Magnetic resonance imaging–derived relative cerebral blood volume characteristics in a case of pathologically confirmed neurocysticercosis: illustrative case

Abstract

BACKGROUND

Neurocysticercosis (NCC) is a parasitic infection of the brain caused by ingesting water or food contaminated with tapeworm eggs. When it presents as a solitary mass, differentiation from a primary brain tumor on imaging can be difficult. Magnetic resonance imaging (MRI)-derived relative cerebral blood volume (rCBV) is a newer imaging technique used to identify areas of neovascularization in tumors, which may advance the differential diagnosis.

OBSERVATIONS

A 25-year-old male presented after a seizure. Computed tomography (CT) and MRI demonstrated a partially enhancing lesion with microcalcifications and vasogenic edema. Follow-up rCBV assessment demonstrated mild hyperperfusion and/or small vessels at the lesional margins consistent with either an intermediate grade glioma or infection. Given the radiological equipoise, surgical accessibility, and differential diagnosis including primary neoplasm, metastatic disease, NCC, and abscess, resection was pursued. The calcified mass was excised en bloc and was confirmed as larval-stage NCC.

LESSONS

CT or MRI may not always provide sufficient information to distinguish NCC from brain tumors. Although reports have suggested that rCBV may aid in identifying NCC, here the authors describe a case of pathologically confirmed NCC in which preoperative, qualitative, standardized rCBV findings raised concern for a primary neoplasm. This case documents the first standardized rCBV values reported in a pathologically confirmed case of NCC in the United States.

Neurocysticercosis (NCC) is the most common parasitic infection of the human central nervous system (CNS).¹ When humans ingest food or water contaminated with tapeworm eggs, these eggs can hatch in the intestine. The resulting larvae can migrate through the intestinal mucosa and potentially form cysts in various tissues, including the CNS.² Although many types of body tissue can be invaded by the infection, the larvae display the strongest affinity for the CNS.^3,4 While many NCC infections are asymptomatic, seizures present in up to 78.8% of patients infected depending on the evolutionary stage of the cysticercus and anatomical location.^5,6 Clinical manifestations of the infection vary widely based on several factors, including the size, number, location, and developmental stage of the cysticerci.¹ The highly variable nature of the presentation of NCC can complicate accurate diagnosis using conventional imaging techniques alone. A 2020 study aimed to address this difficulty by comparing conventional magnetic resonance imaging (MRI) sequences to newer MRI sequences including three-dimensional constructive interference in steady state, susceptibility-weighted imaging (SWI), and arterial spin labeling. Authors of that study concluded that magnetic resonance (MR) spectroscopy alone could not be used to diagnose NCC, but that more advanced techniques may enhance the specificity of NCC diagnosis.^7,8 In the case described here, NCC presented as a solitary brain mass in a 25-year-old male with nonspecific imaging features. Dynamic susceptibility contrast (DSC)-MRI was performed to obtain relative cerebral blood volume (rCBV) images, which raised concern for an intermediate or high-grade primary neoplasm. Although numerous studies use MR perfusion to characterize features of various infections, few document the perfusion characteristics of NCC using standardized rCBV, and there are no such reports in pathologically confirmed cases in the United States.^9,10 Therefore, here we describe the first standardized rCBV findings in a case of pathologically confirmed NCC to aid those who may also seek to distinguish primary CNS neoplasms from NCC using this technique.

Illustrative Case

History and Examination

A 25-year-old male from Mexico who had moved to the United States 14 months prior to presentation came to an emergency department (ED) in Milwaukee, Wisconsin, following a full-body generalized tonic-clonic seizure that lasted approximately 1 minute. The patient felt dizzy prior to his seizure and was postictal for approximately 15 minutes. At the time of evaluation in the ED, he was without deficits and had no acute complaints. The patient denied fever, cough, or other generalized symptoms, and he was afebrile with a normal white count. The patient reported a history of childhood seizures, and he described undergoing surgery for removal of a “bug that laid eggs” at age 9 or 10.

Initial computed tomography (CT) scanning of the head without contrast revealed a 1.2-cm right parietal lobe lesion with central hypodensity, tiny peripheral calcifications, and surrounding vasogenic edema with sulcal effacement (Fig. 1). Multisequence multiplanar MRI of the brain with and without contrast performed 1 day later confirmed a cortical/subcortical right parietal lobe intra-axial lesion now measuring up to 1.9 cm in maximal diameter with peripheral enhancement, central susceptibility artifact, areas of peripheral T1 shortening, partially reduced diffusivity, and perilesional vasogenic edema with localized sulcal effacement (Fig. 2). The differential diagnosis included primary CNS neoplasm (e.g., intermediate grade oligodendroglioma), cerebral metastasis, NCC in the colloid vesicular form, and nonpyogenic brain abscess.

FIG. 1.

Initial noncontrast axial (left) and coronal (right) head CT scans depicting an intra-axial lesion in the right parietal lobe with heterogeneous attenuation, peripheral microcalcifications, and adjacent vasogenic edema.

FIG. 2.

Preoperative axial FLAIR (A), precontrast T1-weighted (B), postcontrast T1-weighted (C), T2-weighted (D), apparent diffusion coefficient (E), and SWI (F) MRI depicting a combination of enhancement, microcalcification, and partial reduced diffusivity.

DSC-MRI was performed, from which rCBV maps (IB Neuro, Imaging Biometrics LLC.) were created to help with the differential diagnosis. Qualitative assessment of the rCBV maps revealed nonspecific heterogeneous hyperperfusion at the margins of the right parietal lobe intra-axial lesion potentially attributable to a neoplasm with an intermediate or high-grade component (Fig. 3). Overall, the findings were believed to be sufficiently concerning for a primary neoplasm, indicating the need for excisional biopsy of the mass.

FIG. 3.

Axial MR perfusion with postcontrast T1-weighted image (A), Delta T1 color map (B), and rCBV color map (C) depicting slightly increased perfusion (light blue-green rim) at the enhancing component of the lesion, whereas the green-yellow area along medial margin most likely corresponds to a sulcal blood vessel.

Preoperatively, peripheral blood work was unremarkable and did not demonstrate any indications of infection. Serum markers and blood cultures were negative for evidence of infection. A CT of the chest, abdomen, and pelvis was also negative for other lesions. Prior to surgery, empirical treatment of NCC with antiparasitic medications was considered. However, given the clinical equipoise and surgically favorable location of the mass, all options were discussed with the patient, and the decision was made to pursue a right parietal craniotomy for en bloc resection of the enhancing component.

Operation

The patient underwent a right parietal craniotomy for resection of the mass with neuronavigation and intraoperative ultrasound. Postoperative MRI with fluid-attenuated inversion recovery (FLAIR) sequences depicted gross-total resection of the enhancing lesion (Fig. 4). A firm, tan, partially calcified mass was encountered and resected en bloc. Once the specimen was in the pathology suite, it was cut open for gross confirmation of the diagnosis of NCC (Fig. 5). The surrounding FLAIR tissue was also biopsied separately and found to be consistent with reactive astrocytosis. The patient was then closed in the standard fashion, and the case was concluded. After the procedure, the patient was continued on dexamethasone, levetiracetam, and pantoprazole. He was also started on 400 mg albendazole twice daily for 6 days per infectious disease recommendations. The patient did well postoperatively and has not experienced any further seizures. Baseline postoperative imaging included MRI with and without contrast, which demonstrated gross-total resection of the enhancing lesion.

FIG. 4.

Postoperative axial FLAIR (A), precontrast T1-weighted (B), and postcontrast T1-weighted (C) MRI depicting gross-total resection of an enhancing lesion with scattered linear areas of reactive postoperative enhancement.

FIG. 5.

Pathological examination of the removed NCC. A: Gross examination showed a bisected cystic, partially calcified structure filled with clear fluid and a white-tan scolex (asterisk). B: Microscopic examination of hematoxylin and eosin (H&E)-stained sections at low power revealed the scolex (box) within the undulating cyst wall. Bar = 50 µm. C: Further examination at a higher power revealed the scolex with several refractile hooklets (arrow). H&E. Bar = 200 µm.

Patient Informed Consent

The necessary patient informed consent was obtained in this study.

Discussion

Observations

DSC-MR perfusion, or perfusion-weighted imaging, uses a bolus of gadolinium-based contrast monitored by a series of T2-weighted images to construct a concentration-time curve from which parametric maps of CBV can be obtained.¹¹ A 2018 study investigated whether DSC perfusion MRI could be useful in differentiating between NCC and tuberculoma, based on CBV, cerebral blood flow, and mean transit time. They found that higher rCBV values were demonstrated in the wall of tuberculoma lesions than those in NCC lesions, signifying angiogenesis in tubercular lesions, consistent with other literature.¹² As a result, the authors concluded that the addition of MR perfusion to conventional MRI may eliminate the need for brain biopsy to differentiate NCC from tuberculosis.¹³ These results were consistent with the findings of Ghosh et al.,¹² who reported higher mean rCBV values in the walls of tuberculomas than in NCC, with values of 3.36 ± 1.38 and 1.39 ± 0.42, respectively. This group also cited neoangiogenesis as an explanation for the hyperperfused tuberculoma wall.¹² The authors further noted that the walls of both NCC and tuberculomas showed increased mean rCBV values as compared to normal white matter, whereas the cores of both lesions showed decreased mean rCBV values.

Floriano et al.¹⁴ similarly reported that when looking at infectious and neoplastic focal brain lesions on contrast-enhanced perfusion MRI, neoplastic lesions generally had higher rCBV values (4.28 ± 2.11) than infectious lesions (0.63 ± 0.49; p < 0.001). The authors suggested that when an rCBV value of <1.3 was set as the parameter for differentiating infectious lesions from primary neoplasms, positive and negative predictive values were 91.8% and 98%, respectively, with an accuracy of 95%, demonstrating the potential significant utility of rCBV in diagnostic differentiation between infectious and neoplastic brain lesions.

Typically, when a quantitative assessment of rCBV is necessary, rCBV values of the region of interest are normalized to a reference region, usually normal-appearing white matter. The technique of normalization, however, is somewhat subjective and may leave room for user-dependent variability. Thus, more recent methods of constructing DSC-MRI rCBV maps instead of standardized rCBV values over different tissue types, scanners, and subjects, therefore limiting the possibility for subjectivity while maintaining comparability to normalized rCBV values.¹⁵ In the present case, the mean standardized rCBV was 1.11, consistent with infection. Although this spatially averaged value is consistent with infection according to the threshold determined by Floriano et al.,¹⁶ this threshold of <1.3 overlaps with standardized rCBV values reported for different grades of gliomas. This makes it difficult to distinguish infection from primary brain tumor based on averaged rCBV values. A conflicting 2011 report described a case of NCC in which a twofold increase in rCBV in perfusion MRI was demonstrated in comparison to the patient’s contralateral side.¹⁶ As demonstrated in previous reports and the present case, distinguishing infection from primary neoplasm based on rCBV alone remains a challenge.

Limitations

As with any case report, this work presents a single interesting case, so broad generalizations and extrapolations to the general population should not be made. The present case demonstrates symptomology and imaging of NCC only in the colloidal vesicular stage. The earliest form of larval NCC invasion of brain parenchyma is noncystic and typically not detectable on imaging because symptoms may not be present, whereas later stages are more readily seen on CT.¹⁷ In addition, later, more calcified stages of NCC would likely demonstrate lower rCBV values than NCC in the colloidal vesicular form.¹⁸ Finally, subjective features of the acquisition of the rCBV, including manual region of interest selection, calibration of MRI scanners, or patient-specific factors, may be sources of variability.

Lessons

Noninvasive diagnosis of NCC can be challenging when the disease presents as a solitary mass without other clinical indicators. Conventional imaging techniques such as CT and MRI may not always provide sufficient information to distinguish NCC from similarly presenting conditions. Although other reports have suggested that advanced imaging such as rCBV measured by DSC-MRI may play a role in the identification and characterization of NCC, here we report a case in which a qualitative assessment of preoperative standardized rCBV was considered more consistent with a primary neoplasm despite subsequent pathological confirmation of NCC during surgery. However, the mean standardized rCBV of 1.1 was consistent with previously suggested value thresholds of <1.3 for infection. We, therefore, report these findings to the broader neurosurgical community as the first standardized rCBV values in a pathologically confirmed case of NCC in the United States.

Author Contributions

Conception and design: Botros, Mrachek, Krucoff. Acquisition of data: Botros, Mrachek, Krucoff. Analysis and interpretation of data: Botros, Polinger-Hyman, Mrachek, Schmainda, Krucoff. Drafting the article: Botros, Mrachek. Critically revising the article: Botros, Polinger-Hyman, Mrachek, Schmainda, Krucoff. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Botros. Study supervision: Krucoff.