The extraperitoneal space extends between peritoneum and investing fascia of muscles of anterior, lateral and posterior abdominal and pelvic walls, and circumferentially surrounds the abdominal cavity. The retroperitoneum, which is confined to the posterior and lateral abdominal and pelvic wall, may be divided into three surgicoanatomic zones: centromedial, lateral (right and left), and pelvic. The preperitoneal space is confined to the anterior abdominal wall and the subperitoneal extraperitoneal space to the pelvis. In the extraperitoneal tissue, condensation fascias delineate peri- and parasplanchnic spaces. The former are between organs and condensation fasciae, the latter between this fascia and investing fascia of neighboring muscles of the wall. Thus, perirenal space is encircled by renal fascia, and pararenal is exterior to renal fascia. Similarly for the urinary bladder, paravesical space is between the umbilical prevesical fascia and fascia of the pelvic wall muscles-the prevesical space is its anterior part, between transversalis and umbilical prevesical fascia. For the rectum, the "mesorectum" describes the extraperitoneal tissue bound by the mesorectal condensation fascia, and the pararectal space is between the latter and the muscles of the pelvic wall. Perisplanchnic spaces are closed, except for neurovascular pedicles. Prevesical and pararectal (presacral) and posterior pararenal spaces are in the same anatomical level and communicate. Anterior to the anterior layer of the renal fascia, the anterior interfascial plane (superimposed and fused mesenteries of pancreas, duodenum, and colon) permits communication across the midline. Thus parasplanchnic extraperitoneal spaces of abdomen and pelvis communicate with each other and across the midline.
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