Can you ID paragonimus on canine CT?

Serial CT Findings of Paragonimus Infested Dogs and the Micro-CT Findings of the Worm Cysts

Chang Hyun Lee, MD,1,2 Jung-Gi Im, MD,1 Jin Mo Goo, MD,1 Hyun Ju Lee, MD,1 Sung-Tae Hong, MD,3 Cheng Hua Shen, MD,3 Doo Hyun Chung, MD,4 Kyu Ri Son, MD,1 Jung Min Chang, MD,1 and Hong Eo, MD1

Background
Paragonimiasis is a food-borne disease caused by lung flukes of the genus Paragonimus. Among its 45 species, P. westermani is the most widespread, infecting millions globally. The disease can mimic pulmonary tuberculosis or lung cancer radiologically. This study aimed to analyze serial CT findings in Paragonimus-infected dogs and investigate the microscopic structures of worm cysts using Micro-CT.

Methods
The study involved 15 dogs infected with P. westermani metacercariae. Serial contrast-enhanced CT scans were performed pre-infection, at day 10, and monthly for six months. Three dogs were sacrificed at 1, 3, and 6 months to correlate radiologic findings with pathology. Fixed lung specimens underwent high-resolution CT and Micro-CT scanning. Histopathological examinations were conducted on selected tissue samples.

Results
CT Findings: Initial findings at day 10 included pleural effusion and subpleural ground-glass opacities or linear opacities. Subpleural and peribronchial nodules appeared at day 30, with hydropneumothorax and air bubbles in the abdominal or chest walls. Cavitary changes and bronchial dilation became evident at day 60 and persisted until day 180, alongside lymphadenopathy.

Micro-CT Findings: Worm cysts had dilated interconnected tubular structures communicating with the cavity and adjacent bronchi. Cyst walls showed inflammatory cells and fibrosis, with granulomas and eggs present in surrounding tissues.
Pathological Findings: Hemorrhagic consolidations and adult worms within cysts were observed, with chronic inflammation evident around cysts.

Limitations
The study used a higher infection load than typical in human cases, potentially limiting direct applicability. Although findings provide insights into Paragonimus migration and cyst formation, they may not fully reflect human disease progression.

Conclusions
CT and Micro-CT findings elucidate the migratory stages of Paragonimus and the formation of worm cysts. Understanding these radiological patterns can help distinguish paragonimiasis from similar pulmonary conditions, potentially preventing misdiagnoses. The study highlights the value of Micro-CT in detailing cyst structure and its connections to airways.

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