Objectives
Advances in laparoscopy have demonstrated that supraumbilical primary ports can be desirable in complex cases with large masses. This study evaluated distances to vital retroperitoneal vasculature that were encountered with 45- and 90-degree angle entry from the umbilicus and 2 commonly described supraumbilical entry points at 3 and 5 cm cephalad from the umbilicus.
Study Design
Retrospective analysis of computed tomography scans of the abdomen and pelvis from 100 randomly selected women who were 18-50 years old with normal anatomy was performed. Three-dimensional models of sagittal sections were generated using IMPAX software. Measurements from the abdominal wall at the umbilicus and 3 and 5 cm cephalad with 45- and 90-degree angles to retroperitoneal structures were performed.
Results
With 90-degree angle entry, the abdominal wall thickness (AWT) was thinnest at the umbilicus; however, the thickness at 3 and 5 cm was similar. AWT increased at all sites with 45-degree angle entry, and the same pattern was observed. AWT and intraperitoneal distance positively correlated with body mass index and supraumbilical entry points. With 90-degree angle entry, the aorta was 1.9 cm (95% confidence interval [CI], 1.4–2.4) and 2.5 cm (95% CI, 2.0–2.9) farther away at 3 and 5 cm cephalad compared with umbilical entry. In one-third of the cases, regardless of port placement, a vascular structure other than the aorta was the most anterior vessel. With 45-degree angle entry at the umbilicus, no vessels were encountered. With 45-degree angle entry at 3 and 5 cm cephalad, the aorta was the most anterior vessel in 1% and 2% of cases, respectively, and was noted to be 1.0 cm (95% CI, 1.0–1.0) and 2.3 cm (95% CI, 1.2–3.3) farther away than with 90-degree angle entry. A vessel other than the aorta was encountered in 4% and 7% of cases at 3 and 5 cm, respectively.
Conclusion
According to theoretic modeling, supraumbilical primary port placement can be implemented safely in laparoscopy. With supraumbilical entry, the distance to retroperitoneal vessels was greater than at the umbilicus. Compared with a 90-degree angle, with a 45-degree angle entry, it was uncommon to encounter vasculature, and all measured distances were greater.
Successful laparoscopic minimally invasive surgery relies on optimal port placement at the beginning of the procedure. Knowledge of the most advantageous port placement from an advanced understanding of anatomy can improve dramatically the surgical team’s operative field exposure and the technical ease and efficiency of the surgery, while reducing surgical injuries. Most injuries in minimally invasive surgery occur at the time of primary entry into the peritoneal cavity because of penetrating damage to either the viscera or the surrounding retroperitoneal vasculature.
The umbilicus commonly is selected as the site for primary trocar insertion because it offers the shortest distance between the skin and the anterior peritoneum and is cosmetically appealing. In addition, its anatomic relation to retroperitoneal vital structures is well understood. Hurd et al in 1991 retrospectively analyzed computed tomography (CT) and magnetic resonance imaging scans of 33 women and measured the distance from the base of the umbilicus to retroperitoneal vessels at 45- and 90-degree angles. It was discovered that, in women with a normal body mass index (BMI), a 45-degree angle had minimal risk of preperitoneal trocar placement or major vessel injury; however, in obese women, only the 90-degree angle consistently avoided preperitoneal placement. Hurd et al in 1992 published a similar anatomic retrospective review of CT images from 35 women and reported that, in women with a normal BMI, the umbilicus is 0.4 cm caudal to the aortic bifurcation. However, in overweight and obese women, they reported that the umbilicus is 2.4 and 2.9 cm caudal to the aortic bifurcation, respectively, and that the umbilicus is cephalad to the common iliac as it crosses the midline in all cases.
Despite its common use and its documented relation to vital structures, there are often times in gynecology when an umbilical port is suboptimal. In cases that involve large uteri or pelvic disease, a primary umbilical port’s usefulness will be limited severely because of the close proximity to the uterus or pelvic mass. This decreases operative exposure and markedly increases the difficulty of instrument manipulation and of the overall surgery. In such cases, a supraumbilical primary trocar is highly advantageous to increase the distance from enlarged structures and thereby improve exposure and surgical efficiency. Supraumbilical port use has been reported in the literature to enable minimally invasive surgical management of large fibroid uteri at the time of myomectomy or hysterectomy and of large adnexal masses for cystectomy or oophorectomy. Its use has also been reported in pregnant patients with gravid uteri in the second trimester of pregnancy for nonobstetric surgery that involves adnexal masses. In these instances, creating distance between the primary trocar and the uterus is especially important to avoid any penetrating injury to the gravid uterus from trocar insertion. Supraumbilical port use is also reported in the literature by gynecologic oncologists for laparoscopic excision of large ovarian cancers. The supraumbilical primary port is also frequently used in robotic surgery when increased interport distances are desirable to eliminate robotic arm collisions. Reports in the literature describe the common locations of the supraumbilical port site are 2-5 cm above the umbilicus and at least 6 cm above a second-trimester gravid uterus.
Although supraumbilical primary trocar use has been demonstrated in the literature to facilitate complex cases such as the aforementioned to be managed via minimally invasive surgery, no study has evaluated whether the advanced cephalad distance from the umbilicus effects the risks of encountering retroperitoneal vital structures and therefore the risks of vascular or visceral injury at the time of primary trocar insertion. The objective of this study was to evaluate the retroperitoneal structures that are encountered at 45- and 90-degree angles from the level of the umbilicus and 3 and 5 cm cephalad from it to construct and compare the possible or likely points of injury from umbilical and supraumbilical primary trocar insertion.
Materials and Methods
CT scans of the abdomen and pelvis of 100 female patients from the Cleveland Clinic between September 2012 and May 2013 were reviewed retrospectively. Institutional review board exemption status was obtained. Data for patients who had a CT scan performed within the study parameters were sampled randomly and then selected for review based on the inclusion criteria of female patients 18-50 years old with benign conditions and normal anatomy, without anatomic defects, masses, or abnormalities.
Baseline patient characteristics were collected that included age, ethnicity, and BMI for demographic information. Sagittal images from the patients’ CT scans were then reconstructed into 3-dimensional models with the use of the IMPAX software (Agfa Healthcare Corporation, Greenville, SC) for analysis. Entry points were designated along the anterior abdominal wall at the umbilicus and at 3 and 5 cm supraumbilically in the linea alba. Several measurements from these appointed entry points were then made. The distances between the skin and the anterior and posterior peritoneal layers were measured. In addition, the distances between the skin and vital retroperitoneal structures were measured at 90 and 45 degrees from the horizontal. All structures and measurements were identified and obtained by 3 investigators including a radiologist.
Statistical analysis was then performed on both the baseline patient characteristics and the CT scan measurements with the use of the Student t test, Fisher exact test, analysis of variance, and Kruskal-Wallis rank sum test.
Results
One hundred women were included. The average age was 36.8 ± 9.7 years, with a range from 19–50 years. There was a broad range of BMI from 13–70 kg/m 2 , with an average of 27.9 ± 8.1 kg/m 2 . Seventy-eight percent of subjects were white; 16% were African American; 3% were Hispanic, and 3% were listed as Other.
When measured at a 90-degree entry angle, the abdominal wall thickness was least at the umbilicus, compared with all other entry points (1.7 cm [95% confidence interval (CI), 1.5–1.9 cm] vs 2.9 cm [95% CI, 2.7–3.2 cm]; P < .001); however, the thickness at 3 and 5 cm was similar (2.8 cm [95% CI, 2.6–3.1 cm] vs 2.9 cm [95% CI, 2.7–3.2 cm]; P = .85). The abdominal wall thickness was increased at all sites when measured at a 45-degree angle of entry; the same pattern was observed with the thinnest measurement at the umbilical entry (2.9 cm [95% CI, 2.6–3.3 cm] vs 4.5 cm [95% CI, 4.0–4.8 cm]; P < .001) and no significant difference between 3 and 5 cm ( Table 1 ). Abdominal wall thickness was correlated positively with BMI at all sites and angles of entry (r > 0.65 and P < .001 in all cases) and was noted to increase 0.14 cm (95% CI, 0.137–0.143 cm) with every point of BMI increase. Abdominal wall thickness was also correlated positively with supraumbilical entry and increased an average of 1.38 cm (95% CI, 1.36–1.39 cm) and 1.42 cm (95% CI, 1.40–1.43 cm), respectively, at entry points 3 and 5 cm above the umbilicus.
| Variable | Umbilicus, cm | Supraumbilical, cm | P value | |
|---|---|---|---|---|
| 3 cm | 5 cm | |||
| 90-degree abdominal wall thickness | 1.7 (1.5–1.9) | 2.8 (1.5–1.9) | 2.9 (2.7–3.2) | < .001 |
| 45-degree abdominal wall thickness | 2.9 (2.6–3.3) | 4.4 (4.0–4.8) | 4.5 (4.1–4.9) | < .001 |
| 90-degree distance from skin to retroperitoneal vessel | 8.5 (8.0–9.2) | 10.1 (9.5–10.7) | 10.6 (10.0–11.2) | < .001 |
To be functional, the trocar length must travel through the abdominal wall and extend into the intraperitoneal cavity; it is advantageous when some shaft length is also superior to the skin to allow for trocar adjustment. Therefore, it was deemed that at least 2 cm of trocar length in excess of the abdominal wall thickness is necessary for optimal trocar placement and use. The standard trocar shaft length is 10 cm; Table 2 provides a list of the BMIs at which the measured abdominal wall distance with each access location and angle of entry reaches 8 cm and therefore represents the maximum BMI for standard trocar use. At each site, the 90-degree entry angle permitted a higher maximum BMI to accommodate the desired trocar length.
| Location | Angle, degrees | BMI, kg/m 2 a |
|---|---|---|
| Umbilicus | 90 | 74.98 |
| Umbilicus | 45 | 64.61 |
| 3 cm SU | 90 | 65.09 |
| 3 cm SU | 45 | 54.73 |
| 5 cm SU | 90 | 64.83 |
| 5 cm SU | 45 | 54.47 |
a The BMI at which 8 cm of the 10 cm of standard trocar length are embedded in the abdominal wall.
When the trocar was introduced at a 90-degree angle, the aorta was encountered 1.9 cm (95% CI, 1.4–2.4 cm) and 2.5 cm (95% CI, 2.0–2.9 cm) farther away when the entry point was moved 3 or 5 cm cephalad, respectively, (8.5 cm [95% CI, 8.0–9.2 cm] vs 10.1 cm [95% CI, 9.5–10.7 cm] vs 10.6 cm [95% CI, 10.0–11.2 cm]; P < .01; Table 1 ), compared with entry at the umbilicus. However, in approximately one-third of cases regardless of port placement, a vascular structure other than the aorta was the most anterior retroperitoneal vascular structure (30% at umbilicus, 33% at 3 cm, and 36% at 5 cm). Of these cases, the most common anterior vessel was the right common iliac vessels at the umbilicus (43%) and the superior mesenteric vein supraumbilically (67% at 3 cm and 81% at 5 cm; Table 3 ).
