This is an interesting case in that we were able to see nice longitudinal and cross-sections of the adult worm(s) within a blood vessel in the wall of the small intestine. The morphologic features, including intestine and (somewhat compressed) lateral cords are clearly visible. Foreign bodies surrounded by a granulomatous response are also seen in the tissue around the worm and most likely represent eggs or larvae. The fact that the patient had recently travelled to Costa Rica fits perfectly with the identification and supports our morphologic diagnosis. Here are some of the characteristic features:
Possible egg (arrow) within a granuloma. Note the abundant eosinophilic host response.
John B. suggested the possibility of a that there is a protist within this nematode. A great thought, although I believe what we are seeing are just the internal structures of A. costaricensis. Thank you all for the great comments!