Transforaminal endoscopic colloid cyst resection
Transforaminal endoscopic colloid cyst resection is well described. However, some anatomical colloid cyst variants may warrant a modified approach. Rarely, colloid cysts separate the forniceal columns and grow superiorly within the leaflets of the septum pellucidum. Thus, the authors' goal was to characterize the imaging features, clinical presentation, surgical strategy, and outcomes of patients with this superiorly recessed colloid cyst variant. Superiorly recessed intraseptal colloid cysts are larger and tend to splay the bodies of the fornix, thus requiring a parasagittal transseptal interforniceal endoscopic approach. This achieves complete removal with comparatively negligible morbidity or rare recurrence (5.9%) 1).
The dual endoscope technique via the bilateral transforaminal approach can achieve better surgical outcome by obtaining direct visualization of the cyst attachment. Although the indication should be limited, this approach can be considered especially for patients with recurrent lesions involving possible adhesion to vital structures 2).
Neuroendoscopy, has been recognised as a viable and safe alternative to microsurgery for the treatment of third ventricle colloid cyst.
Controversy remains as to which is superior 3).
Powell et al. are credited with the first successful endoscopic aspiration of the colloid cysts. 4)
Less invasive endoscopic techniques have employed rigid endoscopes with single or dual working channels.
The increased range of viewing angles of the endoscope within the cylinder of access maintained by the tubular retractor facilitates resection of the cyst through a smaller opening 5).
Entry point and trajectory
An optimal entry point and trajectory for endoscopic colloid cyst (ECC) resection helps to protect important neurovascular structures. There is a large discrepancy in the entry point and trajectory in the neuroendoscopic literature.
The endoscopic approach to colloid cysts of the third ventricle is usually performed through the foramen of Monro. However, this route does not provide adequate visualization of the cyst attachment on the tela choroidea. The combined endoscopic transforaminal-transchoroidal approach (ETTA), providing exposure of the entire cyst and a better visualization of the tela choroidea, could increase the chances of achieving a complete cyst resection 6).
Using a more anterior approach, it is easier to reach the roof of the cyst and its possible adherences with the tela choroidea 7) 8).
Trajectory views from MRI or CT scans used for cranial image guidance in 39 patients who had undergone ECC resection between July 2004 and July 2010 were retrospectively evaluated. A target point of the colloid cyst was extended out to the scalp through a trajectory carefully observed in a 3D model to ensure that important anatomical structures were not violated. The relation of the entry point to the midline and coronal sutures was established. Entry point and trajectory were correlated with the ventricular size. Results The optimal entry point was situated 42.3 ± 11.7 mm away from the sagittal suture, ranging from 19.1 to 66.9 mm (median 41.4 mm) and 46.9 ± 5.7 mm anterior to the coronal suture, ranging from 36.4 to 60.5 mm (median 45.9 mm). The distance from the entry point to the target on the colloid cyst varied from 56.5 to 78.0 mm, with a mean value of 67.9 ± 4.8 mm (median 68.5 mm). Approximately 90% of the optimal entry points are located 40-60 mm in front of the coronal suture, whereas their perpendicular distance from the midline ranges from 19.1 to 66.9 mm. The location of the “ideal” entry points changes laterally from the midline as the ventricles change in size.
The results suggest that the optimal entry for ECC excision be located at 42.3 ± 11.7 mm perpendicular to the midline, and 46.9 ± 5.7 mm anterior to the coronal suture, but also that this point differs with the size of the ventricles. Intraoperative stereotactic navigation should be considered for all ECC procedures whenever it is available. The entry point should be estimated from the patient's own preoperative imaging studies if intraoperative neuronavigation is not available. An estimated entry point of 4 cm perpendicular to the midline and 4.5 cm anterior to the coronal suture is an acceptable alternative that can be used in patients with ventriculomegaly 9).