Answer to Case 462

Answer: Echinococcus sp. protoscoleces, free hooklets and laminated layer. The thick laminated layer is consistent with E. granulosus although the findings would need to be correlated with the clinical and radiologic findings.

This case generated a lot of great comments and discussion! Some of the main features shown in these beautiful photographs by Idzi Potters are the calcareous corpuscles (found in all cestode larvae and adults), protoscoleces with internalized hooklets, free hooklets, and the laminated layer of the cyst wall. The laminated layer is the outer-most layer of the parasite-derived cyst, and is usually surrounded externally by a layer of fibrotic host tissue. Just internal to the laminated layer is the germinal membrane (not easily seen in this case) from which the protoscoleces arise.

The protoscoleces contain an internal ring of hooklets. If they are ingested by a definitive canid host, then the head (scolex) will evert to expose the hooklets; these then aid in attachment to the intestinal lining.

Over time the protoscoleces will degenerate, releasing free hooklets into the cyst fluid. Depending on the state of the cyst, free hooklets may be the only identifiable structures seen. The hard hooklets (both free and within protoscoleces) give a 'gritty' consistency to the aspirated cyst fluid; hence the term "hydatid sand".