Third ventricular tumor treatment
A plethora of surgical strategies have been described to reach deep-seated lesions situated within the third ventricle including the Rosenfeld, or transcallosal anterior interfoniceal approach.
These tumors cause obstructive hydrocephalus and thus necessitate a CSF diversion procedure such as an endoscopic third ventriculostomy (ETV), often coupled with an endoscopic biopsy (EBX). Lesions located posterior to the massa intermedia pose a technical challenge, as the use of a rigid endoscope for performing both an ETV and EBX is limited.
Roth and Constantini, recommend using a combined rigid-flexible endoscope for endoscopic third ventriculostomy and biopsy to approach posterior third ventricular tumors (behind the massa intermedia). This technique overcomes the limitations of using a rigid endoscope by reaching 2 distant regions 2).
The first choice treatment option for third ventricle lesions with dilated ventricles was endoscopic management 3). Among microsurgical approaches, the expanded transcallosal transforaminal approach was a more recently practiced and safe method of accessing the anterior and middle third ventricle. With this approach, the risk of damage to most of the vital structures, such as the fornix or the thalamus was avoided 4). The location of the junction of the anterior septal and internal cerebral vein is essential. Preoperative magnetic resonance (MR) venography can identify the junction. Some areas remain inaccessible, such as the anterosuperior and posterosuperior regions of the third ventricle 5).
The expanded transcallosal transforaminal approach remains a safe and relatively secure method of gaining access to the third ventricle 6).
There are three broad categories – anterior, lateral, and posterior routes. The anterior routes include transforaminal, interforniceal, transchoroidal, and subchoroidal. The subtemporal route is the main lateral corridor to the third ventricle and recommended if the tumor is located lateral to the sella turcica or extends into the middle cranial fossa 7). A transtubular access to the third ventricle is also practical. It enables blunt dissection of the corpus callosum which may minimize retraction injuries. Three-dimensional endoscopic visualization, coupled with a transparent plastic retractor, provides absolute and undeviating monitoring of the surgical corridor 8). In the third ventricle’s anterior portion, the endoscopic endonasal approach permits surgical maneuverability. The lamina terminalis and tuber cinereum are thought to be safe entry points for this approach 9). Tumors leading to the blockage of the Sylvian aqueduct can cause obstructive hydrocephalus; this calls for a CSF diversion procedure, endoscopic third ventriculostomy, combined with an endoscopic biopsy. Posterior third ventricular tumors should be approached using a combination of a rigid-flexible endoscope 10).
Operative approaches to tumors of the third ventricle, mainly the bifrontal approach through the lamina terminalis, has several advantages. First, the main arteries can be exposed and the operative field is sufficiently wide to render the operative procedure safe. Second, cortical incision or excision is unnecessary. By cutting the lamina terminalis, which is usually thin and expanded as a result of hydrocephalus, even a large tumor can be removed. In addition, lethal complications are avoided, because this approach has less possibility of damage to the lateral wall of the third ventricle. Seventeen cases of tumor in the third ventricle underwent operation via this approach. The operative technique for the bifrontal approach through the lamina terminalis and three representative cases are reported. This approach can be applied not only to tumors, but to arteriovenous malformations or giant aneurysms adjacent to the third ventricle 11).