The Operation for Supratentorial Tumors of the Lateral and Third Ventricles in Children
Head fixation: A three-pinned head holder is used for children older than 2 years of age (some avoid pin fixation until after 3 years of age). In children younger than 2 years, a horseshoe headrest is used. If fixation is required for image guidance, the head may be secured to the horseshoe headrest with a sterile drape or a U drape.
Anterior approaches: Anterior approaches are used for tumors of the frontal horn and body of the lateral ventricles. They can also be used to gain access to the third ventricle via the foramen of Monro. The anterior interhemispheric transcallosal approach and the anterior frontal transcortical approach to the ventricles are the two approaches in this category.
Posterior approaches: Posterior approaches are used for tumors of the posterior portion of the lateral ventricle’s body, trigone, and occipital horn. A posterior approach provides early access to arterial feeders originating from the posterior choroidal arteries. The posterior paramedial parietal approach and the posterior interhemispherical, transcallosal approach are the approaches in this category.
Inferior approaches: Inferior approaches are used for tumors of the trigone and temporal horn of the lateral ventricles. They are useful when the tumor is fed by the anterior choroidal artery or its branches. A cortical incision will be necessary irrespective of the approach chosen. Consequently, many important structures such as optic tracts, medial hypocampus, brainstem, and eloquent cortical areas must be respected. The temporal transcortical (middle temporal gyrus) approach, the parieto-temporal approach, the anterior temporal approach, and the subtemporal approach are examples in this category.
Anterior approaches:Anterior approaches are used for tumors of the anterior third ventricle as well as tumors in and around the foramen magnum. The transforaminal approach, interforniceal approach, and subchoroidal approach are in this category.
Posterior approaches: Posterior approaches are used for tumors of the posterior part of the third ventricle and tumors of the pineal region invading the posterior part of the third ventricle. The posterior interhemispherical transcallosal approach and suboccipital supracerebellar approach belong in this category.
Inferior approaches: Tumors of the pineal region displacing the great vein of Galen superiorly are approached with these techniques. The subfrontal approach and frontolateral or pterional approach are in this category.
Selecting the Approach
Avoidance of injury: Less morbidity from manipulation of brain structures. Ideally, there should be minimal or no retraction of brain tissue.
Good visualization of tumor and its feeding vessels: Adequate visualization of the tumor. Early access and control of the feeding vessels.
Location: The selected approach should provide the shortest distance to the lesion that avoids eloquent structures.
Probable histological type: When a malignant tumor is suspected, biopsy should be considered before a more aggressive surgery.
Vascularity: Highly vascular tumors should not be removed through restricted approaches, and preoperative embolization should be considered in some cases.
Origin of blood supply: Ideally, early control of feeding vessels should be obtained at initial stages of the operation.
Hemispheric dominance: Cortical approaches on the dominant hemisphere may result in neurological deficit. A special problem relates to crossed hemispheric dominance, and in such cases anterior transcallosal interhemispheric approaches should be avoided.
Presence or not of hydrocephalus: When ventricles are small, the transcallosal approach is preferable because the anatomy is constant and the distance to the target is shorter.
Size of the lesion: The transcallosal approach is usually not suitable to large lesions that demand more brain retraction and control of feeding arteries.
Surgeon’s experience and preference
Dealing With Hydrocephalus
Obstruction flow: Hydrocephalus is commonly found in association with tumors of the lateral and third ventricles due to obstruction of CSF flow at the level of either the foramen of Monro or the sylvian aqueduct.
Overproduction: Overproduction of CSF is regarded as an important cause of hydrocephalus in choroid plexus papillomas.
Treatment: The ideal treatment is removal of the obstruction. EVD is useful while approaching the lesion. When the patient requires immediate relief from the hydrocephalus or a permanent shunt is needed, an ETV may be used. This can be combined with CSF sampling for tumor markers and cytology and, occasionally, a biopsy if indicated.