Supracerebellar Transventricular Approach
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Small tumors in the posterior third ventricle, such as cavernous malformations, pose a significant technical challenge during their resection. Because of their small size, they do not significantly displace deep structures and therefore cannot create a suitable supratentorial operative corridor.
In these situations, I have attempted to use the supracerebellar transventricular approach. The small size of these tumors may expand and affect the tectum, and provides just enough space for me to work through the attenuated nervous tissue. Gaze disturbances are a risk, but most deficits are temporary.
The specific region of interest is the posterior segment of the third ventricle. The aqueduct and the suprapineal recess demarcate this segment.
Diagnosis and Evaluation
For a general discussion of diagnosis and evaluation for ventricular tumors, see the Principles of Intraventricular Surgery chapter.
Because of their proximity to the third ventricle and the aqueduct, patients with tumors in this region often present with obstructive hydrocephalus. Parinaud’s syndrome may develop with intratumoral hemorrhage (pineal apoplexy). The tumors in this area that demand resection despite their small size include cavernous malformations, pineoblastomas, and pineal parenchymal tumors of intermediate differentiation.
Indications for Surgery
Because of the very limited exposure afforded via the trans-pineal or trans-tectal corridor, large and especially vascular tumors are not ideal candidates. Hydrocephalus and uncertainty regarding diagnosis are reasonable indications for surgical intervention. Cavernous malformations that have caused repetitive symptomatic hemorrhages also require excision.
A careful study of the preoperative magnetic resonance images should determine the location of the internal cerebral veins and the veins of Rosenthal and Galen, in relation to the tumor. If the veins are displaced posteriorly and ventrally rather than superiorly, the supracerebellar transventricular approach is contraindicated.
The use of an external ventricular drain in the presence of hydrocephalus is advised.
The relevant anatomy is discussed in the Midline Supracerebellar Craniotomy and Anatomy of the Ventricular System chapters.
SUPRACEREBELLAR TRANSVENTRICULAR APPROACH
The infratentorial supracerebellar approach is favored for small posterior third ventricular lesions such as cavernous malformations, even if the lesion is not primarily within the pineal region. The advantages of this approach are substantial and include a minimal risk of injury to the adjacent structures and avoidance of supratentorial contents, including conservation of the corpus callosum. In my experience, the posterior pulvinar can be gently manipulated without significant risks.
The disadvantages of this approach include the vulnerability of the habenula, vein of Galen, and quadrigeminal plate. Most deficits related to manipulation of the tumor-affected tectum are temporary.
The technical details of the midline supracerebellar and paramedian supracerebellar craniotomies are discussed elsewhere in this Atlas. Although the unilateral paramedian craniotomy is adequate, most neurosurgeons prefer to use the midline supracerebellar approach to reach such deep-seated midline masses. Therefore, the following discussion refers to this type of exposure.
A standard midline suboccipital supracerebellar craniotomy is performed.
Closure and Postoperative Considerations
For a detailed discussion of recommendations for closure and postoperative care of patients with ventricular tumors, please see the Principles of Intraventricular Surgery chapter.
Pearls and Pitfalls
- The described approach is applicable in very select cases. The presence of diencephalic veins and intact tectum significantly limits its utility. Special anatomical considerations are necessary to justify its use.
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