Background
Neurocysticercosis has been increasingly recognized as a major cause of neurologic disease worldwide and an important problem among immigrant populations in the United States. This recognition is largely due to the widespread availability of sensitive neuroimaging techniques. Neurocysticercosis is the most common parasitic infection of the CNS. Tissue-invading larval forms of the pork tapeworm Taenia solium cause the disease.
Historically, neurocysticercosis was endemic to only Latin America, Asia, and Africa, although it has become increasingly frequent in the United States since the 1980s. Because of this epidemiologic change, all general pediatricians should become familiar with this disease process. The disease has been the subject of several reviews. [1, 2, 3, 4, 5, 6]
See the images below.
Case 1: Coronal image MRI of a 6-year-old boy from Peru with single right frontal cyst.
Case 1: Axial image MRI of a 6-year-old boy from Peru with single right frontal cyst.
Pathophysiology
The larvae of T solium (Cysticercus cellulosae) cause neurocysticercosis. This pork tapeworm can vary in size but is notable for a scolex (head) with approximately 25 hooklets, 4 suckers, and a body with 700-1000 proglottids. The ova of the tapeworm are spread via the fecal-oral route and are approximately 40 microns in diameter with a radially striated shell. The intermediate host is the pig, which harbors the larvae after eating ova, and the definitive host is the human being.
If pig products infected with larvae are ingested, a tapeworm infection in the intestines ensues; however, if ova are ingested, neurocysticercosis may occur in this normally intermediate host. The ingested ova develop into larvae (cysticerci) and lodge in soft tissues, especially skin, muscle, and brain. Cysticerci are fluid-filled oval cysts, approximately 1-2 cm in diameter, with an internal scolex.
The eggs are found in human feces because humans are the only definitive hosts. Greatest risk for infection occurs in regions where plants in gardens or farms are fertilized with human feces and humans are exposed to contaminated soil.
In the CNS, T solium is deposited in the cerebral parenchyma, meninges, spinal cord, and eyes. Unless large numbers of cysts are present, the body's immune system does not act to destroy the organism, and cysts can live for many years undetected. A live cyst can go undetected for as long as 5 years before dying or causing symptoms in the host.
Neurologic symptoms arise when the encysted worm dies and the human mounts an associated inflammatory response. If the cyst lodges in the ventricular system (especially the fourth ventricle), hydrocephalus can occur.
Etiology
Larvae (cysticercus) of the tapeworm T solium cause neurocysticercosis. Larvae are acquired by ingestion of T solium ova, found in the feces of humans infected with the pork tapeworm.
The disease is most common in the developing world, especially in environments where sanitation is poor. Such environments exist in rural areas of Latin America, Asia, Africa, Spain, and Eastern Europe.
Since the 1980s, this disease has been recognized more commonly in the United States, frequently in the states of California and Texas and in the city of Chicago, where Hispanics make up a large proportion of the community. The emergence of CT scanning and MRI studies as diagnostic tools also probably accounts for the increased detection since the 1980s.
Epidemiology
United States data
Neurocysticercosis is more common among immigrants from endemic areas or children in contact with these immigrants. [7, 8] Several studies report approximately 1000 cases annually in adults and children. One study reported neurocysticercosis as the cause of 2% of the neurologic and neurosurgical admissions in southern California. [9] With increasing immigration from Mexico and other endemic areas, incidence in the southern United States has been increasing. In a meta-analysis of the US medical literature, 1494 cases have been reported from 1980-2004. [10]
International data
Neurocysticercosis is highly endemic in Latin America, Mexico, Eastern Europe, Asia, Africa, and Spain. The estimated serologic prevalence in Mexican adults is 3.6%, with positive confirmation by autopsy in 1.9%. Approximately 50 million people worldwide are infected. World Health Organization estimates that more than 50,000 individuals die each year from neurocysticercosis. [11]
Race-, sex-, and age-related demographics
Neurocysticercosis tends to be diagnosed more frequently in Hispanics because of the prevalence of the organism in the countries of origin, rather than an innate property of the host child.
No sexual predilection has been noted.
Reports of cysticercosis are unlikely in children younger than 2 years because of the prolonged incubation period of T solium. Most often, the disease is recognized in children older than 7 years because of this incubation period.
Prognosis
In patients with single lesions, prognosis is excellent. In those with multiple lesions, especially extraparenchymal, prognosis can be poor.
Treatment with antihelminthics results in complete resolution or significant regression in 80-90% of patients. Most children with calcified single lesions that do not require antihelminthic treatment have spontaneous resolution in 2-9 months, usually within 3 months.
Usually, seizures are easy to control, and most children can be weaned from their anticonvulsants within 1-2 years. Most children remain free of seizures.
Morbidity/mortality
Neurocysticercosis is typically benign, and most lesions spontaneously resolve within 2-3 months; however, mortality is highly dependent on whether the disease process is simple or complicated.
Simple neurocysticercosis occurs in children with only a single exposure to cysts. These children tend to have solitary cysts and fewer complications. Often, children can be treated symptomatically and have a favorable prognosis. This type of neurocysticercosis tends to be observed in the United States and other nonendemic areas.
Complicated neurocysticercosis occurs in children in endemic areas who are repeatedly exposed to ova. Because of complications from increased intracranial pressure and difficulty controlling seizures, these children may have a less favorable prognosis. Complications can arise from uncontrolled seizures, hydrocephalus, papilledema, and occasionally, headaches and emesis, although all of these complications are rare.
Complications
Complications include the following:
Patient Education
Educate patients and their families regarding prevention.
Emphasize improvement in sanitation, separation of pigs from humans, and food preparation hygiene in endemic areas.
For excellent patient education resources, please see eMedicineHealth's Infections Center.
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Case 1: Coronal image MRI of a 6-year-old boy from Peru with single right frontal cyst.
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Case 1: Axial image MRI of a 6-year-old boy from Peru with single right frontal cyst.
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Case 2: MRI of a 40-year-old patient with a single parietal calcified cyst.
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Case 2: CT scan of a 40-year-old patient with a single parietal calcified cyst.
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Case 3: MRI of a 47-year-old man with 2 right parietal cysts, one with edema.
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Case 3: MRI of a 47-year-old man with 2 right parietal cysts, one with edema, after the larger cyst had involuted.
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Case 4: CT scan of 28-year-old woman with occipital headaches and diplopia; imaging reveals a superior cerebellar cyst, mild ventricular dilatation, and old calcifications in the right insular region. Image courtesy of Gholam Motamedi, MD.
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Case 4: MRI of 28-year-old woman with occipital headaches and diplopia; MRI discerns prepontine and suprasellar lesions, as well as the superior cerebellar cyst. Image courtesy of Gholam Motamedi, MD.
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MRI of multiple cysts. Image courtesy of the Centers for Disease Control and Prevention.
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MRI of an 87-year-old patient from Europe with bitemporal lesions found incidentally. Image courtesy of Jon Poling, MD.
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Two parietal lesions observed on autopsy specimen.
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MRI of a 40-year-old woman with severe epilepsy and a left temporal single cyst.
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MRI of a 21-year-old woman with left temporal lobe epilepsy and a single cyst.
