LUS - How to do
On this page a description of the laparoscopic ultrasound procedure for different indcations are listed. The procedure might be different from center to center, but are meant as a guideline for new users of LUS. For illustrations and hints for better staging GoTo the LUS Atlas
GoTO: Esophageal Cancer Gastric Cancer Pancreatic Cancer BileDuct
Before
performing LUS diagnostic staging laparoscopy without dissection should be
performed on each patient . Two standard trocar sites can be used.For the laparoscopic camera, a 10-mm trocar is placed just to the left of
the umbilicus in order to be able extend the incision in case of a laparotomy .
An additional trocar is placed to the left and cranial to the umbilicus. This
was used for the LUS procedure.(See picture
of trocard placement.)
After the diagnostic laparoscopy is performed, the LUS probe is introduced. The LUS procedure should followed a pre-defined examination scheme in order to cover all relevant intra-abdominal areas. The peritoneal fluid at the organs is able to establish a sufficient acoustic window for the transducer. Only the anterior surface is scanned because the penetration of the ultrasound is sufficient to visualize the entire depth of the liver. Hepatic metastases can be seen as dark hypo-echoic or light hyperechoic spots in the tissue.
The abdominal lymph node stations
are examined and registered.
The malignant lymph nodes are finally assessed, and the tumor is visualized, if possible, in order to assess the T-stage. Only distal esophageal and cardiac tumors can be assessed with LUS. Tumors placed approximately 5-cm. from the diaphragm are not visualized. The different layers in the esophagus can be considered corresponding with the ultrasonic outlined layers. The luminal hyperechoic layer corresponding with mucosa/submucosa, the second hypo-echoic layer with muscularis propria, and the third hyperechoic layer with adventitia. The LUS of cardiac and esophageal tumors are difficult. The scanning angle to the tumor are often oblique and the lumen of the esophagus is difficult to visualize due to the lack of intra-esophageal fluid. However a nasogastric tube can in some cases be helpful. The probe have to bend 90 degrees backwards in order to scan the tumor, and in this position, the lack of flexibility complicates the interpretation of the tumor.
The T stage is assessed with the probe placed at the edge of the left
liver lobe, using the liver as an acoustic window. If the tumor cannot be
visualized from this position, the probe is placed at the anterior surface of
the stomach. Large tumors with invasion through the lamina muscularis can easily
be assessed whereas small tumors and tumors located at the posterior wall need
intragastric water instillation. Approximately 500 cc of temperated water can be
instilled through a nasogastric tube. Removal of air in the stomach by suction
is essential before scanning. The scanning should be recorded for post-operative
evaluation.
LUS outline a five-layer wall in the stomach. These layers resembles the
layers outlined in EUS studies with similar ultrasound frequencies .
The layers were defined as;
A luminal hyper-echoic layer corresponding to mucosa.
A second hypo-echoic layer corresponding to muscularis mucosa.
A third hyper-echoic layer corresponding to submucosa.
A fourth hypo-echoic layer corresponding to muscularis propria.
A fifth hyper-echoic layer corresponding to serosa.
The N-stage is assessed using the criteria for malignancy and investigating the lymph node stations
Scanning for distant lymph node stations or liver metastases assess the M stage. If metastases are seen, biopsies should be taken, if possible, in order to confirm malignancy. Only a positive pathological confirmation of malignancy should be considered proof of M1 disease.
The pancreas is scanned using the stomach as an acoustic window. The
stomach should be compressed gently to remove air bubbles. The vessels are used
as landmarks for the anatomy, and the relation of the tumor to the portal vein,
superior mesenteric artery and vein and splenic vein and artery are carefully
examined. The head of pancreas is visualized by placing the probe at the
duodenum under slight compression. For tumors adjacent to the papilla of Vater,
water is instilled into the duodenum in order to facilitate the visualization of
small tumors. The pancreatic tumor is hypo-echoic and often poorly delineated.
Loss of a hyperechoic interface between the tumor and a vessel can be considered
as a sign of tumor ingrowth.
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