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Parasites and prion-CNS

Taenia solium (neurocysticercosis)


Javier Redding-Ochoa, M.D.
Liam Chen, M.D., Ph.D.

Last author update: 21 January 2025
Last staff update: 21 January 2025

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PubMed Search: Taenia solium (neurocysticercosis)

Javier Redding-Ochoa, M.D.
Liam Chen, M.D., Ph.D.
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Table of Contents
Definition / general | Essential features | Epidemiology | Sites | Pathophysiology | Diagrams / tables | Clinical features | Diagnosis | Laboratory | Case reports | Radiology description | Radiology images | Treatment | Gross description | Gross images | Microscopic (histologic) description | Microscopic (histologic) images | Differential diagnosis | Board review style question #1 | Board review style answer #1 | Board review style question #2 | Board review style answer #2
Cite this page: Redding-Ochoa J, Chen L. Taenia solium (neurocysticercosis). PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/parasitologytaeniasolium.html. Accessed April 1st, 2025.
Definition / general
  • CNS infection caused by the ingestion of Taenia solium (pork tapeworm) eggs through fecal - oral route
    • Cysticercus: the larval stage of the cestode (i.e., flatworm) Taenia solium
  • Neurocysticercosis includes intraparenchymal, extraparenchymal and ocular forms of disease
Essential features
  • Neurocysticercosis occurs when humans ingest the eggs of Taenia solium
    • Taeniasis occurs when the larval cysts are ingested
    • Clinical presentation ranges from asymtomatic to fatal, mimicking many other neurological disorders
  • Neurocysticercosis is a common cause of seizure disorder in endemic areas (e.g., Latin America, India)
  • Intraparenchymal disease is the most common form of neurocysticercosis
Epidemiology
Sites
Pathophysiology
  • Humans are the only definitive host
  • Pigs and humans are intermediate hosts
  • Life cycle (Clin Microbiol Rev 2020;33:e00085, ScientificWorldJournal 2012;2012:159821)
    1. Eggs pass into the environment in feces
    2. Intermediate hosts (e.g., pigs or humans) ingest the eggs in contaminated food or water
    3. Eggs hatch in the gastrointestinal (GI) tract when exposed to bile
    4. Oncospheres (i.e., the embryo inside the egg) penetrate the intestinal wall to gain access to the systemic circulation
    5. Dissemination to the skeletal muscle, subcutaneous tissue, eye or brain, where the oncospheres develop as cysticerci (i.e., larval cysts)
      • If the cysticerci are ingested in raw or undercooked meat of infected pigs
        1. Cyst wall disintegrates
        2. Scolex attaches to the small bowel mucosa
        3. In months, the cysticercus grows as an adult hermaphrodite tapeworm
          • Adults have ≥ 1,000 segments or proglottids
    6. Proglottids of the adult tapeworm contain eggs; these are released into the GI tract and excreted in feces
Diagrams / tables

Classification of T. solium
Kingdom Animalia
Phylum Platyhelminthes
Class Cestoda
Order Cyclophyllidea
Family Taeniidae
Genus Taenia
Species solium


Images hosted on other servers:
Taenia solium life cycle

Taenia solium life cycle

Clinical features
  • 4 phases of infection are recognized
    • Initial (viable): commonly asymptomatic
    • Early inflammatory
    • Degenerating
    • Nonviable
  • Location of the infestation determines the clinical manifestations
Diagnosis
  • Definite neurocysticercosis diagnosis is based on neuroimaging and clinical / epidemiologic criteria (Clin Microbiol Rev 2020;33:e00085, Acta Neurol Scand 1997;96:76, J Neurol Sci 2017;372:202)
    • 1 absolute criterion or
    • 2 major neuroimaging criteria and epidemiological exposure criteria or
    • 1 major imaging criterion and 2 epidemiological exposure criteria and exclusion of diseases with a similar radiologic presentation
  • Probable neurocysticercosis
    • 1 major neuroimaging criterion and 2 epidemiological exposure criteria
    • 1 minor neuroimaging criterion and 1 epidemiological exposure criterion
  • Absolute criteria
    • Neuropathological assessment
    • Subretinal cysticercus visualization
    • Neuroimaging: cystic lesion with a scolex
  • Neuroimaging criteria
    • Major criteria
      • Cystic lesion(s) with no discernible scolex
      • Enhancing lesions
      • Multilobulated subarachnoid cystic lesions
      • Solid calcified lesion (usually < 1 cm)
    • Minor criteria
      • Obstructive hydrocephalus
      • Abnormal enhancement of basal leptomeninges
  • Clinical / epidemiologic criteria
    • Major criteria
      • Serologic evidence of specific anticysticercal antibodies or cysticercal antigens
      • Extraneural cysticercosis
      • Household contact with taeniasis
    • Minor criteria
      • Suggestive clinical manifestations
      • Residence in an endemic area
Laboratory
Case reports
Radiology description
  • More commonly located in cerebral gray-white matter junction (Neuroimaging Clin N Am 2012;22:659)
    • Early noninflammatory lesions (vesicular stage)
      • Computed tomography (CT) and magnetic resonance imaging (MRI): small (5 - 20 mm), thin walled cyst without contrast enhancement
        • Cyst fluid and CSF have similar imaging characteristics
        • Little or no edema associated with cysts
        • Scolex: eccentrically located iso or hyperintense nodule on T1 and T2 weighed MRI (N Engl J Med 1984;311:1492, AJNR Am J Neuroradiol 1989;10:1011)
        • Swiss cheese appearance: multiple parenchymal cysts present
    • Degenerative phase
      • Thicker and irregular cyst walls with contrast enhancement
        • Single lesions with ring-like enhancement raise questions about neoplastic or other infectious differential diagnoses
      • Cystic fluid becomes hyperdense (CT) and hyperintense (T1 → mild hyperintensity; T2 or FLAIR → marked hyperintensity)
      • Scolex may be absent
    • Calcified / inactive phase
      • Nodular mineralized lesions
      • No perilesional edema
  • Intraventricular and meningeal / subarachnoid forms
    • Hard to detect on CT and MRI due to similar density (CT) or intensity (MRI) between the lesions and CSF
    • Distortion of the ventricular system due to CSF flow obstruction may be the only neuroimaging indicator of neurocysticercosis (Neuroimaging Clin N Am 2012;22:659)
Radiology images

Contributed by Victor H. Ramos-Pacheco, M.D.
CT scan

CT scan

Treatment
  • Acute symptom management (Am J Trop Med Hyg 2018;98:945)
    • Intracranial hypertension
      • Steroid therapy to reduce cerebral edema
      • Obstructive hydrocephalus: surgical removal of cysticerci or placement of extraventricular drain
      • Communicating hydrocephalus: third ventriculostomy or ventriculoperitoneal (VP) shunt (CSF diversion techniques)
      • Antiparasitic therapy is contraindicated in individuals with intracranial hypertension
    • Antiseizure therapy
  • Parenchymal disease
    • Antiparasitic therapy
      • Praziquantel
      • Mebendazole
      • Albendazole
      • Antiparasitic drugs are contraindicated in severe cysticercal encephalitis due to risk of inflammatory response triggering cerebral edema and herniation (PLoS Negl Trop Dis 2021;15:e0009883)
Gross description
  • Cysts range in size from 0.5 to 2 cm
  • Cysts are round or oval and contain semitranslucent or white more dense fluid (Arch Pathol Lab Med 2010;134:1560)
  • Number of cysts varies between a single lesion to hundreds
  • Protoscolex is visualized grossly as the solid central portion of the cysticercus
  • Exudate may be observed in leptomeningeal cysticercosis
    • In subarachnoid neurocysticercosis, the exudate turns into a fibrous plastron that obliterates the subarachnoid space
  • CSF blockage by the cysts or the exudate results in ventricular expansion
Gross images

Contributed by Laura G. Chávez-Macías, M.D., Erick Gómez-Apo, M.D., Ph.D., Mario T. Espinosa-Romero, M.D. and Aurea Escobar-España, M.D.
Fourth ventricle cyst

Fourth ventricle cyst

Extraparenchymal neurocysticercosis

Extraparenchymal neurocysticercosis

Basal organized exudate

Basal organized exudate

Subarachnoid pontine cysticercus

Subarachnoid pontine cysticercus

Cysticercal cysts

Cysticercal cysts

Resected cysticerci

Resected cysticerci

Microscopic (histologic) description
  • Cysticercus consists of
    • Bladder wall
    • Fluid
    • Invaginated scolex (i.e., protoscolex) surrounded by a spiral canal; the scolex contains suckers and rostellum with hooklets
  • Bladder wall measures 100 - 200 micrometers in thickness and consists of
    • Outer tegument with microvilli
    • Haphazardly arranged smooth muscle cells
    • Loose stroma
    • Excretory channels
    • Calcareous bodies (calcium concretions) (Rev Latinoam Microbiol 1999;41:303)
  • 4 cysticercal stages are recognized (Lancet Infect Dis 2002;2:751)
    • Vesicular stage: vesicles with viable organisms (Arch Pathol Lab Med 2010;134:1560)
      • Viable organism → larva with an invaginated scolex surrounded by fluid and a thin wall
      • Limited host tissue reaction is seen associated with viable cysts
      • Early inflammatory phase
        • Initial neutrophilic response with scattered eosinophils and granulation tissue
        • Organism may survive for years if a weak inflammatory response is mounted (Epilepsy Curr 2004;4:107)
    • Colloidal stage (Arch Pathol Lab Med 2010;134:1560)
      • Cysticercus hyalinization
      • Cystic fluid becomes more turbid
      • More severe inflammatory response with lymphocytes, neutrophils, eosinophils and multinucleated giant cells is elicited
    • Granular nodular stage
      • Scolex degeneration and vesicle involution
      • Cyst wall thickening
      • Calcification: indicates the nonviable phase
    • Nodular calcified stage
      • Cysticercus is replaced by collagen and is calcified
  • Racemose form: distinct multilobulated grape-like cysts without a scolex
    • Common in subarachnoid neurocysticercosis
    • Aggressive disease which may present as hydrocephalus, intracranial hypertension, meningitis and neurologic deficit
Microscopic (histologic) images

Contributed by Laura G. Chávez-Macías, M.D., Erick Gómez-Apo, M.D., Ph.D., Aurea Escobar-España, M.D. and Mario T. Espinosa-Romero, M.D.
Cysticercus

Cysticercus

Cysticercus hooklet

Cysticercus hooklet

Cysticercus wall   Cysticercus wall

Cysticercus wall


Tegument

Tegument

Microvilli

Microvilli

Chronic granulomatous inflammation

Chronic granulomatous inflammation

Calcareous bodies

Calcareous bodies


scolex   scolex

Scolex

Differential diagnosis
  • Abscess:
    • Central suppurative area is surrounded by vascular congestion and fibroblastic proliferation
    • Tegument and scolex are absent
  • Tuberculoma:
  • Paragonimiasis:
    • Eggs contain an operculum (i.e., a brown shell) and measure 80 - 120 micrometers
  • Hydatid disease:
    • Cysts are usually much larger
    • Its thick outer wall measures 2 - 3 mm
    • Scolices show 4 suckers with 2 rows of hooklets
  • Pilocytic astrocytoma:
    • Rosenthal fibers and eosinophilic granular bodies
    • Compact fibrillar background
    • Vascular proliferation
    • Activation of mitogen activated protein kinase (MAPK) pathway
Board review style question #1


A 35 year old man without prior disease presented with focal seizures with secondary generalization. There is no prior history of head trauma. A computed tomography (CT) scan reveals a solid / cystic, 0.5 cm lesion with focal calcification in the middle temporal lobe. Due to concerns of neoplastic origin, a surgical resection is scheduled. The microscopic image of the surgical specimen is shown above. What is the intermediate host in the life cycle of this parasite?

  1. Cows
  2. Pigs
  3. Rabbits
  4. Rats
Board review style answer #1
B. Pigs. Although humans may act as intermediate hosts in the life cycle of Taenia solium, pigs are more commonly involved as intermediate hosts after ingesting contaminated food or water by gravid proglottids or eggs. Answer A is incorrect because only cows are intermediate hosts of Taenia saginata. Note that the eggs of T. saginata and T. solium are identical. Answer D is incorrect because rats are intermediate hosts of Taenia taeniaeformis. Answer C is incorrect because rabbits are intermediate hosts of Taenia pisiformis.

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Reference: Taenia solium (neurocysticercosis)
Board review style question #2
A 45 year old man without relevant medical history is brought to the ER with a stupor and a recent onset of vomit, headache and seizures. CT and MRI show marked dilation of the ventricular system and partial compression of the right lateral ventricle. There is a rapid worsening of the clinical status and the patient dies. A brain autopsy is performed, which is remarkable for a 3.5 x 1.8 x 1.2 cm, grape-like lesion in the subarachnoid space of the right Sylvian fissure. Which parasitic structure is absent in this form of cysticercosis?

  1. Bladder wall
  2. Outer tegument with microvilli
  3. Scolex
  4. Smooth muscle
Board review style answer #2
C. Scolex. The grape-like subarachnoid lesion represents an example of the racemose form of cysticercosis, which is remarkable for the absence of the scolex, in addition to the grape-like morphology. Also, these forms of cysticercosis are difficult to detect by CT and MRI due to the similarity in density (CT) or intensity (MRI) with the surrounding CSF. Answers A, B and D are incorrect because the outer tegument with microvilli (which contain smooth muscle fibers) and a bladder wall are present in this form of cysticercosis.

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Reference: Taenia solium (neurocysticercosis)
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