The clinical data, along with CT and MRI imaging, were collected from 12 pediatric patients with CP, including 8 males and 4 females, aged 6–14 years, with a median age of 9 years old. All cases originated from Guizhou Province, China. Of the 12 patients, 9 had dizziness and headache, 6 had nausea and vomiting, 5 had limb movement or sensory disturbances, and 4 had seizures. Nine patients were treated with the insect repellents Praziquantel. Two patients were treated with oral insect repellents Praziquantel after lesion resection + decompressive craniectomy. One patient was discharged after intracranial decompression and went to another hospital for surgical treatment with unknown information concerning the drug administration and surgical therapy. The patients were followed up 1 year after discharge. There were no significant abnormal symptoms in eight patients, significant improvement of the symptoms in two patients, and the existence of limb weakness in one patient. While one patient was lost during the follow-up.

The patients were scanned using a Siemens SOMATOM Sensation 16-row spiral CT scanner and a GE Signa 1.5T superconducting head-specific MRI scanner. Both plain CT and contrast-enhanced scanning were conducted with a thickness layer of 5 mm. The contrast enhancement was conducted with conventional scanning after an injection of 80 ml of non-ionic iodine contrast agent through the elbow vein. The parameters in MRI scanning were as follows: T1-weighted images (T₁WI), T2-weighted images (T₂WI), T2 fluid-attenuated inversion recovery (T₂/FLAIR), and diffusion-weighted images (DWI) were scanned. The T₁WI axial, coronal, and sagittal scans were conducted with an injection of gadopentetate glucosamine (Gd-DTPA) through the elbow vein at 0.1 mmol/kg of body weight at the time of enhancement.

The clinical manifestations in the 12 pediatric patients with paragonimiasis were mainly dizziness, headache, vomiting, seizure, and hemiparesis, with varying degrees of respiratory symptoms. With inquiry into the relevant clinical history, it was found that all 12 children had a history of eating raw stream crabs and drinking raw stream water, thus the clinical diagnosis should be highly suspicious of CP. The insect repellents Praziquantel is the preferred choice for the treatment of cerebral paragonimiasis. Praziquantel was administered and achieved good therapeutic effects in the remaining 11 patients except for one case who went to another hospital for treatment in the present group.

Cranial CT and MRI scans were conducted in the 12 pediatric patients with CP, and the lesions in all 12 cases were located in the cerebral parenchyma, with 10 in the supratentorial area, 2 in the subtentorial area, and involvement of the meninges in three cases (as shown in Table 1). The morphology of the lesions in the CT and MRI was mainly nodular and striated, with clear or indistinct borders and varying degrees of surrounding edema. The lesions showed isodense or slightly hyperdense opacities on the CT scan. The MRI manifested as ring-shaped cystic lesions, with heterogeneous equal or slightly decreased signal intensities on the T₁WI scans, heterogeneous equal or slightly increased signal intensities on the T₂WI scans, and equal or slightly increased signal intensities on the DWI scans. In four cases, the cyst wall showed equal T1 and short T2 signals, and in six cases, the characteristic “tunnel sign” and “worm-eaten sign” were visible. The contrast-enhanced MRI showed strip-shaped enhancement in five cases, nodular or ring-shaped enhancement in three cases, linear enhancement in two cases, and uneven enhancement in two cases. The meninges adjacent to the lesions were thickened with significant enhancement in four cases (as demonstrated in Figure 1, Table 2).

Paragonimiasis is a Zoonotic Parasitic disease mostly caused by eating raw or semi-raw crabs and crickets or drinking raw stream water in endemic areas (6). Paragonimus is pathogenic to humans and includes the Paragonimus westermani and Pagumogonimus skrjabini Chen species. The main pathological features of Paragonimiasis are the formation of sinus and multilocular cysts (7). The pathogenic mechanism is mainly that the metacercariae enter the intestine through the mouth and decapsulate in the small intestine, becoming juvenile. The juveniles enter the abdominal cavity through the diaphragm and enter the lungs where they develop into adult worms. Both adults and larvae of Paragonimus have the habit of invasion and migration (1, 8). The mechanism of Paragonimus migration to the brain is not very clear. One hypothesis is that immature larvae migrate through the loose connective tissue surrounding the jugular vein or carotid artery, penetrate the meninges, and invade the cerebral tissue. This is consistent with the finding that the distribution of lesions tends to be in the middle cerebral artery and posterior artery. The lesions are often located in the temporal lobe, parietal lobe, and occipital lobe (1). Migration and catabolism of the Paragonimus in the cerebral tissue cause an inflammatory response, leading to eosinophil infiltration and granuloma formation with edema of the surrounding cerebral tissue (9, 10). As time progresses, the worm destroys the cerebral tissue, causing necrosis and the formation of partially calcified fragments, which are encapsulated by a cyst wall of granulation and fibrous tissue (8). Meanwhile, eosinophilia can extensively erode the cerebrovascular system and eventually cause rupture of the eroded blood vessels, resulting in various degrees of hemorrhage (10).

CP is most common in children and adolescents, with a significantly higher incidence in children than in adults, and more common in males than in females (1). Most patients with CP have a slow onset and progressive exacerbation. In a few patients, especially the pediatric patients, the onset may be acute, with the neurological clinical manifestations being mostly headache, dizziness, vomiting, seizure, partial sensory disorders, and other localized brain symptoms; these are often accompanied by respiratory symptoms (11–13). According to the literature, most patients with CP have had respiratory symptoms before the appearance of neurological symptoms, with cough, shortness of breath, and chest pain as the main manifestations (8). In addition, symptoms and manifestations caused by lesions at other sites may develop, and even result in sudden death (6). Due to the lack of specificity, the clinical manifestations of CP are complex and varied, thus it is highly susceptible to being misdiagnosed.

The laboratory examinations for CP include eosinophil counting, intradermal testing for the Paragonimus antigen, and ELISA (4, 14). Eosinophil counting is the most simple and easy examination to perform. A large number of eosinophil aggregates can be visible in the cerebral tissue in patients with CP, which can also be accompanied by a large number of plasma cells, neutrophils, lymphocytes, etc. It is an important screening method commonly used in clinical practice. The confirmed diagnosis of CP relies on detection by ELISA of Paragonimus antibodies in the serum of the patient (4).

The lesions of CP are often located in the cortical and medullary junction areas of the supratentorial area of the cerebral hemispheres, mostly in the temporal, parietal, and occipital lobes, but can also occur in the subtentorial area (1, 15). The morphology of the lesions in CT and MRI scans is mainly nodular and striated, with varying degrees of surrounding edema. The image appearance varies at different stages of the lesion. For most patients, the most common CT presentation is an isodense or hyperdense lesion, and MRI presents as a ring-shaped cystic lesion (16). With a review of the previous literature, the authors suggested that the “tunnel sign” might be the characteristic imaging manifestation in CP, which appeared on the CT as a strip lesion with decreased intensity and opacity and varying degrees of surrounding edema. On the MRI, the tunnel sign appeared as a decreased intensity signal on the T1WI scans and an increased intensity signal on the T2WI scans, showing a tubular structure with an aperture of 1–3 mm. On the T2/FLAIR images, it appeared as a strip of decreased intensity signal surrounded by increased intensity signal, and it might also appear as a strip or a piece of increased intensity signal. On the T1WI enhanced scans, the lesion appeared as a significantly enhanced tunnel opacity or a significantly enhanced tunnel opacity between two adjacent lesions, which was the migration trajectory of the Paragonimus in the brain. The “tunnel sign” reflected the pathological changes that occurred after the penetration of the Paragonimus into the cerebral tissue (3, 8, 16). In the present study, the tunnel sign was observed in four cases, and the imaging findings were consistent with those reported in the literature. In addition, the manifestations of ring-shaped, nodular, and linear enhancement on the T1WI enhanced scans were also due to different pathological changes (17). The ring-shaped enhancement was mostly caused by cavities formed by stagnant worms destroying the cerebral tissue, with necrotic and liquefied brain tissue inside, surrounded by a cyst wall composed of granulation and fibrous tissue (7), while the granulomatous hyperplasia and vasculitis in the infiltrative stage might manifest as a nodular enhancement. If the lesion involved the meninges, the adjacent meninges might be thickened with significant enhancement in the T1WI enhanced scan, which might be caused by the invasion of Paragonimus migration into the meninges. In the present study, the ring-shaped and nodular enhancements observed in three patients, as well as the meningeal involvement, thickening, and significant enhancement in four patients, were consistent with previous reports in the literature. Two cases manifested as liner enhancement. The different features of enhancement in these cases might be correlated with the different stages of the disease. Intracranial hemorrhage can occur in children with CP, and the hemorrhage signal has a variety of manifestations on MRIs, mainly showing a high T1 signal and an equal, slightly high, or low T2 signal (11, 18). Susceptibility-weighted imaging (SWI) is a sensitive examination for the micro-hemorrhagic foci (19). However, no significant hemorrhage was observed in the cases enrolled in the present study, and no additional SWI sequence scanning was conducted. Therefore, a larger sample size is needed for further investigation.

In the diagnosis of cerebral paragonimiasis, attention should be paid to differentiating from cerebral tuberculosis, metastases, brain abscess, glioma, etc: ① Patient with brain tuberculoma mostly has poisoning symptoms or history of tuberculosis, with small tuberculous granuloma in the single brain parenchyma, with the rare occurrence of bleeding and mild peripheral edema, often accompanied by hydrocephalus. ② Patients with brain abscess have local or systemic signs and symptoms of infection, with elevated leukocytes, and one or more thin and luminous annular enhancements on the enhancement scans, with restriction spreading of pus cavity on DWI having the diagnostic value. ③ Brain metastases are common in middle-aged and elderly patients, usually with a history of the primary tumor, and present as multiple scattered nodular or ring-shaped enhancing lesions in the corticomedullary junction area, with unsmooth walls, rare calcifications, and significant perifocal edema disproportionate to the size of the lesion. ④ Gliomas are mostly located in the deep white matter of the brain. There may exist hemorrhage and necrosis within the tumor, which manifest as plaque-like or wreath-like enhancement with obvious space-occupying effect (as shown in Table 3).