人芽囊原蟲(Blastocystis hominis)是常見於人類胃腸道的單細胞寄生蟲。它的致病性仍未知。一位78歲女性，為腎臟癌合併肺部轉移，抱怨右上腹疼痛。腹部超音波及電腦斷層顯示肝臟右葉一個巨大囊腫，囊液檢測顯示許多人芽囊原蟲。之後接受首次metronidazole 14天療程。一年後，因囊腫引流導致囊內出血及橫膈下腔血腫，接受手術切除肝臟囊腫。囊液檢測再次顯示許多人芽囊原蟲。在metronidazole 20天療程後的45天糞便檢查呈現陰性。據我們所知，這是第一個肝臟囊腫感染人芽囊原蟲的案例報告。對於此受感染肝臟囊腫足夠抗生素療程的確認及其引流或切除的必要性，仍待未來進一步的研究探討。

Blastocystis hominis is a unicellular parasitic microorganism commonly found in the gastrointestinal tracts of humans. Its pathogenicity remains uncertain. A 78-year-old female patient with renal cell carcinoma and lung metastasis complained of right upper quadrant pain. Abdominal ultrasonography and computed tomography scan showed a huge liver cyst in which a plethora of Blastocystis hominis was identified through cyst fluid analysis. The patient then received her first course of metronidazole treatment for 14 days. One year later, she underwent resection of the liver cyst due to internal bleeding and subphrenic hematoma induced by cyst drainage procedure. Cyst fluid analysis again revealed a profusion of Blastocystis hominis. Stool examination showed a negative result 45 days after a course of metronidazole for 20 days. To the best of our knowledge, this is the first case of the presence of Blastocystis hominis in liver cyst. However, further studies are required to determine the adequate course of antibiotic treatment and necessity of drainage or resection of the infected liver cyst.