Endoscopic Transseptal Approach for Removal of Colloid Cysts: 2-Dimensional Operative Video

To the Editor: We reviewed with interest the recent publication by Scagnet et al1 titled “Endoscopic Transseptal Approach for Removal of Colloid Cysts: 2-Dimensional Operative Video”. Transseptal colloid cysts pose a particular challenge for endoscopic resection. Namely, they tend to be larger given the added room for expansion afforded by the septal leaflets; they compress the foramina of Monro, and they displace the forniceal columns. We commend the authors for the use and dissemination of this minimally invasive technique, but we would like to put forth some thoughts based on our growing experience in the endoscopic treatment of these lesions (surpassing 200 cases), as well as our recent publication on this subtype in which we detailed the surgical nuances relevant to the transseptal technique.2 The authors consider the risk of sudden death as part of the rationale for the procedure. This has been reported in the literature, but in our experience, it is uncommon. Moreover, it is more likely to happen in cysts located within the third ventricle, whereby a ball-valve mechanism may cause acute obstruction of the foramina of Monro. This is usually not the case for superiorly recessed cysts because of their anatomic location which permits larger growth before causing ventriculomegaly. We agree that a young, symptomatic patient like the one presented is an ideal surgical candidate. When surgery is deemed necessary, planning of the operative trajectory is of paramount importance. On the illustration provided by the authors, the fornix is depicted on the inferior aspect of the cyst wall. Although it is possible to find it in such a location, we have found it to be often displaced laterally in septal variants. That brings up an important decision point: where to start the septal fenestration and how to identify the forniceal columns. Lack of planning of the site of incision can lead to potential injury of this critical neural structure which is likely to be thinned out by the underlying cyst. We now have neuroimaging protocols in place to map the forniceal tracts preoperatively (unpublished data) to assist with our surgical planning. Furthermore, as the authors point out, the ventricles may be normal in size. However, there can be some relative asymmetry which affords a relative advantage to approaching from one side or the other. This must also be considered in presurgical planning. The authors discuss supine positioning, placing the head on a gel ring. We believe the head should be placed in a 3-point fixation device like a Mayfield head holder. This will prevent any unnecessary movement which could lead to tissue trauma, bleeding, and loss of visibility. The head must remain above the level of the heart but kept low to ensure the unhindered passage of the operative instruments along their full length while avoiding unnecessary torsion. The authors demonstrate a limited opening of the septal leaflet followed by aspiration of the cyst contents using 5 cc syringes. We have adopted the use of semitransparent, nonfenestrated (6 Fr) endotracheal suction tubes which fit through the operative channel of the endoscope. We cut the distal part to create a beveled tip which gives the operator the ability to puncture the cyst wall and aspirate the contents in a controlled fashion. It is worthwhile to mention that partially calcified contents within the cyst, which are hypointense on T2-weighted MRI imaging, can extrude from the cyst cavity and migrate into the ventricular system. Although it is rare for these cyst remnants to cause symptomatic obstruction, care must be taken to remove the cyst contents with caution. Furthermore, the use of syringes during the procedure risks aspiration of cerebrospinal fluid which can affect visualization if the ventricles are not enlarged and the unintentional aspiration of other structures such as the choroid plexus which may cause inadvertent bleeding. Finally, we see that the authors have elected to use coagulation of the cyst wall instead of resection. Although symptomatic recurrence is infrequent, we have published on the significance of cyst remnants after endoscopic colloid cyst resection. In our study, we found that recurrence rates are significantly higher in cases where cyst remnants persist (33% vs 2%).3 We, therefore, attempt complete resection when clinically relevant. There is usually a noticeable plane of separation between the cyst wall and the tela choroidea (or septal leaflet in superiorly recessed cysts) that lends itself to manipulation of the wall with endoscopic forceps and complete removal. If impossible to resect completely, coagulation of the cyst walls must be done comprehensively to decrease the chance of recurrence. However, care must be taken as the use of cautery along the deep aspect of the cyst wall has the potential of injury to underlying structures, most notably the internal cerebral veins.