Neuroimaging in Neurocysticercosis 

Updated: Oct 05, 2016
Author: Arturo Carpio, MD; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM 

Overview

Background

Taeniasis and cysticercosis remain a global public health problem in both the developing and developed countries. Infection is becoming increasingly common in the latter because of the increasing immigration and more frequent travel to regions of endemic disease. These parasitic diseases are related to poverty and poor sanitary infrastructure. Therefore, cysticercosis has been designated as a biological marker of the social and economic development of a community.

Neurocysticercosis (NC) commonly is associated with clinical manifestations such as seizures, headache, and focal neurological deficits, and may lead to long-term neurological sequelae such as epilepsy, hydrocephalus, and dementia. The pleomorphism of NC makes its diagnosis impossible on clinical grounds alone. An accurate diagnosis is possible only after suspicion on epidemiologic grounds, proper interpretation of clinical data, and synthesis of findings on neuroimaging studies specific immunologic tests on the cerebrospinal fluid (CSF).[1, 2, 3]

Biology

Humans are the only known host to harbor the adult cestode parasite, Taenia solium, in the intestine. Infection is acquired by ingesting undercooked pork infected with Taenia larvae (ie, cysticerci). The cysticerci evaginate into the intestines where they mature into adult worms. The worms consist of a scolex, which attaches itself to the intestinal wall, and numerous proglottids (ie, segments). Proglottids and eggs are shed intermittently into the stool.

The intermediate host, typically the pig, is infected by ingesting parasite eggs or proglottids containing eggs (ie, porcine cysticercosis). The oncospheres escape from the eggs, penetrate the intestinal mucosa, migrate through the bloodstream, and lodge in the tissues. Over weeks to months, they evolve into larvae that enlarge and mature into cysticerci. The life cycle is completed when humans ingest pork contaminated with the cysts.

Human cysticercosis is acquired after eating food contaminated with fertilized eggs excreted in the feces of Taenia carriers. In humans, the most common routes of infection are ingestion of T solium eggs from contaminated food and rarely from fecal-oral autoinfestation from patients harboring the adult parasite in their intestines. While the cysts can develop in any human tissue, they have a predilection for the central nervous system (CNS), skeletal muscle, subcutaneous tissue, and eyes.

Immune response

In humans and pigs, the cysticerci may live within the host tissue without causing inflammation or disease. The immune response is unpredictable and may vary from a complete tolerance to an intense immune response. A single patient may show an intense inflammation around a cyst at any stage of the degeneration process, together with viable cysts with lack of inflammation and several calcifications scattered in the brain. Autopsies of victims of warfare and road/traffic accidents have revealed that a large proportion of NC infection is asymptomatic and discovered incidentally at necropsy. Individuals who undergo computed tomography (CT) of the head for unrelated reasons (eg, head injury) may demonstrate multiple parenchymal calcifications.

Several studies have analyzed the mechanisms of the immune response elicited against T solium cysticercus, such as the heterogeneity of the humoral immune response, the existence of immune evasive mechanisms, and the fact that the immune response can both protect and harm the host.

The humoral immune response to antigens of T solium cysticerci is evident from the number of immunodiagnostic assays that have been developed using different types of antigens. Several immunoglobulin (Ig) classes are produced as specific antibodies against the parasite. The most frequent is immunoglobulin G (IgG), which can be detected in serum, CSF, and saliva and suggests that infection is of long duration. The immune response against T solium cysticerci appears to have components of both T helper type 1 cells (Th1) and T helper type 2 cells (Th2), although the underlying mechanisms are yet to be clarified. The parasite is probably killed by eosinophils, which are attracted to the site by lymphoid cells. It is assumed that this specific response is mediated by Th2 cytokines.

Pathophysiology

The natural history of cysticerci in the CNS is not entirely understood. CT scan and magnetic resonance imaging (MRI) have been useful in the study of the evolution of the cysticercus within the brain parenchyma. MRI is more useful than CT scan in detecting intraventricular and subarachnoidal cysts, as well as the accompanying signs of cyst degeneration and pericystic inflammatory reaction. However, CT scan is preferred for detection of parenchymal calcifications.[4]

Once the oncosphere has passed into the parenchyma, it grows and evolves through vesicular, colloidal, nodular-granular, and calcified phases. In the vesicular phase, the host tends to show immune tolerance, and, in most cases, no surrounding parenchymal reaction occurs. The larva lives inside a translucent liquid-filled cystic structure surrounded by a thin membrane, where it can remain viable from a few months to several years. When the larva is viable, the CT scan depicts circumscribed, rounded, hypodense areas, varying in size and number, without enhancement by contrast medium (see the images below). The average size of the cysts is 10 mm in diameter, but they range from 4-20 mm.

Neuroimaging in neurocysticercosis. CT scans showi Neuroimaging in neurocysticercosis. CT scans showing different phases of neurocysticercosis. Top left: CT scan showing many calcifications and active cysts with scolices in both hemispheres. Top right: T1-weighted MRI showing 2 active cysts with the scolex in their interior (vesicular phase). Bottom left: Postcontrast CT scan showing a ring-enhancing cyst (colloidal phase) on left. Bottom right: Proton density-weighted MRI showing a thick capsule with adjacent scolex and perilesional edema (colloidal phase).
Neuroimaging in neurocysticercosis. Natural histor Neuroimaging in neurocysticercosis. Natural history of neurocysticercosis. Top left: This CT scan shows a large occipital active cyst (vesicle phase), many calcifications, and small cortical cysts. Top right: After 18 months, the occipital cyst has been replaced by a calcification and the remaining cysts have disappeared. Bottom left: A single parietal nodular-enhancing lesion (transitional, nodular-granular phase) is shown. Bottom right: Six months later, the lesion has disappeared.

On MRI, the vesicular larva appears as CSF-like intensity signal on all sequences (as shown in the first image above), with no surrounding high signal on T2-weighted images. Both MRI and CT scan may show a high intensity, 2-4 mm mural nodule, depicting the scolex in the interior of some parenchymal vesicular cysts (as shown in the first image above). This picture could be considered pathognomonic of cysticercosis, and it corresponds to the active parenchymal form of NC. Two phases of pathologic changes take place when the host-immune system reacts to the parasite.

Colloidal phase

In this phase, the parasite begins to show degenerative changes, the vesicular fluid takes on a gelatinous colloidal aspect, and the wall thickens. The contrast-enhanced CT scan shows an annular enhancement surrounded by irregular perilesional edema. On MRI, the capsule shows higher signal than the adjacent brain with thick-ring enhancement on T1-weighted images, while on T2-weighted images a low-ring signal surrounded by high signal lesion is seen (see the images below).

Neuroimaging in neurocysticercosis. CT scans showi Neuroimaging in neurocysticercosis. CT scans showing different phases of neurocysticercosis. Top left: CT scan showing many calcifications and active cysts with scolices in both hemispheres. Top right: T1-weighted MRI showing 2 active cysts with the scolex in their interior (vesicular phase). Bottom left: Postcontrast CT scan showing a ring-enhancing cyst (colloidal phase) on left. Bottom right: Proton density-weighted MRI showing a thick capsule with adjacent scolex and perilesional edema (colloidal phase).
Neuroimaging in neurocysticercosis. Natural histor Neuroimaging in neurocysticercosis. Natural history of neurocysticercosis. Top left: This CT scan shows a large occipital active cyst (vesicle phase), many calcifications, and small cortical cysts. Top right: After 18 months, the occipital cyst has been replaced by a calcification and the remaining cysts have disappeared. Bottom left: A single parietal nodular-enhancing lesion (transitional, nodular-granular phase) is shown. Bottom right: Six months later, the lesion has disappeared.

Nodular-granular phase

In this phase, the vesicle tends to shrink, and its contents become semisolid, being progressively replaced by granulomatous tissue. These findings could correspond to a diffuse hypodense area with irregular borders on noncontrast CT scan. Following administration of contrast medium, a small, hyperdense, rounded, nodular image surrounded by edema is observed (see the images below). In this stage, T2-weighted images depict the most striking picture of these lesions, as they show a change in the signal from the cyst fluid.

Neuroimaging in neurocysticercosis. Natural histor Neuroimaging in neurocysticercosis. Natural history of neurocysticercosis. Top left: This CT scan shows a large occipital active cyst (vesicle phase), many calcifications, and small cortical cysts. Top right: After 18 months, the occipital cyst has been replaced by a calcification and the remaining cysts have disappeared. Bottom left: A single parietal nodular-enhancing lesion (transitional, nodular-granular phase) is shown. Bottom right: Six months later, the lesion has disappeared.
Neuroimaging in neurocysticercosis. Noncontrast an Neuroimaging in neurocysticercosis. Noncontrast and contrast-enhanced CT scan of neurocysticercosis. Left: Normal noncontrast CT scan. Right: After administration of the contrast medium, the CT scan of the same patient shows a single parietal nodular-enhancing lesion (transitional, nodular phase).

These 2 consecutive phases correspond to an intermediate stage named transitional form, inasmuch as the cysticercus has entered into a degenerative process. Although these pathologic changes generally are associated with symptoms (eg, seizures, headaches), some patients with these changes remain asymptomatic. The cysts in the transitional phase may be single or multiple. If multiple, and coexisting with other cysts in the vesicular phase and disseminated calcified nodules in the cerebral parenchyma, the most likely diagnosis is NC. However, when only one cyst is seen in the transitional phase, it corresponds to the so-called "single enhancing lesion on CT" (SECTL), signifying a special syndrome.

When the parasite dies, a mineralization and resorption process occurs that ends in a calcified nodule that lodges permanently in the CNS. Noncontrast CT scan shows a rounded, homogeneous hyperdense area showing no enhancement with contrast medium. This phase corresponds to the inactive parenchymal form of NC.

The parasite in the active stage may remain viable from a few months to several years. The transitional stage may last about 3-12 months or longer, usually 4-6 months. Finally, the dead parasite is reabsorbed, or it calcifies and lodges permanently in the CNS.

A NC form with different clinical and radiologic characteristics from those already described is termed "cysticercotic encephalitis." It occurs primarily in children and young women. The noncontrast CT image shows diffuse and intense cerebral edema and small or collapsed ventricles. Contrast-enhanced images show multiple, small, hyperdense, nodular or annular images disseminated throughout the whole cerebral parenchyma (see the image below).

Neuroimaging in neurocysticercosis. Cysticercotic Neuroimaging in neurocysticercosis. Cysticercotic encephalitis. Left: Contrast-enhanced CT scan showing multiple, small, nodular, and annular areas of abnormal enhancement in brain parenchyma. Right: Gadolinium-enhanced T1-weighted MRI showing hyperintense lesions.

When the parasites are located in the subarachnoidal space or inside the ventricular system, the clinical course also varies from the typical presentation. Being immersed in a CSF-rich environment, the cysticerci evolve into the racemose form of NC.

Racemose form

The racemose form constitutes a hydropic change that leads to large or even giant vesicles usually devoid of a scolex. These racemose cysts show a rapid process of hyalinization of the cyst wall. They are located most frequently either in the basal cisterns or inside the sylvian valley, and they can be as large as 100 mm in diameter. Noncontrast CT scans depict hypodense images in the subarachnoid or ventricular space. The cysts deform the surrounding structures, and a noncommunicating hydrocephalus occurs.

MRI shows the cyst more precisely as a hypointense CSF-like image in all the phases (proton or T2 weighted). It permits direct visualization of the intraventricular cysticerci by identifying the cyst wall, scolex, or both. The ventricular ependymal lining reacts to the cysts and an inflammatory reaction or ependymitis occurs, which can be visualized on CT scan or MRI as a high-intensity signal in the ependymal layer. When the parasite is located in the subarachnoid space, it can cause a meningeal inflammatory process, with pleocytosis and increased protein in the CSF. The parasite degenerates to a hyaline mass and remains trapped inside the gummatous thickening of the leptomeninges. As a sequel to the chronic intense inflammatory process, fibrosis and thickening of the leptomeninges also may lead to chronic hydrocephalus. Vasculitis with secondary ischemic lesions may be noted.

Classification of NC

Carpio proposed an improved and widely accepted classification system based on the viability and location of the parasite in the host CNS.

  • Active, when the parasite is alive

  • Transitional, if it is in the degenerative phase

  • Inactive, if evidence of its death is apparent

Each viability category is subdivided into parenchymal and extraparenchymal forms. On the basis of this classification, relating clinical manifestations to each category of the proposed classification is possible. No definitive data exist regarding the duration of individual stages. Anecdotal evidence indicates that, once the parasite lodges in the brain, it may remain viable from months to years. The transitional phase lasts 4-6 months. Finally, the dead parasite is resorbed or it calcifies and lodges permanently in the CNS.

Epidemiology

Frequency

United States

Traditionally NC has been considered an exotic disease in the United States. This infection now accounts for as many as 2% of neurologic and neurosurgical admissions in southern California. More than 1000 cases are reported per year in the United States. Persons who have never left the United States are at risk as well as visitors to disease-endemic regions. An outbreak of cysticercosis among orthodox Jews living in New York City was reported after food was contaminated with T solium eggs by immigrant cooks infected with the pork tapeworm. The Centers for Disease Control and Prevention (CDC) considers NC an emerging infection, and they are developing programs to track and hopefully eradicate the condition.

International

NC is the most common neurological infection in the world. NC is endemic in much of the developing world. Most publications on the frequency of NC are based either on autopsy or biopsy materials or on data culled from neurologic settings and general hospitals. These data are hardly representative of the general population.

T solium is endemic in Latin America, India, and China, and it also may be endemic in sub-Saharan Africa. In countries where the disease is endemic, NC is also widely prevalent in the urban middle class areas.

Epidemiological surveys for human cysticercosis, using immunoserologic assays, such as the enzyme-linked immunoelectrotransfer blot assay (EITB) or the enzyme-linked immunosorbent assay (ELISA) have been explored. These assays are useful for identification of individuals who have had systemic contact with the parasite at some time. However, seropositivity does not necessarily mean an active systemic infection or CNS involvement at any time.

EITB assays report a seroprevalence from 8-12% in some regions of Latin America. Most seropositive individuals in these populations are asymptomatic. No prospective studies provide information on the proportion of seropositive individuals that will develop seizures or other neurological symptoms. Some studies, but not all, have reported an association between seizures and seropositivity. Although a higher proportion of patients with epilepsy have been shown to be EITB positive when compared to those without epilepsy, the proportion of seropositivity in epileptic patients is similar to that reported in the general population in these same areas.

Recent epidemiological studies have shown that persons engaged in household contacts with patients with NC had a risk of positive serology for cysticercosis that was 3 times higher than the general population. While these findings are still consistent with a common environmental source of infection with T solium eggs, they also suggest a potential for direct human-to-human contamination.

Mortality/Morbidity

No reliable information is available regarding mortality rates. This is probably because a large percentage of patients (perhaps as many as 50%) with NC are asymptomatic. Most patients with parenchymal NC have a benign clinical cause. However, patients with subarachnoidal cysticercosis (approximately 10-15%, including intraventricular cysts) may develop complications such as vasculitis and hydrocephalus.

  • Permanent neurological deficits may result secondary to infarction in the case of vasculitis, and high mortality rates or severe clinical morbidity such as dementia may result from hydrocephalus.

  • Hydrocephalus has been reported as a complication (8%) of treatment of NC with albendazole or praziquantel.

  • Anecdotal reports have circulated concerning patients with intraventricular cysts who experienced sudden death due to acute obstruction of the intraventricular system, particularly the aqueduct of Sylvius.

Sex

Men and women are affected similarly. However, cysticercotic encephalitis, one of the most severe forms of NC, is seen more frequently in young women than in men.

Age

NC has been reported in all age groups. The most frequent presentation occurs in the third and fourth decades of life.

Reports of cysticercosis are very unlikely in children younger than 2 years of age because of the prolonged incubation period of T solium. Most often, the disease is recognized in children older than 7, due to this incubation period.

The clinical course of NC in children is usually benign and self-limited and the prognosis good.

 

Presentation

History

Neurocysticercosis (NC) is frequently asymptomatic. Cysticercosis of other tissues is almost always asymptomatic.

Clinical manifestations of NC are variable and dependent on the number and location of cysts as well as the host-immune response to the parasite.

The most frequent clinical manifestations are the following:

  • Seizures

  • Intracranial hypertension

  • Focal neurological deficits

  • Mental changes

A myriad of syndromes have been described, including brainstem dysfunction, cerebellar ataxia, sensory deficits, involuntary movements, stroke, dementia, and hydrocephalus.

A survey carried out in Mexico on 205 patients with NC (114 adults and 92 children younger than age 15 y) who were diagnosed by means of neuroimaging reported that seizures were more frequent in children (80% vs 56%), while headache was more frequent in the adults (27% vs 15%).[5]

Ten percent of patients present with ventricular cysts, with seizures, or with meningeal inflammation.

Symptoms include nausea, vomiting, headache, ataxia, and confusion.

Most of these clinical manifestations develop over a period of a few days, weeks, or months, with periods of remission and relapse, probably due to different evolutionary stages of the parasite.

Physical

No pathognomonic physical findings unmistakably identify a patient with NC. Virtually any neurological sign or symptom can occur, depending on the CNS location of the parasite.

Patients with cysts in the basal cisterns can present with meningeal signs, hydrocephalus, vasculitis, and stroke.

Cysticercal encephalitis with multiple parenchymal cysts (ie, associated inflammatory response, diffuse cerebral edema) is a rare presentation often seen in young girls. These patients are at a risk of developing severe neurological sequelae.

In patients with seizures, SECTL or hyperintense lesions on MRI are a common finding. The lesion is usually small, about 5-10 mm, well defined, annular or nodular, contrast enhancing, cortical or subcortical, and generally associated with perilesional edema and minimal mass effect, but without midline shift (see the image below). These patients, mainly children and young adults, have some benign and transitory clinical manifestations, predominantly partial or partial secondary generalized seizures, and occasionally Todd paresis or focal neurological deficits.

Neuroimaging in neurocysticercosis. Noncontrast an Neuroimaging in neurocysticercosis. Noncontrast and contrast-enhanced CT scan of neurocysticercosis. Left: Normal noncontrast CT scan. Right: After administration of the contrast medium, the CT scan of the same patient shows a single parietal nodular-enhancing lesion (transitional, nodular phase).

Causes

Risk factors associated with the disease include the following:

  • Immigration from areas of endemic disease

  • Family history of parasitic infestation

  • Household visitors from an endemic area

  • History of travel to an endemic area

Other diagnostic considerations include the following:

  • Focal signs may occur abruptly in patients who develop a cerebral infarction as a complication of subarachnoid NC.

  • Some manifestations of spinal NC are nonspecific, and the differential diagnosis with other diseases of the spinal cord is difficult on clinical grounds.

  • Arachnoiditis is characterized by root pain and weakness of subacute onset. Cysts in the spinal cord parenchyma usually occur with motor and sensory deficits that vary according to the level of the lesion.

  • Diffuse muscle involvement may result in a pseudohypertrophic myopathy. Patients have diffuse swelling of the muscles mimicking hypertrophy, myalgia, and muscle weakness.

 

DDx

Diagnostic Considerations

Blastomycosis

Chronic meningitis

Histoplasmosis

Postinfectious vasculitis

Spinal cysts

Differential Diagnoses

 

Workup

Laboratory Studies

Laboratory studies are inferior to imaging in the diagnosis of cysticercosis but may play an adjunctive role.

On complete blood count (CBC), peripheral eosinophilia is usually not present, but eosinophils may comprise 10-15% of white blood cells (WBCs).

Immunoserologic assays may be useful.

Immunoserologic assays, such as EITB or enzyme-linked immunosorbent assay (ELISA) can detect antibodies against T solium or cysticercus and are useful in identifying the population at risk of contact with the parasite.

These assays demonstrate a potential impact of cysticercosis on public health, but clinicians should be aware that the presence of antibodies in the host against both T solium and/or cysticercus does not necessarily indicate that an individual has active neurocysticercosis.

In ELISA, cross-reactions with other helminthic infections may occur.

An EITB using specific glycoprotein antigens was developed for the immunodiagnosis of human cysticercosis, the sensitivity and specificity of which are reported to be high (98% and 100%, respectively). Another study confirmed these results in patients with 2 or more cysts shown by CT scan or MRI (94% sensitivity), but sensitivity was markedly low in patients with single enhancing cysts and calcifications (28%).

ELISA and EITB are performed in many (but certainly not all) laboratories in the United States.

Immunologic techniques for the detection of anticysticercal antibodies in the CSF are more reliable than those performed in serum. However, the accuracy depends on the viability of cysticerci and their location within the CNS.

EITB are used mainly in serum samples. The complement fixation test and the ELISA in the CSF are highly sensitive and specific in cases of subarachnoidal neurocysticercosis.

Sensitivity decreases considerably when the lesions are calcified or when viable parenchymal cysts are not in contact with the subarachnoid space.

Imaging Studies

The only truly reliable standard for diagnosing neurocysticercosis (NC) is pathologic confirmation through biopsy or autopsy. Nevertheless, even without definitive scientific data, CT scan and MRI are considered the main tools for the diagnosis of NC.[6, 7]

Multiple calcifications disseminated in the parenchyma simultaneously with viable cysts and transitional stage lesions are a typical finding on imaging studies in NC.

The relationship between imaging studies and the anatomopathologic changes has been well described. It can be summarized with the following recommendations:

  • Brain CT scan should be obtained as a first imaging study. CT is more widely available, less expensive, and has a faster imaging time than MRI. Contrast and noncontrast studies should be obtained.

  • Noncontrast studies will show calcification of inactive cysts, which is the most common disease form at presentation.

  • Contrast studies will show ring enhancement, signifying edema surrounding the involuting live cysticercus.

MRI is recommended as an adjunctive diagnostic tool.

Demonstration of viable cystic lesions with a mural nodule (ie, the invaginated scolex) associated with transitional or degenerative cysts and calcifications corresponds to a typical image of cysticercosis (see the image below). However, this typical imaging is not necessarily the most frequent one. Conversely, single enhancing lesions are probably more common, especially in children

Neuroimaging in neurocysticercosis. CT scans showi Neuroimaging in neurocysticercosis. CT scans showing different phases of neurocysticercosis. Top left: CT scan showing many calcifications and active cysts with scolices in both hemispheres. Top right: T1-weighted MRI showing 2 active cysts with the scolex in their interior (vesicular phase). Bottom left: Postcontrast CT scan showing a ring-enhancing cyst (colloidal phase) on left. Bottom right: Proton density-weighted MRI showing a thick capsule with adjacent scolex and perilesional edema (colloidal phase).

MRI is a superior imaging study for intraventricular or subarachnoid cysts, while CT is better for calcification of inactive lesions.

Lesions at different stages are not uncommon. Multiple calcifications disseminated in the parenchyma with viable cysts and transitional stage lesions are actually the rule as opposed to the exception in NC.

Soft tissue x-ray: Plain films may show calcification of inactive cysts.

Other Tests

See the list below:

  • Electroencephalography: EEG may be normal or may show focal or generalized abnormalities.

  • Stool for ova and parasites: Many patients will have simultaneous intestinal tapeworm infestation. The test is nonspecific for T solium species.

  • Serologic-based assay: An immunoblot assay, EITB-T, has been developed for detection of human taeniasis carriers. It uses coproantigens of adult T solium tapeworms. The results from studies that use coproantigen detection have indicated that these assays are considerably more sensitive than microscopy.

Procedures

See the list below:

  • Biopsy of a subcutaneous nodule or muscle lesion: Demonstration of the organism is diagnostic of cysticercosis.

  • Brain biopsy: Brain biopsy is not justified in a suspected NC lesion. In addition to the obvious morbidity (and possibly mortality) associated with this procedure, the cysts can reduce spontaneously. Moreover, cysts can resolve in response to anticysticercal therapy. Finally, waiting 1-2 months and repeating the CT scan or MRI can clarify the diagnosis.

  • Lumbar puncture

    • Lumbar puncture should be performed when arachnoiditis is suspected (ie, headache, cranial nerve palsies, cognitive changes).

    • Inflammatory changes in the CSF are largely related to the extraparenchymal location, especially with arachnoiditis. The most consistent finding is moderate mononuclear pleocytosis, usually not exceeding 200-300 cells/mm3. Protein levels are also raised to within the range of 50-200 mg/dL. CSF glucose levels are normal or moderately low. These CSF abnormalities may be difficult to distinguish from those of granulomatous infections such as tuberculosis meningitis.

    • This test is insensitive and nonspecific in the diagnosis of cysticercosis.

  • An imaging study should be done prior to lumbar puncture to exclude an intracranial mass lesion.

Histologic Findings

Macroscopic and microscopic pathology

Cysticercus cellulosae presents a characteristic rounded and ovoid form of about 4-20 mm in length (see the first image below) covered by a thin membrane surrounding hyaline liquid. It invaginates in some sites of the membrane, giving origin to the scolex (see the second image below), which is constituted by a neck, 4 suckers, and a double crown of hooks.

Neuroimaging in neurocysticercosis. Cysticercus ce Neuroimaging in neurocysticercosis. Cysticercus cellulosae in neurocysticercosis.
Neuroimaging in neurocysticercosis. Cysticercus ce Neuroimaging in neurocysticercosis. Cysticercus cellulosae showing the invaginated scolex in neurocysticercosis.

The cysts usually are located in the gray matter due to the richer vascularization of this tissue, and in the subcortical white matter (see the image below). In severe cases of parenchymal cysticercosis, the number of parasites may reach several hundreds, but commonly only a scattered few are seen. Cysts also may be found in the subarachnoidal location, and less frequently inside the ventricles and in the spinal cord.

Neuroimaging in neurocysticercosis. Subcortical pa Neuroimaging in neurocysticercosis. Subcortical parenchymatous cysticercosis

The parasite produces an inflammatory reaction composed of a conglomerate of round mononuclear lymphocytic and plasma cells. Some of the inflammatory cells are found around the perivascular spaces in the adjacent nervous tissue. A variable number of eosinophils are also present; this eosinophilic reaction is highly variable and occurs in almost every patient (see the image below).

Neuroimaging in neurocysticercosis. Inflammatory r Neuroimaging in neurocysticercosis. Inflammatory reaction in parenchymatous cysticercosis.
 

Treatment

Medical Care

Because of the variable clinical course of neurocysticercosis (NC), treatment must be individualized for each patient.

Symptomatic treatment (see the image below) includes corticosteroids for intracranial edema and inflammation, antiepileptic drugs for secondary acquired epilepsy, analgesic medication for headache, and osmotic agents such as mannitol or glycerol for intracranial hypertension.

Treatment of Neurocysticercosis Treatment of Neurocysticercosis

Antiepileptic treatment

First seizures due to inflamed cysticercal lesions should be considered acute symptomatic seizures. Therefore, they should be treated only for the duration of the acute condition. However, treatment may be continued during the period when the inflammatory response is active, which might last several months.

No guidelines exist for the time for which antiepileptic drugs (AED) should be continued following an acute neurocysticercosis episode. The risk of seizures is substantial as long as an active ongoing process, as characterized by persistence of edema around the degenerating lesion, is present. Because of this risk, CT scans are useful for treatment decisions.

Seizures in the context of edema and a degenerative lesion should be considered acute symptomatic seizures, even if they occur many months after presentation. After resolution of the acute lesion, AED administration may be discontinued.

Seizures occurring after resolution of edema or calcification of the degenerating cyst should be considered unprovoked, and, in this situation, long-term AED administration is warranted (see the image below). Other authors also suggest that AED administration can be safely withdrawn once the follow-up CT scan shows resolution of the lesion.

Neuroimaging in neurocysticercosis. Antiepileptic Neuroimaging in neurocysticercosis. Antiepileptic treatment for patients with first seizure due to neurocysticercosis.

Cysticidal treatment

Clinical controversy has centered on the role of cysticidal agents for the treatment of symptomatic NC. Cysticidal agents in current use for NC include praziquantel and albendazole.[8, 9] Cysticidal therapy may hasten radiologic resolution of cysts but can be associated with exacerbation of neurologic symptoms; the possibility exists of massive cerebral edema and death in some individuals who have multiple cysts.

Some authors have advocated simultaneous administration of steroids to reduce the inflammatory response and exacerbation of symptoms, but the safety of this treatment has not been evaluated fully. In developing countries, most neurologists administer the steroids and cysticidal drugs at the same time.

Patients with NC are possibly more likely to remain seizure-free if cysticidal treatment is administered; however, recent studies have shown that there is no correlation between treatment with cysticidal drugs and seizure recurrence.

A meta-analysis of randomized trials assessing the effect of cysticidal drugs (albendazole and praziquantel) on neuroimaging and clinical outcomes of patients with NC has been reported.[10] The search identified 764 papers, of which only 11 met the inclusion criteria, from which 5 were qualified as “good quality.” Among these 5 studies, just 2 were carried out on patients with active or viable cysts, and the remaining 3 studies were performed on transitional or degenerative cysts, in which the parasite is already dead and therefore the treatment with cysticidal drugs is probably worthless. The effects of treatment on neuroimaging end points were relatively small (odds ratios > 2.2). The editors of this paper concluded that the 11 selected studies were small and heterogeneous and provided limited evidence of a modest effect of cysticidal treatment in patients with NC.

During the last few years, 2 double-blind, randomized, placebo-controlled trials to evaluate the effects of cysticidal treatment (albendazole) in patients with NC have been published. Garcia et al concluded that antiparasitic therapy in patients with viable parenchymal cysts is safe and effective; however, 6 months after treatment, only 38% of patients had cysts that disappeared on neuroimaging in comparison with 15% of patients who used placebo.[11] Carpio et al reported disappearance of cysts in 35% of patients with viable cysts in comparison with 12% of the placebo group. In both studies, these differences were statistically significant (p < 0.05).[12]

Based on these 2 studies, cysticidal treatment using albendazole is effective in terms of disappearance of viable parenchymal cysts in one third of patients.

The study of Carpio et al found a reduction in the number of active extraparenchymal cysts (intraventricular and subarachnoideal) in the albendazole group compared with the placebo group, although it was not statistically significant.

No definitive data exist pertaining to combination antihelminthic therapy or whether the use of steroids increases or decreases antihelminthic dosage requirements.

Surgical Care

Surgical treatment should be restricted to removal of the parasite located in the subarachnoid (racemose form) or ventricular area, and to ventriculoperitoneal shunting for the treatment of decompensated hydrocephalus (see the image below).

Treatment of Neurocysticercosis Treatment of Neurocysticercosis

Surgery should not be considered for parenchymal cysts without regard to location, size, or stage of evolution, because this form of NC can be controlled only by symptomatic treatment (or presumably by etiologic treatment). In addition, surgical sequelae could result in more brain damage than the parasite itself.

Transitional or degenerative cysts, regardless of their size or location (see the images below), should not be biopsied or removed since the parasite is dead and will disappear or be calcified spontaneously.

Neuroimaging in neurocysticercosis. CT scans showi Neuroimaging in neurocysticercosis. CT scans showing different phases of neurocysticercosis. Top left: CT scan showing many calcifications and active cysts with scolices in both hemispheres. Top right: T1-weighted MRI showing 2 active cysts with the scolex in their interior (vesicular phase). Bottom left: Postcontrast CT scan showing a ring-enhancing cyst (colloidal phase) on left. Bottom right: Proton density-weighted MRI showing a thick capsule with adjacent scolex and perilesional edema (colloidal phase).
Neuroimaging in neurocysticercosis. Noncontrast an Neuroimaging in neurocysticercosis. Noncontrast and contrast-enhanced CT scan of neurocysticercosis. Left: Normal noncontrast CT scan. Right: After administration of the contrast medium, the CT scan of the same patient shows a single parietal nodular-enhancing lesion (transitional, nodular phase).
 

Medication

Medication Summary

The goals of pharmacotherapy are to reduce morbidity and prevent complications.

Anthelmintics

Class Summary

Parasite biochemical pathways are sufficiently different from the human host to allow selective interference by chemotherapeutic agents in relatively small doses.

Albendazole (Albenza)

Broad-spectrum agent that chemically belongs to benzimidazole group. Has been used to treat enterobiasis, ascariasis, trichuriasis, strongyloidiasis, and hookworm infections, but in US, approved only for use in hydatid disease and neurocysticercosis. Inhibits parasite's ability to assemble tubulin dimers into tubulin polymers, thus arresting microtubule formation. This affects several aspects of parasite's life, including larval development, carbohydrate transport, and enzyme function, as well as maintenance of parasite integument and digestive system.

Praziquantel (Biltricide)

Effective against various trematodes and cestodes including Schistosoma species and tapeworms. Works by increasing parasite's cell membrane permeability. Results in loss of intracellular calcium, massive muscle contractions, and spastic paralysis of parasites, as well as damage to schistosome tegument, followed by attachment of phagocytes to parasite.

 

Follow-up

Further Outpatient Care

See the list below:

  • Follow-up CT scan is needed to assess response to medical and surgical treatment.

  • Long-term anticonvulsant therapy is usually not necessary.

Further Inpatient Care

See the list below:

  • Neurosurgical intervention is required only in cases of obstructive hydrocephalus or ventricular or subarachnoid cysticerci.

  • Ophthalmic surgery is recommended in all cases of ocular cysticercosis, because the inflammatory reaction to medical therapy may threaten vision.

  • Isolation is not required for hospitalized patients.

Deterrence/Prevention

Family members should be screened for parasitic disease. Attention should be given to personal hygiene.

Complications

See the list below:

  • Intracranial herniation

  • Stroke

  • Status epilepticus

  • Hydrocephalus

Prognosis

See the list below:

  • Prognosis is excellent in almost all cases. Many investigators affirm that most patients with neurocysticercosis (NC) with seizures or epilepsy have a good prognosis. Conversely, in patients with extraparenchymal forms the prognosis is unfavorable, especially those patients with hydrocephalus due to arachnoiditis.

  • Recent prospective cohort studies determined the risk of seizure recurrence after a first seizure due to NC and evaluated risk factors for seizure recurrence, including the influence of antihelminthic treatment.

    • Seventy-seven patients were prospectively followed for over 7 years. Thirty-one patients (40.3%) experienced seizure recurrence.

    • Kaplan-Meier estimated recurrence to be 22% at 6 months, 32% at 12 months, 39% at 24 months, and 49% at 48 and 84 months. Treatment with albendazole did not influence recurrence. No significant differences in the Kaplan-Meier curves of recurrence were present when treatment groups were compared (see the image below).

      Neuroimaging in neurocysticercosis. Probability of Neuroimaging in neurocysticercosis. Probability of seizure recurrence (Kaplan-Meier curve) after a first seizure in patients with NC as function of cysticidal treatment.
    • The authors concluded that seizure recurrence is high following a first acute symptomatic seizure due to NC, but this risk seems related to persistence of active brain lesions. Recurrence risk is low and in keeping with seizure risk following other brain insults leading to a static encephalopathy in those in whom the neurocysticercosis lesion clears.

Patient Education

See the list below:

  • Education, especially in developing countries, should include the following:

    • Teaching self-diagnosis of taeniasis/cysticercosis; promotion of preventive measures through proper feeding habits

    • Encouragement of general hygiene education

    • Disclosure of relevant information to schools and universities

    • Use of mass media in education

  • Veterinary educational activities should include the following:

    • Advise on farm hygiene and on the importance of meat inspection

    • Development of special educational programs for farmers and workers in the meat industry

  • Ecological and environmental measures include the following:

    • Improvement of sanitation throughout the country, particularly elimination of open-air defecation by farm workers and peasants

    • Improvement of sewage systems

    • Improvement of methods of animal husbandry