Anterior Approaches to the Lateral Ventricle in Children

Anterior Interhemispherical Transcallosal Approach

Patient Positioning

• Supine: The head is straight, flexed 20-30 degrees, and fixed on a three-pin skull clamp. Some authors favor turning the head to a more lateral position with the hemisphere requiring surgery down so that gravity will cause the hemisphere to fall away from the falx. This positioning will reduce the use of retractors (23, 38).

Surgical Approach

• Bicoronal scalp incision: This incision is made 2 cm behind the coronal suture. As a right-sided approach is usually performed, the incision extends more inferiorly on the right side, ending 1 cm above the tragus. On the left, the incision should be long enough to allow reflection of the scalp for about 6 cm anterior to the coronal suture. Once the calvarial surface is exposed, the coronal and sagittal sutures are identified so that the position of the craniotomy can be determined.
• Right-sided craniotomy: A craniotomy that extends to the midline is tailored as follows: two bur holes adjacent to the sagittal suture in order to have a bone flap with the anterior two-thirds ahead of the coronal suture extending 3-4 cm laterally in a semicircular fashion The sinus is then separated from the inner table of the skull, and any remaining skull along the midline is removed with rongeurs,
• Brain inspected for relaxation: If the brain appears tense or swollen, a ventriculostomy is placed into either the ipsilateral or the contralateral lateral ventricle. Ultrasound can be used at this point for orientation.
• Dura mater opened: The dura is opened in a horseshoe fashion and reflected over the sagittal sinus.
• Interhemispheric fissure opened: Bridging veins from the cortex to the dura and sagittal sinus anterior to coronal suture should be preserved as much as possible. If venous lacunae or intradural bridging veins are found, the intervening dura can be reflected as separate dural leaflets (45).
• Hemisphere retracted: The cerebral hemisphere is gently and gradually retracted away from the falx. Cotton balls inserted between the falx and the medial surface of the cerebral hemisphere help to keep retraction and exposure of the corpus callosum. The cingulate gyrus should not be mistaken for the corpus callosum that is white and has no vascularization.
•  Corpus callosum incision: 2 – 3 cm long between or lateral to the pericallosal arteries. Depending on the angle of the incision, the contralateral ventricle or even a cavum septum pellucidum can be entered. In the latter case bilateral fenestration of the septum walls will provide a midline exposure of both ventricles.
• Identify ventricular landmarks: Before proceeding with work on the tumor, time is taken to identify structures such as the choroid plexus, talamostriate, and septal veins to securely localize the foramen of Monro.

Approach Advantages

• Anatomy constant
• Distance shorter
• Cortical lesion avoided

Approach Disadvantages

• Not suitable to large tumor
• Venous infarction due to division of large draining veins
• Hemiparesis, transient: There is a risk for transient or permanent hemiparesis if retraction over the supplemental motor or premotor area is excessive.
• Lower extremity paresis, permanent: A pericallosal artery injury is a risk of this approach, and either mono- or paraparesis can result.

Anterior Transcortical Approach to the Lateral Ventricle

Patient Positioning

• Supine: The head is rotated 30 degrees toward the shoulder opposite to the side of surgery and is fixed in surgical head holder. Some surgeons prefer to keep the head straight up.

Surgical Approach

• Bicoronal scalp incision: The scalp incision is made 2 cm behind the coronal suture.
• Craniotomy: A right-sided approach (nondominant hemisphere) is preferred unless the tumor’s position in the lateral ventricle dictates otherwise. A rectangular flap of approximately 6 x 4 cm, starting 2 cm behind the coronal suture and centered on the middle of the middle frontal gyrus, is made. Its medial limit is about 1 cm off the midline. Image guidance helps in planning the craniotomy
• Brain inspected for relaxation: If the brain appears tense or swollen, a ventriculostomy is placed into either the ipsilateral or the contralateral lateral ventricle. Ultrasound can be used at this point for orientation.
• Dura mater opened: The dura is opened and reflected toward the sagittal sinus.
• Surface landmarks identified: The middle frontal gyrus is usually found 3.5 cm from the midline and 1 cm in front of the coronal suture. Its location can be confirmed with aid of image guidance. Image guidance can be helpful at this point for planning frontal transcortical access to the anterior third ventricle (foraminal entry).

• Cortical incision: A 3 – 4 cm cortical incision parallel to the sulcus in the center of the middle frontal gyrus is enough to access the lateral ventricle. In cases of small ventricles or large tumors, a longer cortical incision prevents brain injury.
• Approach to ventricle: Surface landmarks can be used to guide one to the ventricle. The approach is directed from the middle frontal gyrus toward the contralateral inner cantus in a plane extending from the coronal suture to the external auditory meatus. The dissection is done with blunt instruments. The lateral ventricle is usually entered near the foramen of Monro. Once inside the lateral ventricle, the anatomical landmarks are the same as described above.

Approach Advantages

• Easier excision of frontal horn tumors
• Allows larger cortical incisions: This approach, therefore, is suitable for very large tumors.
• Easier subchoroidal exposure of the third ventricle

Approach Disadvantages

• Transect fiber tracts: Multiple layers of white matter tracts traversed before the ventricle is entered (45)
• Increased risk of seizure (2, 38, 44, 45)
• Exposure: Greater difficulty in exposing the lateral ventricle on the opposite side (2, 38)
• Speech problems when working in the dominant hemisphere (13)
• Poor visualization of the contralateral foramen of Monro