- Approach dependent: Depending on the approach used, the patient will be positioned supine, in a lateral decubitus position, or prone.
- Head fixation: Young children, especially those with hydrocephalus, cannot be pinned in a Mayfield or Sugita frame, but the head can be stabilized on a horseshoe headrest or with the use of a gel pad system.
- Using gravity to assist retraction: When approaching the tumor with an interhemispheric transcallosal route, placing the patient in a lateral decubitus position with the involved hemisphere facing down will allow the falx to act as a retractor on the contralateral hemisphere, and gravity will keep the ventricle open.
- Dictated by tumor’s location: As a general principle, the shortest route to a tumor is the best approach. It will be decided upon by the location of the tumor and the presence of eloquent cortex in the vicinity, as well as whether or not the tumor is in the dominant hemisphere. The second consideration is the vascular supply of the tumor, which should be identified and targeted first.
Lateral ventricles (atrium/trigone)
- Temporal or parietal cortisectomy, nondominant: In the nondominant hemisphere the tumor should be approached with a temporal cortical incision anterior to the vein of Labbe to decrease the risk of hemianopsia, or a parietal incision behind the angular gyrus (but increased risk of hemianopsia). Incisions through the superior parietal lobule are also commonly used, with an increased risk of visual field deficit and hemiparesis, however. The parietal approach also increases the distance to the tumor, making it a longer reach for the surgeon, and having the vascular supply usually hidden by the tumor.
- Temporal or parietal cortisectomy, dominant: In the dominant hemisphere a temporo-parietal cortical incision behind the angular gyrus is recommended to avoid language deficits. While a cortical lesion in that location can lead to a Gerstmann syndrome (dysgraphia, alexia, dyscalculia, finger agnosia, and left-right disorientation) in adults, it has rarely been described in children due to plasticity of the brain. This approach allows the visualization of the entire trigone.
- Occipital cortisectomy: Incision has also been used for posteriorly situated tumors; however, it creates a visual field deficit with a homonymous hemianopsia.
- Anticipated postoperative deficits: Visual field loss (homonymous) and/or hemiparesis can occur with these approaches, although they are usually transient.
Lateral ventricles (anterior and extension into the third)
- Middle frontal gyrus approach: The anterior ventricle can be reached by a middle frontal approach incision, at the level of the coronal suture. If there is extension of the tumor into the third ventricle, it can then be followed through the foramen of Monro.
- Transcallosal approach: A transcallosal approach enables the surgeon to reach most tumors, except in the temporal and occipital horns. Careful dissection is important during the initial approach to preserve the venous drainage and avoid a venous infarction.
- Anticipated postoperative deficits: On the dominant side, the transcortical approach might result in some speech impairment, especially when there is marked hydrocephalus preoperatively. Attention deficits might arise with an approach through cortex of either hemisphere. The transcallosal approach can be associated with a disconnection syndrome when the callosal sectioning needs to be extended posteriorly. Alexia and visual agnosia might also be problems in patients with preoperative homonymous hemianopsia and a dominant hemisphere tumor.
These tumors are approached via the lateral ventricles using one of the above approaches. The third ventricle can then be entered via a subchoroidal approach. Alternatively, an extraaxial approach can be taken to the quadrigeminal cistern when the tumor abuts or has grown through the posterior wall of the third ventricle.
- Subchoroidal approach into third ventricle: Description of this approach, with minor variations, has differed over time (interthalamino-trigonal (39) or subchoroidal transvelum interpositum (51)). Common to all are the elevation of the choroid plexus off of the floor of the lateral ventricle and the separation of the velum interpositum from the ipsilateral thalamus to enter into the third ventricle.
- Transcallosal approach: An anterior callosotomy exposes the anterior aspect of the ventricle, and enables an early identification of the feeding vessels, as well as the dissection of the tumor from the tela choroidea.
Fourth ventricle (outside the scope of this chapter)
- Via sulcus overlying foramen of Magendie: A telo-velo-tonsillar approach can be taken to avoid splitting the vermis, as in other tumors of the fourth ventricle.
- Shrink and cauterize: High vascularization hinders the removal of the tumor, and therefore it is better to shrink the tumor first with bipolar cautery, instead of entering it to debulk it. Constant hemostasis enables better visualization of the different planes and decreases the need for retraction to stop the bleeding (43).
- Expose vascular feeders and cauterize: The tumor should then be gently mobilized to identify and isolate the feeding arteries that can be coagulated or clipped. However, blind clipping of the vessels is not recommended since venous drainage should be spared.
- Fragment large tumors: In small tumors, an “en bloc” removal can be tried at that point, whereas larger tumors need some fragmentation once they have been devascularized.
- Goal is complete resection: Total removal of the tumor has been reported to be in the high 90% range for choroid plexus papillomas (43), while only in the 60% range for choroid plexus carcinomas (65).
- Massive blood loss may accompany the resection of choroid plexus carcinomas: For some large choroid plexus carcinomas, massive blood loss may be a problem. If this occurs, it may be best to abort the resection and obtain hemostasis. Treatment with chemotherapy may allow a less bloody resection at a second operation.
- Irrigate to clear: Irrigation of the ventricular cavity to rinse off blood clots might decrease hydrocephalus. If the foramen of Monro is partially obstructed, then perform a septostomy to decrease the chances of a trapped ventricle.
- Closure of surgical corridor: Application of gel foam and fibrin glue, as well as suture of the pia to close the corticectomy site have been shown to decrease the incidence of subdural collections (65).
- Hemostasis: Do a careful hemostasis, and check PTT/INR at the end of the procedure, especially if the patient has received many transfusions.
Treatment of hydrocephalus
- 25–50% require postoperative treatment: Nearly half of patients with choroid plexus tumors will require a shunt postoperatively for persistent hydrocephalus (23, 65, 83). Leaving an EVD in place allows for testing for the need a shunt, but overdrainage should be avoided to lessen the risk of the brain collapsing into the ventricle after removal of the tumor. This will subsequently lead to CSF leaking from the corticectomy into the subdural space.