Tumor resection is usually carried out under magnification. The first step consists of a careful microdissection of the tumor away from the surrounding cerebellar tissue. Although AT/RT is easily distinguished from the normal tissue, appearing as a reddish pink (or gray), richly vascularized mass, an obvious interface with the surrounding neural structures may be lacking because of its infiltrative growth. The peripheral supplying vessels are progressively coagulated to reduce the bleeding from the tumor. Since such a bleeding is often profuse, the visual intraoperative control of the major arteries providing the vascular supply (namely, PICA) is recommended. Therefore, both PICAs should be identified at the beginning of the procedure prior to attempt the tumor excision. When a demarcation plane from normal tissue is completely missing, the mass removal has to start from inside the neoplasm. The tumor excision is carried out in a piecemeal fashion as the tumor size and infiltration rarely allow the surgeon to perform an “en bloc” resection (Fig. 40.2). The piecemeal removal, however, favors the tumor bleeding, and, considering that this bleeding usually stops only when the resection is completed, the removal should be realized as quickly as possible using both microsurgical instruments and ultrasonic aspirator. At the end of the procedure, the walls of the surgical field are carefully checked looking for possible tumor remnants or sources of bleeding. During this step, self-retaining retractors can be used to improve the visualization of the residual surgical cavity. We actually utilize retractors only during the late phases of cytoreduction in order to avoid unnecessary retraction and stretching of the cerebellar structures which may result in further edema when applied on the normal tissues already compressed by the tumor itself at the beginning of the operation.

The involvement of brainstem and cranial nerves is one of the most critical steps of AT/RT excision. When dealing with AT/RT located within the fourth ventricle, it is recommended to dissect the tumor up to visualize the ventricular floor before starting the tumor reduction; such a maneuver allows the surgeon to use the ventricular floor as a marker to avoid injury to the brainstem. When the superficial portion of the mass has been removed, the tumor is progressively excised starting from the inferior portion (close to the cervical region) and proceeding cephalad until the Sylvius’ aqueduct is visualized, opened (if needed), and protected with Gelfoam; finally, the tumor can be gently detached from the fourth ventricle floor trying to reduce its manipulation as well as bipolar cautery on the ventricular surface as much as possible. In case of infiltration of the floor (which is not infrequent), attempts to follow the tumor inside the brainstem should be avoided to decrease the risk of perioperative and postoperative damages (namely, cardiorespiratory impairment, VI and VII cranial nerve palsy, vomiting syndrome) (Fig. 40.3). Similarly, a cautious dissection of the tumor from the lower cranial nerves is recommended unless a clear infiltration of nerve sheath or a severe encasement of the structures of the CP angle is present (Fig. 40.4). Such a dissection may result very hard as the anatomy is often completely distorted. For this reason, it is advisable to separate the tumor from the cranial nerve proceeding from laterally to medially, trying to individuate as many marker points as possible (e.g., internal acoustic foramen to preserve VII and VIII cranial nerves, jugular foramen to preserve IX and X cranial nerves). The dissection of the tumor from the cranial nerve carried out from the medial surface of the brainstem, indeed, is more likely to result in cranial nerve loss because of the usually severe encasement at this level.