Dr Charles B.S. Tsang,
MBBS, M.Med(Surg), MS(Exp.Surg),FRCS(Ed), FRCS(Glasg), FAMS
Head and Senior Consultant Surgeon, Division of Colorectal Surgery,
University Surgical Cluster,
National University Health System, SINGAPORE
We use the following equipment:
1. BK Medical Profocus® scanner with a 2052 probe.
2. Karl Storz rigid sigmoidoscope with a length of 20 cm and inner diameter of 22 mm. 3. Suction equipment
4. Normal saline to irrigate rectum if necessary
5. Boiled water to fill rectal balloon
6. 100 cc syringe with a Luer lock to connect to water standoff fitted over shaft of 2052 probe
We currently use a 2052 probe from BK Medical. This is a probe with multi-frequency transducer and in built motor puller. The transducer has a focal length of 2-5 cm and a 90 degree scanning plane. When the probe is rotated at 4-6 cycles per second, a radial scan of the rectum and surrounding structures is obtained. Frequencies available are 6, 9, 12 Mhz and 10, 13, 16 Mhz. The transducer can be pulled back manually or automatically in the situation of a 3D acquisition scan. For endorectal ultrasound, a special balloon is used to drape over the shaft of the 2052 probe and over the water standoff. This is secured at the base with a series of rubber band. Holding the probe with the balloon in the most dependent position, the balloon is filled with 150-200 cc of water via the water standoff. Through a process of repeated aspiration and filling, any air bubbles in the system are aspirated through the syringe attached to the water standoff and expelled. Some water-soluble gel is placed on the exterior of the balloon and the probe is then ready for insertion.
The patient bowels are prepared with two Fleet enemas® 30 minutes apart starting one hour before the examination. The procedure is explained to the patient and a verbal consent is obtained. Demographic data of the patient is entered into the ultrasound computer. The examination proceeds with the patient in the left lateral position.
A digital examination is performed to evaluate location, size, morphology and fixity of the rectal lesion. A rigid sigmoidoscopy is then performed. Any residual stool fluid is removed using suction equipment as it can interfere with the image. The tumor is visualized to determine its size, circumferential involvement and distance from the anal verge. The rigid sigmoidoscope is advanced past the tumor as high up in the rectum to ensure complete imaging of the tumor and mesorectum. This is because tumor depth of invasion can vary at different portions of the growth. It is also important to visualize the mesorectum proximal to the tumor to look for enlarged metastatic lymph nodes. Whilst the endoprobe can be inserted blindly to visualize low and small rectal lesions, it is uncomfortable and extremely dangerous for mid and upper rectal lesions. Hence the use of a rigid sigmoidoscope to facilitate placement of the endosonic probe above the proximal limit of the tumor.
With the sigmoidoscope placed above the tumor, the endosonic probe is gently introduced through it. The probe is advanced thru the sigmoidoscope until resistance is felt. The sigmoidoscope is then pulled back over the probe thus exposing the transducer 6cm beyond the end of the sigmoidoscope. The balloon is then instilled with approximately 100-150 cc of water, the smallest volume required to achieve contact of the water balloon with the rectal wall. The probe is then activated by pressing a button at the proximal end or on the main console.
With the patient lying in the left lateral position and the single start/stop button on the base of the 2052 probe facing the operator , the anterior aspect of the rectum will be shown on the superior aspect of the monitor screen. The right lateral aspect of the rectum will be on the left side of the screen. Likewise, the left lateral aspect of the...