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ret·ro·per·i·to·ne·al -.per-ət-ən-'ē-əl adj situated or occurring behind the peritoneum <\retroperitoneal bleeding> <a \retroperitoneal tumor>
ret·ro·per·i·to·ne·al·ly -ə-lē adv
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ret·ro·peri·to·ne·al (ret″ro-per″ĭ-to-neґəl) external to or posterior to the peritoneum.Medical dictionary. 2011.