Purpose: This retrospective study was performed to assess the beneficial effect of preoperative embolization of juvenile nasopharyngeal angiofibromas (JNA) in terms of blood loss during surgery. Methods:Intraoperative blood loss in a group of 7 patients who underwent 10 procedures for JNA without preoperative embolization was compared with the blood loss of 13 patients who underwent 16 procedures after embolization of one or both external carotid arteries.Results: Mean blood loss was 5380 ml in patients without embolization and 1037.5 ml in those with embolization. This difference was not statistically significant because of the high standard deviation in the nonembolized group. However, when data were analyzed by tumor stage, a significant difference was noted between the embolized and the nonembolized patients with high-grade tumors but not between those with lowgrade tumors. Conclusion:Preoperative embolization of the branches of the external carotid appears to facilitate removal of high grade tumors. The benefit of embolization in those with low-grade tumors is less clear cut, probably because there is less vascularity in low-grade tumors and so removal is easier.

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After UMLS was used for five years as a knowledge source for representing 1500 complex medical procedures in MAOUSSC, its value is considered significant. Future editions of the UMLS are expected to improve representation of inter-concept relationships and global consistency.