Final answer:
Alveolar cysts caused by Echinococcus multilocularis typically present as irregularly shaped cysts with solid contents and may have calcified walls, differing from the fluid-filled cysts of Echinococcus granulosus.
Step-by-step explanation:
Echinococcus multilocularis is the parasite that causes alveolar echinococcosis, which is characterized by the formation of alveolar cysts in organs, most commonly the liver. The growth pattern of these cysts is similar to a malignant tumor, as they infiltrate and destroy surrounding tissues. In the gross picture of alveolar cysts caused by Echinococcus multilocularis, you typically see cysts with irregular shapes that resemble a cluster of grapes. These cysts can have solid contents due to the presence of numerous small vesicles and septations inside the cysts, and they can also become calcified over time. However, they do not present as multiple cysts filled with fluid like simple cysts, as seen with Echinococcus granulosus.