A 55-year-old woman in Iran spent five months with abdominal pain, epigastric tenderness, and steady weight loss that accelerated over the final three. She had no fever, no jaundice, and no change in bowel habits. Microscopic examination of her stool found nothing at all: no worms, no eggs.
An ultrasound of the abdominal wall found something the stool test never would have. An ill-defined, echogenic mass measuring roughly 4.7 by 1.9 by 4.1 centimeters sat inside the muscle of her right upper quadrant, extending toward the navel. Surgeons excised it. Inside the muscle was an adult Fasciola hepatica, the common liver fluke, a parasite that is supposed to live in bile ducts.
The case appears in the Journal of Medical Case Reports, written by a team from Alborz University of Medical Sciences and Tehran University of Medical Sciences. The authors describe it as the first report of rectus abdominis fascioliasis from Iran to the best of their knowledge, and as one of the rarest forms of extrahepatic involvement recorded there.
Five Months of Pain and a Test That Kept Coming Back Clean
Her workup looked unremarkable on paper. Liver function tests and basic biochemistry were close to normal. Her erythrocyte sedimentation rate was mildly raised at 32 millimeters per hour, triglycerides sat at 330 milligrams per deciliter, and her eosinophils were elevated. Testing for hepatitis B surface antigen and hepatitis C antibody was non-reactive.
That combination is precisely the problem with ectopic parasitic disease. Stool microscopy, the standard screen for fluke infection, only works if the adult worm has reached the bile ducts and is laying eggs that exit through the intestine. A fluke lodged in abdominal wall muscle produces nothing to find.
An MRI showed an enlarged liver, roughly 220 millimeters in craniocaudal span, but no mass inside it and no fluid in the abdomen. The lesion that mattered was in the muscle, not the organ.
What the Surgeons Pulled Out of the Right Rectus Abdominis
The excised specimen measured about 6 by 5 by 2 centimeters and was attached to the right portion of the rectus abdominis. Histopathology showed parasitic myositis with abscess formation and a foreign body type granulomatous reaction, which is the immune system building a wall around something it cannot dissolve. There was no dysplasia and no evidence of malignancy.
The worm itself was leaf-shaped, with spines embedded in its outer surface and a ventral sucker near the front end, the classic morphology of an adult F. hepatica. A follow-up ELISA detected antibodies against excretory-secretory proteins of the adult fluke, confirming the identification serologically.
That serological confirmation arrived after the operation, not before it. The authors note she had gone to surgery for what was being treated as a muscle tumor, and the ELISA result reframed the specimen afterward. Antibodies against Fasciola typically appear two to four weeks after exposure, and the work the authors cite puts the test's sensitivity near 97 percent and specificity above 91 percent.
She was treated with triclabendazole at 10 milligrams per kilogram twice daily for two days after surgery. Over three months of follow-up, her eosinophilia resolved, repeat serology came back negative, and she reported no further complaints.
Why Flukes End Up Where They Do Not Belong
The normal route is well mapped. Larvae excyst in the duodenum, punch through the intestinal wall, cross the peritoneal cavity, tunnel through liver tissue, and settle in the bile ducts to mature and lay eggs. Occasionally, something goes wrong with the navigation.
A 2019 systematic review of human ectopic fascioliasis documented flukes turning up in the gastrointestinal tract, heart, blood vessels, pleural cavity, lymph nodes, eye, brain, and skeletal muscle. Three routes are proposed: spread through the bloodstream, spread through lymphatic vessels, or direct migration through adjacent tissue.
The authors argue this patient's fluke took the third route. There were no lesions inside the abdominal cavity containing the parasite, and no eggs in stool, blood, or lymphatic vessels, which they read as evidence the worm burrowed across from neighboring tissue rather than being carried there. That is their interpretation of a single case, not a demonstrated mechanism.
Muscle is not unheard of as a destination. Doctors in Korea removed an adult F. hepatica from the rectus abdominis of a 66-year-old woman who had been treated for a suspected liver abscess and confirmed the species by DNA sequencing.
Watercress, Wells, and Who Is Actually at Risk
People acquire fascioliasis by eating raw freshwater plants carrying infectious larvae, most often watercress, or by drinking contaminated water. The CDC notes that Fasciola occurs in over 70 countries on every continent except Antarctica, concentrated where sheep, cattle, and goats are raised. It does not spread person to person.
The scale is substantial. A global foodborne disease burden analysis cited by the authors puts the number of people currently infected somewhere between 2.4 and 17 million, with roughly 180 million more living at risk. Iran's northern regions are endemic, and a national review covering 1999 to 2019 put overall Fasciola prevalence in the country near 6 percent.
Muscular involvement remains among the rarest presentations reported anywhere. The practical takeaway the authors draw is narrow and aimed at clinicians: an unexplained subcutaneous or intramuscular nodule in someone who has traveled to or lived in an endemic area deserves Fasciola somewhere on the differential, even when the stool test is clean.
Key Questions Answered
What is Fasciola hepatica? A flat, leaf-shaped parasitic flatworm known as the common liver fluke. It normally infects the liver and bile ducts of humans and grazing animals.
Why did the stool test miss it? Stool microscopy detects eggs shed by adult flukes living in the bile ducts. A worm lodged in the abdominal wall muscle is not connected to that pathway and produces no eggs to find.
How do people get infected? Usually by eating raw freshwater plants such as watercress that carry infectious larvae, or by drinking contaminated water. It is not passed from person to person.
Was the woman cured? She had the mass surgically removed and was treated with triclabendazole. Over three months of follow-up, her eosinophilia resolved and repeat serology was negative.
How unusual is muscle involvement? Very. The authors describe it as one of the rarest forms of ectopic fascioliasis and the first such case they are aware of from Iran, though a similar case has been reported in Korea.
Should people in the United States be concerned? Fascioliasis is uncommon in the US, and this presentation is rarer still. Anyone with an unexplained lump and a history of travel to an endemic region should discuss it with a clinician.
