The toothpick perforated her gullet and lodged in a lobe of her liver.
The patient, who is not being identified, has now recovered after having the toothpick removed.
Such cases are rare, but the report, published by the British Medical Journal, says doctors need to look out for signs of "foreign bodies", as detection can be challenging.
It is one of thousands of cases being logged at BMJ Case Reports, an online resource to allow doctors to share information about the treatment of difficult or unusual cases.
Swallowing foreign bodies is relatively common, particularly among children.
But the subsequent development of a liver abscess was rare, the authors, from Bristol's Frenchay Hospital and Halifax University in Canada, said.
The condition has mostly been associated with inadvertently swallowing pins, nails, fish and chicken bones, rather than toothpicks.
But the authors said toothpicks could be "difficult to deal with effectively, because they don't show up on conventional X-rays and symptoms are often non-specific and remote".