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Neurocysticercosis (NCC)

Definition & Etiology

• Fecal-oral contamination from a tapeworm carrier (including auto-infection)
• Contaminated food or water

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Epidemiology

• Endemic in Latin America, sub-Saharan Africa, South and Southeast Asia, Eastern Europe
• Most common cause of adult-onset epilepsy in endemic regions
• Estimated 0.45–1.35 million epilepsy cases due to NCC in Latin America; ~1 million in India; 0.31–4.6 million in Africa
• Increasingly important in the US due to immigration: estimated 1,320–5,050 new cases/year; 33,060 cysticercosis-related hospitalizations from 1998–2011

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Life Cycle and Pathophysiology

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Classification by Location

1. Parenchymal NCC (most common)

• Cysts in brain parenchyma, predominantly at the gray-white junction
• Seizures are the dominant presentation
• Over 1–2 years, cysts degenerate → fibrosis → calcification

2. Extraparenchymal NCC

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Stages of Cyst Evolution (Critical for Imaging Interpretation)

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Clinical Manifestations

• Headache — most common non-seizure symptom
• Increased intracranial pressure — from intraventricular cysts or communicating hydrocephalus
• Focal neurological deficits — depending on cyst location
• Meningitis — subarachnoid NCC; chronic basilar meningitis pattern
• Stroke — vasculitis from subarachnoid cysts
• Cysticercotic encephalitis — rare; massive cyst burden with diffuse cerebral edema; can be fatal if antiparasitics are given prematurely
• Psychiatric symptoms — cognitive decline, dementia (in heavy infection)
• Hydrocephalus — obstructive (intraventricular) or communicating (arachnoiditis)

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Diagnosis

Neuroimaging

• 1–2 cm cystic lesion with thin walls and a 1–3 mm mural nodule (scolex)
• Ring-like enhancement with surrounding edema
• Calcified lesion (chronic stage)
• Hydrocephalus

• Vesicular stage: CSF-isointense cyst, hypointense scolex ("hole-with-dot")
• Colloidal stage: ring enhancement, perilesional edema on FLAIR
• Calcified stage: hypointense on T2/GRE; may have perilesional FLAIR signal in seizure-causing calcifications

Serology

• EITB (enzyme-linked immunoelectrotransfer blot) — most specific serologic test; sensitivity ~94–98% with ≥2 cysts, but only ~50–70% with single cyst or calcified lesion
• ELISA (CSF or serum) — less specific
• CSF pleocytosis (lymphocytic/eosinophilic) with elevated protein in subarachnoid NCC

Del Brutto Diagnostic Criteria

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Treatment

Treatment Table (IDSA/ASTMH 2017 Guidelines)

Antiparasitic Drugs

• Dose: 400 mg twice daily for up to 21 days (or 15 mg/kg/day in two divided doses)
• Advantages over praziquantel: shorter course, lower cost, better subarachnoid penetration, drug levels increased (not decreased) by dexamethasone
• Contraindicated in pregnancy, children <2 years, and hepatic cirrhosis
• Drug interactions: dexamethasone and praziquantel increase albendazole levels; phenytoin, phenobarbital, carbamazepine, and ritonavir decrease levels

• Used in combination with albendazole for patients with >2 cysts (improves efficacy)
• Levels decreased by dexamethasone and antiepileptic drugs (carbamazepine, phenytoin)

Corticosteroids

• Essential adjunct to antiparasitics to blunt inflammatory response from dying cysts
• Dexamethasone or prednisone; duration tailored to clinical response
• Mandatory when treating subarachnoid/intraventricular NCC (antiparasitics can precipitate acute hydrocephalus)

Antiepileptic Drugs (AEDs)

• All patients with seizures require AEDs
• Monotherapy controls seizures in most
• Duration: typically continued until cyst resolution on imaging; long-term AEDs needed in ~20% who have persistent seizures

Surgery

• Neuroendoscopy: standard approach for intraventricular NCC — avoids need for medical therapy if cyst successfully removed
• VP shunt: for hydrocephalus when cysts are not surgically accessible
• Microsurgery: for fourth-ventricular cysts or selected cases

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Prognosis

• Most parenchymal NCC has a favorable prognosis: cysts resolve in 80–90% within 3–6 months; seizures remit in most patients
• Subarachnoid and intraventricular NCC carry higher morbidity and mortality (hydrocephalus, stroke, arachnoiditis)
• Cysticercotic encephalitis is life-threatening; antiparasitics are contraindicated until edema resolves

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Prevention

• Access to clean water and sanitation
• Cooking pork thoroughly (cysticerci in muscle killed at 56°C for >5 min)
• Good hand hygiene (to prevent fecal-oral transmission of eggs)
• Treating tapeworm carriers (intestinal taeniasis) in endemic communities

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• A 2025 systematic review and meta-analysis (PMID 40381508) supports neuroendoscopic management as the preferred approach for intraventricular NCC, consistent with the IDSA guidelines above.
• A 2026 systematic review (PMID 42087630) on NCC-associated meningitis highlights the aggressive course of subarachnoid/racemose NCC with meningitic complications.
• A 2025 systematic review (PMID 40822429) documents a range of movement disorders as uncommon but recognized manifestations of NCC.

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Anterior Ischemic Optic Neuropathy (AION)

Definition

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Blood Supply of the Optic Nerve Head

• Short posterior ciliary arteries (SPCAs) → form the Circle of Zinn-Haller → supply the prelaminar, laminar, and retrolaminar segments
• The central retinal artery does NOT supply the optic nerve head

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Nonarteritic AION (NA-AION)

Pathophysiology

1. Disc at risk — small, crowded optic disc with a cup-to-disc ratio <0.2 (absent or tiny physiological cup) predisposes to compartment-syndrome-like ischemia when disc edema develops
2. Atherosclerotic narrowing of SPCAs → reduced perfusion reserve
3. Nocturnal hypotension — many patients note visual loss on awakening; arterial blood pressure dips during sleep reduce optic nerve head perfusion pressure below a critical threshold in a compromised vessel
4. Intra-axonal edema → secondary vascular compression within the constrained disc anatomy

Risk Factors

• Systemic: Hypertension, diabetes mellitus, hypercholesterolaemia, ischaemic heart disease, smoking, obstructive sleep apnoea
• Ocular: Small cup-to-disc ratio ("disc at risk") — single strongest local risk factor
• Drug-related: PDE5 inhibitors (sildenafil, etc.) — case reports; causal link uncertain
• Perioperative: Cardiac surgery (CABG), spinal surgery (especially prone positioning) — from hypotension + anaemia + elevated IOP from dependent positioning/fluid overload
• Other: Acute blood loss, antiphospholipid antibody syndrome, collagen vascular disease, migraine

Clinical Features

• Painless, sudden or subacute monocular visual loss — often noticed on awakening
• Altitudinal visual field defect (inferior > superior) — most characteristic; respects horizontal meridian
• Other field defects: arcuate, central, cecocentral, or complete loss
• Relative afferent pupillary defect (RAPD) — present in unilateral or asymmetric cases
• Optic disc edema — typically pallid (pale) edema in the acute phase, often segmental; may be hyperemic
• Peripapillary splinter (flame-shaped) hemorrhages
• Visual acuity: ranges from mildly reduced to hand motions; often 20/200 or better (less severe than arteritic)
• Fellow eye: shows a "disc at risk" (small cup); risk of AION in second eye is ~15–19% over 5 years

Fundus Images

Course and Prognosis

• Visual loss is usually permanent with subsequent optic atrophy
• 32.6% of patients improve somewhat over a 6-month period
• End-stage disc appearance: segmental or diffuse pallor without significant cupping (unlike arteritic AION, which shows increased cupping)
• Spontaneous improvement is more common in younger patients and diabetics with small enhancing lesions

Treatment — NA-AION

• Risk factor modification: optimise blood pressure, glycaemia, lipids; stop smoking
• Avoid nocturnal hypotension: review antihypertensive dosing (avoid over-aggressive evening dosing)
• Aspirin: sometimes used given atherosclerotic aetiology, but no RCT evidence for prevention of fellow eye involvement
• Optic nerve sheath decompression: shown to be ineffective and potentially harmful (Ischemic Optic Neuropathy Decompression Trial)
• Protect the fellow eye — minimise vasculopathic risk factors

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Arteritic AION (A-AION) — Giant Cell Arteritis

Pathophysiology

Clinical Features

Investigations

• ESR — typically >50 mm/hr (often >100); may be normal in ~5% of GCA
• C-reactive protein (CRP) — sensitive and specific; elevated in virtually all
• Platelet count — often elevated (reactive thrombocytosis)
• Temporal artery biopsy — mandatory; harvest a long segment (>2 cm) given skip lesions; examine multiple sections. Do NOT delay treatment while awaiting biopsy.
• Biopsy yield: remains positive for ~2 weeks after starting steroids; obtain as soon as practical
• If biopsy is negative by an experienced pathologist, arteritic AION is highly unlikely and glucocorticoids should be tapered

Treatment — A-AION (Emergency)

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Posterior ION (PION) — Contrast with AION

• Disc appears normal on fundoscopy in acute phase (unlike AION)
• Mainly associated with: severe perioperative anaemia + hypotension (spine/cardiac surgery), shock, massive GI bleeding
• Should always raise suspicion for GCA if disc swelling is absent
• Treatment: reverse anaemia and hypotension immediately; blood transfusion if operative

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Differential Diagnosis

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Summary: NA-AION vs A-AION at a Glance

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