Pulmonary and Liver Toxocariasis Mimicking Metastatic Tumors in a Patient with Colon Cancer

Abstract

Toxocariasis is an uncommon cause of multiple cavitary lung lesions and an ill-defined liver lesion. We herein report a patient with lung and liver toxocariasis, which mimicked metastatic lesions of colon cancer on ¹⁸F-FDG PET–CT and chest and abdominal CT performed for cancer staging after diagnosis of colon cancer. The patient was diagnosed with lung and liver toxocariasis by a positive enzyme-linked immunosorbent assay. Lung toxocariasis may occur as multiple cavitary lung lesions, and liver toxocariasis may appear as a solitary ill-defined nodule, which may be misdiagnosed as metastatic tumors. Clinicians should consider toxocariasis when multiple cavitary lung lesions and a solitary ill-defined focal liver lesion are detected, especially in a patient with cancer.

A 76-year-old man was diagnosed with colon cancer via a routine health examination, including a colonoscopy. As for colon cancer staging, chest computed tomography (CT), abdominal CT, and ¹⁸F-FDG positron emission tomography–CT (PET–CT) were performed. ¹⁸F-FDG PET–CT revealed a hypermetabolic mass in the sigmoid colon, representing colon cancer. It also demonstrated a mild hypermetabolic nodule in segment 5/6 of the liver and multiple mild hypermetabolic cavitary nodules in both lungs (Figure 1). Based on these findings, we suspected sigmoid carcinoma metastasized to the lung and liver as the first differential diagnosis.

Chest contrast-enhanced CT revealed multiple peribronchial, centrilobular, and cavitary nodules in both lungs (Figure 2), and they have upper lung predominance. The radiologist considered this to be pulmonary metastasis from colorectal cancer first and an infectious condition second. Abdominal CT showed a 2 cm sized, ill-defined lesion in segment 5/6 of the liver (Figure 3). As a differential diagnosis for the solitary hepatic lesion, we considered sclerosing hemangioma, inflammatory pseudotumor, or metastasis. Laboratory results showed only a mild increase in the eosinophil ratio (6.6%). Except for that, no abnormalities were found in the coagulation system or general biochemical tests. Serologic markers for hepatitis B and C, acid-fast bacteria (AFB) stain, and AFP culture were negative. Regarding tumor markers, carcinoembryonic antigen and carbohydrate antigen 19-9 were normal. At that time, he did not take any medication or show signs of infection or other systemic symptoms such as fever or night sweats. In addition, his exact history of previously eating uncooked cow liver or meat is unclear.

Liver magnetic resonance imaging (MRI) was performed to differentiate the pulmonary and hepatic lesions from another possible diagnosis. It revealed a 1.5 cm ill-defined nodular lesion contiguously extending into the liver capsule (Figure 4). These findings mostly likely represented liver fluke disease. The diagnosis of toxocariasis was confirmed through the presence of antibodies to Toxocara canis by enzyme-linked immunoassay (ELISA). Other parasite antibody tests, including Clonorchiasis sinesis, Paragonimus westermani, Taenia solium, Spirometra mansoni, Fasciola hepatica, Amoeba, Trichinella spiralis, and Schistosoma, all yielded negative results. Eventually, his colon cancer was treated with laparoscopic low anterior resection. After discharge, the patient took oral albendazole by himself. After 3 months, chest and abdominal CT was performed for the postoperative routine follow-up, and it showed a shrinkage of all pulmonary and hepatic lesions compared to the previous imaging. Finally, after 5 months, the entire multiple cavitary lung and the hepatic nodules disappeared (Figure 2 and Figure 3). In addition, the eosinophil ratio decreased from 6.6% to 0.4%.

Human toxocariasis is a neglected soil-transmitted helminth infection from dogs and cats caused by larvae of Toxocaria canis or Toxocara cati, respectively. It causes various diseases, from compartmentalized to generalized visceral larva migrans [1]. Toxocariasis is a more common parasitic disease in Africa and South East Asia than in Western countries. In particular, in Korea, the prevalence of toxocariasis has increased among Korean adults due to the habit of eating uncooked cow liver or raw fish [2]. Several reports deal with imaging findings of pulmonary or hepatic toxocariasis [3,4,5,6]. Lung involvement of toxocariasis rarely causes multiple nodules [7,8]. Lee et al. stated the pulmonary lesions of toxocariasis tend to be multiple lesions with lower lung predominance and ill-defined ground-glass opacitiess with or without solid portions [9]. Hepatic toxocariasis usually appears as multiple ill-defined, oval-shaped, and low-attenuating nodules on CT. On CT or MRI imaging, hepatic lesions are seen as multiple ill-defined, oval lesions that measure 1.0–1.5 cm in diameter [10]. Sometimes, the lesion may be angular or trapezoid. The lesions are usually best seen on the portal venous phase in dynamic contrast-enhanced CT and MRI imaging; the lesions are either not seen or only faintly seen on arterial and equilibrium phases. However, in this case, the imaging was performed for cancer staging, the patient had no symptoms, eosinophilia was not high enough to suspect parasitic infection, and the imaging findings were not typical to suggest parasitic infection. In particular, the lung and liver are common sites of colorectal cancer metastasis. Hence, the possibility of metastatic cancer had to be considered first. Due to toxocariasis’s non-specific appearance on CT, they can often be mistaken for other conditions. Also, ¹⁸F-FDG PET–CT is currently a valuable diagnostic tool for cancer staging; FDG-avid inflammatory lesions can be misinterpreted as metastatic lesions. To our knowledge, there has been no case where toxocariasis was accidentally discovered during the diagnosis of any cancer, and in particular, there were no reports of simultaneous involvement of the lung and liver. Based on this interesting case, we suggest that clinicians should consider toxocariasis when patients with cancer present with solitary hepatic or multiple cavitary pulmonary nodules associated with eosinophilia and should perform serologic tests to exclude toxocariasis.