[Meningioma of the clivus]. / Meningeómy klivu.

Clivus meningeoma is a relatively rare tumor with difficult surgical accession. Large and giant tumors acquire a very close relation to the brain stem, cranial nerves and brain vessels. In 10 our of 13 patients, the large tumor diameter exceeded 4 cm, and in half of them it was larger than 5 cm (max. 6.5 cm). Small and medium-sized tumors were removed by means of simple neurosurgical approaches. All of the 10 large and giant tumors were removed by a combined supra-infratentorial presigmoid approach which enabled the approach to the whole tumor. Three recurrent tumors were removed subtotally, the primary surgical intervention removed 5 tumors radically, 4 subtotally and 1 partially. The entire removal was precluded due to infiltrative growth of the tumor localized in the cavernous sinus, firm adherence of tumor to the brain stem or to the vertebrobasillar vessels. Authors' own experience support the data from literature dealing with the relationship of unfavourable results to the size of tumor. Permanent impairment of cranial nerves (38.5%) occurred mostly in large and giant tumors. One death (7.7%) during the peri-operative period (up to one month following operation), as well as the second that occurred in later period succeeded the removal of a giant tumor. Regarding the character of the relationship of large clivus meningeoma to the surrounding nerve and vascular structures, the future improvement of functional results can be expected especially owing to early diagnosis. (Tab. 2, Fig. 2, Ref. 19.)

Phase-retrieval analysis of pre- and post-repair Hubble Space Telescope images.

Phase-retrieval measurements of point-spread functions from the pre- and post-repair Hubble Space Telescope are presented. The primary goal was to determine the aberrations present in the second wide-field and planetary camera (WFPC2) to align and validate its corrective optics. With both parametric model-fitting techniques and iterative (Gerchberg-Saxton) methods, accurate measurements have been obtained of the WFPC2 and Hubble Space Telescope optics, including improved maps of the zonal errors in the mirrors. Additional phase-retrieval results were obtained for the aberrated, prerepair cameras and the corrected faint-object camera. The information has been used to improve models produced by point-spread-function simulation programs. On the basis of the measurements a conic constant for the primary mirror of κ = -1.0144 has been derived.