Abstract
Purpose
To describe the role of SWI compared with other MR imaging sequences and CT in diagnosis of cerebral gnathostomiasis.
Materials and methods
CTs and MRIs of patients with cerebral gnathostomiasis were retrospectively reviewed. The types of intracranial hemorrhage, including intraparenchymal hemorrhage (IPH), subdural hemorrhage (SDH), subarachnoid hemorrhage (SAH), and their locations were recorded.
Results
Four patients proven as cerebral gnathostomiasis were included. Intracranial hemorrhage was detected in all patients. There was IPH in all patients, SAH in 2 patients, and SDH in 2 patients. All patients (4/4) revealed hemorrhagic tracts which were very conspicuously seen on SWI. Other imaging sequences could also reveal hemorrhagic tracts in 3 patients (3/4) but are less conspicuously seen than SWI. None of the CT brains could detect hemorrhagic tracts.
Conclusions
Intracranial hemorrhage associated with hemorrhagic tract, best demonstrated by SWI, is the key imaging characteristic in diagnosis of cerebral gnathostomiasis.
Keywords: Cerebral gnathostomiasis, susceptibility weighted imaging, SWI, parasitic infection
Introduction
Cerebral gnathostomiasis is a rare, parasitic infection endemic to Southeast Asia; especially Thailand. 1 Computed tomography (CT) and Magnetic Resonance Imaging (MRI) are parts of the essential investigation tools to evaluate this disease. Although, most of the identified cases of cerebral gnathostomiasis were from Thailand,2–6 it is still uncommon for it to be found in daily clinical practice; leading to misinterpretation and may also delay diagnosis.
Prior studies have shown that the important hallmark of cerebral gnathostomiasis on imaging was identifying hemorrhagic tracts, 6 which could be detected on T1-weighted (T1w), T2-weighted (T2w), and after gadolinium administration images.2,7 Nowadays, there is increasing use of susceptibility-weighted imaging (SWI), and studies have shown that it is better than gradient-echo (GRE) T2*-weighted (T2*w) imaging to identify hemorrhage.8,9 To our knowledge, there is only one case report by Smith et al. 10 demonstrating that hemorrhagic tracts could be clearly visualized on the SWI sequence. SWI, which has been added into our routine protocol of MRI, may play an important role in helping diagnosis. Hence, the aim of this study was to analyze the role of SWI compared with other MR imaging sequences and CT in diagnosis of cerebral gnathostomiasis.
Material and methods
Population
Participants were retrospectively identified through the radiologist information systems from our institution’s database for requests and reports, via the specific terms “Gnathostomiasis” or “parasitic infection”: from September 2007 until November 2021. Final diagnosis of the patients was reviewed from the medical records. Five patients with the clinical diagnosis of gnathostomiasis were included in this study. We excluded one patient without active disease during taken imaging at our institute. She came to follow-up on the myelomalacic change of the spinal cord from gnathostomiasis for 17 years ago. Therefore, leaving four patients in this study, information on patient demographics, clinical presentation, and laboratory investigation were collected from the electronic medical chart. The study was approved by the Institutional Review Board, and informed consent for the participants was waived due to its retrospective nature.
Imaging acquisition
MRIs of the brains were obtained from 4 patients on different MRI scanners, from various hospitals. The MR-specific scanning parameters varied; however, the same essential anatomic sequences used in this current study were always performed; including, axial T1-weighted spin echo (T1w SE), T2-weighted spin echo (T2w SE), fluid attenuated inversion recovery (FLAIR), SWI, and post-gadolinium T1-weighted fat suppression spin echo (T1w FS-Gd SE). Pre- and post-contrast enhanced CT brains were also obtained from two patients.
Imaging analysis
Images were retrospectively reviewed on Picture Archiving and Communication System (PACS) by two neuroradiologists simultaneously. Both neuroradiologists were unblinded to the clinical diagnosis of cerebral gnathostomiasis and were not previously involved in the cases. For participants with multiple CT and MRI scans; the initial scans were analyzed. The types of intracranial hemorrhage, including intraparenchymal hemorrhage (IPH), subdural hemorrhage (SDH), subarachnoid hemorrhage (SAH), and their locations were recorded. The presence of hemorrhagic tracts was recorded as: not detectable (N), mildly conspicuous (M), or very conspicuous (V) on each sequence; including, T1w SE, T2w SE, FLAIR, GRE T2*w, SWI, and T1w FS-Gd SE. The number of hemorrhagic tracts was also counted, if identified as very conspicuous.
Results
A total of 4 patients (1 male and 3 females; mean age 45.8 years; age range, 38–53 years) proven as cerebral gnathostomiasis were identified in this study. The immunoblotting tests were positive for gnathostomiasis in both serum and cerebrospinal fluid (CSF) in 3 patients. The living larva was extracted and taken out from 1 patient via surgical resection. All patients presented with different clinical presentations; and the detailed clinical findings are summarized in Table 1.
Table 1.
Clinical findings of cerebral gnathostomiasis.
| Patient No. | Age (y)/Sex | Clinical presentation | Diagnosis by |
|---|---|---|---|
| 1 | 38/F | Left facial numbness | + Immunoblotting in serum and CSF |
| 2 | 53/M | Alteration of consciousness | + Immunoblotting in serum and CSF |
| 3 | 43/F | Decreased visual acuity of right eye | + Immunoblotting in serum and CSF |
| 4 | 49/F | Urinary incontinence | Surgery |
Intracranial hemorrhage was detected in all patients. There was IPH in all patients, SAH in 2 patients, and SDH in 2 patients. The types and locations of intracranial hemorrhage are summarized in Table 2.
Table 2.
Types and locations of intracranial hemorrhage in cerebral gnathostomiasis.
| Patient No. | Type of intracranial hemorrhage and locations |
|---|---|
| 1 | - IPH at pons |
| - SAH at perimesencephalic cistern | |
| 2 | - IPH at left caudate |
| - SAH at right frontotemporal, left cerebral sulci, left sylvian fissure, the brainstem surface and posterior fossa | |
| - SDH at bilateral cerebral, cerebellar convexities and the falx cerebri | |
| 3 | - IPH at left temporal and occipital lobes |
| 4 | - IPH at right cerebellar hemisphere |
The presence of hemorrhagic tracts as well as the number of tracts on each sequence is summarized in Table 3. All patients (4/4) revealed hemorrhagic tracts which were very conspicuous as seen on SWI (Figure 1). Other imaging sequences also revealed hemorrhagic tracts in 3 patients (3/4); however, these were most conspicuously seen on SWI. None of the CT brains were able to detect hemorrhagic tracts.
Table 3.
The presence of hemorrhagic tracts and the number of tracts on each sequence.
| Patient No. | CT | T1w SE | T2w SE | FLAIR | GRE T2*w | SWI | T1w FS-Gd SE |
|---|---|---|---|---|---|---|---|
| 1 | N | N | N | N | V, 1 | V, 1 | N |
| 2 | N | M | V, 2 | V, 2 | N/A | V, Multiple | M |
| 3 | N/A | M | M | M | V, Multiple | V, Multiple | N |
| 4 | N/A | M | V, Multiple | M | V, Multiple | V, Multiple | M |
Note: The number of hemorrhagic tracts was also counted, if identified as very conspicuous.
More than 3 hemorrhagic tracts would be marked as multiple.
Abbreviations: N = Not detectable, M = Mildly conspicuous, V = Very conspicuous, N/A = Not available.
Figure 1.
T1w SE, T2w SE, FLAIR, and SWI images of 4 patients with cerebral gnathostomiasis is shown. The first patient (A–D) showed a hemorrhagic tract that was only seen via SWI sequence (arrow). The second (E–H), third (I–L), and fourth (M–P) patients showed hemorrhagic tracts in all sequences, but were clearly visualized on SWI.
Computed tomography (CT), T1-weighted spin echo (T1w SE), T2-weighted spin echo (T2w SE), fluid attenuated inversion recovery (FLAIR), gradient-echo (GRE) T2*-weighted (T2*w), susceptibility-weighted imaging (SWI), and post-gadolinium T1-weighted fat suppression spin echo (T1w FS-Gd SE).
Discussion
Our study supports that detecting hemorrhagic tracts seen as a linear-shaped hemorrhage are best detected by SWI. We also noticed microhemorrhage on SWI from other causes, apart from the parasite, was usually seen as a small, round-shaped hemorrhage.
The hemorrhagic tracts are likely due to parasite larvae burrowing through nerve tissue. Parasites burrowing through vessels can result in any type of intracranial hemorrhage; including IPH, SAH, and SDH. Therefore, findings of any types of intracranial hemorrhage associated with the hemorrhagic tracts are the two components that may suggest cerebral gnathostomiasis. Although, most hemorrhages can be detected on CT, microhemorrhages within the hemorrhagic tracts are too small to be visualized by CT. Therefore, an atypical hemorrhage on CT without identifiable reasonable cause may require further MRI brain scans to exclude the possibility of cerebral gnathostomiasis.
Apart from Gnathostoma spp., some other types of nematodes can involve the central nervous system, the most common ones included Angiostrongylus spp. and Sparganum spp. However, they do not commonly cause intraparenchymal hemorrhage or microscopic hemorrhage along the migrating tracts, which may be explained by the relatively smaller size of the organism compared with Gnathostoma spp.2,11
Gnathostomiasis is a food-borne parasitic infection caused by human ingestion of the third-stage larvae of nematodes, named Gnathostoma spp, with the most common being G. spinigerum. 12 The main risks for acquisition are increased consumption of raw or undercooked freshwater fish and travel or living in the endemic regions. The most common manifestation is cutaneous lesions characterized by localized, intermittent, migratory skin swelling, which is often accompanied by localized pain, pruritis, and erythema.6,12 However, besides cutaneous involvement, gnathostomiasis can also involve the brain, which is the most severe manifestation of this visceral disease. 6
The symptoms of cerebral gnathostomiasis can vary depending on the location of migratory parasites. 6 As seen in this study, all of the patients came with different chief complaints. In addition, not all cerebral gnathostomiasis have combined cutaneous lesions, making it difficult to diagnose. Therefore, imaging plays an important role in obtaining the proper diagnosis. Our study described the findings that radiologists should recognize in concerns to this rare disease.
Our study has a few limitations. The first being the small number of participants; as cerebral gnathostomiasis is rare. Second, some of the patients were referred from other hospitals, so the images were obtained from different scanners, via different protocols. However, the results still demonstrate the same direction.
Conclusion
Intracranial hemorrhage associated with the hemorrhagic tract is best demonstrated by SWI, which is a key imaging characteristic, helpful in the diagnosis of cerebral gnathostomiasis.
Footnotes
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding: The author(s) received no financial support for the research, authorship, and/or publication of this article.
ORCID iDs
Pornrujee Hirunpat https://orcid.org/0000-0003-3288-8502
Theeraphol Panyaping https://orcid.org/0000-0002-6051-1772
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