Laparoscopic ultrasound on a real patient’s liver: find the tumour, stain the portal territory, plan the cut

What the hand can no longer feel

In open surgery the surgeon holds the liver and feels a hard one-centimetre nodule between the fingers. In laparoscopy the hand stays outside, and the camera sees only Glisson’s capsule, smooth and glistening.

This liver measures 1,790 mL. It hides a colorectal metastasis of 4.1 mL, about 2.0 cm across, 1.1 mm from a hepatic vein and touching a portal branch at the resolution of the CT. Nothing shows at the surface. The liver turns transparent only on screen: this is how its vessels and the tumour look on the preoperative CT.

• portal branches
• hepatic veins and cava
• the metastasis

A slice beneath the probe

The laparoscopic probe is a linear transducer on a flexible tip, working at 5–10 MHz and seeing 4–10 cm deep 11; the Southampton consensus considers intraoperative ultrasound essential in laparoscopic liver surgery 12. Here the array is 4 cm long. The image is a slice of tissue perpendicular to the surface it touches: the top is the capsule under the probe, the bottom is depth, here 7.2 cm. The yellow mark on the probe head shows which end is the left of the image.

In the transparent view the slice appears where it lies, inside the liver. Move the probe by clicking or dragging on the surface; hold the right button and drag to turn the liver (two fingers on a phone). Rotate the probe with the ⟲ ⟳ buttons or the Q and E keys, and tilt it with “Probe tilt”.

The image is computed as you move, from this patient’s segmentation: an echogenicity for each tissue, attenuation along each scan line, speckle fixed in the tissue. The image is computed by a model.

Where the veins meet the cava

Below the diaphragm the hepatic veins drain into the inferior vena cava. In colour Doppler, red and blue mean “towards the probe” and “away from it”, whether the vessel is an artery or a vein: tilt the probe and the same vein can change colour. Where a vessel runs across the beam, the colour disappears.

Beneath the image, the spectrum from the Doppler gate shows hepatic-vein flow, conventionally called triphasic: two waves towards the heart and a brief reversed wave, all set by the right heart 10. Tap a vessel on the image to move the gate. The velocities are typical values chosen for the model.

Portal pedicle or hepatic vein?

Two kinds of black tube cross the liver. Portal branches run inside Glisson’s sheath with the artery and the bile duct, so their wall is thick and bright. Hepatic veins have almost no visible wall.

Tap the image on what you think is a portal branch.

The metastasis, against the vein

There it is: a rounded lesion with a dark rim, the target pattern of many colorectal metastases, next to a hepatic vein. On the preoperative CT the gap between them is 1.1 mm.

This is where intraoperative ultrasound decides the operation: follow the vein and detach the tumour from it, or take the vein with the liver it drains. In an observational cohort in open surgery, after the tumour was detached from a major vessel the recurrence rate at the cut surface was 4.3% per patient, not significantly different from 5.3% after R0 resection, compared with 19.6% when tumour cells reached a cut through parenchyma 8. Torzilli’s team operated on 93 patients with this ultrasound-guided strategy and saw no recurrence at the cut surface over a mean follow-up of 18 months 7.

Examining the whole liver

Preoperative imaging misses lesions. In 100 patients examined after helical CT, intraoperative ultrasound found more metastases in 23 5; with contrast, ultrasound found 14 further lesions in 6 of 127 patients 6. The probe sees only the slice beneath it, so the liver is examined in overlapping sweeps.

Sweep this liver. The parts your beam has crossed turn blue, and the counter shows how much of the liver you have examined, to a depth of 7 cm.

Staining a portal territory

In 1985 Makuuchi, Hasegawa and Yamazaki described a resection guided by ultrasound: a needle placed under ultrasound control and a dye injected, so the subsegment to be removed shows on the surface 3. With indocyanine green injected into the portal vein, the territory glows in near-infrared light 4.

Adjust the angle and depth until the needle tip reaches the portal branch on the image, then inject. The stained volume is computed from this liver’s portal tree: each point of the liver belongs to the nearest portal branch visible on CT. It is an approximation: real portal territories do not follow the classic planes exactly 13.

Draw the transection line

Click the liver surface to place diathermy marks, at least two; right-button drag turns the liver. The transection plane runs into the liver along your line of sight.

The panel computes for your cut: the closest distance to the tumour, the liver that remains, the vessels you would divide, and the remaining liver that, in this model, loses its portal inflow or its venous drainage. Below it, this patient’s operation as reconstructed by the authors.

Margin width matters less than one might think: in 557 patients a clear margin under 1 cm did not shorten survival 9. The percentage shown is the volume left of the measured liver, tumour included. The remnant thresholds used in practice refer to total liver volume: about 20% for a healthy liver, 30% after intensive chemotherapy, 40% in compensated cirrhosis; below them, portal vein embolisation is discussed 14.

The probe is yours

Every mode at once: transparent liver, the ultrasound slice in place, Doppler, labels, fluorescence, coverage and the transection line. The buttons below switch them on and off.