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Because of a dark spot on her lung X-ray, a patient is referred to the Medical Center - University of Freiburg. Lung cancer is suspected. But the specialists find a phenomenon that is actually only known in dogs.

Due to a persistent cough, 62-year-old Paula T.* goes to the doctor. But on the X-ray he discovers an unusual alteration deep down in the lungs, as big as a one-Euro coin. "This type of shading may indicate a lung tumor and should be clarified by an expert as soon as possible," says Professor Dr. Bernward Passlick, Medical Director of the Department of Thoracic Surgery at the Medical Center - University of Freiburg. He heads the hospital's Lung Cancer Center, where more than 1,300 patients are treated each year.

Because of this suspicion, Paula T. is referred to the Medical Center - University of Freiburg. She is in good shape physically, and the blood test also shows no evidence of cancer. But in computed tomography, the doctors see a definite change in the tissue. "The area was clearly delimited from the rest of the lung tissue, as is often the case with tumors," says physician Konstantin Grapatsas of the Department of Thoracic Surgery at the Medical Center - University of Freiburg. So he treats the patient.

Lung surgery: Minimally invasive and very gentle

Although the suspicious tissue lies deep in the lowest lung lobe, the Freiburg thoracic surgeons decide on a minimally invasive procedure. During video-assisted thorascopic surgery (VATS), the diseased tissue is removed via three small orifices. Using a tiny, high-resolution camera, the surgeons control every step and cut. "Minimally invasive lung resections are more demanding technically than standard open surgeries. For these, the team has to be well-trained and -rehearsed," says Professor Passlick. "But they bring significant benefits for the patient: The procedure is less painful, patients recover faster, and they are usually functional again after only a short time."

In a 30-minute procedure, the thoracic surgeons completely remove the suspicious tissue from Paula T.'s lung. While the operation is still in progress, it is examined by a pathologist. The good news: It is not a tumor. While the patient can already leave the hospital in good health three days later, the thoracic surgeons and pathologists of the Medical Center - University of Freiburg continue to puzzle over the case. Finally, in a detailed analysis of the tissue sections, they discover unusual round structures inside a blood vessel.

A worm goes astray the lungs - only 400 cases worldwide

When the pathologists find the circular shapes, a parasite is suspected. In the end, the doctors can identify the exact worm species: Dirofilaria immitis, also known as the "heartworm", had wandered into the lung tissue. "Lung infestations by this type of worm are extremely rare. Less than 400 cases have been reported worldwide," says Professor Passlick. Those affected report shortness of breath, cold sweats and bloody coughs.

This mosquito-borne roundworm actually targets dogs. They can die from an infection. But in humans, the parasite dies quite quickly. The immune system encapsulates the intruder. This encasing of the worm was seen on Paula T's X-ray.

In the past, the parasite has mainly been reported in dogs in southern Europe. "It seems, however, that the worm has increasingly spread to northern Europe in recent years," says Professor Passlick. To what extent this proliferation endangers people is not yet clear, since the transmission path to humans is still unknown. For those affected, it is above all essential that they do not mistakenly receive cancer treatment. Then they can heal quickly - like Paula T.

* Name changed by the editor