The Operation for Pineal Region Tumors in Children

Different approaches may be used for resection of tumors of the pineal region.  Each approach has advantages and disadvantages and should be chosen on the basis of radiographic appearance of the tumor and patient anatomy.   Factors important in choosing which approach to use are as follows:

• Surgical goals: Is a diagnostic biopsy desired or will an attempt at a complete resection be made.
• Anatomy: The tumor’s location and extension, as well as the anatomy of the deep venous system and surrounding neural structures, must be considered when planning an approach to a pineal region tumor.
• Patient: The patient’s age, the presence or absence of hydrocephalus, and the head shape will determine which approach will be most effective in accomplishing the goals of the operation. 
• Surgeon’s comfort: The surgeon’s familiarity and confidence with an approach is of great importance.

Management of Hydrocephalus

• Tumor removal preferred treatment: Obstructive hydrocephalus due to pineal region tumors may be resolved with tumor mass reduction.  In cases where persistent obstruction at the aqueduct of Sylvius precludes prompt resolution of hydrocephalus (for example, patients with staged tumor resections or those treated medically with gradual decrease in tumor mass), ETV or shunting may be considered.

Biopsy

• Helpful if germ cell tumor suspected: Due to the histological variation of tumors in the pineal region, histological data can be valuable.  In the case of germinomas, which may be diagnosed on by tumor markers and radiographic appearance and treated with radiation alone, surgery for tissue diagnosis may not be needed. .  In contrast, in cases where the diagnosis is not certain histological verification is needed to determine an appropriate treatment plan.  Stereotactic biopsy of pineal region tumors has emerged as a valuable tool for diagnosis and management with up to a 94% diagnostic yield (99).  The efficacy and safety of this technique have improved with implementation of the neuroendoscope, with a mortality rate of 1.3% and a morbidity rate of less than 1% in a series of 370 patients (94). Incorporation of neuroendoscopy is also advantageous in that it provides the opportunity to biopsy and perform third ventriculostomy for CSF diversion, when needed, in the same setting. Endoscopic biopsy of pineal region tumors does incur risk of CSF seeding, particularly in cases of germinoma and pineoblastoma (99).

Craniotomy – Patient Positioning

Supratentorial approach

• Prone or sitting position: Either the sitting or prone position may be used.  The senior author prefers the prone position for all pediatric patients. 
• Head fixation in pins: In patients who are old enough, a three-pin fixation device is used.  In these cases the head is turned slightly (approximately 15 degrees) to the side of the intended approach to facilitate retraction of the ipsilateral occipital lobe by gravity. 

 

• Head held in horseshoe frame: A horseshoe headrest is frequently used in infants whose skulls will not tolerate the pressure of pin fixation.  The head is kept in a neutral position facing downward.  The face should be checked to ensure no pressure is placed on the patient’s eyes so that retinal injury is avoided.

Infratentorial supracerebellar approach

• Prone or Concorde position: The pineal region can be approached with the patient in the prone or modified prone (Concorde) positions.  These positions lessen the changes of an air embolism.  They become slightly more awkward for the surgeon as the patient reaches adult stature.
• Sitting position: If a sitting position is used, gravity assists in retraction of the tumor down and away from the deep galenic venous plexus, minimizing the need for additional cerebellar retraction.  Gravity will also prevent blood and CSF from collecting in the surgical field.  This position cannot be used for infants whose heads cannot be placed in pin fixation.  It carries the risk of venous air embolism, hypotension, and overdrainage of CSF with the attendant risk of subdural hematomas for patients with untreated hydrocephalus. 

Craniotomy – Surgical Approach

• Brain relaxation: Care is taken to avoid undo pressure on the hemisphere being retracted to access the tumor. When hydrocephalus is present, an intraoperative ventriculostomy or direct ventricular drainage is used to facilitate an interhemispheric approach.  In the case of slit ventricles, the brain is relaxed with hyperventilation and the administration of mannitol.  In some cases intraoperative externalization of an existing shunt may be necessary.
• Right-sided approach: The craniotomy is usually made on the patient’s right side unless the extension of the tumor suggests easier access for resection from the left side.

Occipital transtentorial approach

• Indication: The occipital transtentorial approach is a preferred method of access to midline lesions or those with unilateral lateral extension, as it offers a wide surgical field of view while minimizing risk to occipital cortex and midline bridging veins. This approach minimizes retraction on the occipital lobes while facilitating direct visualization of peritumoral venous structures such as the vein of Galen.
• Scalp incision: A midline occipital incision is made, and dissection of subcutaneous tissue and muscle is carried down along the midline to bone with care taken to maintain a bloodless plane.
• Craniotomy: One may achieve a wide range of angles for entry using a craniotomy extending from the inion to approximately 3 cm rostral to the lambda. The craniotomy is typically 10 cm in length and 5 cm in width crossing the superior sagittal sinus.  There are typically no cortical veins at the interhemispheric fissure posterior to the lambda, allowing safe intradural dissection to the tentorium along this corridor.
• Sectioning of tentorium: The ipsilateral tentorium is sectioned approximately 1 cm lateral to the straight sinus in a length of 2–3 cm, exposing the underlying superior vermis. This approach provides the surgeon and assistants with adequate exposure from the upper posterior fossa to the lateral ventricle of the ipsilateral side, as well as the anterior portion of the third ventricle. 
• Mobilization of veins off of tumor: The veins of the galenic system may be encountered overlying the tumor.  By positioning the trajectory of the intraoperative microscope in a more horizontal angle, these veins may be separated from the tumor surface under direct vision.

Lateral transventricular approach

• Indication: A lateral transventricular approach is selected in cases with tumor extension into the lateral ventricular system. It may also be used to reach tumors with third ventricular extension through the foramen of Monro.
• Scalp incision: A curvilinear/U-shaped incision is planned, based ipsilateral to the side of tumor extension. If a midline lesion is targeted, craniotomy should be planned on the nondominant hemisphere.
• Craniotomy. A posterior frontal craniotomy is performed. The location of the craniotomy should be planned based on tumor extension and to facilitate a transcortical trajectory that spares motor cortex.
• Transventricular approach: A frontal cortisectomy is performed and carried down to the lateral ventricle. Access to the third ventricle is achieved either through a subchoroidal approach or by dividing the velum interpositum medial to the choroid plexus inferolaterally toward the pineal region. Care must be taken to preserve the internal cerebral veins coursing along the roof of the third ventricle.

Interhemispheric transcallosal approach

• Indication: The anterior interhemispheric approach is for tumors occupying the third ventricle with extension into the lateral ventricle through the foramen of Monro or subchoroidal space, or for tumors with extension into both lateral ventricles.
• Scalp incision:A U-shaped incision is planned, based ipsilateral to the side of tumor extension, that crosses midline.
• Craniotomy: A posterior frontal craniotomy is performed, crossing midline and centered around the tumor. Bur holes may be drilled on either side of the superior sagittal sinus, with care being taken to strip the dura beneath prior to elevation of the bone flap. A wide craniotomy will facilitate a variety of working channels between numerous superficial bridging veins.
• Interhemispheric approach: The initial approach is through the interhemispheric cistern to the corpus callosum. Care must be taken not to create excessive retraction and to preserve bridging veins and identify callosomarginal and pericallosal arteries.
• Subchoroidal approach to third ventricle: The corpus callosum is sectioned (usually <2cm in length) between the pericallosal arteries, and the lateral ventricle is entered. From here the third ventricle can be entered via the subchoroidal approach through the choroidal fissure. This fissure can become thinned and widened in the medial wall of the lateral ventricle due to tumor mass effect from below on the roof of the third ventricle.   
• Interforniceal approach: A strict midline access is used through a cavum septum pellusidum after transecting the corpus callosum in the midline. The cavum septum pellucidum is often open during childhood.
• Posterior interhemispheric approach: An interhemispheric approach to the quadrigeminal cistern can be taken for tumors in the pulvinar and posterior thalamus. Tumors extending into the atrium and forward into the body of the lateral ventricle can be accessed by sectioning the splenium. 

Infratentorial supracerebellar approach

• Indication: This approach has the advantage of a midline trajectory for midline tumors of the pineal region with superior extension, no ventricular involvement, and minimal lateral extension. It facilitates avoidance of the deep venous system in the pineal region when it lies above and lateral to the tumor.  This approach has several disadvantages, however.  The posterior fossa in infants and young children is small, and this can restrict the surgical field. This approach is not effective for tumors located above the deep venous system, or those that extend laterally beyond the tentorial opening, or those extending into the lateral ventricle.  Tumor tissue in the anterior medullary velum between the superior vermis and inferior colliculi is also difficult to resect with an infratentorial approach.
• Scalp incision: A midline skin incision is made, and dissection is carried down to suboccipital bone. Depending on the size and extent of the lesion, the incision may need to be carried as low as C2–C4.
• Craniotomy:A suboccipital craniotomy is performed, with care taken to dissect the bone flap from the underlying transverse sinus and torcula. Lesions with significant caudal extension may also require exposure of the cervical spine and possibly C1–C2 laminectomy.
• Subtentorial approach: A subtentorial approach to the quadrigeminal cistern is then performed. A durotomy should be created with reflection of the dural flaps laterally, based on the transverse sinus; care must be taken to avoid excessive retraction and prevent transverse sinus occlusion. Dissection is carried out to safely create a plane between the cerebellum and overlying dura. The vermis is retracted inferiorly, and superior vermian veins should be identified and sectioned with the precentral vein to safely access the pineal region.  An arachnoid veil overlying the tumor may be identified and opened. The superior vermis is depressed inferiorly to allow a low trajectory with the operating microscope to avoid injury to the vein of Galen. Small branches of the superior cerebellar artery and choroidal artery may require division to safely access the tumor, which can then be internally debulked. After internal debulking, the tumor may be resected laterally and then inferiorly along the brainstem. With this approach, the superior-most extent of the tumor should be approached last, as this is in closest proximity to the great veins.

Craniotomy – Intervention

Resection via quadrigeminal cistern

The technical difficulty of this exposure is viewing the contralateral surface of the tumor. It is brought into surgical view after internal decompression of the tumor, which allows its walls to be infolded.  Once the tumor is resected, the structures of the anterior wall of the third ventricle are in the surgical view.

• Open arachnoidal membrane: The initial view of the quadrigeminal cistern will be obscured by a thick arachnoid membrane.  Opening this membrane exposes the pineal tumor under the vein of Galen.
• Working with the tumor – pineal germinomas: Germinomas are well encapsulated, granular, and fibrous. 
• Working with the tumor –teratomas: Teratomas have a distinct capsule containing multiple cystic structures with thin to mucoid contents.  The septations and solid tissue in most teratomas are firm.  This tissue may be too fibrous or rubbery to aspirate, requiring a tedious piecemeal resection or use of a laser coagulator. 
• Working with the tumor – choriocarcinomas and yolk sac tumors: These tumors are well encapsulated and vascular; intraoperative bleeding may preclude complete surgical resection.
• Working with the tumor –pineoblastomasand pineocytomas: Pineoblastomas are soft with a necrotic core that can often be removed with simple suction. However, pineoblastomas are also often quite vascular due to tumor neovascularization.  Pineocytomas, in contrast, are well demarcated and less vascular.
• Working with the tumor –astrocytomas: Gliomas of the quadrigeminal plate or thalamus are also resectable.  On opening the quadrigeminal cistern, the surgeon should take care to remain in the midline of the superior colliculi and avoid trauma to the inferior colliculi to prevent postoperative hearing deficit.  Glial tumors may be covered by a thin cortex of tectal plate or by tissue of the posterior thalamus.  In these cases, one may identify the grayish tissue of the normal pineal gland in the vicinity of the tumor.   Benign astrocytomas are often well demarcated, making gross resection attainable with the appropriate surgical approach.
• Use of neuroendoscope: The neuroendoscope can enhance the surgeon’s visibility and allow more accurate tumor resection by inspecting the resection cavity. 
• Tumor extension into the fourth ventricle, upper posterior fossa, and the tectal plate: These tumors can also be removed with this approach. 
• Tumor extension into the third ventricle: For resection of tumors that extend into the anterior third ventricle, the surgical microscope can be adjusted to accommodate a more horizontal trajectory. See point below for very large tumors.
• Tumor extension into the lateral ventricle: Tumors originating from the posterior thalamus or growing into the atrium of the lateral ventricle may be reached via lateral retraction of the retrosplenial parahippocampal gyrus to facilitate entry to the lateral ventricle.  Sectioning the splenium of the corpus callosum may be necessary for resection of very large tumors of the third ventricle or tumors that extend into the lateral ventricle, but this should be avoided if possible. 

Craniotomy – Closure

• Hemostasis: On completion of tumor resection, the surgical field should be irrigated and inspected, with hemostasis ensured. 
• Dura closure: The dura is closed in a watertight fashion.
• Craniotomy closure: The craniotomy defect is closed with replacement of bone flap. Our preference is to use microplate and screw fixation, however some surgeons may prefer absorbable plating systems or sutures alone. 
• Soft tissue closure: The posterior cervical muscle and fascia are closed in layers to prevent pseudomeningocele formation.  The skin is reapproximated and our preference is to use absorbable suture.