[A human case of pulmonary dirofilariasis suspected to be lung cancer]

A 50-year-old man in Kitakyushu City visited a hospital for evaluation of an opacity in a routine chest X-ray film. After examinations by bronchoscopy and chest roentgenography, a clear coin lesion was found in the middle lobe of the right lung and was suspected to be a lung cancer. A right thoracotomy was performed to remove it. The lesion (10.6 X 9.8 mm) was a well-defined ellipsoid granuloma due to a foreign body with a central zone of necrosis surrounded entirely by a fibrous wall. In a cross section of the dissected granuloma two degenerated worm-like structures were revealed. The sections of the worm (216-240 X 296 mu m at the greatest diameter) had at least a 3-layered cuticle and prominent internal longitudinal cuticular ridges but no external cuticular ridges. The lateral chords were as high as the muscle layer which consisted of abundant somatic muscle (more than 30 muscle cells/quadrant). Judging from these morphological characteristics, the pulmonary granulomatosis was diagnosed to be due to an immature dog heartworm, Dirofilaria immitis. This identification was further supported by results from immunological methods. The present case is the 56th human case of dirofilariasis (the 39th as a pulmonary case only) in Japan.