Drive safely through the pelvis – know your pelvic roads: Pararectal space

b Senior Registrar in Department of Obstetrics and Gynaecology, Faculty of Medical Sciences, University of Sri Jayewardenepura, Sri Lanka. c Senior Registrar in Department of Obstetrics and Gynaecology, Faculty of Medical Sciences, University of Sri Jayewardenepura, Sri Lanka. d Registrar in Department of Obstetrics and Gynaecology, Faculty of Medical Sciences, University of Sri Jayewardenepura, Sri Lanka.

This is the fourth article in the series of articles unfolding avascular spaces of the pelvis. Authors recommend reading the series of articles starting from "Drive safely through the pelvis -know your pelvic roads: Retropubic space of Retzius" published in the Sri Lanka Journal of Obstetrics and Gynaecololgy 1 .
The pararectal space is divided into lateral and medial spaces. The lateral pararectal space (Latzko space) is entered by dissecting between the ureter and internal iliac artery. The medial pararectal space (Okabayashi space) is opened up by dissecting between the ureter and the lateral wall of the rectosigmoid colon 2 .
The pararectal space is bordered medially by the apex of the uterosacrals and the lateral border of the rectum and mesorectum, roofed by the posterior leaf of broad ligament, laterally by the internal iliac artery, anteriorly by the base of the cardinal ligament and posteriorly by the curvature of the lateral sacrum, while the floor is continuous with the laevator ani muscles. The entire space is roughly divided into two by the ureter.
This space contains hypogastric nerve fibers which can be approached through both the medial and lateral pararectal spaces. Figure 1 gives an overview of anatomy of the pelvic spaces. Table 1 describes the surgical procedures, which use these spaces.    Nerve sparing radical hysterectomy is possible only when this space is adequately exposed. The hypogastric nerve lies in the Okabayashi space and can be found about 2 cm below the ureter. Careful dissection around the hypogastric nerve and the origins of the pelvic splanchnic nerves from S2, S3, and S4 nerve roots can be visualized near the pelvic floor in this space. Careful exposure of the inferior hypogastric plexus can avoid damage to this important nerve plexus thus making the radical hysterectomy nerve sparing.
(b) (a) CME Deep infiltrating endometriosis can involve the sciatic nerve, sacral nerve roots and the hypogastric nerve. Endometriosis can also involve the anterior surface of the rectum and the ureters. Careful dissection into the pararectal spaces will enable the surgeon to perform a proper excision of endometriosis from the sacral nerve roots, ureter, as well as from the bowel and utero sacral ligaments. Because there are two hypogastric nerves on either side, damage to one may not cause a considerable effect on bowel, bladder or vaginal function 3 . It is always beneficial to spare the inferior hypogastric plexus during excision of deep infiltrative endometriosis. However, delicate dissection is necessary for the excision of endometriosis from the sciatic and hypogastric nerve roots 4 .
Excision of ureteric endometriosis, reanasotomosis or reimplantation will require dissecting the ureter along the pararectal space before it veers away laterally to the uterosacral ligament. Ureteric reimplantation or ureterocystoneostomy is often needed when a segment of the ureter closest to the bladder is altered beyond salvation due to infiltration or compression by endometriosis 1 .
Segmental bowel resection for bowel endometriosis is carried out rarely, where the Okabayashi space must be developed completely enabling circumferential segmental resection of the bowel. This requires opening into the retrorectal space 5 . Care must be taken to avoid injury to the medial rectal vessels which originate from the anterior division of the internal iliac artery 6 .
In conclusion, the pararectal space contains the hypogastric nerves and ureters. A wide range of gynaecological surgeries require dissection in this space as described above. Surgery in this space should be guided by meticulous anatomical knowledge. It is essential that a proper selection of suture material and needles are chosen and to have expertise in laparoscopic suturing.
Thorough knowledge about pelvic anatomy of these spaces is important for the pelvic surgeon to achieve surgical excellence while minimizing morbidity. Articles describing the other pelvic spaces will follow in future issues.