The Operation for Infratentorial Ependymomas in Children
Prone: Positioning is typically prone with the head flexed for a midline craniotomy. The lateral oblique and sitting positions can also be used in older children.
Head fixation: Pin fixation is preferred in older children, but it should be used with caution in young children in whom pin fixation can cause skull fractures.
Midline scalp incision: In general, a midline scalp incision is preferred. It is initiated 1–2 cm above the inion and extends down to the level of C2 (or lower, if necessary). The fascia is cut with a linear or Y-shaped incision, and the suboccipital muscles are dissected from the skull and retracted with self-retaining retractors. The suboccipital craniotomy is performed below the transverse sinuses, approximately 3 cm from midline.
Craniotomy: A craniotomy is preferred over craniectomy by many neurosurgeons who believe that craniotomy may provide better cosmesis and may help prevent cerebellar ptosis.
Ultrasound: The ultrasound is useful before and after tumor resection to identify echogenic tumor.
Dural opening: The dura is opened in a Y-shaped fashion with caution for occipital and circular venous sinuses, especially in young children in whom these sinuses can be very large and can be associated with massive blood loss when opened.
Tumor resection: Smaller, inferiorly located tumors can be resected with only tonsil elevation. Larger tumors require either incision of the inferior vermis or a telovelar approach to facilitate tumor resection.
Intraoperative monitoring: Use of intraoperative physiological monitoring can warn of impending damage to the brainstem or cranial nerves. Any changes in vital signs during surgical exploration near the floor of the fourth ventricle should be considered a serious warning sign of intolerance of the brainstem to the surgery. The cardiovascular reflexes are mediated by the nucleus tractus solitarius and dorsal motor nucleus of the vagus nerve, which are located in the area where these tumors commonly attach to the floor. Surgical resection should be paused until the vital signs have been normalized.
Resection of the posterior arch of C1: This resection is performed if the tumor extends below the foramen magnum or if there is tonsilar herniation.
Frozen section: Initially the tumor is biopsied and submitted for pathological analysis via frozen section.
PICA and its lateral medullary branches: These vessels should be identified and preserved during tumor resection (13, 14).
Technique of resection: After dural opening, the overlying arachnoid is opened and sent for pathological assessment of seeding. The lateral border of the tumor is dissected to find and preserve PICA branches. Tumor debulking, often guided by ultrasound, facilitates tumor dissection.
Floor of fourth ventricle protected: As the tumor is resected, care is taken to protect the floor of the fourth ventricle, often with a cottonoid patty, in regions where the floor of the ventricle is not infiltrated by the tumor.
Gradual uncovering of ventricle floor: Resection is continued along the floor of the fourth ventricle to reach the point of origin of the tumor. This is usually caudal to the stria medullaris.
Goal is complete resection of tumor: The total resection of an ependymoma, if achievable, is far superior to an incomplete resection. Because infratentorial ependymomas usually arise from the floor of the fourth ventricle and frequently adhere to the lower cranial nerves, it is often quite difficult to achieve gross total resection. Surgical risks have to be assessed according to the extent of the tumor and the surgeon’s experience (2, 13).
Tumor adherent to floor individualized: If the tumor is adherent to the floor, a judgment by the surgeon is required. One choice is to leave a small amount of the tumor at the point of attachment. If the tumor has merged deep into the brainstem, a thin carpet of tumor can be left. On the one hand, it is commonly held that the first operation is the best opportunity to achieve gross total resection and long-term survival. On the other hand, the risks of causing permanent motor deficits and cranial neuropathies, including the need for a tracheostomy and percutaneous esophageal gastrostomy or significant lower cranial neuropathies, must be weighed in each case against the benefits of gross total resection.
Watertight dural closure: This is performed to minimize the risk of pseudomeningocele and CSF leak. Duraplasty is often required and can be performed with pericranial, cervical fascia, or a variety of dural substitutes.
Bone flap: The bone flap is typically secured with nonabsorbable sutures.
Muscle and fascia: The wound should be closed in layers. Good muscle and fascia closure can prevent CSF leakage and pseudomeningocele formation.