This week's case was donated by Drs. Meredith Kavalier, Megan Shaughnessy, and David Cartwright. The patient has a history of treated urothelial cell carcinoma and remote travel to Asia. The cytopathologist was concerned by the presence of the following structures seen in a routine screening urine sample. How would you interpret these findings?
Tuesday, October 10, 2023
Answer to the Parasite Case of the Week 728: Not a parasite egg; uric acid crystals.
Uric acid crystals are a very convincing mimic of Schistosoma haematobium eggs! They are both found in urine, and they both have a terminal spine. However, there are a number of features that can be used to easily differentiate the two:
- Uric acid crystals vary in size and shape and are often much smaller than S. haematobium eggs. In contrast, S. haematobium eggs are regular in size and shape, and quite large (approximately 150 micrometers in length).
- Uric acid crystals commonly have points on both ends instead of the single 'pinched-off' spine of S. haematobium eggs. They can also have lateral points or take on other shapes.
- There are no internal parasite structures (i.e., miracidium) in uric acid crystals
- Finally, crystals often fracture and break, and may have irregular contours.