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DOI:10.2214/AJR.05.1416
AJR 2006; 187:W622-W629
© American Roentgen Ray Society

Original Research

Hepatic Visceral Larva Migrans of Toxocara canis: CT and Sonographic Findings

Samuel Chang1, Jae Hoon Lim1, Dongil Choi1, Cheol Keun Park2, Nam-Hee Kwon3, Seung-Yull Cho4 and Dong-Chull Choi3

1 Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon-dong, Kangnam-ku, Seoul, South Korea 135-230.
2 Department of Pathology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea 135-230.
3 Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea 135-230.
4 Department of Parasitology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea 135-230.

Received August 14, 2005; accepted after revision November 3, 2005.

 
Address correspondence to D.-C. Choi (dcchoi{at}smc.samsung.co.kr).

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Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
OBJECTIVE. The aim of this study was to describe the CT and sonographic findings of hepatic visceral larva migrans of Toxocara canis.

MATERIALS AND METHODS. Fifty-four patients (44 men, 10 women; age range, 30-80 years; mean age, 53 years) with serologically confirmed visceral larva migrans of Toxocara canis underwent evaluation of the liver with CT (n = 25), sonography (n = 48), or both. Two radiologists used consensus for retrospective evaluation of CT and sonographic findings. Correlation between the presence and severity of hepatic abnormalities on images and the degree of peripheral eosinophilia was assessed.

RESULTS. Seventeen (68%) of 25 patients who underwent CT had single or multiple ill-defined, oval or elongated, small, low-attenuating lesions in the liver. Eighteen (38%) of 48 patients who underwent sonography had single or multiple small, poorly defined, oval or elongated, hypoechoic scattered focal lesions in the liver. In the 19 patients who underwent both CT and sonography, the two techniques had no significant difference in rate of detection of hepatic lesions (p = 0.375, McNemar test). The lesion numbers on CT and sonography showed excellent linear correlation (r = 0.844, p = 0.001) by Pearson's correlation test. An independent samples t test showed that eosinophil count and percentage in the peripheral blood were significantly higher in patients with hepatic lesions on CT and sonography than in patients without lesions.

CONCLUSION. CT and sonographic findings of hepatic visceral larva migrans of T. canis are multiple, ill-defined, oval or elongated, small, nodular lesions scattered in the liver parenchyma. The presence of hepatic lesions on images was associated with higher peripheral eosinophil count and percentage.

Keywords: CT • infectious diseases • liver • sonography


Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
The term visceral larva migrans (VLM) is used to describe the migration of second-stage larvae of nematodes through the tissue of human viscera [1, 2]. Toxocara canis is the most common etiologic agent, although Toxocara cati, Baylisascaris procyonis, Capillaria hepatica [3], Ascaris suum [4] and some Ancylostoma species [5] have been reported to cause the disease. Humans are infected by T. canis by ingestion of infective eggs from soil or of encapsulated larvae in the uncooked tissues of a paratenic animal host [5]. The larvae are liberated in the intestine, burrow into the intestinal wall, enter the portal flow, and reach the liver, where they may stay or from where they may continue to be distributed to other tissues [6]. In humans, the larvae are deposited in the liver, lungs, eye, heart, and brain. The living or dead larvae form abscesses or granulomas, which can cause serious complications such as hepatomegaly, endophthalmitis, and neurologic disturbances [5]. A specific diagnosis is made when the larvae are identified in tissue sections or with serologic testing [7, 8]. The role of imaging in the diagnosis of hepatic VLM of T. canis has not been well established.

VLM appears to have a worldwide distribution and has been reported in the United States, Great Britain, continental Europe, Egypt, West Africa, South Africa, Iran, Australia, India, China, Taiwan, Japan, and Brazil [6, 8-12]. The rate of seropositive results is 5-40% with enzyme-linked immunosorbent assay (ELISA) with T. canis excretory/secretory antigen from the general population or patient groups [13-15]. There have been series and case reports of VLM [3, 4, 6, 8, 10-12, 16-18], and the radiologic findings have been described briefly in several case reports [4, 6, 10, 12, 19-21]. To our knowledge, there has been no large-series study of the imaging features of hepatic VLM of T. canis. The purpose of this study was to describe the CT and sonographic findings of a systematic retrospective analysis of the cases of a relatively large number of patients with serologically proven hepatic VLM of T. canis.


Figure 1
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  		Fig. 1A —44-year-old man with hepatic visceral larva migrans of Toxocara canis. Transverse contrast-enhanced CT scan obtained at arterial phase shows faint, rim-enhancing lesion (arrow) in Couinaud segment VII of liver.

 


Figure 2
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  		Fig. 1B —44-year-old man with hepatic visceral larva migrans of Toxocara canis. CT scan obtained at portal venous phase shows multiple small, ill-defined, oval or elongated, low-attenuating lesions scattered throughout liver.

 


Figure 3
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  		Fig. 1C —44-year-old man with hepatic visceral larva migrans of Toxocara canis. CT scan at equilibrium phase shows barely visible lesions.

 


Figure 4
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  		Fig. 1D —44-year-old man with hepatic visceral larva migrans of Toxocara canis. Oblique subcostal sonogram of right lobe of liver shows multiple, small, oval or elongated, hypoechoic lesions (arrows) with indistinct margins.

 

Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Patient Selection
Our institutional review board did not require its approval or patients' informed consent for this retrospective study. During the period October 2001 to January 2005, 103 patients came to the outpatient department of medicine of our institution with hypereosinophilia in peripheral blood (> 500 cells/µL) and were enrolled in the hypereosinophilia registry. Thirty-three patients were excluded because of following diagnoses: Paragonimus westermani and Clonorchis sinensis infection according to positive results of parasite ELISA or stool examinations in 18 cases, bronchial asthma in two cases, and allergic rhinitis according to positive results of methacholine provocation tests and mild eosinophilia (< 1,500 cells/µL) in one case, drug reaction according to positive history of drug ingestion and spontaneous resolution after cessation of drug ingestion in one case, other etiologic factors in four cases, and idiopathic factors in seven cases.

The diagnosis of T. canis infection was made in 70 cases and was based on ELISA results. The medical records and laboratory data were reviewed, and demographic and clinical data were collected by a physician. Twenty-eight (40%) of the 70 patients reported symptoms such as cough (n = 10), itching (n = 4), weakness (n = 2), myalgia (n = 3), and fever (n = 1), but there were no symptoms or signs suggesting the possibility of a specific disease. Forty-two (60%) of the 70 patients had a history of ingestion of uncooked bovine liver. Six (9%) of the 70 patients had underlying malignant disease: stomach cancer (n = 3), renal cell carcinoma (n = 1), malignant melanoma (n = 1), and prostate cancer (n = 1). All of these patients were tumor free when they underwent CT or sonography because of T. canis infection. No patient had hepatic cirrhosis. Among the 70 patients, 19 underwent both CT and sonography, six underwent CT only, and 29 underwent sonography only. Among the 19 patients who underwent both CT and sonography, the median time interval between CT and sonography was 12 days (mean, 25.7 days; SD, 34.1 days; range, 0-120 days). Sixteen patients who did not undergo imaging studies were excluded. Thus 54 patients (44 men, 10 women; age range, 30-80 years; mean age, 53 years) formed the basis of the study. Blood tests and imaging studies, primarily CT when both CT and sonography were available, were performed on the same day for 30 patients and within 66 days for 24 patients (mean, 5.2 days; SD, 12.5 days). The eosinophil count and percentage of eosinophils in the peripheral blood at imaging ranged from 0 to 23,540/µL (mean, 2,870/µL; SD, 4,466/µL) and 0 to 88.0% (mean, 21.9%; SD, 18.5%). Sonographically guided liver biopsy performed on seven patients disclosed focal eosinophilic infiltration (n = 1) or eosinophilic abscess (n = 6) in the liver parenchyma. In the department of medicine of our institution, the indications for therapy for hepatic VLM of T. canis are hepatic dysfunction or infection of another major organ. Twelve patients were treated with a steroid only (n = 6), albendazole combined with prednisolone (n = 4), or praziquantel (n = 2).

ELISA
An ELISA kit (Bordier Affinity Products) was used for the diagnosis of human toxocariasis. This assay is used to detect human IgG antibodies to Toxocara excretory/secretory antigens. This kit has been reported to have a sensitivity of 91% and a specificity of 86% [22]. The titers for positive results varied according to the daily reference control. Although some cross reaction occurs in other types of human helminthiasis, such as trichinosis, fascioliasis, and strongyloidosis, the titers in these types of helminthiasis are lower than those in positive control serum of patients with T. canis infection [22].

Imaging Technique
CT—The CT techniques were not standardized because of the relatively long span of the study and the rapid development of CT scanners. CT was performed with one of four helical CT scanners (HiSpeed, LightSpeed QX/i, LightSpeed Ultra, or LightSpeed 16; GE Healthcare). Unenhanced scans were obtained with 5- to 7.5-mm reconstruction intervals and slice thickness. Contrast-enhanced CT scans were obtained after injection of 120 mL of nonionic iodinated contrast material (iopamidol, Iopamiro 300, Bracco) at a rate of 3-4 mL/s through an antecubital vein with 2.5- to 7.5-mm reconstruction intervals and slice thickness. Arterial, portal venous, and equilibrium phase scans were obtained 30, 70, and 180 seconds, respectively, after the start of injection of contrast material. Four patients underwent unenhanced, arterial, portal venous, and equilibrium phase scanning; seven patients underwent arterial, portal venous, and equilibrium phase scanning; two patients underwent unenhanced, arterial, and portal venous phase scanning; and 12 patients underwent routine abdominal CT in the portal venous phase only. Thus all patients underwent portal venous phase imaging.

Sonography—Routine transabdominal sonographic examination of the upper abdomen was performed with the patient in the supine or right anterior oblique position. Because the study was retrospective, many abdominal radiologists with various lengths of experience were involved in sonographic scanning. All sonographic examinations were performed with commercially available high-end sonography units (Acuson XP 10, Acuson; HDI 3000, 3500, Advanced Technology Laboratories; Logic 700, GE Healthcare) and 2- to 5-MHz probes. No patient underwent color Doppler or contrast-enhanced sonographic examination.

Image Analysis
All CT and sonographic images were reviewed retrospectively by consensus of two board-certified radiologists. Portal venous phase CT images were evaluated for number of lesions, predominant shape (round or elongated) of lesions, distinctiveness of margins, attenuation, rim enhancement, maximum diameter of largest lesion, central or peripheral location, periportal distribution, and traversing vessel. In the cases in which they were available, arterial and equilibrium phase images were evaluated for number of lesions, lesion conspicuity, distinctiveness of margins, and enhancement. When lesions in the same patient had different imaging findings, the predominant pattern was recorded. Lower lung fields included in CT of the liver or abdomen were reviewed for focal pulmonary infiltration. CT images were reviewed in the lung window setting on monitors of a PACS workstation (Centricity 2.0, GE Healthcare). Sonography reports were reviewed for lesion number and maximum diameter of largest lesion. Sonographic images were reviewed for shape, distinctiveness of margins, and echogenicity.

Statistical Analysis
In the case of patients who underwent both CT and sonography, the rates of detection of hepatic lesions with the two techniques were compared by McNemar test and for number of lesions by paired t test and Pearson's correlation test. To assess whether there was a difference in the degree of peripheral eosinophilia between the group with and the group without hepatic lesions, the means of eosinophil count and percentage in the peripheral blood were compared by independent samples t test. To assess whether there was correlation between degree of peripheral eosinophilia and severity of hepatic abnormality on CT or sonography, bivariate analysis between eosinophil count and percentage and number of hepatic lesions on CT or sonography was performed with Pearson's correlation test. Statistical analysis was performed with a statistical software package (SPSS for Windows, version 13.0, SPSS). A statistically significant difference was p < 0.05.


Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Imaging Characteristics of Hepatic Lesions
Seventeen (68%) of the 25 patients with CT scans obtained at the portal venous phase had single (n = 2) or multiple (n = 15) ill-defined, oval or elongated, low-attenuating lesions in the liver parenchyma (Figs. 1A, 1B, 1C, and 1D). The portal venous phase CT characteristics of hepatic lesions of VLM are summarized in Table 1. The median number of hepatic lesions was seven (mean ± SD, 18.1 ± 23.8; range, 1-93). The lesions were less than 2 cm in diameter in 12 patients and 2-4 cm in four patients. One patient had multiple ill-defined, low-attenuating lesions larger than 5 cm at the periphery of the liver, some of which were crossed by portal vein branches (Fig. 2). Rim enhancement was seen at the portal venous phase in seven patients. The lesions tended to be in the periphery of the liver (n = 10) and along the portal vein branches (n = 10). In some cases, the portal vein traversed the lesions (n = 6) (Fig. 2). Abnormalities were not seen in the other eight patients.


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  		TABLE 1: Portal Venous Phase CT Characteristics of Hepatic Lesions of Toxocariasis (n = 17)

 

Figure 5
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  		Fig. 2 —36-year-old man with subsegmental hepatic involvement of visceral larva migrans of Toxocara canis. Transverse contrast-enhanced CT scan obtained at portal venous phase shows multiple, ill-defined, low-attenuating lesions at periphery of liver. Portal veins (arrows) traverse lesions. Percutaneous liver biopsy disclosed eosinophilic abscess.

 


Figure 6
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  		Fig. 3A —68-year-old man with hepatic visceral larva migrans of Toxocara canis. Transverse contrast-enhanced CT scan obtained at arterial phase shows small, ill-defined, enhancing nodule (long arrow) in right hepatic lobe. Short arrow points to branch of portal vein.

 


Figure 7
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  		Fig. 3B —68-year-old man with hepatic visceral larva migrans of Toxocara canis. CT scan obtained at portal venous phase shows nodule in A as low attenuating lesion (short arrow). Another ill-defined lesion (long arrow) at anterolateral part of right lobe is evident on portal venous phase image but not on arterial phase image.

 


Figure 8
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  		Fig. 3C —68-year-old man with hepatic visceral larva migrans of Toxocara canis. Photomicrograph of needle biopsy specimen shows eosinophilic abscess (arrowheads) and moderate to marked eosinophilic infiltration (arrows) in hepatic sinusoids. (H and E, x100)

 
The lesions were best seen or only seen at the portal venous phase in six (75%) of the eight patients who underwent unenhanced dynamic arterial, portal venous, and equilibrium phase CT (Figs. 1A, 1B, 1C, and 1D). Even when seen on arterial or equilibrium phase images, the lesions were less prominent, and the number of visualized lesions was small. The arterial phase images of six patients showed only multiple low-attenuating nodules with (n = 3) or without (n = 3) peripheral rim enhancement (Figs. 1A, 1B, 1C, and 1D). Images of one patient showed multiple enhancing nodules only (Figs. 3A, 3B, and 3C). The other patient had both low-attenuating nodules with peripheral rim enhancement and enhancing nodules. Images at the portal venous phase showed multiple low-attenuating nodules with (n = 2) or without (n = 7) peripheral rim enhancement in all eight patients, one of whom had lesions with both characteristics. Images at equilibrium phase showed no visible lesions in four patients. In three of the other four cases images showed ill-defined, slightly high-attenuating nodules; in the other case images showed a few ill-defined, low-attenuating lesions. Unenhanced CT images depicted only a few of the lesions that were visible on contrast-enhanced CT scans. CT scans of seven (28%) of 25 patients showed one or several small areas of round nodular infiltration with peripheral ground-glass attenuation at the bases of the lungs. The pulmonary lesions measured 1.0-1.2 cm in diameter.

Images of 18 (38%) of 48 patients who underwent sonography showed single or multiple poorly defined, oval or elongated, hypoechoic, small scattered focal lesions in the liver (Figs. 1A, 1B, 1C, and 1D). The sonographic characteristics of hepatic lesions of VLM are summarized in Table 2. Thirteen (72%) of the lesions were less than 2 cm in diameter. In the patient who had multiple large, low-attenuating lesions at the periphery of the liver on CT images, the lesions appeared as multiple large hypoechoic lesions on sonography. Thirty patients had no focal hepatic lesion detected on sonography.


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  		TABLE 2: Sonographic Characteristics of Hepatic Lesions of Toxocariasis (n = 18)

 

Biopsy-proven eosinophilic infiltration (n = 1) and abscess (n = 6) were seen as small, ill-defined, low-attenuating nodules at the portal venous phase of CT and as small, ill-defined, hypoechoic nodules on sonography and could not be differentiated.

Images of 11 (58%) of the 19 patients who underwent both CT and sonography showed hepatic lesions with both techniques. The lesion numbers on CT and sonography in the 11 patients were 17.2 ± 27.6 and 7.4 ± 5.7, respectively, which showed excellent linear correlation (r = 0.844, p = 0.001) by Pearson's correlation test and no statistical difference (p = 0.183) by paired t test. Images of three (16%) of the patients showed discrepancy between the CT and sonographic results. CT showed 43 and 18 hepatic lesions only in two patients, and sonography showed one hepatic lesion in one patient. The time intervals between CT and sonography for these three patients were 12, 4, and 23 days, respectively, and the patients were not treated pharmacologically between the two examinations. In five cases no imaging technique showed hepatic lesions. The two techniques had no statistically significant difference in detection rate of hepatic lesions (p = 0.375, McNemar test).


Figure 9
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  		Fig. 4A —42-year-old woman with hepatic visceral larva migrans of Toxocara canis. Transverse contrast-enhanced CT scan obtained at portal venous phase shows multiple small, ill-defined, oval or elongated, low-attenuating nodules throughout liver.

 


Figure 10
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  		Fig. 4B —42-year-old woman with hepatic visceral larva migrans of Toxocara canis. CT scan at same level as A 4 months after A without antihelminthic treatment shows similar but fewer low-attenuating nodules and different loci of lesions, suggesting migration of larvae.

 
Among the 17 patients with hepatic lesions on CT, follow-up CT images were obtained for nine patients. In eight cases hepatic lesions had disappeared on follow-up CT images obtained 324 ± 270 days (median, 213 days; range, 50-814 days) after the original images. In the other patient, the number and position of the nodular lesions on follow-up CT were different from those on the initial CT images (Figs. 4A and 4B). Follow-up sonography was performed for eight of the 18 patients with hepatic lesions detected with sonography. Hepatic lesions had disappeared in five patients on follow-up sonography 164 ± 42 days (median, 155 days; range, 119-224 days) after the original examination. In the other three patients, hepatic lesions persisted with a change in number. Among the pharmacologically treated patients, only three patients underwent follow-up examinations. One patient was treated with steroid only and underwent follow-up CT. The other two patients were treated with prednisolone and albendazole. One of these patients underwent follow-up sonography, and the other underwent both imaging techniques. The lesions had disappeared on follow-up examinations performed, 217, 224, and 50 days after the original images were obtained.

Relation Between Hepatic Abnormality on Images and Peripheral Eosinophilia
Eosinophil count and percentage of eosinophils in the peripheral blood at CT or sonography were considerably higher in the patient group with hepatic lesions than in the group without hepatic lesions, a finding that was statistically significant by independent samples t test (Tables 3 and 4). However, eosinophil count and percentage did not correlate with the number of hepatic lesions on CT (r = 0.375, p = 0.138; r = 0.352, p = 0.165) or sonography (r = 0.265, p = 0.288; r = 0.444, p = 0.065) by Pearson's correlation test.


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  		TABLE 3: Correlation of Eosinophils in Peripheral Blood and Presence of Hepatic Lesions on CT (n = 25)

 

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  		TABLE 4: Correlation of Eosinophils in Peripheral Blood and Presence of Hepatic Lesions on Sonography (n = 48)

 


Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
VLM of T. canis is known to be mainly a disease of children. Children who live with dogs in poor sanitary conditions are likely to ingest contaminated soil, hair, and the infective form of the eggs of T. canis. In the United States, approximately 80% of puppies younger than 6 months and 20% of dogs older than 6 months are infected, and 20-25% of soil in parks and playgrounds is contaminated with the eggs of T. canis [23]. Therefore, there is high risk of infection among children. In addition to egg ingestion, larvae in animal tissues can be transferred from host to host through predation [5], which has been proven experimentally [24], and from animals to humans [5]. Some adults ingest uncooked cow or cattle liver or meat containing the infective form of T. canis, encapsulated larvae [5, 6]. Ishibashi et al. [6] reported the cases of two adults with VLM of Toxocara caused by ingestion of raw meat or bird, boar, or horse liver. Forty-two (60%) of 70 patients in the present study had a definite history of ingestion of a considerable quantity of raw cow liver within 6 months of the hospital visit.

The infective larvae of T. canis, which are 0.5 mm long, move slowly from place to place (larva migrans) in the hepatic parenchyma. In the wake of migration, the larvae cause eosinophilic infiltration followed by abscess or granuloma formation [8]. The common histopathologic finding of focal eosinophilic infiltration in the liver is periportal and lobular infiltration of eosinophils with normal histologic architecture [25]. Eosinophilic abscess refers to a lesion composed of massive eosinophils and destroyed liver parenchyma with inflammation. Eosinophilic granulomas are typically multiple and consist of central necrosis and mixed inflammatory cell infiltrate with numerous eosinophils, varying numbers of neutrophils and lymphocytes, and a palisade of epithelioid histiocytes or giant cells. Remnant parasites may be identified [8].

CT and sonographic findings reflect the pathologic findings. Pathologic changes such as periportal eosinophilic infiltration, abscess, or granuloma with central necrosis and peripheral edema caused by slow migration of T. canis have been depicted as multiple small, ill-defined, oval or elongated, low-attenuating nodules on portal venous phase images of dynamic CT [4, 6, 10, 20]. These CT findings seem to be nonspecific and similar to the findings of other types of granuloma or inflammatory lesions. However, the eosinophilic lesions were best seen or only seen in the portal venous phase. This finding seemed to be somewhat characteristic of eosinophilic infiltration, granuloma, and abscess. In most cases, the enhancement pattern of hepatic lesions on dynamic CT could be explained by variable degrees of arterial hyperemia from the periphery of the hepatic lesions during the arterial phase or later and by complete central fill-in during the equilibrium phase. Although several cases have been confirmed on the basis of histopathologic findings, no difference in enhancement pattern that could explain the pathologic difference was found between eosinophilic infiltration and abscess. The lesions were small in most cases, but larger, low-attenuating lesions were present in which portal vein branches traversed the center of the lesion (Fig. 2). Because larvae of T. canis are distributed by portal blood flow, these larger lesions may be attributed to occlusion or alteration of the microvascular portal blood supply [26] in addition to eosinophilic inflammation itself. Sonography showed multiple small, focal, hypoechoic lesions in the liver parenchyma [4, 6, 10, 12]. The lesions were usually oval or elongated and sometimes were angulated or trapezoid rather than round, and the margins were ill-defined. These sonographic findings were nonspecific and could not be used to differentiate the lesions from other types of granuloma and inflammatory lesions.

The rates of detection of hepatic lesions of VLM of T. canis with CT (68%, 17/25) and sonography (38%, 18/48) in our study could not be compared simply because the patient populations in each group were partly different. Among 19 patients who underwent both CT and sonography, the detection rates with the two techniques were not statistically different. When both techniques were used, the numbers of lesions seen on CT and sonography were not different. However, lesion site and size could not be compared lesion by lesion because of incomplete sonographic data. The two patients with multiple small hepatic lesions recognized only on CT had homogeneous and slightly heterogeneous parenchymal echogenicity, respectively, on retrospective review of sonograms. The time intervals between CT and sonography were short enough to exclude resolution of the lesions. When lesions are so numerous the lesions touch one another, sonographers may overlook and perceive ill-defined focal hepatic lesions as heterogeneous parenchymal echogenicity. However, no acceptable hypothesis other than physical differences in the imaging mechanism between CT and sonography could explain the other two cases of discrepancy.

Eosinophil count and percentage in the peripheral blood were considerably higher in the patient group with hepatic lesions on imaging than in the patient group without lesions. When there was no abnormality on CT or sonography, peripheral eosinophilia was mild. However, the degree of eosinophilia and the number of hepatic lesions on CT or sonography were not proven to have positive linear correlation.

Several articles have described imaging findings of eosinophilic infiltration in the liver in association with peripheral eosinophilia [25-32]. Some investigators [25-27, 31] have addressed the hypothesis that the cause of eosinophilic infiltration is related to idiopathic hypereosinophilia or to cancer through a tumor-associated eosinophilotactic factor [27, 29, 30, 32]. Others investigators have offered no explanation of causes [30, 33]. The CT and sonographic findings in the aforementioned articles [25, 27-32] appear to match the imaging findings in our series. According to a recent pathologic report, 30% (13/43) of hepatic eosinophilic granulomas, excluding cases of Langerhans' cell histiocytosis, had remnants of Toxocara organisms in the tissue (n = 8) and had positive serologic results for Toxocara species (n = 5) [8]. Although the proportion of focal hepatic eosinophilic lesions due to toxocariasis is not known, we believe that VLM of T. canis is the likely cause of hepatic eosinophilic abscess or granuloma in many patients.

Patients with mild infection usually have no symptoms. Heavy infection can cause fever, nausea, epigastric discomfort, abdominal pain, weight loss, and ocular and neurologic symptoms [8, 20]. Pulmonary infiltrates are also common in severe infection [8]. The diagnosis of VLM of T. canis is clinically important because the patients can be treated with specific antihelminthic agents such as albendazole [10]. Identification of an eosinophilic lesion in the liver on imaging studies suggests the diagnosis of VLM as the cause of hypereosinophilia. Physicians who find such a lesion should initiate a prompt serologic and pathologic search for causative organisms. In patients with hypereosinophilia and hepatic parenchymal nodules on CT and sonography, ELISA with Toxocara excretory/secretory antigen should be performed. Imaging studies are also useful for guiding percutaneous biopsy, which may reveal eosinophilic inflammation or the remnants of T. canis larvae. Percutaneous biopsy of this benign inflammatory lesion under imaging guidance is necessary to differentiate the lesion from hepatic metastasis when a patient has a history of malignancy and the hepatic lesion cannot be differentiated with imaging alone. Hypereosinophilia and CT and sonographic abnormalities resolve slowly after antihelminthic or steroid treatment [10, 29].

Although in our study the time intervals between the initial examinations and follow-up examinations were not regular, follow-up imaging studies were valuable in showing changes in and resolution of hepatic lesions (Figs. 4A and 4B). Despite complete resolution of all hepatic lesions, only three patients among the pharmacologically treated patients underwent follow-up imaging studies, so therapeutic response could not be evaluated and analyzed properly.

The clinical significance of hepatic lesions of VLM of T. canis resides in the differential diagnosis from nodular hepatic metastasis. Some of the patients in this series had a history of underlying malignant disease. Because of mysterious beliefs, some patients with malignant or longstanding wasting disease prefer to eat "health-promoting" foods, such as uncooked flesh, organs, horns, and the blood of animals, which may have nodular lesions of T. canis. Nodules in toxocariasis differ from metastatic lesions in that nodules of VLM have fuzzy margins, are subtly low attenuating, are oval or elongated, and are best seen or only seen in the portal venous phase of CT [27]. Rim enhancement at the equilibrium phase is seen almost exclusively in metastasis but is seldom found in eosinophilic necrosis [27]. This finding may be explained by the variable degree of centripetal enhancement into tissues of different compositions. These findings of fuzzy margins and nonspherical shape are criteria for differential diagnosis from metastasis. Another element of clinical significance exists in evaluation of the severity of toxocariasis and the therapeutic effect of antihelminthic treatment.

This study had several limitations. When the patients were selected, the results of ELISA, which has a sensitivity of 91% and a specificity of 86%, were used as the standard of reference in determining the diagnosis. Therefore, false-positive results caused by cross reaction with other parasites might have been included in this patient group, obscuring the true CT and sonographic findings of VLM of T. canis. However, common parasites causing cross reaction were excluded by ELISA or stool examination, and the remaining false-positive proportion would have been too small to alter the major CT and sonographic findings. The presence or absence and the severity of abnormality on images may depend on the quantity of ingested uncooked bovine tissue and consequently on the worm burden, but we could not substantiate this factor because there is no specific test or method for quantifying worm burden. There also were limitations associated with the use of different imaging techniques for this retrospective study. Although most of our imaging studies were performed with reasonably modern CT, there was lack of standardization in terms of imaging protocols. However, all patients underwent portal venous phase CT, in which the lesions of VLM are best observed. Sonographic examinations were performed by many radiologists with varying expertise; therefore, the detectability of small hepatic nodular lesions might have been affected. Another limitation of this study was that CT and sonographic images were reviewed by two radiologists by consensus rather than through independent evaluation. However, this study was performed not to evaluate the accuracy of the diagnostic technique or interpreters but to describe the imaging characteristics of hepatic VLM of T. canis.

In summary, VLM of T. canis is a cause of hypereosinophilia. In patients with sustained hypereosinophilia showing multiple small, oval or elongated, ill-defined, low-attenuating or hypoechoic nodular lesions in the liver on CT and sonography, VLM of T. canis should be considered.


Acknowledgments
 
The authors thank John Roberts, Harrisco, for editorial assistance, and Young Joo Moon, Department of Radiology, Samsung Medical Center, for assistance in manuscript preparation.


References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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