Today dawned bright and early for me. Immediately after the SuperBowl festivities, I started fasting for my annual check-up. Scheduling this event the morning after a major binge of junk food and alcohol was not my smartest move.
I arrived and the usual ceremonies occurred: signing consent, scanning the insurance card, and determining the body weight and vital signs. My doctor entered, and we went through the usual history and physical stuff, and finally ended up at the favorite part for all we female types, the pelvic exam. My doctor asked an interesting question during the pap smear: why are they instructed to rotate the sampling brush counter clockwise? This topic led to discussions about cervical cell growth; perhaps the cells had a right-left asymmetry that made the rotation of the sample crucial. I decided to find out for myself!
This screening test for cancer bears the name of its inventor, Georgios Papanikolaou (detailed discussion here). The basic idea seems simple; a swab placed at the cervix of the uterus collects cells that are smeared on a slide, stained, and examined for (pre)-cancerous changes. Routine use of the test in developed countries led to earlier detection of cervical cancer and markedly reduced mortality from the disease. Over the years, improvements have been made.
When I went to medical school, the cell-sampling device was a wooden spatula (D in image at right). One slightly elongated end entered the center of the cervix, and the shorter portion circled the opening as you twirled it. No mention of direction of collection occurred in my instructions many years ago.
In the 1980's a better collection device emerged, namely a cervical brush (E in the image). These bristly devices had more surface area than the spatula, and collected more cells. The brushes also got placed into liquid storage medium. Companies wrestled with the design, and ultimately came up with the broom (see A in image at right).
The Cervix or the Broom
Ultimately every question should have an answer. In this case, the counter clockwise instructions either had something to do with the cells of the cervix or the character of the broom.
Before you dismiss the cervix as the answer, remember that our bodies demonstrate left-right asymmetry. The heart leans left. The liver normally resides on the right. The gut has a left to right to left kind of flow.
But you can dismiss the cervix now, because this answer is the broom.
At left you see the largest image I could find of the SurePath broom. Turns out those bristles are not round but flattened on one side. Those precise counter-clockwise instructions (or whatever is specified by each manufacturer) allow the collecting side of the device to contact the cervical cells and pick the little suckers up.
So Now You Know
You now know what is happening under the sheet during a pelvic exam, and why it proceeds in a certain direction. Now, I plan to not think about Pap smears for another year or two.
Original sources may be viewed by clicking on the images.