AISIM Laprascopic Surgery

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index:

Hepatectomy

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See also the notes at visite de l'IRCAD.

Description of a hepatectomy

We will concentrate on a hepatectomy, an operation involving cutting out and removal of a part of the liver (one or several segments). The procedure is lengthy (210 minutes on one of the video tapes that we watched).

• Freeing the liver

  The first of the surgeon's tasks is to free the liver (by cutting the tissue fibres which wrap it). Despite being long and a bit tedious, this process doesn't pose any major difficulties. For our simulation, we will concentrate on the second part.

• Removal of segments

  Once the liver has been freed, the removal of segments begins. The problem is to avoid rupturing important blood vessels which haven't previously been cauterised, in order to avoid a hemorrage. We have seen two different techniques.

  First of all, the surgeon makes a superficial burn with an electric lancet on the surface of the liver, to mark where he thinks the join between the lobes he wants to take out, and the rest of the liver, is. (There is nothing on the surface of the liver to indicate the whereabouts of the different segments; they are defined by the vascular tree inside the liver, which is obviously invisible from the outside). Without marking this out, it would be very difficult for the surgeon to get his bearings once he had started cutting.

  • In the first procedure, the surgeon cuts out the edge of the liver, then tears towards the hepatic parenchyma. It is the difference in resistance between the parenchyma and the vessels that enables him to identify the presence of a vessel. At this point, he isolates the vessel by removing the surrounding connective tissue, then clamps it. He can finally cut the vessel, without any danger to the patient.

    There is the obvious risk of "missing" a vessel and tearing it. In this instance (which occurs in the video that we saw), the surgeon must quickly release a still healthy part of the vessel to enable it to be clamped. This task is made more difficult by the amount of blood around, which makes it more difficult to see.

  • The other procedure involves, before starting to cut out the segments, looking for the large vessels feeding the segments to be removed. The surgeon operates first at the level of the veins, to free and then clamp the vessels required. Finally, he can make incisions in the liver without worrying about meeting little vessels (assuming that they are branches of a vessel already clamped).

    The risk here is, on the one hand, to make mistakes in the first stage whilst clamping the big vessels (anatomical variations between patients are sufficiently great as to allow confusion over these large vessels), and on the other hand to leave a large part of the liver without a blood supply, resulting in its death. (This would pose problems if there was some area of the liver not destined for removal, yet fed by a vessel which had been cut).

  The surgeons at IRCAD seem to prefer the first technique.

Some comments regarding the two operations

• A number of organs other than the liver are visible during the operation.
• The little vessels clamped in the first operational method are not detectable in medical images. This means that the surgeon does not know where they are, and so one can place them at random in a numerical model of the liver.
• The large vessels clamped in the second operational method are detectable on MRI scans. Therefore they must be segmented and then introduced into the numerical model.
• The liver (with the Glisson capsule on its surface) is very slippery to the touch. A viscous friction (of the form F=-kV) is sufficient as a model.
• It is necessary to simulate the differences in mechanical behaviour of the vessels and of the parenchyma, since the detection of vessels is based principally on this.
• There is also a difference in behaviour between the surface of the liver (the Glisson capsule) and the interior (parenchyma). The parenchyma is very weak: it can be crushed by the pliers, whilst the Glisson capsule must be cut or burnt.
• The simulator must be able to detect ruptures in the vessels (by assessing the movements of the surgeon).
• The action of the electric lancet can only be detected visually (initially there is no special feel, no kind of vibration or any other sign), by a change in appearance (loss of brightness, yellow colouration) of tissues and by the smoke (which is not localised, but clouds the whole camera).

• The surgeon cannot make a clean cut; the parenchyma crumbles with the action of the pincers. There is therefore no need to model a regular cutting surface; a mesh (at sufficiently high resolution to show the volume to be cut out) is sufficient.

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Please send any comments/ corrections/ complements to jc lombardo.