to prevent blood seepage into the ventricleresulting in a blurred endoscopic view.

Endoscopic foraminoplasty

The endoscopic sheath with the trocar is inserted to cannu-late the lateral ventricle. CSF egress takes place at a depthof about 5 cm. The endoscope is then inserted, and irriga-tion with warm Ringer’s lactate is started. The region of theforamen of Monro is inspected and is found to be occupiedby an obstructing membrane that approximates the

foraminal edges. Notably, a very small aperture is presentwithin the obstructing membrane and allows the choroidplexus tissue to pass from the lateral into the third ventriclevia the obstructed foramen of Monro (Fig. 2a). A closedsmall forceps is then inserted into the membranous aper-ture (Fig. 2b) and opened judiciously to initially enlargethe opening within the obstructing membrane (Fig. 2c).Further enlargement is achieved using a 3-F Fogarty bal-loon catheter (Fig. 2e and f). Resistant parts of the mem-brane are then sharply opened using a scissors initially in asuperficially oriented fashion (Fig. 2h and i) before cuttingthrough (Fig. 2k) so as not to injure any of the surroundingstructures. Foraminoplasty is then finalized with a ballooncatheter inflation (Fig. 2l). The procedure is then repeatedfor the contralateral side. A septum pellucidotomy is per-formed by connecting multiple points with bipolar coagu-lation in a circular fashion and dilatation with a Fogartyballoon catheter.

Closure

Irrigation with Ringer’s lactate is continued until intraventric-ular hemostasis is achieved. A single EVD tube is insertedthrough one of the burr holes and kept closed during the post-operative period so that it can be used in case of CSF circula-tion obstruction. A piece of Gelfoam® is used to cover thedura within the burr hole, and closure of the galea and skin isthen performed in a standard fashion. Pre- and post- operativeimaging of a case with adult bilateral membranous obstructionof the foramina of Monro is presented in Fig. 3.

Fig. 1 Patient positioning andburr hole site for endoscopicforaminoplasty and septumpellucidotomy

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Indications

Idiopathic membranous obstruction of the foramen ofMonro [4].

Limitations

True foramen of Monro stenosis [5] and stenosis secondary totumors or other space-occupying lesions.

Complication avoidance

Despite being minimally invasive, severe complications suchas hemiparesis and memory deficits can occur because ofinjury to the surrounding neurovascular structures [6].Endoscopic foraminoplasty should only be performed incases with membranous obstruction of the foramen of

Monro. True foraminal stenosis is not an indication of theprocedure in our opinion as it risks injury to the fornix andthalamus. Prontera et al. pointed out that the fenestration of anobstructing, transparent membrane is much safer than thedilation of a stenotic foramen, which may damage the fornixand thalamostriate vein [7]. Initial use of blunt forceps and aFogarty balloon catheter offers help with creating a largeropening through which sharp scissors’ blades can be safelyutilized to complete opening of the membrane. As theobstructing membrane is opened with the scissors, careshould be taken not to cut blindly through neural or venousstructures in the vicinity. Meticulous hemostasis is of crucialimportance.

Specific perioperative considerations

Preoperative MR imaging is crucial for evaluating thepathoanatomical features and dictating the surgical strategy.

Fig. 2 Surgical steps of endoscopic foraminoplasty. a The membraneobstructing the foramen of Monro. A very small aperture is presentwithin the obstructing membrane through which the choroid plexustissue passes from the lateral into the third ventricle via the obstructedforamen of Monro. b A closed small forceps is inserted into themembranous aperture. c The forceps is opened judiciously to initiallyenlarge the opening within the obstructing membrane. d Partially open

foramen of Monro. e, f Further enlargement of the foramen using a 3-FFogarty balloon catheter. g Incompletely open foramen with parts of themembrane resistant to blunt opening. h–k Resistant parts of themembrane are sequentially sharply opened using a scissors. l A finalenlargement using the balloon catheter results in a fully openedforamen of Monro

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Steady-state MR sequences such as CISS or FIESTA are sen-sitive in detecting fine intraventricular membranes and aretherefore essential for the preoperative diagnosis. A closedEVD is kept in place, and close clinical observation is to bepracticed so that the EVD is opened when high ICP issuspected clinically. Postoperatively, patients are consideredcured when the manifestations of high intracranial pressurecompletely disappear. Neuroimaging should be resorted towhen any of these manifestations recur. A routine follow-upMRI is performed at 3 months. Further MR imaging is guidedby the clinical findings during follow-up.

Specific information to give to the patientabout surgery and potential risks

Endoscopic foraminoplasty with or without septumpellucidotomy is a minimally invasive technique that has beenfound to be a safe and effective alternative to shunting ormicrosurgery in treating idiopathic membranous obstructionof the foramen ofMonro. The procedure is performed througha single or two burr holes. Regular clinical and radiological

follow-up is required postoperatively to detect recurrent ob-struction of the foramen of Monro.

Compliance with ethical standards

Patient consent The patient has consented to submission of this BHowI do it^ to the journal.

References

1. Yamamoto I, Rhoton A, Peace D (1981) Microsurgery of the thirdventricle: part 1-microsurgical anatomy. Neurosurgery 8:334–356

2. Segal S (1998) Endoscopic anatomy of the ventricular system. In:King W, Frazee J, De Salles A (eds) Endoscopy of the central andperipheral nervous system. Thieme, New York, pp 38–58

3. Rhoton AL (2002) The lateral and third ventricle. Neurosurgery 51:S207–S271

4. De Bonis P, Anile C, Tamburrini G, Tartaglione T, Mangiola A(2008) Adult idiopathic occlusion of the foramina of Monro: diag-nostic tools and therapy. J Neuroimaging 18:101–104

5. Mizrahi CJ, Cohen JE, Gomori JM, Shoshan Y, Spektor S,Moscovici S (2016) Idiopathic bilateral occlusion of the foramenof Monro: an unusual entity with varied clinical presentations. JClin Neurosci 34:140–144

Fig. 3 Pre- and post-operative imaging of a case with adult bilateralmembranous obstruction of the foramina of Monro. a, b CT brain atpresentation revealing biventricular hydrocephalus. Note the normal-sized third ventricle. c, dAxial and coronal T2-weightedMR images afteran EVD insertion on the right side. Note the deviation of the septumpellucidum by the left lateral ventricle toward the decompressed rightlateral ventricle. e Sagittal CISS MR image revealing a questionable

membranous obstruction of the foramen ofMonro and normal-sized thirdventricle. f, g Reformatted CISS MR images in coronal planedemonstrating an obstructing membrane of the left foramen of Monro(arrows) and deviated septum pellucidum (arrowheads). h, i Post-endoscopic foraminoplasty and septum pellucidotomy axial and coronalT2-weighted MR images revealing well-decompressed lateral ventriclesand patent foramina of Monro

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6. Tubbs RS, Oakes P, Maran IS, Salib C, Loukas M (2014) The fora-men of Monro: a review of its anatomy, history, pathology, andsurgery. Childs Nerv Syst 30:1645–1649

7. Prontera A, Feletti A, Chahine R, Pavesi G (2015) Adult idiopathicocclusion of Monro foramina: intraoperative endoscopic reinterpre-tation of radiological data and review of the literature. Br J Neurosurg29:609–610

Key points

1. Endoscopic foraminoplasty with or without septum pellucidotomyis a minimally invasive technique.

2. The procedure is indicated in cases withmembranous obstruction ofthe foramen of Monro.

3. In cases with idiopathic obstruction of the foramen of Monro,preoperative MR imaging studies may fail to reveal obstructingmembranes found during endoscopy.

4. The procedure should replace shunting and microsurgicalforaminoplasty as an initial treatment modality.

5. The morbidity of the procedure is less than that of shunting andmicrosurgical excision.

6. The procedure is performed through one or two burr holes based onwhether one or two foramina of Monro are obstructed.

7. The technique of endoscopic foraminoplasty varies according to thepathoanatomy of the foraminal obstruction and septal deviation.

8. Although bilateral foraminoplasty is the ideal strategy when bothforamina are obstructed, a unilateral foraminoplasty plus a septumpellucidotomy may be sufficient as a CSF diversion diversion.

9. The procedure requires a high level of experience in intraventricularneuroendoscopy.

10. Shunting should be resorted to in cases of failed endoscopicforaminoplasty.

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