Biology of Disease

Computed axial tomography scanners were introduced into hospitals in the

UK in 1975. The technique uses X-rays to take sequential pictures of the body

from different directions. In practice, the patient may be required to drink a

contrast solution, or this may be administered intravenously, to enhance the

tissue contrast. The patient then lies still on a table that passes through the X-

ray machine, which rotates around the patient taking pictures of thin ‘slices’

of tissue. Computers then combine the images to produce three-dimensional

images or computed tomograms. Magnetic resonance imaging (MRI) and

positron emission tomography (PET), outlined in Chapter 18, may also be

used to visualize abnormal growths within the body and for determining the

extent of tumor growth. Ultrasound (Chapter 14) may be used to locate tumors

within the abdomen, including tumors of the liver and ovaries. However, in

order to determine whether the abnormal growth represents a cancer or a

benign lesion, it is essential to examine biopsies of the growth.

Biopsies and histology

Biopsy material may be obtained from a variety of sources in one of several

ways. Samples from solid tumors may be obtained by endoscopy, or during

surgical procedures involving local or general anesthesia. An endoscope is a

long thin flexible tube with a camera and light on the end. Depending on the

tumor, the endoscope is inserted into a body cavity and allows internal tissues

such as the GIT and the lungs to be viewed. Endoscopes also enable samples of

the suspect tissue to be removed without the need for surgery. One example of

the use of endoscopy is in bronchoscopy, which is used to obtain biopsies

of lung tissue in suspected cases of lung cancer (Figure 17.22;Section 17.8).

Needle biopsy allows small amounts of tissue to be obtained from a variety

of solid tissues. Samples of blood and bone marrow may be examined

to detect leukemias. Some solid tumors may cause the build up of fluid

containing cancer cells within the peritoneal cavity (Chapter 10), where

it is known as ascites fluid, or in the thorax, where a pleural effusion may

develop (Chapter 14). These fluids contain tumor cells in suspension and may

be examined histologically to confirm the presence of cancer cells. Finally,

some precancerous lesions may be detected by taking smears of tissue and

examining them histologically, as for example in the preparation of cervical

smears in order to detect precancerous lesions as outlined below.

Bronchoscope

(Flexible tube)

Bronchioles

Trachea

Figure 17.22Schematic to show a bronchoscopy.

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