Neurocysticercosis (NCC) - Short Note

Etiology

• Causative organism: Larval stage (cysticercus) of Taenia solium (pork tapeworm)
• Transmission: Humans become accidental intermediate hosts by ingesting food or water contaminated with T. solium eggs (feco-oral route), or via autoinfection from a tapeworm carrier (eggs attach to hands, transmitted orally)
• After ingestion, ova hatch in the gut, releasing oncospheres which invade the intestinal wall, migrate hematogenously, and lodge in the CNS (as well as muscle, eye, subcutaneous tissue)
• Endemic regions: Latin America, India, sub-Saharan Africa, Southeast Asia

Clinical Features

• Seizures - the most common presentation; new-onset partial seizures with or without secondary generalization (explains up to 29% of new-onset epilepsy in endemic areas)
• Headache and raised intracranial pressure (ICP) - from hydrocephalus when cysts obstruct CSF flow in ventricles or subarachnoid space
• Focal neurological deficits - depending on cyst location in parenchyma
• Meningitis/encephalitis - when heavy infestation triggers diffuse inflammatory response
• Sudden death - possible with intraventricular cysts causing acute obstructive hydrocephalus
• Spinal cysticerci can mimic intraspinal tumors

Neuroimaging Findings

Stage 1 - Vesicular Stage (Live cyst)

• Cyst contains viable larva with an invaginated scolex
• MRI: Well-defined cystic lesion with a small eccentric nodule (scolex) - the classic "hole-with-dot" sign (cyst + scolex)
• No significant perilesional edema
• No surrounding enhancement
• Fluid isointense to CSF on all sequences

Stage 2 - Colloidal Stage (Degenerating cyst)

• Host immune response begins as larva degenerates
• MRI: Ring or peripheral enhancement on post-contrast images
• Substantial surrounding edema on T2/FLAIR images
• Cyst contents become turbid (hyperintense to CSF on T1)

Stage 3 - Granulonodular Stage

• Cyst shrinks, scolex mineralizes
• MRI post-contrast: Homogeneous solid nodular enhancement (no central cyst cavity)
• No surrounding edema on FLAIR
• Lesion is smaller and more solid

Stage 4 - Nodular-Calcified Stage (Dead/burnt-out)

• Cyst completely dies and calcifies
• CT: Best modality - shows punctate parenchymal calcifications (most common finding overall)
• MRI: Calcifications can be difficult to detect; susceptibility-weighted imaging (SWI) is the most sensitive MRI sequence for these small calcific foci
• No enhancement, no edema

Key teaching point: Multiple lesions at different stages may coexist simultaneously in the same patient - active enhancing lesions, ring-enhancing cysts with edema, and calcified "burnt-out" lesions all visible together.

Special Forms on Imaging

MRI vs CT: MRI is superior for detecting intraventricular cysts and the scolex; CT is better for calcifications.

Management

1. Antiparasitic (Anthelminthic) Therapy

• Standard dose: Albendazole 15 mg/kg/day (in 2 divided doses) x 8-28 days; Praziquantel 50-100 mg/kg/day x 15-30 days

2. Corticosteroids

• Used to control the inflammatory response triggered by dying parasites
• Dexamethasone or prednisolone - mandatory when using antiparasitic drugs to reduce edema and seizure risk

3. Antiepileptic Drugs (AEDs)

• Seizures are typically controlled with antiepileptic monotherapy
• AEDs are first-line for symptomatic seizures regardless of cyst stage

4. Surgical / Interventional

5. Diagnosis Confirmation (if needed)

• Enzyme-linked immunotransfer blot (EITB) is the recommended serological confirmatory test
• Fundoscopy is recommended for all suspected cases (to rule out ocular involvement before starting antiparasitic therapy - treatment can cause inflammatory damage to the eye if cysts are present)

• Harrison's Principles of Internal Medicine, 22E (McGraw Hill, 2025)
• Grainger & Allison's Diagnostic Radiology
• Bradley and Daroff's Neurology in Clinical Practice
• Tintinalli's Emergency Medicine
• Goldman-Cecil Medicine

Types of MRI Imaging (MRI Sequences / Modalities)

Standard / Conventional Sequences

1. T1-Weighted Imaging

• Physics: Uses short TR (repetition time) and short TE (echo time). Highlights longitudinal (spin-lattice) relaxation
• Appearance:
  • White matter: bright (hyperintense)
  • Gray matter: intermediate
  • CSF: dark (hypointense)
  • Fat: bright
  • Extravasated blood (subacute): bright
  • Calcium/bone cortex: dark
• Best for: Anatomy, fat, subacute hemorrhage, gadolinium contrast enhancement, posterior pituitary "bright spot," marrow infiltration
• Gadolinium-enhanced T1: Areas of blood-brain barrier (BBB) disruption (tumors, abscess walls, active inflammation, demyelination) light up brightly due to T1-shortening effect of gadolinium

2. T2-Weighted Imaging

• Physics: Uses long TR and long TE. Highlights transverse (spin-spin) relaxation
• Appearance:
  • CSF: bright (hyperintense)
  • Gray matter: hyperintense to white matter
  • Edema, inflammation, tumor, demyelination: bright
  • Calcium: dark (signal void)
  • Flowing blood: dark (flow void)
• Best for: Edema, demyelination (MS plaques), ischemic lesions, spinal cord lesions, disc herniation, tumors, encephalitis
• Key teaching: In neurocysticercosis, perilesional edema (colloidal stage) shows bright on T2

3. FLAIR (Fluid-Attenuated Inversion Recovery)

• Physics: A T2-weighted sequence with an inversion pulse that nulls/suppresses the bright CSF signal. This makes lesions near CSF-containing spaces (periventricular, cortical) much easier to see
• Appearance:
  • CSF: dark (suppressed)
  • White matter lesions, cortical lesions: bright against dark background
  • Gray-white differentiation: accentuated
• Best for: Periventricular MS plaques, cortical and subcortical lesions, subarachnoid hemorrhage (SAH - CSF appears bright rather than dark on FLAIR), leptomeningeal disease, establishing chronicity of lesions
• In NCC: Vesicular (live) cysts show no FLAIR signal; granulonodular stage shows no surrounding edema on FLAIR

4. Proton Density (PD) Weighted Imaging

• Uses long TR and short TE
• Reflects the actual density of hydrogen protons in tissue
• Both CSF and lesions appear bright; good tissue contrast
• Used mainly in musculoskeletal MRI; less common in brain imaging now

Diffusion-Based Sequences

5. DWI - Diffusion-Weighted Imaging

• Physics: Measures the free diffusion of water molecules within tissue. Uses strong gradient pulses that dephase/rephase moving water
• Appearance on DWI:
  • Restricted diffusion (impeded water movement) = bright (hyperintense)
  • Free/facilitated diffusion = dark
• Key uses:
  • Acute ischemic stroke - the most important indication. In stroke, failure of Na-K ATPase causes cytotoxic edema and intracellular swelling, restricting water movement. DWI becomes positive within minutes to hours, far earlier than T1, T2, or CT
  • Brain abscess (pus shows restricted diffusion)
  • Epidermoid cysts
  • Dense tumors
  • Creutzfeldt-Jakob disease (cortical ribboning)

6. ADC Map (Apparent Diffusion Coefficient)

• Always interpreted alongside DWI
• True restricted diffusion: Bright on DWI + dark (hypointense) on ADC = confirms restriction (e.g., acute infarct, abscess)
• T2 shine-through: Bright on DWI + bright on ADC = not true restriction (just residual T2 signal)
• ADC map is a calculated quantitative map of water diffusivity

Advanced Functional/Specialized Sequences

7. SWI - Susceptibility-Weighted Imaging

• Physics: Exploits the magnetic susceptibility differences between tissues. Blood products (deoxyhemoglobin, hemosiderin), calcium, iron, and air create local field distortions
• Appearance: These substances appear as dark "blooming" signal voids, more conspicuous than on standard sequences
• Best for:
  • Microhemorrhages (e.g., in diffuse axonal injury, cerebral amyloid angiopathy)
  • Cerebral venous thrombosis (thrombus appears dark)
  • Cavernous malformations
  • Old calcifications in NCC - SWI is the most sensitive MRI sequence for detecting small calcific foci in the nodular-calcified stage
  • Mineral deposition disorders

8. MR Perfusion Imaging

• Best for: Brain tumor grading (high CBV in high-grade gliomas), tumor vs. treatment effect, infarct penumbra, vasospasm assessment

9. MRS - MR Spectroscopy

• Physics: Instead of using spatial gradient info to build an image, MRS creates a spectrum of resonance peaks for different metabolites in tissue
• Key metabolites:
  • NAA (N-acetylaspartate): Neuronal viability marker - reduced in neuronal loss/injury
  • Cho (Choline): Cell membrane turnover marker - elevated in tumors, inflammation
  • Cr (Creatine): Reference metabolite in metabolically active tissue
  • Lac (Lactate): Anaerobic metabolism marker
  • Lip (Lipids): Released with cell membrane damage - necrosis
  • mI (Myo-inositol): Marker of gliosis/Alzheimer's
• Best for: Brain tumor grading, tumor vs. radiation necrosis, metabolic/leukodystrophic diseases, infection characterization

10. fMRI - Functional MRI

• Physics: Uses BOLD (Blood-Oxygenation-Level-Dependent) signal - neural activity causes local over-delivery of oxygenated blood, changing T2* signal in active cortex
• Best for: Pre-operative mapping of eloquent cortex (motor, language, memory) before tumor or AVM surgery; epilepsy surgical work-up; research

11. DTI - Diffusion Tensor Imaging

• Advanced form of DWI that measures directionality of water diffusion (anisotropy) along white matter tracts
• Used to generate tractography - 3D maps of white matter fiber bundles
• Best for: Pre-surgical white matter tract mapping, traumatic brain injury, demyelinating disease progression

12. MR Angiography (MRA)

• Time-of-Flight (TOF) MRA: No contrast; relies on flow-related enhancement of moving blood against suppressed background tissue
• Contrast-enhanced MRA: Gadolinium-based; better for large vessels
• Best for: Intracranial aneurysms, arteriovenous malformations (AVMs), carotid/vertebral stenosis, cerebral venous sinus thrombosis

Summary Table

• Adams and Victor's Principles of Neurology, 12th Edition (McGraw Hill)
• Grainger & Allison's Diagnostic Radiology (Elsevier)
• Bradley and Daroff's Neurology in Clinical Practice (Elsevier)
• Neuroanatomy through Clinical Cases, 3rd Edition