Contralateral Interhemispheric Transfalcine Transprecuneus Approach
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The posterior interhemispheric craniotomy provides access to deep midline parafalcine and paraventricular spaces through the natural interhemispheric fissure. Although working in this natural plane has numerous benefits, such as a minimal need for brain retraction and transgression, the working corridor can be deep and narrow, making surgery in this region technically challenging.
The reach to expose the peritrigonal/atrial territories poses special challenges. The highly functional overlying cortices and white matter tracts such as the optic radiations lateral to the ventricle, postcentral gyrus laterally and more superficially, and the thalamus anteroinferiorly, constrain the surgical corridors to the atrium. Standard interhemispheric or transcortical approaches involve significant retraction and resection of the normal parenchyma.
Our colleagues have described the following trajectories to access the atrium that require brain transgression: the anterior-inferior temporal resection, the posterior-inferior temporal resection, the parahippocampal resection, the paramedian posterior parietal resection, the parasagittal resection and cingulate resection. I have used the contralateral posterior interhemispheric transfalcine transprecuneus approach (PITTA) to the atrium that provides several benefits. The PITTA offers flexible working angles to expand the operative corridor and minimal ipsilateral brain manipulation.
In this chapter, I will highlight the nuances of the PITTA for resection of the lesions affecting the atrium and its medial wall through optimizing the interhemispheric contralateral approach.
Indications for the Approach
I use PITTA to approach tumors and vascular lesions confined to the medial wall of the atrium and within the trigone of the ventricle.
Tumors that extend anteriorly into the diencephalon from the periatrial region or predominantly involve the lateral wall of the atrium are not reasonable candidates for this route.
Lesions in this location may affect the patient’s vision, so a preoperative visual field evaluation is warranted. However, most lesions in this location present primarily with nonspecific symptoms and signs and are rare.
Intraoperative cerebrospinal fluid (CSF) drainage facilitates brain relaxation and expands the interhemispheric corridor because the CSF cisterns are not accessed during the PITTA. This maneuver obviates the need for fixed retractors on the normal hemisphere. A lumbar drain is my method of choice for this purpose. Approximately 50-60 cc of CSF is gradually (in 10-15 cc aliquots) removed through the lumbar drain during the craniotomy and after the dural opening.
The superior sagittal sinus and corresponding bridging veins over the superior parietal lobule should be evaluated on preoperative magnetic resonance images, and if necessary, a magnetic resonance venogram (MRV) or computed tomography angiogram (CTA) should be performed. The parasagittal bridging veins are often sparse in this region. However, the risk of significant venous infarction with ligation of any large vein persists.
Exposure of the posterior aspect of the atrium requires an incision within the flax that can be close to the straight sinus. Therefore, preoperative evaluation of this vital dural venous sinus is also important on imaging.
If there are numerous large parasagittal veins draining into the sagittal sinus overlying the contralateral hemisphere in the region, it would be ill-advised to use the PITTA and ligate these veins; instead, a transcortical approach through the superior parietal lobule is warranted.
An understanding of the parasagittal venous anatomy is important for execution of this approach.
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POSTERIOR INTERHEMISPHERIC CONTRALATERAL TRANSFALCINE TRANSPRECUNEUS APPROACH
Once hemostasis is achieved, a ventricular catheter in implanted to drain debris within the ventricle and decrease the risk of hydrocephalus. The falcine dural flaps are returned to their original position and the convexity dura is closed.
Patients are observed in the intensive care unit for one or two days before they are transferred to the ward. Hypertension and overmedication with narcotics must be avoided. The ventriculostomy catheter is usually removed on the 2nd postoperative day. Anticonvulsant medications are administered.
Pearls and Pitfalls
- Placement of the patient in the park-bench position during surgery allows gravity retraction to minimize injury to the normal hemisphere.
- The PITTA is technically challenging because of its depth and narrow operative corridor and should be used selectively and judiciously.
- This approach emphasizes the importance of the operative working angles over the operative space for accessing difficult-to-reach tumors. Meningiomas of the region can be devascularized early in their dissection due to a direct exposure of their feeders from the choroid plexus.
- The interhemispheric transfalcine approach facilitates an adequate exposure of the medial atrial AVM’s and proximal control over the choroidal and posterior cerebral artery feeders early on with minimal normal brain transgression.
Bohnstedt BN, Kulwin C, Shah MV, Cohen-Gadol AA. Posterior interhemispheric transfalcine transprecuneus approach for microsurgical resection of periatrial lesions: Indications, technique, and outcomes. J Neurosurg 2015 May 1:1-10.
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