Читать книгу Intracranial Gliomas Part III - Innovative Treatment Modalities - Группа авторов - Страница 50

Targets for stereotactic biopsy and cryodestruction were identified with a computerized stereotactic planning system [34] with the use of sequential axial post-contrast T1-weighed MRI, T2-weighted MRI in cases of non-enhancing glioma, and MET-PET or ^99mTc-MIBI SPECT for identification of tumor areas with maximal proliferative activity. Stereotactic trajectories were planned with a goal to avoid crossing of the eloquent cortex, cortical sulci, and cerebral ventricles in order to reduce the risk of neurological morbidity and hemorrhage. Their overall number varied from 2 to 9, which depended on the size and shape of the neoplasm, and generally was kept ad minima; this was facilitated by the use of cryoprobes with different volumes of the cooling chamber and/or by the selection of several ablation targets along the single stereotactic trajectory.

Fig. 1. Scheme of the device for stereotactic cryosurgery. The cold exchanger (1) has two cylindrical containers for acetone (2) connected to the cryoprobe (3) and its cooling chamber (4). The cooling effect is attained by dry ice (5) surrounding the acetone-containing containers within the heat-resistant reservoir. The cold acetone is circulating up to the tip of the cryoprobe (6) through thin pipes made of fluorocarbon polymer (7) connected with cone joints (8). The control unit (9) provides information on the temperature at the tip of the cryoprobe and air pressure, which is increased by a compressor (10) in either one or another acetone-containing container depending on the position of a switching valve (11).

In adults the surgery was done under awake condition with local anesthesia and intravenous sedation, whereas children were operated on under general anesthesia. Location of the entry point(s) on a head surface was determined by preplanned stereotactic trajectories. A burr hole(s) with a diameter of 12–14 mm was made and stereotactic biopsy needle was inserted to obtain tissue specimen. After establishment of the histopathological diagnosis on frozen sections, a cryoprobe was inserted into the target and test freezing up to temperature of –20°C was applied to ensure that it did not cause neurological deficit. Thereafter, cryodestruction was done. The exposure period for one cycle of cooling ranged from 4 to 6 min. At least two cycles of freezing-defrosting were considered mandatory at each target point to attain destruction of the cellular elements within the tumor without damage to the main vascular structures [33]. Upon completion of the required number of freezing-defrosting cycles the procedure was performed in another preplanned target reached with the same or another stereotactic trajectory.

Table 1. Perioperative complications after stereotactic biopsy and cryodestrucion of supratentorial gliomas in the present series

From our experience for avoidance of severe postoperative brain edema the maximal volume of cryoablation for a single procedure should be kept <21 cm³ (linear diameter of the spherical lesion around 3.5 cm). On the other hand, if necessary, stereotactic cryodestruction may be repeated in 4–6 weeks.