Gravity Assisted Retraction Less Occipito Transtentorial and Trans-Splenial Approach for Posterior Third Ventricular Dermoid
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.333527
Source of Support: None, Conflict of Interest: None
Keywords: Dermoid cyst, occipital transtentorial approach, trans-splenial approach
The dermoid cyst is a rare benign tumor of the posterior third ventricular region. Common surgical approaches for this region include the supra-cerebellar infratentorial, occipital transtentorial, and posterior interhemispheric., Other techniques include anterior transcallosal transventricular approach, lateral paramedian infratentorial approach, and stereotactic biopsy. The decision for the surgical approach depends on factors like the displacement of the galenic venous complex and asymmetrical extension to either side. We selected the right occipital transtentorial approach because the tumor had asymmetric extension toward the right side, and the galenic venous complex was shifted downward by the tumor., The video demonstrates the surgical technique of gravity-assisted retraction less occipito transtentorial and trans-splenial approach for the posterior third ventricular dermoid.
The video in this article demonstrates a right-sided gravity-assisted occipital transtentorial approach for a posterior third ventricle dermoid cyst.
The patient was operated on under general anesthesia. With two wide bore cannula, the central venous pressure line, an arterial line, adequate intravenous access was taken. The patient was positioned in a lateral semi-prone position with the head slightly rotated toward the right side with a slight neck extension and fixed with a Sugita frame. With the help of gravity, the occipital lobe falls to avoid any brain retraction. The sagittal sinus, transverse sinus, and torcula were the important landmarks marked before the incision. Then a parieto-occipital craniotomy was done, exposing the posterior sagittal sinus, transverse sinus, and torcula. The dura mater was opened in a T-shaped manner, and the occipital horn was tapped with a ventricle catheter. Straight sinus was identified, and the tentorium was cut 1–2 cm lateral to the straight sinus. Then, through the galenic venous system, the tumor was approached, but the tumor was also extended inferior to the splenium, approached with the combined trans-splenial approach. Near-total excision of the tumor was achieved.
Video link: https://youtu.be/yffrHvNA2sk
Video timeline with audio transcript
0.05–0.14 min: A 36-year-old gentleman presented with a headache and one episode of seizure without neurological deficit.
0.14–0.26 min: The radiological image was suggestive of a well-defined heterogeneous lesion in the posterior third ventricular region, mainly toward the right side, just beneath the splenium, pushing the galenic venous system downward.
0.26–0.36 min: The patient was placed in the lateral semi-prone position with the head slightly rotated toward the right side with a slight neck extension.
0.36–0.46 min: A right occipital scalp incision was made, and a right parieto-occipital craniotomy was performed, exposing the transverse sinus, superior sagittal sinus, and torcula.
0.46–1.53 min: The cerebrospinal fluid (CSF) was drained from the right occipital horn to relax the brain and facilitate the retractor's less wide exposure of the posterior incisura structures. At the level of the incisura, meticulous arachnoidal dissection and preservation of the veins were important objectives. The arachnoidal dissection along significant veins defined the venous corridor and ensured a bloodless trajectory, decompressing the posterior splenial region, and helping in draining the CSF from the quadrigeminal cistern. The venous plexus could be seen embedded with thick white arachnoid adhesions. Fine dissection was performed along the venous plexus to expose the intervenous corridor to the tumor. Sharp cutting off the thick arachnoid adhesions along the vein helped in the mobilization of the vein and facilitate the exposure of larger corridors to the posterior third ventricle.
1.53–2.30 min: Rosenthal veins coming from both sides via the ambient cistern met the vein of Galen in the quadrigeminal cistern. The idea was to dissect the inter-Rosenthal corridor to approach the posterior third ventricular region for tumor dissection. The trajectory of the straight sinus leads to the incisura. It was not far away from the torcula. A common mistake was to lose track and go along the surface of the tent lateral to the incisura, retracting the occipitoparietal lobe, and not being able to find the free edge of the tentorium.
2.30–3.32 min: The tent was cut anterograde or retrograde, taking care to coagulate adequately as some venous channel could be present within the tentorium. It was cut within 1–2 cm lateral and parallel to the straight sinus. The tentorium was composed of two layers. Both needed to be coagulated to avoid venous bleeding during the tentorial division. Any venous lake directly connected to the sinus should be avoided to be cut during this procedure. While dividing the tentorium close to the incisura, the position of the basal vein of Rosenthal and the vein of Galen must be ascertained, so that the injury to this vein may be avoided. The edge of the tent should be hooked and retracted to expose the inter-Rosenthal and the splenial corridor.
3.32–4.05 min: As the tumor was situated high up in the posterior third ventricle just below the splenium and had pushed the veins down, we chose a corridor between the vein of Galen and the splenial vein., Dissection around the splenial vein was done to expose the lowermost part of the splenium, and thus, a trans-splenial corridor was used to approach the tumor.
4.05–5.09 min: The thick tumor wall was coagulated and opened. Cheesy off-white material was seen coming out through the opening. Calcified sebaceous material was seen within the tumor capsule suggestive of a dermoid cyst., The tumor capsule was dissected from all around, from the venous plexus, and the pulvinar of the thalamus, and the capsule was completely excised.
5.09- 5.35 min: After the decompression of the tumor, the occipital transtentorial approach provided adequate access to the habenular commissure and the pineal recess. These occult spaces should be looked for any residual tumor. The aqueduct is not directly visible because it is hidden by the posterior commissure's oblique orientation and the corpus callosum's overhanging splenium.
5.35- 5.41 min: The postoperative scan was suggestive of complete tumor excision.
5.41- 6.00 min: In the postoperative period, the patient had improvement in headache. There were no visual field cuts and the patient was discharged on the fifth postoperative day without any neurological deficits. The histopathology was suggestive of a dermoid cyst.
After surgery, the patient had significant improvement in headache without any neurological deficit. The postoperative CT scan showed complete removal of the tumor. The patient was discharged on day 5.
Pearls and pitfalls
The position of the superior sagittal and transverse sinus should be marked before turning the head laterally. In the case of parieto-occipital lobe bulging, trigone should be tapped to release CSF, facilitating the interhemispheric corridor opening. An ultrasound-guided tap is preferred as the orientation is complex after positioning. A wide opening of the interhemispheric corridor is recommended, which can be done by elevating the head end of the table to gain an anterior interhemispheric trajectory, and lowering down the head end of the table helps achieve the posterior interhemispheric trajectory. The tentorium should be divided parallel to the straight sinus, and both layers should be coagulated first before dividing the tentorium to avoid venous bleeding. Inferior sagittal sinus and the free edge of the falx may be excised to get access to the contralateral side of the straight sinus. At the level of incisura, a meticulous arachnoidal dissection should be done to avoid venous injury. Usually, the space between the internal cerebral vein and the vein of Rosenthal is not enough to enter the posterior third ventricle. However, any growing tumor in this region shall push these veins superiorly and splay them widely.
The disadvantage of this approach includes obtaining an adequate corridor between either the posterior parietal anastomotic veins or veins of the deep venous system. The approach for the contralateral extension of the tumor part is very difficult. However, one can even access a tumor of the contralateral ependymal lining due to oblique trajectory, but the ipsilateral attachment may be challenging to access.,
Endoscopic approach and cyst decompression are common approaches used by many neurosurgeons in the current era. However, adequate decompression may not be feasible via this approach in some instances. Various other approaches which were described earlier also should be in consideration for approach selection. This differs mainly due to the experience and comfort of the operating surgeon., We preferred the gravity-assisted retraction less occipital transtentorial approach in our case.
In this surgical video, we have demonstrated a gravity-assisted retractor less occipital transtentorial and trans-splenial approach to a posterior third ventricular dermoid cyst and successful complete excision of the tumor. Gravity helps in the fall of the occipital lobe, which helps avoid injury to the lobe during retraction. The operative nuances have already been described.
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Conflicts of Interest
There are no conflicts of interest.