But it wasn't a piece of coral, or even something doctors had removed themselves - it was an intact, perfectly formed blood clot cast that a patient had spat up after "an extreme bout of coughing".
The 36-year old man was being treated for a serious heart condition, according to a new report of the case, published November 29 in The New England Journal of Medicine.
"A 36-year-old man was admitted to the ICU with an acute exacerbation of chronic heart failure".
A 2005 report in the European Journal of Cardio-Thoracic Surgery refers to a similar case where a pregnant woman coughed up a less-extensive blood clot cast also in the shape of her bronchial tree.
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Wieselthaler told the publication that it was the man's blood medication that made the clot rubbery and able to survive the trip out his airway instead of breaking up, since blood clots are typically hard plugs of blood.
"We were astonished", Dr Wieselthaler said.
However, anticoagulants can cause problems if a breach occurs in the blood-vessel network, which happened in this extraordinary case; blood broke out of the patient's pulmonary network into his lower right lung.
It occurred after the patient had been coughing up much smaller clots for days.
Sadly, despite the best efforts of the medical team, the man died a week after coughing up the bronchial tube cast.
After coughing up the bronchial tree, doctors immediately intubated him and performed a bronchoscopy, but he later died from heart failure complications ('volume overload and poor cardiac output'), despite the placement of the ventricular assist device.