GALLBLADDER CANCER AND BILE DUCT CANCER: DIAGNOSIS

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Diagnosis of Gallbladder and Bile Duct Cancer: An Overview

Computerized Axial Tomography (CAT) Scan

This is usually one of the best initial tests if you are worried about bile duct cancer and is considered the single most useful imaging technique. Since a CT scan visualizes all of the abdominal organs, it is also very useful in detecting any spread of the cancer to the liver or nearby lymph nodes. A CT is often performed to monitor patients after treatment to determine whether the cancer has recurred (typically as a "metastasis" to the liver) or is changing in size.There are different variations of the CT technique:

Conventional CT

(also called dynamic incremental scanning), is generated by directing an X-ray beam at several different angles and levels of the abdomen. Contrast dye, given to the patient orally and/or intravenously, helps to make the organs visible by appearing white on the X-ray films. A computer processes the X-ray information and produces the CT images, usually as 1/2-inch cross-sectional slices of the abdomen. Exquisitely detailed three-dimensional images can now be produced by using the most recently developed spiral CT scanners with advanced image processing methods.

Using this method, once the patient is positioned, the X-ray beam is turned on for approximately 1-2 seconds and then turned off. The table is then moved to the next position or increment and the X-ray is turned on again. Because this method is relatively slow, the timing may not coincide with when the dye is optimal for imaging. The resulting image may not be adequate.

Dual Phase CT

accounts for the different optimal scanning times for the pancreas and the liver. It is essentially two conventional CT scans synchronized with the optimal time for the dye.

Spiral CT

(also called helical) is the most recently developed and accurate method. Unlike the conventional CT, during the spiral CT the X-ray beam remains on continuously and rotates around the patient as the patient is moved through. This is a much more efficient technique that reduces the scanning time of the entire abdomen from approximately two minutes using the conventional CT to 20-30 seconds using the spiral. The resulting images are three-dimensional rather than the two-dimensional images created with conventional techniques.

Accuracy:

• The primary limitation of CT scanning is its resolution, approximately 1 centimeter. A cancer smaller than this cannot be easily detected using this technique. However, recently developed scanners such as "helical" and "spiral" CT scanners are able to detect smaller masses. (see below)

• Duration of scan vs. duration of dye- The optimal scanning time lasts for about 20 seconds. If the scanning proceeds slowly, as with conventional CT, the dye can sometimes wear off before the scanning is complete.

• The optimal time to image the bile duct after intravenous injection of the dye is not the same as for the liver. This can account for some inaccuracies with conventional CT.

Results:

Small fluid collections may be seen in the abdominal cavity through CT imaging. This may indicate the presence of metastatic disease.

Occasionally, the bile duct appears thickened on a CT but shows no other visible abnormalities. This is also cause for concern. If the patient has pre-existing primary sclerosing cholangitis, it can be difficult to determine by imaging alone whether cancer is also present.

A mass detected in the bile ducts is not necessarily a cancer, so imaging is usually followed up with a biopsy. During this procedure a tissue sample is obtained and tested to confirm a diagnosis of bile duct cancer.

Risks :

• The level of radiation received during a CT scan is modest. Apart from the minute risk (much less than 1% of patients) of an allergic reaction to the contrast dye, a CT scan is without complication. It is always advisable to inform your doctor of any allergies you have.

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