Chest CT features of North American paragonimiasis

Abstract

Objective: The purpose of this study was to characterize the chest CT findings of North American paragonimiasis due to Paragonimus kellicotti in the largest (to our knowledge) case series reported to date and to compare the findings with those reported for paragonimiasis infections in other regions.

Materials and methods: A retrospective review was performed of chest CT examinations of eight patients with North American paragonimiasis treated at our institution between 2006 and 2010. Findings were characterized by site of involvement, including lungs and pleura, heart and pericardium, lymph nodes, and upper abdomen.

Results: The most common chest CT findings in this case series were pleural effusions and internal mammary and cardiophrenic lymphadenopathy. Pulmonary parenchymal findings included peripheral lung nodules of 1-3.5 cm in size with surrounding ground-glass opacity; many nodules had a linear track to the pleural surface that may correspond to the worm's burrow tunnel. Pericardial involvement (5/8 patients) and omental inflammation (5/7 patients), which are uncommon in Asian paragonimiasis, were common in this series.

Conclusion: Pleural and pulmonary features of North American paragonimiasis are generally similar to those reported from Asia. The presence of a track between a pulmonary nodule and the pleura may help distinguish paragonimiasis from mimickers, including chronic eosinophilic pneumonia, tuberculosis, fungal infection, or malignancy. Pericarditis, lymphadenopathy, and omental inflammation were more common in our series than in reports on paragonimiasis from other regions. These differences may be related to the infecting parasite species or to the fact that radiologic examinations in the present series were performed relatively early in the course of infection.

Fig. 1

20-year-old man with North American paragonimiasis. Axial contrast-enhanced CT image through lower thorax shows bilateral pleural effusions (straight arrow) with pleural thickening and increased extrapleural fat in left hemithorax, indicative of chronic inflammation. Mild pericardial thickening (arrowheads) and anterior diaphragmatic lymphadenopathy (curved arrow) are also present.

Fig. 2. Three patients with North American paragonimiasis and nodules connected to visceral pleura by linear tracks

A and B, 30-year-old man. Oblique-axial CT image (A) shows ill-defined nodule (arrow) in left upper lobe with surrounding ground-glass opacification. Nodule is connected to visceral pleura anteriorly by small linear track (arrowhead). Also note bilateral pleural effusions. Oblique-axial unenhanced CT image (B) shows thin linear track to pleura (arrowhead) and ill-defined nodule (straight arrow), which is intermediate attenuation to fluid and muscle. Also note bilateral pleural effusions (curved arrow) with thickening of mediastinal pleura in left hemithorax. C and D, 31-year-old man. Axial CT (C) shows lobulated nodule (arrow) in apical segment of right upper lobe with surrounding ground-glass opacification. Thin linear track (arrowhead) connects nodule to visceral pleural surface. Axial contrast-enhanced CT (D) more clearly defines linear track (arrowhead) extending to visceral pleura and intermediate attenuation of lobulated right upper lobe nodule (arrow). Also note right pleural effusion and high right paratracheal lymph node. E and F, 22-year-old man. Oblique-axial CT image (E) shows lobulated left upper lobe nodule (arrow) and areas of surrounding ground-glass opacification. Nodule is connected to visceral pleura by curvilinear track (arrowhead). Oblique-axial contrast-enhanced CT (F) shows that nodule (arrow) has lobulated contour and heterogeneous attenuation, and linear track (arrowhead) connecting it to pleural surface is faintly visible. Small left pleural effusion was present (not shown).

Fig. 3. Two patients with North American paragonimiasis and peripheral nodules abutting visceral pleura

A, 28-year-old man. Axial contrast-enhanced CT shows peripheral nodule (arrowhead) in apical segment of right upper lobe, abutting visceral pleura. Note large halo of ground-glass attenuation and posteriorly layering right pleural effusion. B, 10-year-old boy. Axial contrast-enhanced CT shows peripheral nodule (arrowhead) abutting visceral pleural in apicoposterior segment of left upper lobe. Note moderate left pleural effusion.

Fig. 4. Two patients with North American paragonimiasis and isolated linear tracks. (Courtesy of Graham WK, St. Frances Medical Center, Cape Girardeau, MO)

A, 32-year-old man. Axial contrast-enhanced CT shows isolated linear track (arrowhead) in anterior segment of left upper lobe extending from anterior pleural surface. Note subtle ground-glass attenuation surrounding this track. Patient had bilateral lung involvement, including multiple tracks with nodules in right lung (not shown) and right hydropneumothorax. B, 26-year-old woman. Oblique coronal multiplanar reformation of contrast-enhanced CT shows long linear track (arrowheads) in left upper lobe emanating from visceral pleural at left lung apex. Track was approximately 5.5 cm long as it meandered toward left hilum. Note ground-glass attenuation surrounding portions of this track.

Fig. 5. Two patients with pericardial involvement of North American paragonimiasis

A, 10-year-old boy. Axial contrast-enhanced CT scan through heart shows moderate-sized pericardial effusion (arrows) with pericardial thickening and enhancement. Echocardiography (not shown) revealed increased echogenicity within fluid, suggestive of exudative effusion. B, 32-year-old man. Axial contrast-enhanced CT shows mild pericardial thickening (arrowheads). Patient also had bilateral pleural effusions and pleural thickening (arrows).

Fig. 6

28-year-old man with North American paragonimiasis. Axial contrast-enhanced CT scan through midthorax shows bilateral internal mammary lymphadenopathy (arrowheads), typical finding in our series of patients. Also note right pleural effusion and pericardial effusion tracking into superior pericardial recess.

Fig. 7

22-year-old man with North American paragonimiasis. Axial contrast-enhanced CT scan at soft-tissue windows shows extensive inflammation of greater omentum (arrowheads). Also note areas of peritoneal thickening and enhancement (arrow). Patient also had small volume of perihepatic ascites (not shown).

Fig. 8. Life cycle and intermediate host of Paragonimus kellicotti

A, Graph illustrates life cycle of P. kellicotti. Reprinted from Centers for Disease Control and Prevention Web site (www.dpd.cdc.gov/dpdx/HTML/ImageLibrary/Paragonimiasis_il.htm). B, Photograph of golden crayfish (Orconectes luteus), one of several crayfish species that serves as intermediate host for P. kellicotti. (Courtesy of Fischer P, Washington University School of Medicine, St. Louis, MO)