[Presacral haemorrhage during rectal cancer resection: morphological and hydrodynamic considerations]

Our aim is to identify the location and size of the anterior foramina of sacral vertebral bodies and analyse the haemodynamic variables that could influence the haemorrhagic severity of the injury of the presacral venous plexus.

Using computed axial tomography the morphological data of 70 sacral bones in 67 patients with rectal cancer were recorded, as well as measuring the height between the vena cava and S5. After transfemoral catheterisation the inferior vena cava pressure was recorded in 10 patients with rectal cancer. Hydrodynamic principles, according to Bernoulli's Law, were applied to calculate sacral venous plexus pressure, and the flow rate according to the calibre of a hypothetical venous injury.

The maximum diameter ranged from 0.5mm to 4mm in 22% of the cases. All foramina of 2 or more millimetres were located in the S4-S5 region. Sacral plexus venous pressure in lithotomy was almost double the inferior vena cava pressure in normal position. Blood flow ranged from 498 to 1,994 ml/min for injuries of sizes between 2 and 4mm, respectively.

Larger calibre foramina are found in vertebral bodies of S4-S5. Venous injury at these levels can reach a flow rate of 2 l/min.