Transcallosal Suprachoroidal Approach for a Small Third Ventricular Colloid Cyst
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.344613
Source of Support: None, Conflict of Interest: None
Keywords: Corpus callosotomy, interhemispheric, suprachoroidal, transcallosal, venous angle
Greenwood first described the anterior transcallosal approach for accessing the third ventricle in 1949. The deep and central location of the third ventricle and the anatomical complexity of the structures surrounding it can make it challenging to access it safely. The variations in the parasagittal cortical venous anatomy can also pose difficulties during initial part of the transcallosal approach. The natural history of colloid cysts is frequently ominous as they can cause acute obstructive hydrocephalus, sudden neurological deterioration, and even death. Even small colloid cysts in strategic locations around the foramen of Monro (FoM) can be symptomatic. Various approaches to the anterior and middle third ventricle have been described with regard to the venous variations and tumor extent [Table 1].,,
Compared to the transcortical approach, the transcallosal approach to the third ventricle is technically more demanding. A safe surgical strategy and its execution require avoidance of complications, the most worrisome of which include interruption of major venous structures and trauma to eloquent cortex. In this video, we highlight various steps to overcome these challenges.
The patient was placed supine with the head in neutral position, elevated and flexed 15–20 degrees, and fixed in a skull clamp [Figure 1]. The midline and coronal suture line were marked. A 7–8 cm linear skin incision crossing the midline but eccentric to the right was marked parallel to and 1 cm anterior to coronal suture [Figure 2]. A right sided 4 × 3 cm parasagittal craniotomy (⅔ anterior and ⅓ posterior to coronal suture) exposing the SSS was fashioned. At this stage, a microscope was brought in to complete a durotomy based on the SSS. Dura was reflected with tack up sutures taking care of the underlying cortical veins. After gentle brain retraction and arachnoid dissection, callosomarginal and pericallosal arteries were mobilized to their respective sides. A whitish corpus callosum was identified and the right lateral ventricle was entered after callosotomy (around 1 cm) [Figure 3]. The anatomy of the roof of the third ventricle, FoM, and deep venous system was defined [Figure 4]. Teniae fornicis was incised, and the choroid plexus was mobilized laterally to expose the colloid cyst via the suprachoroidal approach preventing injury to the deep veins [Figure 5]. The cyst was excised completely along with its capsule.
Video link: https://youtu.be/gBj8ihAdWt0
0.00–0.13 min: A 16-year-old boy presented with features of raised ICP intermittently and focal seizures for the past 6 years; however, he was neurologically intact.
0.13–0.44 min: Noncontrast CT scan of the head shows a small hyperdense lesion in the anterior–superior third ventricle without hydrocephalus. The same lesion is, however, not visible on contrast magnetic resonance imaging (MRI) brain, which shows the importance of obtaining thin sections when looking for diminutive colloid cysts. Sagittal T2 MRI is very important for locating the parasagittal cortical draining veins shown with yellow arrows for planning the craniotomy.
0.44–1.03 min: The positioning is supine, with head maintained in neutral position with mild flexion. The suture line is parallel to the coronal suture. A 4 × 3 cm right-sided craniotomy is made across the midline exposing the superior sagittal sinus, as shown in the illustration.
1.03–1.43 min: 3 × 2.5 cm Durotomy is performed taking care to avoid injuring the cortical draining veins, and dural tack up sutures are placed. The draining vein is mobilized off from the dura using a microscope under high magnification. The illustration shows another way of protecting the cortical vein if it has a prolonged intradural course en route to the venous sinus. The plane of sharp dissection with microscissors is biased toward the dural surface to avoid venous injury.
1.43–2.15 min: The SSS is retracted contralaterally by pulling the tack up sutures taut. The interhemispheric fissure is opened up by dissecting the arachnoid utilizing the full extent of durotomy. The arachnoid dissection is carried out between the ACA branches, that is, the callosomarginal and the pericallosal arteries, and they are dissected off extensively in antero–posterior direction to allow atraumatic mobilization.
2.15–2.26 min: The arteries are dissected and retracted laterally, and corpus callosum is visible.
2.26–2.44 min: Navigation is used to mark the most appropriate callosotomy site. Around a centimeter long callosotomy is done using bipolar cautery. The size of the retractor blade serves as a rough guide.
2.44–2.52 min: The body of the right lateral ventricle is entered and the choroid plexus is visible.
2.52–3.04 min: The choroid plexus is followed anteriorly to locate the FoM, where it disappears as it turns medially to form the roof of the third ventricle.
3.04–3.12 min: The deep veins and fornix are identified.
3.12–3.36 min: The attachment of the choroid plexus to the ASV is dissected preserving the vein itself. A glimpse of the cyst is now visible behind the choroid plexus.
3.36–3.50 min: The illustration in the inset shows the variations of the venous angle and the free space available to expand the FoM posteriorly while remaining clear of the deep veins.
3.50–4.16 min: In this suprachoroidal approach, the attachment of the choroid plexus to the fornix known as Teniae fornicis is divided using sharp scissors avoiding any injury to fornix and exposing the colloid cyst beneath it.
4.16–4.48 min: The wall of the colloid cyst is dissected off from the surrounding neural tissue and venous structures. The cyst is then removed in toto.
4.48–5.14 min: The picture describes the anatomy in further detail showing the venous angle formed by TSV, which in this case is Type 1B (as per Ture et al.) as the ASV–ICV Junction is posterior to the FOM level. The FOM is expanded after dividing the Teniae fornicis exposing the suprachoroidal corridor [Figure 6].
5.14–5.18 min: The area is explored to look for any residual cyst.
5.18–5.28 min: Postoperative CT head shows complete excision and no hydrocephalus.
5.28–-5.36 min: Postoperative MRI brain shows no residual and open bilateral FOM.
5.36–5.48 min: The patient was extubated after surgery on table and shifted to the ICU. He had no neurological deficits and was discharged day 4 after surgery. His headache improved on follow-up.
The postoperative course was uneventful. The patient was discharged on post-op day 4 without any neurological deficits.
The transcallosal approach allows us to approach the anterior and middle part of the third ventricle via the natural anatomical planes of the brain (interhemispheric) with minimal brain incision and retraction. It also allows good visualization of contralateral FoM via septostomy. The knowledge of various anatomical landmarks (choroid plexus, venous angle, fornix, etc.) is of utmost importance. The cognitive function is better preserved in the transcallosal approach vs transcortical approach. A relaxed brain is an absolute prerequisite for this approach. A more posterior location of the venous angle and ASV-ICV junction relative to FoM provides more space to access the mid-superior position of the third ventricle via the transchoroidal approach.
The current video focuses on the applied anatomy around the third ventricle and operative nuances of the transcallosal suprachoroidal approach to the anterior–middle third ventricle.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]