Hello Carolyn, Thanks for posting on HCM, If the symptoms of your daughter s gastroenteritis were abrupt and with no fever then there is the likely possibility that she suffered or is suffering of food poisoning (intoxication from eating a contaminated food). The liver cyst was surely discovered by chance from the CAT scan and is will rarely be accused as the cause of her gastroenteritis. Rarely, liver cysts may indicate a serious, underlying condition such as: - Polycystic liver disease, an inherited disorder - Echinococcus infection, a parasitic infection - Liver cancer If too worried biopsy might be required. I suggest her stools get analyzed for possible bacterial or fungal cause of the gastroenteritis. If that be the case, treatment with antibiotics will be required and oral rehydration therapy might also be necessary (depending on her state of dehydration). Thanks and hope this helps