MRI enhances the understanding of critical anatomy during primary laparoscopic port placement

Abstract

Despite the majority of laparoscopic visceral injuries occurring with primary entry, high-fidelity training models are lacking. Three healthy volunteers underwent non-contrast 3T MRI at Edinburgh Imaging. A direct entry 12mm trocar was filled with water to improve MR visibility, placed on the skin at entry points, then images were acquired in the supine position. Composite images were created, and distances from the trocar tip to the viscera were measured, demonstrating anatomical relationships during laparoscopic entry. With a BMI of 21 kg/m2, gentle downward pressure during skin incision or trocar entry reduced the distance to the aorta to less than the length of a No. 11 Scalpel blade (22mm). The need for counter-traction and stabilisation of the abdominal wall during incision and entry is demonstrated. With a BMI of 38 kg/m2, deviating from the vertical angle for trocar insertion can result in the entire trocar shaft being placed within the abdominal wall without entering the peritoneum, creating a 'failed entry.' At Palmer's point distance between the skin and bowel is only 20mm. Ensuring the stomach is not distended will minimise gastric injury risk. The use of MRI to provide visualisation of the critical anatomy during primary port entry allows the surgeon to gain better understanding of textually described best practice techniques.

Figure 1

Composite image with MRI in the sagittal plane using a water-filled 12mm direct entry trocar at the umbilicus. This volunteer had a BMI of 21 kg/m2, and with the trocar positioned at rest (Figure 1A), at 90 degrees to the horizontal, at the base of the umbilicus, the distance from the tip to the aorta was 31.9mm (Annotation A). With the same volunteer and trocar position, the addition of gentle downward pressure (Figure 1B) reduced the distance from the trocar tip to the aorta to 17.1mm (Annotation B). The length of an 11 Scalpel Blade (22mm) is marked for comparison (Annotation C).

Figure 2

Composite image with MRI in the sagittal plane using a water-filled 12mm direct entry trocar at the umbilicus. This volunteer had a BMI of 39 kg/m2, and with the trocar positioned at rest, at 90 degrees to the horizontal, at the base of the umbilicus, the distance from the tip to the aorta was 67.5mm. (Annotation A) With the same volunteer, the deviation of the trocar shaft to 50 degrees from the horizontal, the distance from the trocar tip to the aorta was over 115mm (oblique dotted line).

Figure 3

Composite image with MRI in the axial and oblique sagittal plane using a water-filled 12mm direct entry trocar at Palmer’s point. This volunteer had a BMI of 24 kg/m2, and the trocar shaft positioned perpendicular to the skin, the tip at Palmer’s point and gentle downward pressure. The distance to the non-fasted, non-insufflated stomach was 42.6mm (Annotation A). The distance from the trocar tip to the small bowel was 20.0mm (Annotation B). The length of an 11 Scalpel Blade (22mm) is marked for comparison (Annotation C).