Sunday, August 11, 2013

Answer to Case 269

Answer:  Trichuris trichiura, (a.k.a. Whipworm), adult female.

The overall shape of the worm (resembling a whip) is diagnostic, as are the outlines of the characteristic eggs seen within the worm (compare to the egg that I superimposed on the image):

With a little imagination, you can see where the bipolar plugs of the intrauterine eggs are. The presence of eggs lets us know that this is a female.  Also, the tail (the thicker portion of the worm) is not curled; males have curled tails while females have straight tails.

So the answer to the bonus question (as alluded to above) is that the end shown below is the head:

As Heidi points out, this is opposite to what most people would think.  To help my students understand this, I use the following explanation:  

First, think of how the worm lives inside the human intestinal tract:  it embeds one end into the colon wall while the rest hangs in the lumen.  If you had to choose one end of the worm to embed into the colon, it would make sense to choose the thin needle-like end and not that fat blunt end. Hence, the thin end is embedded and the thick end hangs free.

OK, so that answers the question of how the worm is oriented in the intestine, but which end is which?
To answer that, think about egg production:

The female whipworm produces hundreds of eggs which need to be excreted in stool in order to continue the worm's lifecycle.  Therefore, it makes sense that the part of the worm containing the uterus packed full of eggs hangs in the lumen, where eggs can easily be deposited with the stool.  The head is the thin part that is embedded into the colon wall.

So it all makes sense after all!

And now our poem from the talented Blaine Mathison 
 (for Henry B. and all other Case of the Week Viewers):

"Colonoscopy?!?!" Henry was about to flip!
For he certainly didn't want to make that trip
So many horrors on his mind
of what the doc might find,
such as Trichuris flailing around like a whip!

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