Answer to Case 562

Answer to Parasite Case of the Week 562: Likely anisakid, given the gross and microscopic appearance and position in the body. This also fits with the clinical history that I held back - this patient was an avid sushi lover!

From the gross image, you can tell that this is a roundworm, and that it appears to be embedded in the gastric mucosa:

You can also see that the caliber of the worm is similar throughout its length. That, as well as the location (stomach), make Trichuris trichiura unlikely. The longer length also allows us to rule out Enterobius vermicularis and the hookworms (which admittedly would also be unlikely in the stomach).

The microscopy is a bit harder to interpret, given that we only have a portion of the worm to examine. What we can make out, however, is the thick eosinophilic cuticle, tall coelomyarian musculature with multiple muscle cells (polymyarian), the intestinal tract that runs the length of the visible portion of the section, and the lack of reproductive structures, which are consistent with an L3 anisakid larva:

I believe that the netting like structure is a section through the muscle cells. We unfortunately can't see the lateral cords (best seen in cross-section) and additional features that would help us identify the anisakid to the genus level (e.g., cecum). This brings us to the conclusion that we always draw from this case, which is to send the worm to the microbiology lab and not the surgical pathology bench!

From Blaine:

Why are pathologists so quick to slice-and-dice

When a diagnosis would be much more precise

If they just left it intact

and the microbiologists have a whack

Alas now a diagnosis is a roll of the dice