Neurocysticercosis arises when larvae of the pork tapeworm Taenia solium lodge in the brain after a person swallows eggs shed by a human carrier, most often through contaminated food or water. Where the larvae settle determines how sick the patient becomes. When cysts embed in the brain parenchyma, they typically cause seizures and headaches, symptoms that usually respond to antiepileptic drugs, analgesics, and anthelmintic therapy, and the illness often follows a relatively benign course. When the parasites instead float freely within the cerebrospinal fluid compartments, the ventricles and the subarachnoid space, the picture changes dramatically. This extraparenchymal form responds poorly to anthelmintic drugs and can produce vasculitis, disrupted fluid circulation, and raised intracranial pressure driven by hydrocephalus. Basal subarachnoid disease is regarded as the most lethal presentation, carrying high rates of mortality and neurological disability.

The therapeutic dilemma at the heart of extraparenchymal disease is that treatment itself can make things worse. When cysts begin to degenerate, they ignite a marked inflammatory response inside the fluid compartments of the brain. Corticosteroids are routinely deployed to suppress this inflammation and prevent catastrophic complications, yet the same drugs may blunt the effectiveness of cysticidal agents, protecting the host but also sheltering the parasite. Clinical recommendations for managing these patients rest on studies with limited levels of evidence, which is precisely why researchers have long sought laboratory models that faithfully recapitulate the anatomy and immunology of the human infection.

Several experimental platforms exist, built on different parasites, including Taenia solium, Taenia crassiceps, and Mesocestoides corti, and different hosts, ranging from monkeys and pigs to rats and mice. A rat model developed by the Cysticercosis Working Group in Peru uses intracranial injection of activated T. solium oncospheres and has the advantage of employing the very species that causes human disease, but harvesting oncospheres from patients with taeniasis is not always feasible. The Brazilian team, led by Sophia Rossi de Barros Almeida and Pedro Tadao Hamamoto Filho of Botucatu Medical School at São Paulo State University, instead exploited a model in which 50 intact T. crassiceps cysticerci, each roughly half a millimetre in diameter, are suspended in saline and injected through a 25-gauge needle into the cisterna magna of six-week-old Wistar rats, mostly males, anesthetized with a ketamine and xylazine mixture.

To validate disease induction and chart the distribution of cysts throughout the cerebrospinal fluid compartments, the investigators examined magnetic resonance images acquired on a 0.25-T scanner with 0.6-millimetre slice thickness and T2-weighted gradient-echo acquisition, performed between one and six months after inoculation. Ventricular enlargement was quantified using the frontal horn ratio, a standard human neuroradiological measure calculated by dividing the maximal width of the frontal horns of the lateral ventricles by the inner-table-to-inner-table cranial diameter at the same level, with values above 0.3 indicating hydrocephalus. Because the low-field equipment could not resolve individual cysts, the team treated enlarged cisterns as indirect evidence of cyst presence, an assumption grounded in their empirical experience of imaging followed by euthanasia and necropsy.

The results were unambiguous. Intracranial abnormalities appeared in 189 of the 300 animals, or 63.0 percent, in the form of ventricular enlargement, subarachnoid space enlargement, or both. More than 90 percent of the animals with abnormalities showed ventricular dilation, predominantly of the lateral ventricles. The cisterna magna was the most frequently affected compartment at 85.2 percent, followed by the supratentorial basal cisterns at 78.8 percent, peritruncal cisterns anterior to the brainstem, the region near the pineal gland, the spinal canal, and, less commonly, the cerebral convexity, where abnormal spaces were seen in 10.6 percent of cases. Cysts were also detected outside the skull entirely, burrowing into the subcutaneous tissue of the neck in 39.2 percent of infected animals, a reminder of the parasite’s remarkable migratory capacity.

The frontal horn ratio ranged from 0.28 to 0.92, with a mean of 0.62 plus or minus 0.13, roughly double the human threshold for hydrocephalus and a striking severity given the animals’ mild clinical impairment. Notably, the presence of cysts in any cerebrospinal fluid compartment was associated with higher frontal horn ratios, whereas subcutaneous cyst location made no difference to ventricular size, with mean ratios of 0.622 versus 0.616 and a non-significant p-value of 0.743. Eleven animals, or 5.8 percent, were judged infected despite the absence of ventricular enlargement; in these, cysts clustered in the subcutaneous tissue and the cisterna magna. Subcutaneous cysts were found in 39.2 percent of intracranially infected animals and 30.2 percent of noninfected animals, with no statistically significant difference between the groups, suggesting skin involvement alone does not predict brain disease.

The parallels with human imaging are what give the model its translational punch. In a clinical study cited by the authors, 86.1 percent of patients with extraparenchymal neurocysticercosis harbored cysts in the posterior fossa cisterns, figures that correspond almost exactly to the 85.2 percent cisterna magna involvement and 57.1 percent peritruncal involvement seen in the rats, an expected overlap given that cysts are injected directly into that compartment. More intriguingly, cysts were also identified within the ventricles and supratentorial cisterns of the animals, demonstrating that the parasites can migrate across different fluid compartments just as they do in humans. The model even reproduces spinal disease, an uncommon but feared manifestation of human cysticercosis in which subarachnoid cysts cause motor deficits, back pain, and hydrocephalus, offering a potential platform for studying spinal cord compression.

Mechanistically, the model captures both routes by which hydrocephalus develops in human disease. Direct injection of cysts into the subarachnoid space obstructs the outflow of cerebrospinal fluid from the fourth ventricle, while inflammation along the ependymal lining adds an additional block to absorption. Yet the inflammatory response in infected animals appears attenuated, probably through the action of regulatory T cells, mirroring the immune evasion that allows cysts to survive for years in patients. Only after anthelmintic treatment, and particularly in the absence of corticosteroid cover, does inflammation intensify, reproducing the clinical paradox in which therapy for humans can worsen hydrocephalus and intracranial hypertension. Earlier work from the same group showed that T. crassiceps cysts injected into the subarachnoid space of rats simulate the radiological and morphological features of racemose neurocysticercosis, the multiloculated, grape-like form of the disease.

The authors acknowledge the inherent limitation of using a parasite species that differs from the one responsible for human illness, since species-specific host responses may not be fully reproduced, and they concede that their low-field open MRI system could neither count cysts nor reliably distinguish enlarged cisterns from cyst presence, a distinction that in humans does not always correspond either. Even so, their findings are comparable to those obtained with a 7-Tesla scanner in an adapted version of the model, and the higher parasite burden used here, 50 versus 30 cysts, may explain the greater disease severity, particularly the pronounced hydrocephalus. Taken together, the neuroimaging evidence cements this rat model as a practical, reproducible, and ethically sustainable platform for preclinical testing of new anti-inflammatory schedules, optimized anthelmintic regimens, surgical adjuncts, and even vaccines, against a neglected but potentially eradicable disease that still burdens millions across Latin America, Asia, and Africa.

Subject of Research: Neuroimaging features of an experimental rat model of extraparenchymal neurocysticercosis

Article Title: Neuroimaging Features of an Experimental Model of Extraparenchymal Neurocysticercosis

Article References: Almeida, S. R. D. B., Martins, T. D. C., Caldeira, F. M. C., Machado, V. M. D. V., Zanini, M. A., & Hamamoto Filho, P. T. (2026). Neuroimaging Features of an Experimental Model of Extraparenchymal Neurocysticercosis. Acta Parasitologica, 71(5), Article 200. https://doi.org/10.1007/s11686-026-01393-z

Image Credits: AI Generated

DOI: 10.1007/s11686-026-01393-z

Keywords: neurocysticercosis, Taenia crassiceps, hydrocephalus, MRI, experimental model, cerebrospinal fluid, frontal horn ratio, subarachnoid space, cisterna magna, Wistar rats, parasitic infection, neglected tropical disease